Naunyn-Schmiedeberg's Arch Pharmacol (1992) 345:523-529

Naunyn-Schmiedeberg's

Archivesof

Pharmacology © Springer-Veriag 1992

The release of dopamine from nerve terminals and dendrites of nigrostriatal neurons induced by excitatory amino acids in the conscious rat B . H . C . Westerink 1, M. Santiago 2, and J.B. De Vries 1 1University Centre for Pharmacy, Department of Medicinal Chemistry, University of Groningen, Antonius Deusinglaan 2, NL-9713 AW Groningen, The Netherlands 2Department of Biochemistry, Faculty of Pharmacy, University of Sevilla, Sevilla, Spain Received July 1, 1991/Accepted January 21, 1992

Summary. The possible localization of excitatory amino acid (EAA) receptors on dopaminergic neurons was studied by microdialysis in conscious male rats. Varying concentrations of 3 specific EAA agonists, N-methyl-D-aspartate (NMDA), kainate and amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA), were infused into the striatum or into the substantia nigra, and the extracellular dopamine (DA) was recorded by the same probe. All 3 compounds induced a dose-dependent increase in both striatal and nigral extracellular DA. Kainate and AMPA were more potent than NMDA. Nigral DA release was stimulated by lower concentrations of kainate and AMPA than striatal DA release. The effects of two concentrations of NMDA and kainate on the release of DA were analyzed in terms of tetrodotoxin (TTX) dependency and sensitivity to ibotenic acid-induced striatal lesion. It appeared that NMDA and kainate stimulated DA release by 3 different mechanisms. The first mechanism is seen at low concentrations of kainate, it fulfills the criteria for a functional receptor-interaction: it is TTX-sensitive and independent of the ibotenic acid lesion. The second mechanism was observed when relatively low concentrations of NMDA stimulate the release of DA; in this effect postsynaptic structures are involved. The third mechanism lacks specificity as it is seen after high concentrations of kainate as well as of NMDA. The latter mechanism is TTX-independent and is probably of a toxic nature. Finally NMDA and kainate were infused into the nigra, whereas DA was recorded with a second probe implanted into the striatum. Kainate and NMDA induced an increase of striatal DA, but kainate was about 100 times more potent in this model than NMDA. The present data therefore support localization of kainate and (probably) AMPA-receptors on nigrostriatal dopaminergic neurons. The receptors on the somatodendritic sites were observed to be more sensitive than those on the nerve terminals.

Send offprint requests to B, H.C. Westerink at the above address

Key words: Dopamine - Substantia nigra - Striatum Excitatory amino acid receptors - Microdialysis

Introduction There is growing evidence that the endogenous amino acids glutamate and aspartate participate in projections to dopaminergic cell bodies or nerve terminals of nigrostriatal neurons (Fonnum et al. 1981; Carter 1982; Fonnum 1984). Elucidation of the glutaminergic nature of corticostriatal and corticonigral projections is of possible clinical significance. Such studies may provide a new strategy to treat disorders that are caused by deficiencies in nigrostriatal dopaminergic neurotransmission, such as Parkinson's disease. Stimulatory effects of glutamate and aspartate on the release of dopamine (DA) have been described in tissue slices (Roberts and Sharif 1978; Roberts and Anderson 1979; Jhamandas and Marien 1987; Clow and Jhamandas 1989; Krebs et al. 1991), in cultured cells (Mount et al. 1990) and in vivo models (Ch6ramy et al. 1986; Girault et al. 1986; Carter et al. 1988; Westerink et al. 1989; Leviel et al. 1990; Shimizu et al. 1990). Glutamate and aspartate may activate a set of excitatory amino acid (EAA) receptor subtypes that are named after the preferred agonists: N-methyl-D-aspartate (NMDA), amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA), and kainate. Evidence that each of these agonists was able to stimulate 3H-DA release from dopaminergic cells came from studies using mesencephalic cultures (Mount et al. 1990). Although most authors agree that EAAs are able to release DA from nerve terminals of nigrostriatal dopaminergic neurons, there are several questions to be answered. Leviel et al. 0990) described a biphasic effect of glutamate infusion in a push-pull perfused rat, whereas others, using the microdialysis technique, questioned the significance of the effect of glutamate on DA release (Moghaddam et al. 1990). In addition it is unclear wheth-

524 er the effects o f t h e E A A s are direct or indirect a n d which subtype o f receptor is involved. F o r example in a recent study o n brain slices a n d s y n a p t o s o m e s Krebs et al. (1991) described t h a t N M D A directly influences the release o f D A f r o m nerve terminals, whereas microdialysis studies co u l d n o t provide evidence for the presence o f a N M D A - r e c e p t o r o n d o p a m i n e r g i c nerve t e r m i n a ls (Carter et al. 1988; I m p e r a t o et al. 1990a, b). In the present study were have studied th e possible localization o f E A A receptors o n d o p a m i n e r g i c neurons u s i n g - t h e microdialysis t e c h n i q u e in c o n s c i o u s animals. T h e possible i n t e r a c t i o n b e t w e e n E A A receptors an d dop a m i n e release was investigated at 3 different levels. First, varying c o n c e n t r a t i o n s o f the 3 specific E A A agonists N M D A , kainate a n d A M P A were i n f u s e d into the striatum, an d the release o f striatal D A was recorded by the same probe. Next, the m e c h a n i s m s o f the effect o f N M D A an d kainate on striatal D A release were analyzed in terms o f t e t r o d o t o x i n ( T T X ) - d e p e n d e n c y a n d sensitivity to ibotenic a c i d - i n d u c e d lesions. T T X - c o i n f u s i o n reveals the possible i m p u l s e - f l o w d e p e n d e n c y o f the observed effects and c h r o n ic ibotenic acid lesions o f the s t r i a t u m indicate the c o n t r i b u t i o n o f p o s t- s y n a p t i c cell bodies. Secondly, the i n v o l v e m e n t o f E A A s o n cell b o d i e s/ de n d ri t es o f d o p a m i n e r g i c cells was investigated by i n f u s i o n o f E A A s into the substantia nigra during recording o f nigral DA. Fi n a ll y N M D A a n d kainate were infused into the substantia nigra, and D A was recorded with a second p r o b e i m p l a n t e d into the ipsilateral striaturn.

Materials and methods Animals, drug treatment and lesions. Male albino rats of a Wistar derived strain (275-320 g) (C.D.L., Groningen, The Netherlands) were used for the experiments. The rats were housed in plastic cages (35 × 35 ×40 cm) and allowed free access to food and water. The following drugs were used: NMPA, AMPA (Tocris Neuramin, Essex, England), nomifensine (Hoechst, Frankfurt, FRG), kainate, ibotenic acid and tetrodotoxin (Sigma Chemical Co., St. Louis, Mo., USA). The drugs were first dissolved in water in a concentration of 10 mmol/1 and further diluted with the perfusion fluid. Unilateral lesions were made by injecting stereotaxically 10 gg ibotenic acid into the striatum in a volume of 1 gl; coordinates were: A/P 0.7, L/M 2.5 and V/D 6.0 from bregma point and dura. Microdialysis experiments were carried out 2 weeks later. The functional efficacy of the ibotenic acid lesion was evaluated by determining the acetylcholine output (in successfully lesioned animals this output was decreased by more than 90% when compared to the control side).

Surgery and brain dialysis. Microdialysis recordings and infusions were performed with a I-shaped cannula (Santiago and Westerink 1990). The exposed tip of the dialysis membrane was 2 mm (substantia nigra) or 4 mm (striatum). The dialysis tube (ID: 0.22 mm; OD: 0.31 mm) was prepared from ployacrylonitrile/sodium methalyl sulfonate copolymer (AN 69, Hospal, Bologna, Italy). The in vitro efficiency of the probe (4 mm exposed) for DA was 23.2+ 1.9°/0 (mean_+SEM; n = 4). Coordinates for the nigral cannula were: A/P 3.8, L/M 3.8, V/D 8.7, from the interaural line, at an angle of 12°; and for the striatal cannula: A/P 0.7, L/M 2.5, V/D 6.0, from bregma point and dura. The probes were implanted during general chloral hydrate anaesthesia (400 mg/kg, i.p.) and local lidocaine (6o/0) anaesthesia. The perfusion experiments were carried out 24-48 h after implantation of the probe. Brain dialysis of DA was performed with a fully auto-

mated on-line system as described elsewhere (Westerink et al. 1987). In brief, two polyethylene tubes (length: 45cm; inner diameter = 0.28 mm) were connected to the outlets of the dialysis tube. One tube was connected to the perfusion pump, and the other to the injection valve of the HPLC apparatus. The connection with the HPLC equipment introduced a lag time of about 30 min, for which the data presented are corrected. With the help of an electronic timer, the injection valve was held in the load position for 15 min, during which the sample loop (40 ~tl) was filled with dialysate. The valve then switched automatically to the injection position for 15 s. This procedure was repeated every 15 min, which was the time needed to record a complete chromatogram. The substantia nigra and the striatum were perfused with a Ringer solution at a flow rate of 2.8-3.0 ~tl/min (perfusor VI, B. Braun, Melsungen, FRG). The composition of the Ringer solution was (in mmol/1): NaC1, 140.0; KC1, 4.0; CaC12, 1.2; and MgC1z, 1.0. In the case of perfusion of the substantia nigra the DA uptake inhibitor nomifensine was added to the perfusion fluid in a concentration of 5 gmol/1. When the experiment was terminated the rat was given an overdose of chloral hydrate and the brain was fixed with 4°70 paraformaldehyde via intracardiac perfusion. Coronal sections (40 gm thick) were made, and the placement of the dialysis probes localized according to the atlas of Paxinos and Watson (1982).

Chemical assays. DA and 3,4-dihydroxyphenylacetic acid (DOPAC) were quantitated by HPLC with electrochemical detection. A Perkin-E1mer series 10 HPLC pump was used in conjunction with a glassy carbon working electrode set at -780 mV (with respect to an Ag/AgC1 reference electrode) (ANTEC, Leiden, The Netherlands). An Altech-RSL cartridge (150×4,6 mm) column filled with reverse-phase Cls 5 ~tm material was used. The mobile phase consisted of a mixture of 0.1 mol/1 of sodium acetate adjusted to a pH 4.1 with acetic acid, t.8 tool/1 of 1heptanesulfonic acid, 0.3 mmol/1 of NA2EDTA, and 120ml methanol/l; at a flow of 0.7 ml/min. The detection limit of the assay was about 10-15 fmol per sample. Expression of results and statistics. The average of the last four stable samples before the drug treatment was considered as the control and was defined as 100O7o.All values given are expressed as percentages of controls. Differences between the average dialysate concentrations of the control and drug treatment (Figs. 1- 3, 6 and 7) were compared by Kruskal-Wallis analysis of variance by ranks and; where appropriate (Hvalue greater than the 95°7o confidence level) comparison of the means was carried out using the Wilcoxon matched-pairs signed-ranks two-sided test. The data presented in Figs. 4 and 5 were analyzed by Student's t-test.

Results Basal values T h e average basal values o f the extracellular c o n c e n t r a tions o f D A for the different experiments (except for the i b o t e n i c acid lesioned animals) did n o t differ significantly. T h e r e f o r e they are g r o u p e d here together. Basal values o f D A in striatal perfusates were 9.8_+0.5 f m o l / m i n (_+ S E M , n = 30). Basal values o f D A r e c o r d e d f r o m ibotenic acid pretreated an i m al s were 6.1 + 1.2 f m o l / m i n (n = 10). T h e c o n c e n t r a t i o n o f extracellular D A in the substantia nigra (in the presence o f 5 ~tmol/l n o m i f e n s i n e ) was 5.2+_0.8 f m o l / m i n (n = 30). Basal values o f D O P A C ( of t h e experiments given in Fig. 6 and 7) were 0.58 -+0.05 p m o l / m i n (n = 10).

Effect o f N M D A , infused into the striatum or the substantia nigra, on the dialysate content o f striatal and nigral D A N M D A was infused during 60 m i n into the s t r i a t u m in a c o n c e n t r a t i o n o f 0.1, 0.3 or 1 m m o l / l . T h e extracellular

525 SUBSTANTIA NIGRA

STRIATUM

t DA release

1000

1000

% of controls 500

500

400

40O

3OO

30O

2oo

200

100

100

T I 0

1

2

i

i

I I

0

h

i

I 2

I

I h

Effect of AMPA, infused into the striatum or the substantia nigra, on the dialysate content of striatal and nigral DA

Effect of kainate, infused into the striatum or the substantia nigra, on the dialysate content of striatal and nigral DA

AMPA was infused during 60 min into the striatum in a concentration of 0.03, 0.1 or 1 mmol/1. The extracellular content of striatal DA was recorded with the infusion cannula (Fig. 3, left panel). Infusion of 0.03 mmol/1 AMPA was without effect on the release of striatal DA. Infusion of 0.1 retool/1 induced a slight but statistically significant increase in the release of DA to about 125% of basal values. Infusion of I ram•l/1 AMPA induced an increase in extracellular DA to approx. 275°7o of controls. The latter increase was statistically significant.

Kainate was infused during 60 rain into the striatum in a concentration of 0.03, 0.1 or 0.3 ram•l/1. The extracellular content of striatal DA was recorded with the infusion cannula (Fig. 2, left panel). The increases were statistically significant. Infusion of 0.03 ram•l/1 had a slight but statistically non-significant effect on the release of DA. Infusion of 0.1 or 0.3 ~tmol/1 kainate increased the extracellular DA to respectively 190 and 580% of basal values.

STRIATUM

I

Kainate was infused during 60 min into the substantia nigra in a concentration of 0.01 or 0.03 mmol/1. The extracellular content of nigral DA was recorded with the infusion cannula (Fig. 2, right panel). Kainate had a dosedependent stimulatory effect on the release of DA from the nigra, and kainate stimulated the release of DA more in the nigra than in the striatum. Infusion of 0.01 and 0.03 mmol/1 kainate increased the extracellular DA in the nigra to respectively 150 and 210% of basal values.

content of striatal DA was recorded with the infusion cannula. Infusion of 0.1 ram•l/1 NMDA was without effect on the extracellular DA concentration, whereas 0.3 or 1 mmol/1 increased the extracellular DA to respectively 220% and 1350% of basal values (Fig. 1, left panel). These increases were statistically significant. NMDA was infused during 60 min into the substantia nigra in a concentration of 0.3 or 1 mmol/1. The extracellular content of nigral DA was recorded with the infusion cannula (Fig. 1, right panel), the increases in nigral DA as percentages of controls were very similar to the ones obtained in the striatum.

t

Fig. 1. Left panel: effect of NMDA, infused during 60 min (black bar) into the striatum, on the release of striatal DA. Concentrations of N M D A were: 0.1 mmol/1 ([] .77); 0.3 mmol/1 ( 0 e ) and 1 mmol/1 (o 0). Right panel: Effect of NMDA, infused during 60 min into the substantia nigra, on the release of nigral DA. Concentrations of N M D A were: 0.3 ram•l/1 ( 0 •) and 1 mmol/1 ( o • ). The values are expressed as % of controls (_+SEM); n = 4

SUBSTANTIA NI6RA 1000 [

1000

DA release 96 of controls 500

500 ]

400

400 1

300

300

200

200

100

100

T~ , 0

,

,

i

;

1

2

,

i

t,

Fig. 2. Left panel: effect of kainate, infused during 60 min (black bar) into the striatum, on the release of striatal DA. Concentrations of kainate were: 0.03 ram•l/1 ( • • ); 0.1 mrnol/1 ( o O) and 0.3 mmol/1 (11 i ) . Right panel: Effect of kainate, infused during 60 min into the substantia nigra, on the release of nigral DA. Concentrations of kainate were: 0.01 m m o l / l (• - • ) and 0.03 mrnol/1 (© ©). The values are expressed as % of controls (+_SEM); n = 4

i 0

1

2

526 STRIATUM

t

SUBSTANTIA NIGRA

300

300

200

200

DA release 96 of controls

100

Fig. 3. Left panel: effect of AMPA, infused during 60 min (black panel) into the striatum, on the release of striatal DA. Concentrations of AMPA were: 0.03 mmol/1 ( • • ); 0.1 mmol/1 (11 i ) and 1 mmol/1 (© ©). Right panel: Effect of AMPA, infused during 60 min into the substantia nigra, on the release of nigral DA. Concentration of AMPA were: 0.01 mol/1 ( • •) and 0.1 mmol/1 (O ©). The values are expressed as °70 of controls (+SEM), n = 4

100

i

i

f i l l

0

, , 1 1 1 1 2

1

I

i

h

[ 1

I

A M P A was infused during 60 min into the substantia nigra in a concentration o f 0.01 or 0.1 mmol/1. The extracellular content o f nigral DA was recorded with the infusion cannula. Figure 3, right panel, shows that the extracellular D A in the nigra rose to 145 and 220°70 o f basal values after 0.01 and 0.1 mmol/1, respectively. Similarly to findings concerning kainate it is concluded that nigral D A release is more sensitive to A M P A than is striatal DA.

I 2

I

Ih

In the case o f kainate-induced D A release the experiments with T T X also pointed to two different mechanisms : at 0.1 mmol/1 kainate the induced DA release was completely TTX-independent, whereas at 0.3 m m o l / l kainate about 50°7o o f the induced DA release was TTXindependent. These results indicate that b o t h N M D A and kainate induce DA release by two different mechanisms, one o f which that is TTX-dependent and a second that is TTXindependent. The kainic acid-experiment indicates that the latter mechanism is relevant at higher doses.

Effect o f co-infusion with T T X on the N M D A and kainate-induced increase in extracellular D A in the striatum

Effect o f ibotenic acid lesion o f the striatum on the N M D A and kainate-induced increase in extracellular DA in the striatum

The increases in extracellular content o f DA recorded f r o m the striatum during infusion o f N M D A and kainate were investigated for their TTX-dependency. Two different concentrations o f N M D A (0.3 and 1 mmol/1) and kainate (0.1 and 0.3 m m o l / l ) were investigated. Infusion o f T T X in a concentration o f 1 ~tmol/1 resulted in a pron o u n c e d decrease o f extracellular DA to about 10°70 o f basal values (Figs. 4 and 5). T T X suppressed statistically significantly the DA-releasing effects o f both doses o f N M D A . It is also evident from Fig. 4 that a second TTX-independent mechanism is evident in the DA-releasing effects o f N M D A . The increase in D A release during combined N M D A and T T X infusion c o m p a r e d with TTX-infusion alone was highly significant at b o t h concentrations.

700

L

The increases in extracellular content o f DA recorded from the striatum during infusion o f N M D A or kainate were investigated for their dependency on pretreatment with ibotenic acid. Rats were pretreated unilaterally in the striatum with ibotenic acid and a dialysis probe was implanted in the same striatum two weeks later. Two different concentrations o f N M D A (0.3 and 1 mmol/1) and kainate (0.1 and 0.3 mmol/1) were investigated. Basal values o f ibotenic acid pretreated rats were defined as 100°70 (Figs. 4 and 5). The increase o f D A during infusion o f 0.3 as well as 1 mmol/1 N M D A was absent in ibotenic acid pretreated

i

t DA release % of controls 400

300

200

100

100%

=

KAINATE 10-4M TTX

IA-LESION

--

+

i

i

--

+

+

+

--

+

KAINATE 3 IT×

+

+

IA-LESION

xlU-4M

--

+

--

+

--

+

+

+

--

_

+

+

Fig. 4. Effect of co-infusion with TTX (1 ~mol/1) or a striatal ibotenic acid lesion (IA-lesion) on the NMDA-induced increase in striatal DA release. The values are expressed as 070 of controls (±SEM); n = 4. The untreated rats and the IA-control group are defined as 10007o.Two different concentrations of NMDA were investigated: 0.3 mmol/1 (left panel) and 1 mmol/1 (right panel). *P

The release of dopamine from nerve terminals and dendrites of nigrostriatal neurons induced by excitatory amino acids in the conscious rat.

The possible localization of excitatory amino acid (EAA) receptors on dopaminergic neurons was studied by microdialysis in conscious male rats. Varyin...
750KB Sizes 0 Downloads 0 Views