Brain

Research

Bullerin.

0361.9230190 $3.00 t .OO

Vol. 25. pp. 271-284. Q Pergamon Press plc, 1990. Printed in the U.S.A.

Afferent and Efferent Connections of the Laterodorsal Tegmental Nucleus in the Rat J. CORNWALL, Department

of Anatomy,

J. D. COOPER AND 0. T. PHILLIPSON’

School of Medical Sciences,

Received

University

Walk, Bristol, BS8 ITD

12 March 1990

CORNWALL, J., J. D. COOPER AND 0. T. PHILLIPSON. Afferent and ejferent connections of the laterodorsal tegmental nuc1eu.s in the rut. BRAIN RES BULL 25(2) 271-284, 1990.-The connections of the laterodorsal tegmental nucleus (LDTg) have been investigated using anterograde and retrograde lectin tracers with mummocytochemical detection. Inputs to LDTg were found from frontal cortex, diagonal band, preoptic areas, lateral hypothalamus, lateral mamillary nucleus, lateral habenula; the interpeduncular nucleus. ventral tegmental area, substantia nigra and retrorubral fields; the medial terminal nucleus, interstitial nucleus, supraoculomotor central prey. medial pretectum, nucleus of the posterior commissure, paramedian pontine reticular formation, paraabducens and paratrochlear region; the parabrachial nuclei and nucleus of the tractus solitarius. Terminal labelling from PHA-L injections of LDTg was found in infralimbic, cingulate and hippocampal cortex, lateral septum, septofimbrial and triangular nuclei. horizontal limb of diagonal band and preoptic areas; in the anterior, mediodorsal, reuniens, centrolateral, parafascicular, paraventricular and laterodorsal thalamic nuclei, rostra1 reticular thalamic nucleus, and zona incerta; the lateral habenula and the lateral hypothalamus. A number of brainstem structures apparently associated with visual functions were also innervated, mainly the superior colliculus, medial pretectum, medial terminal nucleus, paramedian pontine reticular formation, inferior olive, supraoculomotor. paraabducens and supragenual regions. prepositus hypoglossi and nucleus of the posterior commissure. Also innervated were substantia nigra compacta. ventral tegmental area. interfascicular nucleus, interpeduncular nucleus, dorsal and medial raphe, pedunculopontine tegmental region, parabrachial nuclei, and nucleus of the tractus solitarius. These findings suggest the LDTg to be a highly differentiated part of the ascending “reticular activating” system, concerned not only with specific cortical and thalamic regions, especially those associated with the limbic system, but also with the basal ganglia, and visual (particularly oculomotor) mechanisms. Additional links with the habenula-interpeduncular system are discussed in this context. Neuroanatomical

tracing

Limbic system

Laterodorsal

tegmental

THE regulation of cortical activity is thought to depend on a variety of direct projections from brainstem, hypothalamus and basal forebrain. in addition to projections from the specific and nonspecific thalamus. Recently interest has focussed on the laterodorsal and pedunculopontine tegmental nuclei (LDTg and PPTg) as pontine structures concerned with the direct regulation not only of cortical, but also of thalamic functions in both specific and nonspecific nuclei. These nuclei form a prominent part of the ascending cholinergic reticular activating system (28, 39, 45, 65-67. 75). Projections from neurones in the PPTg and LDTg to nonspecific and mediodorsal thalamic nuclei, the substantia nigra. ventral tegmental area and striatum also place these cholinergic connections firmly in the context of basal ganglia and frontal cortex circuitry (6. 21. 29, 75). The parafascicular-intralaminar, midline and mediodorsal thalamic nuclei all appear to receive LDTg input (9-l 1, 59). Projections relaying from these thalamic nuclei to cortex-striatum. nucleus accumbens and prefrontal cortex, respectively, appear to play a part in the regulation of basal ganglia function via actions on forebrain dopaminergic activity in their respective target areas (35-37). In addition, the PPTg region appears to have a similar functional role in regulating striatal

‘Requests for reprints should be addressed

nucleus

Oculomotor

system

dopamine (44). Taken together the evidence suggests that dopaminergic mechanisms in the basal ganglia and frontal cortex are functionally integrated with ascending cholinergic pathways, both directly and via thalamus. Additional links of interest, which require further study, emerge from a consideration of the connections of the habenula, which appears to occupy a position as an output station for some exclusively descending output channels from prefrontal cortex, and both the limbic and motor divisions of basal ganglia, relaying information caudally to the pontomesencephalic tegmentum. including the LDTg, both directly and via the interpeduncular nucleus (25. 30, 31. 59). Furthermore, a poorly understood relation exists between the accessory optic system and the LDTg, suggesting an involvement of LDTg in the regulation of eye movements (20). a finding also suggested by evidence that LDTg is concerned in directly generating phasic horizontal eye movements in sleep, via projections to the paramedian pontine reticular formation (41). In view of the lack of information regarding links between LDTg and brainstem, particularly centres concerned with the visuomotor system. we have reinvestigated afferents and efferents of the LDTg with techniques of high resolution and sensitivity, which distinguish

to Dr. 0. T. Phillipson.

2.71

CORNWALL. COOPER AND PHILLIPNOr+

272

ABBREVIATIONS

5 AVVL Cg CC CL Dk DR DTg f fr 87 HDB ;“L IMLF IP LC LDTg LDTgv LH LHb LO LP LPB LPO LS MCPC MD MDL Me5 ml mlf MnR El:5

anterior commissure area postrema anteroventral thalamic nucleus, Ventrolateral part cingulate cortex central (periaqueductal) gray centrolateral thalamic nucleus nucleus Darkschewitsch dorsal raphe nucleus dorsal tegmental nucleus fomix fasciculus retroflexus genu of the facial nerve horizontal limb of diagonal band internal capsule infralimbic cortex interstitial nucleus of the medial longitudinal fasciculus interpeduncular nucleus locus coeruleus laterodorsal tegmental nucleus laterodorsal tegmental nucleus, ventral part lateral hypothalamic area lateral habenular nucleus lateral orbital cortex lateral posterior thalamic nucleus lateral parabrachial nucleus lateral preoptic nucleus lateral septum magnocellular nucleus of the posterior commissure mediodorsal thalamic nucleus mediodorsal thalamic nucleus, lateral part mesencephalic trigeminal nucleus medial lemniscus medial longitudinal fasciculus median raphe nucleus mamillary peduncle motor trigeminal nucleus

connections from neighbouring structures and those of the PPTg previously reported by others (29,59), with a view to further clarifying the organization of links between LDTg and apparently disparate regions of cortex, thalamus, habenula and visuomotor centres. METHOD Male Wistar derived rats (250-300 g) were used throughout and all stereotaxic injections were carried out under chloral hydrate anaesthesia (400 mg/kg) with coordinates which were modified after investigation with iontophoresis of pontamine sky blue (2% w/v in 0.5 M sodium acetate). Retrograde

Tracing Experiments

Unconjugated wheat germ agglutinin (WGA; Sigma, U.K., 8 &ml in Tris-HCl saline, pH 8.6) was ejected iontophoretically from glass micropipettes (internal diameter 20-40 brn) using an intermittent positive current (4 p,A; 50% duty cycle) applied over 20 minutes. Following 18-24 hours survival, rats were reanaesthetised and perfused through the ascending aorta with 100 ml isotonic saline, followed by 500 ml modified Bouin’s fixative (326 ml saturated picric acid, 108 ml 10% formaldehyde, 44 ml saturated mercuric chloride, 22 ml glacial acetic acid). Brains were removed and postfixed overnight in the same solution, after which 40-p,rn frozen sections were collected into 0.05 M Tris-HCl

MPB MPO mt MVe M/V0 Pa Pa6 PB E PPTg PR PrH PY Re RMC RRF Rt scp SF SNC sol SPFPC SpVe SP5 SubC su3 TS ts

VDB VLO VTA VTg ZI 7n 12

medial parabrachial nucleus medial preoptic nucleus mamillothalamic tract medial vestibular nucleus medial/ventral orbital cortex paraventricular hypothalamic nucleus paraabducens nucleus parabrachial nuclei posterior commissure parafascicular thalamic nucleus pedunculopontine tegmental nucleus prerubral field prepositus hypoglossal nucleus pyramidal tract reuniens thalamic nucleus red nucleus, magnocellular part retrorubral field reticular thalamic nucleus superior cerebellar peduncle septofimbrial nucleus substantia nigra. compact part nucleus of the solitary tract subparafascicular nucleus, parvocellutar spinal vestibular nucleus spinal trigeminal nucleus subcoeruleus nucleus supraoculomotor central gray triangular septal nucleus tectospinal tract vertical limb of diagonal band ventrolateral orbital cortex ventral tegmental area ventral tegmental nucleus zona incerta abducens nucleus facial nerve hypoglossal nucleus

Part

buffer (pH 7.8) and washed for 20 minutes in alcoholic iodine/ potassium iodide solution to reduce background staining. After further washing in Tris buffer, sections were incubated overnight in first antibody (rabbit anti-WGA, 1:2OOUin Tris buffer, 0.5% Triton X100, 0.7% carrageenan). After washing in Tris buffer, sections were incubated in sheep anti-rabbit IgG (Dako, 1:30 in Tris buffer, carrageenan and Triton X100) for 10 minutes, followed by further washing, and then incubated in rabbit PAP (Dako, 1:75 in Tris buffer, carrageenan and Triton X100) for 1 hour. The final staining was carried out after further washing, with freshly prepared 0.05% 3’,3’diaminobenzidine-HCl (Sigma) and 0.003% H,O,. Staining proceeded in the dark for about 10 minutes and the reaction was terminated with ice-cold Tris buffer. Sections were mounted on gel-coated slides, counterstained with either light green or thionin and coverslipped in the usual manner. Anterograde

Tracing Experiments

Injections of the anterograde neuronal tracer phaseolus vulgaris leucoagglutinin (PHA-L; 2.5% in 10 mM sodium phosphate buffered saline pH 8.0) were made iontophoretically from glass pipettes (internal diameter 10-15 cl,m) using a 5 ~.LApositive intermittent current (50% duty cycle) for 10 minutes. After 7-14 days survival, animals were reanaesthetised, cooled on ice for 20 minutes, and perfused through the ascending aorta with 100 ml normal saline followed by 500 ml 0.1 M phosphate buffer containing 4% parafonnaldehyde, 0.05% glutaraIdehyde and 0.2%

LATERODORSAL

TEGMENTAL

\,i . b \I

NUCLEUS

Ill.-

‘-

FIG. I. Retrograde tracing with WGA. Sections taken through the injection site in centre of the injection site is shown in section B, surrounded by densely stained retrogradely stained neurons is seen which extends to the caudalmost limits of the and adjacent paramedian pontine reticular formation, locus coeruleus, parabrachial

saturated picric acid at 4°C. Brains were removed, postfixed in the same solution for 24 hours and then transferred to 10% sucrose in phosphate buffer overnight. Frozen sections (30 pm) were collected into ice-cold 0.5 M potassium phosphate buffer, pH 7.4 (KPB) and given 3 rinses of 15 minutes each. Prior to immunocytochemistry, sections were incubated overnight in KPB containing 0.3% Triton X-100, 0.5 M NaCl and 2% normal rabbit serum (KPBSTINRS) followed by 10% NRS in KPBST for 20 minutes. Sections were then incubated in affinity purified goat anti-PHA (E+ L) (1:lOOO in KPBST/NRS) for 48 hours at 4°C. All subsequent steps were performed at room temperature. Sections were rinsed 3 X 10 minutes in KPBST followed by 20 minutes in 10% NRS in KPBST, and then reacted with biotinylated affinity purified anti-goat 1gG in KPBST/NRS (second antibody) for 50 minutes (Vector). Following 3 x lo-minute washes in KPBS, sections were incubated in a preformed avidin:biotinylated horseradish peroxidase macromolecular complex (Vectastain ABC) solution in KPBST for 45 minutes and then washed 3 X 10 minutes in KPBST. Sections were then recycled through the second antibody, wash, ABC and wash steps and then incubated in freshly prepared filtered 0.05% diaminobenzidine-4HCl (Sigma) and hydrogen peroxide 0.0025% in phosphate buffer for 5-20 minutes, washed in ice-cold phosphate buffer and mounted on gel-coated slides. Sections were counterstained with thionin prior to coverslipping. The positions of labelled axons and terminal-like arborisations were plotted onto camera-lucida drawings.

case 2 to show its position in relation to the full extent of LDTg. The neuropil (black). Surrounding the injection site a halo of apparently LDTg. Retrograde label is also seen in the contralateral LDTg. VTg, nuclei and dorsal raphe.

RESULTS

Retrograde Tracing (Figs. 1 and 3) Injection sites. Four cases were analysed in which the injection site included the LDTg and adjacent structures. The most favourable of these (case 2) has been reported in detail since, apart from minimal unavoidable track label in the central grey dorsal to the injection site and possibly to the lateral margin of the dorsal tegmental nucleus, there appeared to be no involvement of the medial longitudinal fasciculus (mlf), the dorsal raphe nucleus or the locus coeruleus in the dense centre of the injection site (Fig. 1). Three other cases are also referred to in which the injection site lay immediately rostra1 to the LDTg and involved the mlf (case 3); or involved both LDTg and mlf (case 4); or involved caudal dorsal LDTg and the adjacent locus coeruleus, but without contamination of the mlf, dorsal tegmental nucleus or dorsal raphe nucleus (case 1). Cortex. Terminology used for subregions of cortex follows Zilles (78). Retrograde cell labelling was confined to the most rostra1 regions of the frontal cortex, and although both sides of cortex were labelled, cells were found predominantly ipsilateral to the injection site. A tight band of labelled neurones was seen in areas MO/V0 and LO, but since the cortical layers are unclear in sections at this level it was difficult to assess their exact laminar distribution. Caudally labelled cells were seen in deep cortical

CORNWALL. COOPER AND PHILLIPSOi\

FIG. 2. Anterograde tracing with PHA-L. Sections taken through the injection sites in cases 3 and 11 show the position of labelled cell bodies after injection of the rostra1 (open circles) and caudal (closed circles) LDTg, respectively

laminae in areas VLO and LO. Sparse retrograde label only was present in lamina V in the medial bank of frontal cortex. Basal forebrain. Scattered label was present in the vertical limb of the diagonal band, medial preoptic area, lateral preoptic area and magnocellular preoptic area. No label was found in the bed nucleus of the stria terminalis. Hypothafumus. Large numbers of labelled neurones were seen ipsilateral to the injection site throughout the lateral hypothalamus in the region of the medial forebrain bundle. Caudally label was seen in magnocellular and posterior hypothalamic nuclei. A few labelled neurones were also present in the lateral mamillary nucleus. Epithalumus. Large numbers of labelled neurones were seen bilaterally in both medial and lateral divisions of the lateral habenula. Caudally at the level of fasciculus retroflexus a few labelled cells were seen near the midline, mostly medial to the fasciculus and the parafascicular thalamic nucleus. Midbrain. Densely labelled tightly packed neurones were seen in the interpeduncular nucleus (IPN) chiefly in the rostrolateral subnucleus, where label was strongly bilateral, and in the dorsolateral subnucleus where label was mainly contralateral. In addition, a few lightly labelled cells were seen in the medial unpaired subnuclei of the IPN. Labelled cells were present in substantia nigra pars compacta, ventral tegmental area (especially rostrally), interfascicular nucleus and in the retrorubral field. Labelling in these regions was

predominantly ipsilateral to the injection site. Also labelled were the medial terminal nucleus of the accessory optic tract, the medial pretectal nucleus and the area immediately dorsal to the posterior commissure, and in the magnocellular division of the nucleus of the posterior comtnissure. The ipsilateral interstitial nucleus of the medial longitudinal fasciculus (IMFL) also contained labelled cells, and this extended into the rostra1 subdivision beneath the caudal pole of the parafascicular thalamic nucleus (rostral IMLF), where label was mainly contralateral. In the central grey, labelled neurones were present in large numbers in the rostrodorsal regions and clusters of labelled cells were also seen in the supraoculomotor nucleus (Su3), in the region dorsal to the trochlear nucleus and in the paratrochlear nucleus (Pa4) outside the central grey proper. Label was also found in the nucleus of Darkschewitsch, and the Fdinger-Westphal nucleus. Labelled cells were consistently found within the deepest layers of the superior colliculus mainly ipsilateral to the injection site. Pons/medullu. Ipsilateral label was present in the parabrachial nuclei, both in the ventral and dorsal divisions, in the locus coeruleus, and the dorsal and median raphe nuclei. At the level of the genu of the facial nerve, labelling was seen in many cells of the paraabducens nucleus and a few cells were found apparently lying within the abducens itself. Nucleus prepositus hypoglossi (PrH) was also labelled mainly ipsilateral to the injection. In the most caudal sections examined labelled cells were seen

LATERODORSAL

TEGMENTAL

FIG. 3. Pattern of retrograde

NUCLEUS

labelling in case 2 (WGA) in selected sections throughout

throughout the length of the nucleus of the solitary tract, particularly caudally at the level of the obex where label was strongly bilateral. Scattered label was also found throughout the lateral paragigantocellular and rostroventrolateral nuclei of the reticular formation. Other case;\. In experiments where contamination of the mlf had occurred at the injection site (cases 3 and 4), large numbers of neurones also appeared in paramedian regions of the pontine reticular formation (PPRF) bordering the raphe nucleus. Some neurones were also labelled in this region in case 2 in which mlf was apparently unaffected by the injection. Confirmatory anterograde labelling of a PPRF-LDTg pathway has, however, been obtained by PHA-L tracing (Cooper and Phillipson, 1990). In case 4, where both LDTg and mlf were labelled, similar projections were seen to those described above, while in addition vestibular and somatic oculomotor nuclei were also labelled. Much heavier labelling of the PrH was found in case 4. Our finding that neither the central nucleus of the amygdala nor the bed nucleus of the amygdala were labelled (7) indicates that the locus coeruleus was

the brain. The dots indicate the position of retrogradely

not significantly Anterograde

contaminated

labelled

at the injection site in case 2.

Tracing (Fi,ys. 2. 4. 5 and 6)

Injection sites (Fig. 2). Two cases from a larger series of 12 have been chosen to represent the spectrum of efferents from LDTg. In both, the injection sites lay almost entirely in LDTg (for details, see legend to Fig. 2), one at a rostra1 and one at a caudal level. The results were similar in both cases and significant differences, where they occurred, will be described. Cortex-. Anterograde labelling was present in the infralimbic and cingulate (Cg3) areas of the medial prefrontal cortex. Terminals were seen mainly in the upper laminae, apparently arising from axons in the forceps minor and in places innervating the cortex in patches. Labelling was strongly bilateral after caudal LDTg injection, but mainly ipsilateral after rostra1 injection and mostly confined to Cg3. Area Cg2 of cingulate was also labelled, mainly lamina l-3. and posterior to the genu of the corpus callosum this was strictly contralateral.

CORNWALL.

COOPER AND PHILLIPSON

FIG. 4. Dis~bution of ~~ro~ly labelled fibres in the forebrain in case 11 (P&%-L). Lines (axons) and dots (teams) relative density of innervation in various regions, the details of which are precisely described in the text.

indicate the

LATERODORSAL

TEGMENTAL

NUCLEUS

27X

CORNWALL.

COOPER AND PHILLIPSOR:

FIG. 6. Photomicrographs of PHA-L immunoreactivity. (a) Nucleus reuniens of the thakunus. Bar=50 p. (b) Mediodorsal thaiamii: nucleus (lateral segment). Bar= 100 &. (cc)Nucleus of the posterior com~ssu~. Bar=50 p. fdf Inte~duncui~ nucleus (IP; ros~laferal subnucleus) and ventrat tegmental area (VTA; paranigral nucleus). Bar= 100 h. (e) Paramedian pontine reticular formation. Bar=50 p,. ff) Oculomotor nucleus i.f), supraoculomotor central gray (Su3) and the adjacent interstitial nucleus (IMLFI. Bar= 100 CL. Sparse terminals were seen in the CAl-3 fields of the hippocampus. Septum. Bilateral terminal label was present in the caudal lateral septal nuclei. Sparse label in the medial nucleus was purely axonal. Heavy, strongly bilateral axon and terminal label was seen

in the septofimbrial and triangular Basal forebrain. Dense terminal part of the nucleus of the horizontal ventral p~lid~. Labelling in the band continued laterally into tbe

septal nuclei. label was present in the rostra1 limb of the diagonal band and posterior part of the diagonal magnocellular preoptic area.

LATERODORSAL

TEGMENTAL

NUCLEUS

Sparse terminals were seen in the medial preoptic area. Thalamus. The anterior parataenial nucleus exhibited weak axon label and the anteroventral and anterodorsal nuclei showed intense terminal label. mainly ipsilateral to the injection. Scattered terminal label was found in the rostra1 reticular nucleus (Rt). However, the ventromedial rostra1 Rt contained much heavier terminal label apparently as a continuation of zona incerta label found in further caudal sections. The lateral mediodorsal nucleus (MDL) showed strong bilateral terminal label with ipsilateral predominance, which was especially prominent in the ventral MDL. Light terminal label was seen in the dorsal midline thalamus (in intermediodorsal and paraventricular nuclei). Much heavier paraventricular label was found in posterior thalamic regions clustered around the inferior and medial margins of fasciculus retroflexus, where neurones projecting to the nucleus accumbens are located (48). The intralaminar nuclei showed strong terminal label bilaterally in the centrolateral, paracentral and central medial nuclei. In ventral midline thalamus nucleus reuniens was most heavily labelled (mostly in the ventral wing). but terminals were seen to extend into gelatinosus, rhomboid, the ventral margins of the ventromedial nucleus, and fibres extended to innervate the adjacent zona incerta. The parafascicular nucleus received terminals bilaterally. Label was seen in patches in the lateral posterior complex. In the epithalamus. bilateral terminal label was present in the lateral habenula. In rostra1 sections, label appeared in both medial and lateral parts of the lateral nucleus, while in caudal sections, label was present mainly in the medial part of lateral habenula. Hypothalamus. A continuous column of dense terminal label was seen extending throughout the lateral hypothalamus in the region of the medial forebrain bundle, including the perifomical region. Axonal label was also seen in the optic tract at levels from the optic decussation rostrally to the midhypothalamus, fibres apparently crossing the midline. In posterior sections a very dense band of fibres and terminals emerged medial to the cerebral peduncle running in a tight band in the medial forebrain bundle toward the mamillothalamic tract, apparently innervating supramamillary and posterior hypothalamic nuclei. Terminal label was also seen in the lateral mammillary nucleus. Midbrairl. At the mesodiencephalic junction, heavy terminal label was observed in the nucleus of the posterior commissure (NPC), and some axons crossed the midline in the commissure to lightly innervate the contralateral NPC. Lighter terminal patterns were present bilaterally in the medial pretectal nucleus (MPN) dorsal to the posterior commissure, and this label became heavier in further caudal sections. In the central grey. terminal labelling was found bilaterally in all subregions (dorsal, ventral and periaqueductal) and included nucleus Darkschewitsch and Edinger-Westphal nuclei, extending ventrally into the linear raphe nucleus and caudally into the supraoculomotor central grey (Su3). At the pontomesencephalic junction. Su3 was particularly heavily labelled after rostra1 LDTg injection. Terminals were observed in the posterior part of the interstitial nucleus of Cajal (medial longitudinal fasciculus) (IMLF). Further rostra1 sections of IMLF also showed fine terminal label at a lower density, and the rostra1 IMLF also contained light innervation. Terminal innervation was found in clusters, mainly ipsilateral. in the superior colliculus throughout its anteroposterior extent, chiefly in the intermediate and deep grey layers, although bilateral zonal label was also seen. Light terminal patterns extended ventrolateral through the mesencephalic reticular formation but avoiding the red nucleus. A small contingent of fibres. after penetrating medial lemniscus. apparently innervated pars compacta of substantia nigra (SNC), but heavy SNC label was only found at its most medial edge and heavy terminal innervation was seen in the ventral tegmental area

279

(VTA). Rostrally, heavy bilateral VTA label was found mainly ventral in VTA around the mamillary peduncle, fasciculus retroflexus and in the interfascicular nucleus. In caudal sections, ventral VTA (paranigral division) was heavily labelled. while the dorsal (parabrachial) division was nearly devoid of label. In rostra1 sections, the medial terminal nucleus received heavy. mainly ipsilateral innervation. In the interpeduncular nucleus. heavy labelling was observed in the rostrolateral (IPRL) and dorsolateral (IPDL) subnuclei, and in caudal sections of the rostra1 subnucleus (IPR) [equivalent to the apical subnucleus of Groenewegen et a/. . see (25)]. Terminals were also found at lower density in the central subnucleus (IPC), but only scanty innervation was seen in the rostra1 part of IPR. Extremely heavy innervation of the caudal part of the intermediate subnucleus (IPI) was seen and fibres crossing to the contralateral IPI passed through IPC at this level. At the pontomesencephalic junction, innervation extended dorsally into the caudal VTA and caudal linear raphe nucleus, where heavy localised clumps of innervation lay in adjacent paramedian sites. Extensive terminal arborisation was found at this level in the region of the retrorubral fields and the rostra1 pedunculopontine tegmental region. Ponslmedulla. At the pontomesencephalic junction, parabigeminal nucleus was innervated. Heavy terminal labelling appeared in the median raphe nucleus and extended in lower density to the adjacent paramedian regions of pontine reticular formation (PPRF) in the region of the descending fibres of the tectospinal tract. In rostra1 pontine sections, the pedunculopontine tegmental region, dorsal raphe. ventral central grey and adjacent paratrochlear nucleus were all innervated. In further caudal sections, with the exception of the dorsal tegmental nucleus. which was largely unlabelled. virtually the whole of the dorsal tegmental grey was innervated. including dorsal raphe. locus coeruleus on both sides, and the contralateral laterodorsal tegmental nucleus. Mesencephalic nucleus of the trigeminal at this level was almost free of label except for the dorsal tip ipsilateral to the injection site, but terminals extended laterally most heavily into the dorsal and also into ventral parabrachial nuclei. Fibres continued in the midline in raphe pontis and extended laterally in patches into paramedian pontine reticular formation, including, apparently. the reticulotegmental nucleus. At the level of the facial nerve, terminals were found heavily innervating the supragenual nucleus, while lighter innervation was seen in the paraabducens and the prepositus hypoglossi. Further lateral, terminals were seen in gigantocellular reticular formation dorsal to the pyramids and fanning out into lateral paragigantocellular nucleus and rostroventrolateral reticular nucleus and the region dorsal to the seventh nucleus. Innervation continued caudally in the midline and paramedian regions to innervate lightly both rostra1 and caudal levels of nucleus of the tractus solitarius and adjacent reticular formation (in the region of parvocellular and intermediate divisions). A few fibres were observed which entered the medial inferior olive at the level of the 12th nucleus (beta and C subnuclei). Fibres extending caudally to cervical spinal cord were observed in case 3 (after rostra1 LDTg injection), terminals being observed in ventral horn laminae, but also in a few sections in deeper laminae (5 and 6) of the dorsal horn and regions around the central canal. In case 3, the olfactory bulb was also labelled, and very thin fibres and terminals were seen mainly in the granule cell layer, but also, in smaller numbers, in the external plexiform layer. Other cases. In three other cases, PHA-L was injected into the dorsal tegmental nucleus, the region ventral to the LDTg in the pontine reticular formation, and the subcoeruleus region. In none of these cases was there a similar pattern of fibre projection to that described for LDTg 11. In particular, following dorsal tegmental injection. strong contralateral dorsal tegmental but not laterodorsal

CORNWALL.

tegmental projections were found. Since laterodorsal PHA-L injections produced strong contralateral LDTg projections, but no dorsal tegmental projections, this supports the specificity of the LDTg injection sites. Comparison of our data with that found following injection of anterograde tracers to the locus coeruleus and the dorsal raphe nucleus (2,26) also indicates lack of significant contamination of these structures in case LDTg 11. In addition, the pattern of cortical, basal ganglia, hypothalamic and brainstem innervation by noradrenergic and serotoninergic fibres differs from the distribution of PHA-L labelled fibres found after LDTg injections.

DISCUSSION

The main aim of this study was to gain further information about the connections of LDTg, and in particular to investigate more closely its relationship to structures concerned with the visuomotor system, thalamus, basal ganglia, and habenula. Methodology Retrograde tracing. Controls for detecting transneuronal transport of WGA have been reported previously (9). The results showed that with small quantities of lectin and short survival times, transneuronal transport does not appear to occur. WGA is, however, taken up and transported retrogradely by broken, but not intact, fibres of passage (47). Therefore, some previously undescribed connections demonstrated by this method were checked with the PHA-L method. Anterograde tracing. It has been reported that PHA-L is not effectively transported from fibres of passage (19), and does not undergo transneural transport, and these conclusions agree with our experience to date. There are, however, other reports that in some pathways PHA-L can be transported retrogradely (3862). In our hands, an apparently retrogradely labelled cell has been observed on rare occasions after injection of other brainstem sites, although not after injection of LDTg. WGA Labelled Afferents to LDTg Cortex. Our data suggest that the orbital cortex provides the major cortical input to LDTg, in agreement with previous data using an anterograde method (76). Some evidence also suggests that the medial bank of frontal (cingulate) cortex provides inputs to LDTg (59,61), although our data and that of others (76) suggest that this may be relatively minor, and probably derives mainly from the infralimbic cortex, while cingulate instead projects mainly to more dorsal regions of the central grey. Basal forebrain/hypothalamus. A number of regions have been identified as providing inputs to LDTg from the diagonal band, substantia innominata, medial preoptic area and lateral hypothalamus in the rostral forebrain, and these findings are in agreement with earlier findings using anterograde techniques (8, 58, 64, 7 1). We did not, however, identify inputs from bed nucleus of the stria terminalis as reported by others (59). Habenula and interpeduncular nucleus. The habenular-LDTg pathway shown here is in agreement with earlier findings in the rat (1, 3 1, 59). Interestingly, it seems that both subdivisions of the lateral nucleus of the habenula contribute to this projection, indicating that both entopeduncular-related (motor) and limbicrelated activity may be conveyed to the LDTg, providing further evidence for suggestions of a correspondingly widespread integrative role for the habenula (23, 30, 31). Recent investigations of the IPN have revealed a highly organised subnuclear structure, histochemistry and connectivity (25), and our results are consistent with these findings, indicating

COOPER AND PHILl_IPSOI\

that the major LDTg input arises from the rostrolateral and dorsolateral subnuclei. However, we could find little evidence tar an input arising from the dorsomedial subnucleus. Since the IPN relays information derived from the medial habenula to the LDTg. both the lateral and the medial habenula appear to influence LDTg with activity derived, not only from motor and limbic sites, but also, indirectly via the IPN, from septohippocampal sources. Midbrain dopaminergic cell groups. Our finding of inputs to the LDTg from substantia nigra compacta and the ventral tegmental area has been noted before by others in the rat (4.59). In addition, we find that labelled cells continued posteriorly into the retrorubral fields. Since the LDTg contains a fibre plexus positive for dopamine-like immunoreactivity (unpublished), further work will be necessary to determine whether one or all of these cell groups send dopaminergic fibres to the LDTg. Other midbrain cell groups. Although previous studies have suggested an input to LDTg from the medial terminal nucleus (MTN), buried in the medial edge of the substantia nigra. in the rat and rabbit (20). it is difficult to be certain that this was not due to contamination of nigra. Our findings. therefore, clearly indicate that MTN. which receives retinal information, projects to LDTg, providing strong evidence that the LDTg may be associated directly with visual functions. The fact that MTN also projects to the interstitial nucleus of Cajal suggests that part of this influence may be concerned with the visuomotor system. The projection from the medial pretectum to LDTg does not appear to have been reported before by others. and it is confirmed by studies using PHA-L injections of pretectum (12). This pathway may be of significance for transmitting information from the medial bank of the prefrontal (cingulate) cortex to LDTg, since prefrontal cortex has been shown to provide heavy inputs to the medial pretectum (12.76). Medial pretectum also projects heavily to the interstitial nucleus (12), providing a striking parallel to the MTN-LDTg pathway described above, and further suggesting an association of LDTg with oculomotor circuitry. The label in deep layers of superior colliculus is not conclusive evidence for an input to LDTg, since there is little evidence for such a route from anterograde studies (22). and the minor input to central grey shown in that study appears to involve sites rostra1 and dorsal to the LDTg, indicating that further anterograde studies are needed to confirm this result. Projections from Su3, the IMLF (including the rostra1 extension in Forel’s field), nucleus of the posterior commissure, Edinger-Westphal nucleus, nucleus Darkschewitsch and the paratrochlear region appear to be new findings. Because of the tight packing of these small structures in and near the rostra1 central grey, specific anterograde tracing studies are difficult even with the high resolution offered by the PHA-L method. Even so, well-localised PHA-L injection of the IMLF, Su3. and nucleus of the posterior commissure has been achieved, confirming that these structures appear to project to LDTg [ ( 13)) Cooper, unpublished]. Lower brainstem. Projections from the PPRF to the LDTg, confirmed by anterograde tracing (14), appear to be a new finding, suggesting that oculomotor mechanisms underlying the generation of horizontal eye movements may directly influence the LDTg. Projections from the paraabducens and PrH to LDTg do not seem to have been reported before, and a systematic study of PrH efferents in the cat (40) revealed no PrH input to LDTg. The possibility remains that PrH was labelled by undetected spread of tracer to the mlf in which PrH efferents are known to travel, since in case 4 there was clear contamination of mlf and many more PrH neurones were labelled. Without confirmation with an anterograde method, therefore, this result should be viewed with caution, although it has been remarked elsewhere that PHA-L labelling of PrH resulted in terminal labelling in the LDTg (24). The finding of parabrachial projections to the LDTg confirms

LATERODORSAL

TEGMENTAL

NUCLEUS

the results obtained with the autoradiographic technique (57). Inputs from the nucleus of the tractus solitarius (NTS) do not seem to have been described before, although inputs to unspecified regions in further rostra1 regions of central grey in the cat have been reported (3). The presence of the adrenaline synthesising enzyme in fibres specifically localised in the caudal ventrolateral central grey, LDTg, and in cell bodies associated with the NTS (C2 cell group) suggests that some of the neurones in this NTS-LDTg pathway may be adrenergic (33).

PHA-L Lube/led

Efferents

From LDTg

Corte.r. Bilateral LDTg input to the medial bank of the prefrontal cortex described here is in broad agreement with earlier findings (15. 54, 70, 74). Substance P, acetylcholine and cortcotrophin releasing factor may all act as transmitters, either singly or in combination in this pathway. The improved resolution of the PHA-L method shows clearly that these LDTg transmitter candidates act in the superficial laminae. Sparse projections to the hippocampal cortex are confirmed by the results of retrograde studies (50.77), and appear to arise mainly from the rostra1 part of LDTg. Septal region and basal forebrain. Innervation of the lateral septal nuclei from LDTg confirms previous findings with retrograde techniques, which also indicate that both acetylcholine and substance P act as transmitters in this projection (29, 53, 73). The question of the LDTg input to the medial septum is less clear. Our PHA-L data show that medial septal label is primarily axonal with few terminals, and that these fibres traverse the medial septum to innervate either the lateral septum or further caudal sites in the septofimbrial nuclei, suggesting that fibres of passage were involved in earlier retrograde studies describing an LDTg-medial septum pathway (59,73). Heavy innervation of the posterior septum (septofimbrial and triangular nuclei) appears to be a new finding, further emphasising the close apparent relationship between the circuits of the hippocampus, medial habenula and LDTg (see below) (30). Projections to several regions of the basal forebrain, the horizontal limb of the diagonal band, magnocellular preoptic area, and medial preoptic area have been noted previously (73). Unlike previous reports, however, we did not find LDTg inputs to the medial rostra1 globus pallidus (59). Thalamus. The distribution of labelled terminals found in the thalamus is in agreement with earlier studies (9-l 1, 24, 28, 32, 34, 51, 59, 63, 66, 75). although we appear to have found somewhat heavier projections to the ventral midline thalamic cell groups than previously reported. The notable relation of LDTg to the anterior and mediodorsal nuclei. and their corresponding cortical projection areas, suggest that the relay to cingulate cortex is a significant target of LDTg outputs. Since many of these fibres appear to be cholinergic in nature, the possibility exists for dual cholinergic regulation of cingulate cortex, since it is also influenced by the rostra1 Ch4 cell group (28.55). Epithnlamus. The finding of strongly bilateral inputs to the lateral habenular nucleus shows, in light of our retrograde tracing data. that the direct LDTg-habenular links are bilateral and reciprocal. Hypothalamus. Projections to the hypothalamus are a prominent component of LDTg outputs, reciprocating the hypothalamicLDTg links shown in the retrograde studies. Throughout the lateral hypothalamus fibres appear to be distributed for the most part medial and ventral to ascending serotoninergic fibres from the dorsal raphe and noradrenergic fibres (2,69). LDTg fibres seem to have some relation to the subdivisions of the medial forebrain

281

bundle and some of the many limbic structures which project through it (43,72), occupying mainly, though not exclusively, areas a, c and cl in rostra1 sections, and a, d, g and cl in caudal sections, with predominance in area c (rostral) and g (caudal). There also appears to be a registration between the inputs from the ventral tegmental area, lateral hypothalamus and LDTg to area c rostrally, and inputs from ventral tegmental area and LDTg to area g caudally. The input to the lateral mamillary nucleus is of interest in view of its known links with the anterior thalamus and the circuitry of the cingulate cortex (60). Midbrainiponslmedulla. Earlier studies have described a cholinergic projection from the Ch5/6 region to mesencephalic dopaminergic neurones (6, 2 1, 75), and our findings show that the specific LDTg component of this pathway seems to innervate the medial nigra compacta, mainly the paranigral division of the ventral tegmental area and the interfascicular nucleus. Since there is some evidence for differentiation of the nigra compacta and ventral tegmental neurones in terms of their output targets. this suggests an input to dopaminergic neurones which in part, at least, relay to the medial caudate-putamen (4), medial nucleus accumbens (48). and the habenula (46). Additional LDTg output to thalamic nuclei, which relay to cortex, caudate-putamen and nucleus accumbens, suggests strong interactions between ascending cholinergic reticular activating mechanisms and ascending dopaminergic pathways. This suggestion receives support from functional studies of these thalamic nuclei and their influence on dopaminergic function (35-37). Descending pathways from prefrontal cortex, nucleus accumbens and caudate-putamen may be in part channelled via the lateral habenula and the “dorsal conduction system” to the limbic midbrain (30, 3 1,42,46). Present evidence shows that LDTg is an important target of lateral habenular outflow, which also includes the substantia nigra, ventral tegmental area and dorsal raphe (3 1). Thus, taken together, the evidence points to an ascending reticular activating mechanism from LDTg. involving ascending dopaminergic pathways directly, and a thalamic relay, which is related to a set of descending pathways involving the lateral habenula, which returns information to these serotoninergic. dopaminergic and cholinergic nuclei. These anatomical findings imply specific functional roles for the habenula in the regulation of neurotransmitter functions, and evidence for this is already available in the case of serotonin (49). The highly ordered LDTg projections to the interpeduncular nucleus, which seem to be reciprocal to pathways revealed by the retrograde studies, show further linkages of LDTg with the habenular-interpeduncular system. in agreement with the results of other studies (25). Thus the LDTg receives information from the medial habenula via the interpeduncular nucleus and sends information to the septofimbrial and triangular nuclei, which are the main input nuclei to the medial habenula. Both medial and lateral habenula are therefore in a position to inform LDTg of activity derived from very widespread regions of forebrain activity. These widespread connections are likely to underlie the many functional attibutes ascribed to the habenulointerpeduncular system (68). Of particular interest are the findings of apparent innervation of a number of brainstem sites known to be involved in the regulation of visual, orientation and oculomotor functions. Input to the intermediate and deep layers of the superior colliculus have been described before, and have recently been identified as cholinergic in the rat (5) and cat (27), implying a role for the LDTg in the well-known functions of the colliculus as a centre for visual orientation mechanisms involving the musculature of the head and neck. Furthermore, the apparent overlap in the intermediate grey layer in the area of termination of cholinergic input and the substantia nigra pars reticulata input (27) suggests a further

282

CORNWALL.

potential interaction between basal ganglia outflow pathways and the cholinergic fibres afferent to colliculus, some of which may be from the LDTg. Fibres from LDTg innervating the IMLF, PPRF, supraoculomotor, paraabducens, prepositus hypoglossi, and the nucleus of the posterior commissure appear to be new findings. Connections of the IMLF and PPRF in the rat have recently been investigated with the PHA-L method (13,14), and seem to confirm that these structures are afferent to LDTg. In addition, IMLF and PPRF have a similar pattern of connectivity to that found in other species, where participation in oculomotor control has been demonstrated. Additionally, dendrites of motomeurones in the 3rd and 6th nuclei are known to extend into the Su3 and paraabducens, respectively, and into the supragenual central grey above the genu of the facial nerve (16,17), regions found to contain PHA-L labelled fibres in the present study. These findings, in combination with evidence for the participation of prepositus hypoglossi in key regulatory aspects of oculomotor control (40), suggest a close involvement of LDTg with control of both vertical and horizontal eye movements. Some of these findings may be related to physiological evidence that the LDTg is involved in directly generating eye movements during the dreaming phase of sleep (41). Interactions with input pathways of the visual system are suggested by LDTg connections with the medial terminal nucleus.

COOPER AND PHILLIPSOh

This nucleus receives information directly from the retina and seems to be concerned with registering movements in the vertical plane and perhaps the control of retinal slip t20), as part of the accessory oculomotor system. In addition, MTN sends direct connections to the interstitial nucleus and the St13 region. Connections between the LDTg and Edinger-Westphal nucleus suggest, in addition, that these links may participate in pupillomotor control. In conclusion, the findings of the present study suggest that the LDTg is involved in functions related to the limbic forebrain. the basal ganglia, the habenula and some visuomotor regions of the brainstem. In addition, the ascending LDTg links with thalamic and midbrain nuclei, which are known to regulate forebrain dopaminergic mechanisms, suggest that the basal ganglia are directly involved with ascending cholinergic reticular activating mechansims. The position of habenula in this organisation suggests that the fasciculus retroflexus is an important component of descending pathways which may act to modulate the ascending system described. Together with evidence for participation in visuomotor control circuits, these findings suggest that LDTg may, in part, form a component of mechanisms underlying visual attention, particularly those associated with activity in the limbic system.

REFERENCES 1. A&i, M.; McGeer, P. L.; Kimura, H. The efferent projections of the rat lateral habenular nucleus revealed by the PHA-L anterograde tracing method. Brain Res. 441:319-330; 1988. 2. Azmitia, E. C.; Segal, M. An autoradiographic analysis of the differential ascending projections of the dorsal and median raphe nuclei in the rat. J. Comp. Neurol. 170641-668; 1978. 3. Bandler, R.; Tork, I. Midbrain periaqueductal grey region in the cat has afferent and efferent connections with solitary tract nuclei. Neurosci. Lett. 74:1-6; 1987. 4. Beckstead, R. M.; Domesick, V. B.; Nauta, W. J. H. Efferent connections of the substantia nigra and ventral tegmental area in the rat. Brain Res. 175:191-217; 1979. 5. Beninato, M.; Spencer, R. F. A cholinergic projection to the rat superior colliculus demonstrated by retrograde transport of horseradish peroxidase and choline acetyltransferase imrnunohistochemistry. J. Comp. Neurol. 253:525-538; 1986. 6. Beninato, M.; Spencer, R. F. The cholinergic innervation of the rat substantia nigra. A light and electromicroscopic immunohistochemical study. Exp. Brain Res. 72:178-184; 1988. 7. Cedarbaum, J. M.; Aghajanian, G. K. Afferent projections to the rat locus coeruleus as determined by a retrograde tracing technique. J. Comp. Neural. 178:1-16; 1978. 8. Chiba, T.; Murata, Y. Afferent and efferent connections of the medial preoptic area in the rat: A WGA-HRP study. Brain Res. Bull. 14261-272; 1985. 9. Cornwall, J.; Phillipson, 0. T. Afferent projections to the dorsal tbalamus of the rat as shown by retrograde lectin transport. I. The mediodorsal nucleus. Neuroscience 24: 1035-1049; 1988. 10. Cornwall, J.; Phillipson, 0. T. Afferent projections to the dorsal thalamus of the rat as shown by retrograde lectin transport. II. The midline nuclei. Brain Res. Bull. 21:147-161; 1988. 11. Cornwall, J.; Phillipson, 0. T. Afferent projections to the parafascicular thalamic nucleus of the rat, as shown by the retrograde transport of wheatgerm agglutinin. Brain Res. Bull. 20:139-150; 1988. 12. Cooper, J. D.; Phillipson, 0. T. Connections of the medial pretectum suggest a limbic input to oculomotor mechanisms via the interstitial nucleus in the rat. 1lth ENA meeting, Symposium ’ ‘Afferent Control of Posture and Locomotion,” Rheinfelden, Abstract No. 108; 1988. 13. Cooper, J. D.; Aml, G. S.; Phillipson, 0. T. Projections of the interstitial nucleus of Cajal. A phaseolus vulgaris leucoagglutinin study. Eur. J. Neurosci. Suppl. 2:33; 1989. 14. Cooper, J. D.; Phillipson, 0. T. Anatomical evidence that the paramcdian pontine reticular formation participates in the oculomotor

system of the rat. J. Anat. 170:228-229; 1990. 15. Crawley, J. N.; Olschowka, J. A.; Diz, D. I.; Jacobowitz, D. M. Behavioural investigation of the coexistence of substance-P, corticotrophin releasing factor and acetylcholinesterase in lateral dorsal tegmental neurons projecting to the medial frontal cortex of the rat. Peptides 6:891-901; 1985. 16. Durand, J. Electrophysiological and morphological properties of rat abducens motoneurons. Exp. Brain Res. 76:141-152; 1989. 17. Durand, J. Intracellular study of oculomotor neurons in the rat. Neuroscience 30:639649; 1989. 18. Fabian, R. H.; Coulter, J. D. Transneural transport of lectins. Brain Res. 334:41-48; 1985. 19. Get-fen, C. R.; Sawchenko, P. E. An anterograde neuroanatomical tracing method that shows the detailed morphology of neurons, their axons and terminals: immunohistochernical localization of an axonally transported plant lectin, phaseolus vulgaris-leucoagglutinin (PHA-L). Brain Res. 290:219-238; 1984. 20. Giolli, R. A.; Blanks, R. H. I.; Torigoe, Y. Pretectal and brainstem projections of the medial terminal nucleus of the accessory optic system of the rabbit and rat. J. Comp. Neurol. 227:228-251; 1984. 21. Gould, E.; Woolfe, N. J.; Butcher, L. L. Cholinergic projections to the substantia nigra from the pedunculopontine and laterodorsal tegmental nuclei. Neuroscience 28:61 l-624; 1989. 22. Graham, J. An autoradiographic study of the efferent connections of the superior colliculus in the cat. J. Comp. Neurol. 173:629-654; 1977. 23. Greatrex, R. M.; Phillipson, 0. T. Demonstration of synaptic input from prefrontal cortex to the habenula in the rat. Brain Res. 238: 192-197; 1982. 24. Groenewegen, H. J. Organisation of the afferent connections of the mediodorsal thalamic nucleus in the rat related to the mediodorsalprefrontal topography. Neuroscience 24379-431; 1988. 25. Groenewegen, H. J.; Ahlenius, S.; Haber, S. N.; Kowal, N. W.; Nauta, W. J. H. Cytoarchitecture, fibre connections, and some histochemical aspects of the interpeduncular nucleus in the rat, J. Comp. Neuml. 249:65-102; 1986. 26. Halaris, A. E.; Jones, B. E.; McInany, M.; Moore, R. Y. Ascending projections of the locus coeruleus in the rat. I. Axonal transport in central noradrenaline neurons. Brain Res. 127:1-21; 1977. 27. Hall, W. C.; Fitzpatrick, D.; Klatt, L. L.; Raczkowski, D. Cholinergic innervation of the superior colliculus in the cat. J. Comp. Neurol. 287:495-514; 1989. 28. Hallanger, A. E.; Levey, A. I.; Lee, H. J.; Rye, D. B.; Wainer, B. H.

LATERODORSAL

29.

30.

31. 32.

33.

34.

35.

36.

37.

38.

39.

40. 41.

42. 43.

44.

45.

46. 47.

48. 49.

50.

51.

TEGMENTAL

NUCLEUS

The origins of cholinergic and other subcortical afferents to the thalamus in the rat. .I. Comp. Neurol. 262:105-124; 1987. Hallanger, A. E.; Wainer, B. H. Ascending projections from the pedunculopontine tegmental nucleus and the adjacent mesopontine tegmentum in the rat. J. Comp. Neural. 274:483-515; 1988. Herkenham. M.; Nauta. W. J. H. Afferent connections of the habenular nuclei in the rat. A horseradish peroxidase study, with a note on the fiber-of-passage problem. .I. Comp. Neurol. 173:123-146; 1977. Herkenham. M.; Nauta. W. J. H. Efferent connections of the habenular nuclei in the rat. J. Comp. Neurol. 187:1948; 1979. Herkenham. M. The connections of the nucleus reuniens thalami: Evidence for a direct thalamo-hippocampal pathway in the rat. J. Comp. Neurol. 177:589-610; 1978. Hokfeh, T.; Johansson, 0.; Goldstein, M. Central catecholamine neurons as revealed by immunohistochemistry with special reference to adrenaline neurons. In: Bjorklund, A.; Hokfelt, T., eds. Handbook of chemical neuroanatomy. vol. 2, classical transmitters in the CNS, part I. New York: Elsevier Science Publishers; 1984: 157-276. Hoover, D. B.; Baisden. R. H. Localisation of putative cholinergic neurons innvervating the anteroventral thalamus. Brain Res. Bull. 5:519-524; 1980. Jones, M. W.: Kilpatrick. I. C.; Phillipson. 0. T. Regulation of dopamine function in the prefrontal cortex of the rat by the thalamic mediodorsal nucleus. Brain Res. Bull. 19:9-17; 1987. Jones, M. W.; Kilpatrick. I. C.; Phillipson, 0. T. Regulation of dopamine function in the nucleus accumbens of the rat by the thalamic paraventricular nucleus and adjacent midline nuclei. Exp. Brain Res. 76:572-586: 1989. Kilpatrick. I. C.; Phillipson, 0. T. Thalamic control of dopaminergic functions in the caudate putamen of the rat-I. The influence of electrical stimulation of the parafascicular nucleus on dopamine utilization. Neuroscience I9:965-978; 1986. Lee, C. L.; McFarland, D. J.; Wolpaw, J. R. Retrograde transport of the lectin phaseolus vulgaris leucoagglutinin (PHA-L) by rat spinal motoneurons. Neurosci. Lett. 86:133-138; 1988. Levey, A. I.; Hallanger. A. E.; Wainer, B. H. Choline acetyltransferase immunoreactivity in the rat thalamus. J. Comp. Neurol. 257:317-332; 1987. McCrea, R. A.; Baker, R. Anatomical connections of the nucleus prepositu\ of the cat. J. Comp. Neurol. 237:337+07; 1985. Mitani, A.; Keihachiro, I.; Hallanger, A. E.; Wainer, B. H.; Kataoka, K.; McCarley, R. W. Cholinergic projections from the laterodorsal and pedunculopontine tegmental nuclei to the pontine gigantocellular tegmental field in the cat. Brain Res. 451:397402; 1988. Nauta. W. J. H. Hippocampal projections and related neural pathways to the midbrain in the cat. Brain 81:319-341; 1958. Niewenhuys. R.; Geeraedts, L. M. G.; Veening, J. G. The medial forebrain bundle of the rat. I. General introduction. J. Comp. Neurol. 206:49-8 I ; 1982. Niijima. K.. Yoshida, M. Activation of mesencephalic dopamine neurons by chemical stimulation of the nucleus tegmenti pedunculopontinus pars compacta. Brain Res. 451:163-171; 1988. Pare. D.; Smith, Y.; Parent. A.: Steriade, M. Projections of brainstem core cholinergic and noncholinergic neurones of cat to intralaminar and reticular thalamic nuclei. Neuroscience 25:69-86; 1988. Phillipson, 0. T.: Griffiths, A. C. Neurones of origin for the mesohabenular dopamine pathway. Brain Res. 197:213-218; 1980. Phillipson, 0. T.; Griffiths, A. C. Anterograde and retrograde labelling of CNS pathways with unconjugated lectins using the unlabelled antibody-enzyme method. Brain Res. 265:199-207; 1983. Phillipson, 0. T.; Griffiths, A. C. The topographic order of inputs to nucleus accumbens in the rat. Neuroscience 16:275-296; 1985. Reisine, T.: Soubrie. P.; Artaud. F.; Glowinski, J. Involvement of lateral habenula-dorsal raphe neurones in the differential regulation of striatal and nigral serotonergic transmission in cats. J. Neurosci. 2:1062-1071: 1982. Riley. J. N.; Moore, R. Y. Diencephalic and brainstem afferents to the hippocampal formation of the rat. Brain Res. Bull. 6:437444; 1981. Rotter, A.; Jacobowita. D. M. Neurochemical identification of cholinergic forebrain projection sites of the nucleus tegmentalis dorsalis lateralis. Brain Res. Bull. 6525-529; 1981,

283

52. Rye, D. B.; Lee, H. J.; Saper. C. B.; Wainer, B. H. Medullary and spinal efferents of the pedunculopontine tegmental nucleus and adjacent mesopontine tegmentum in the rat. J. Comp. Neurol. 269:315-341; 1988. 53. Sakanaka, M.; Shiosaka, S.; Takatsuki, K.: Inagaki, S.; Takagi. H.: Senba, E.; Kawai, Y .; Hara, Y .; Iida, H.: Minagawa. H.; Matsuzaki, T.; Tohyama, M. Evidence for the existence of a substance Pcontaining pathway from the nucleus laterodorsalis tegmenti (Castaldi) to the lateral septal area of the rat. Brain Res. 230:351-355; 1981. 54. Sakanaka, M.; Shiosaka. S.; Takatsuki. K.: Tohyama. M. Evidence for the existence of a substance P-containing pathway from the nucleus laterodorsalis tegmenti (Castaldi) to the medial frontal cortex of the rat. Brain Res. 259:123-126; 1983. 55. Saper, C. B. Organisation of cerebral cortical afferent systems in the rat. I. Magnocellular basal nucleus. J. Comp. Neurol. 222:313-342; 1984. 56. Saper. C. B. Organization of cerebral cortical afferent systems in the rat. II. Hypothalamocortical projections. J. Comp. Neurol. 237: 21-46; 1985. 57. Saper, C. B.; Loewy, A. D. Efferent connections of the parabrachial nucleus in the rat. Brain Res. 197:291-317: 1980. 58. Saper, C. B.; Swanson. L. W.; Cowan, W. M. An autoradiographic study of the efferent connections of the lateral hypothalamic area in the rat. J. Comp. Neurol. 183:689-706; 1979. 59. Satoh, K.; Fibiger, H. C. Cholinergic neurons of the laterodorsal tegmental nucleus: efferent and afferent connections. J. Comp. Neurol. 253:277-302; 1986. 60. Seki, M.; Zyo, K. Anterior thalamic afferents from the mamillary body and the limbic cortex in the rat. J. Comp. Neurol. 229:242-256: 1984. 61. Sesack, S. R.; Deutch, A. Y.; Roth, R. H.; Bunney. B. S. Topographical organization of the efferent projections of the medial prefrontal cortex in the rat: an anterograde tract-tracing study with phaseolus vulgaris leucoagglutinin. J. Comp. Neurol. 290:213-242; 1989. 62. Shu. S. Y.; Peterson, G. M. Anterograde and retrograde axonal transport of phaseolus vulgaris leucoagglutinin (PHA-L) from the globus pallidus to the striatum of the rat. J. Neurosci. Methods 25:175-180; 1988. 63. Sikes. R. W.; Vogt, B. A. Afferent connections of anterior thalamus in rats: Sources and association with muscarinic acetylcholine receptors. J. Comp. Neurol. 256:538-551; 1987. 64. Simerly, R. B.; Swanson, L. W. Projections of the medial preoptic nucleus: A phaseolus vulgaris leucoagglutinin anterograde tracttracing study in the rat. J. Comp. Neurol. 270:209-242: 1988. 65. Smith, Y.; Pare, D.: Deschenes, M.; Parent, A.; Steriade, M. Cholinergic and non-cholinergic projections from the upper brainstem core to the visual thalamus in the cat. Exp. Brain Res. 70: 166-l 80; 1988. 66. Sofroniew. M. V.; Priestley, J. V.: Consolazione. A.; Eckenstem, F.; Cuello, A. C. Cholinergic projections from the midbrain and pons to the thalamus in the rat, identified by combined retrograde tracing and choline acetyltransferase immunohistochemistry. Brain Res. 329: 213-223; 1985. 67. Steriade, M.: Pare, D.; Parent, A.; Smith, Y. Projections of cholinergic and non-cholinergic neurones of the brainstem core to relay and associational thalamic nuclei in the cat and macaque monkey. Neuroscience 25:47-67; 1988. 68. Sutherland. R. J. The dorsal diencephalic conduction system: A review of the anatomy and functions of the habenular complex. Neurosci. Biobehav. Rev. 6:1-13; 1982. 69. Swanson, L. W.: Hartman, B. K. The central adrenergic system. An immunofluorescence study of the location of cell bodies and their efferent connections in the rat utilizing dopamine B-hydroxylase as a marker. J. Comp. Neurol. 163:467-506; 1975. 70. Tohyama, M.; Satoh, K.; Sakumoto, T.; Kimoto, T.; Takahashi, Y.: Yamamoto. K.; Itakura, T. Organisation and projections of the neurons in the dorsal tegmental area of the rat. J. Himforsch. 19:165-176; 1978. 71. Tomimoto, H.; Kamo, H.; Kameyama. M.; McGeer, P. L.; Kimura. H. Descending projections of the basal forebrain in the rat demonstrated by the anterograde neural tracer phaseolus vulgaris leucoagglutinin (PHA-L). Brain Res. 425:248-255; 1987.

284

72. Veening, J. G.; Swanson, L. W.; Cowan, W. M.; Nieuwenhuys, R.; Geeraedts, L. M. G. The medial forebrain bundle of the rat. II. An autoradiographic study of the topography of the major descending and ascending components. J. Comp. Neural. 206:82-108; 1982. 73. Vertes, R. P. Brainstem afferents to the basal forebrain in the rat. Neuroscience 24:907-935; 1988. 74. Vincent, S. R.; Satoh, K.; Armstrong, D. M.; Fibiger, H. C. Substance P in the ascending cholinergic reticular system. Nature 306:688-691; 1983. 75. Woolf, N. J.; Butcher, L. L. Cholinergic systems in the rat brain: III. Projections from the pontomesencephalic tegmentum to the thalamus,

CORNWALL.

COOPER

/jND

PHILLIPSOk

tectum, basal ganglia and basal forebrain. Bram Res. Bull. it> 603-637: 1986. 76. Wyss, J. M.; Sripanidkulchai, K. The topography of the mesencephalic and pontine projections from the cingulate cortex of the Mt. Brain Res. 293:1-15; 1984. 77. Wyss, J. M.; Swanson, L. W.; Cowan, W. M. A aiudy of subcortical afferents to the hippocampal formation in the rat. Neuroscience 4~463-476; 1979. 78. Zilles, K. The cortex of the rat. A stereotaxic atlas. Berlin: SpringerVerlag; 1985.

Afferent and efferent connections of the laterodorsal tegmental nucleus in the rat.

The connections of the laterodorsal tegmental nucleus (LDTg) have been investigated using anterograde and retrograde lectin tracers with immunocytoche...
2MB Sizes 0 Downloads 0 Views