Life Sciences Vol . 17, pp . Printed in the U .S .A .
1451-1456
Pergamon Press
CORTICOSTERONE-INDUCED GONADOSUPPRESSION IN PHOTOSTIMULATED TREE SPARROWS Fred E . Wilson and Brian K . Follett Division of Biology, Ransae State Uaiversity, Manhattan, Ransas 66506, and Department of Zoology, Uaiversity College of North Wales, Bangor, Gwynedd, U .K . (Received in final form October 9, 1975) Summary To explore the possibility that adrenal hormones play a role is the natural termination of testicular function in chronically photostimulated tree sparrows, corticoeterone, the principal adrenal ster oid of birds, was implanted intracerebrally in photoresponaive tree sparrows 3 weeks after they were transferred to a gonadostimulatory photoragime . Three weeks later, plasmas were assayed for immuaoreactive luteiaizing hormone (LH), testes were weighed, sad implantation sites ware determined . When implanted in a region of the basal hypothalamw known to be androgen sensitive, corticoeterone reduced the concentration of plasma LH and blocked testicular growth . Control implants is the optic chiasma or tracts ware not gonadoinhibitory . Thasa results confirm the potnatial for inhibition of goaedotropia secretion by as effect of corticoeterone on the hypothalapohypophyseal aais, but the physiological significance and mechanism of corticoaterona's antigonadotropic effect remain to be established . The annual breeding seasons of many photopariodic species of birds and in summer, while dagleagths are still long (1) . Collapse of the gonads appears to be a manifestation of goaadotropic insufficiency (2-6), but despite conslder able study, the etiology of the insufficiency remains unkaowa . Some data on male tree sparrows (7,8) suggest that feedback of androgen onto the hypothalamohypophyaeal axis triggers the seasonal reduction in gonadotropia sacrstioa, yet the observation that chronically photostimulatad castrates have a cycle is plasma LH concentratioa temporally similar to that of intact melee (5) indicates that testicular steroids are not obligatory determinants of the annual cycle of goasdotropin secretion . To e:plaia the nearly ayachroaow LH cycles of castrated sad intact males, Wilson and Follett (5) speculated that castrates might become refractory to photostimulatioa about the same time as intact males if corticoeterone, the principal adrenal steroid hormone of birds (9), could activate the aadrogea fnadbaek mechanism that inhibits gonadotropia secretion . Adrenal-gonad interrelations is birds are poorly understood, but caatratioa in some species reportedly eahaaces adrenal steroid ascretion (9,10), an affect that can be reversed by androgen raplacemeat therapy . Moreover, in mammals, activation of the hypothalamohypophyseal-adrenal axis ie thought to inhibit goaadotropin secretion (11,12), possibly by a nonspecific effect of corticoateroids oa the goaadal feedback mechanism (11) . The possibility that adrenal function influences the reproductive cycles of photopariodic species of birds had been emphasized earlier by Meier et al . (13), who attributed the seasonal conditions of photosensitivity and photorafractoriness to seasonal changes in the relation between the daily rhgthms of corticoeterone sad prolactin secretion . 1451
1452
Corticosterone-Induced Goaadosuppreasion
Vol . 17, No . 9
To clarify whether adrenal etaroida affect the avian hypothalamohypophyseal-gonadal azia, wa implanted corticosteroas intracerabrally in photostimulated tree sparrows . Implantation sites ware regions above in earlier azperi mnata (7,8) to ba androgen seaaitiva or androgen insaneitive . The data, the first to show that corticosteroas can inhibit gonadotropin (LH) secretion in birds by an effect on the hypothalamohypophyeaal azia, confirm the potential for a role of adrenal steroids in the natural termination of testicular function in photoperiodic species . Methods Male tree sparrows (Spizalla arboraa , captured between November 25 and December 15, 1973, near Manhattan, Raasas, ware bald on 8-hr (0830-1630) daily photopariods (BL) until mid-April, 1974, when they were transferred to a gona [For maintenance conditions, indoatimulatory photoregimn (20L (0830-0430)) . cluding source sad intensity of illumination, sea (8) .) Three weeks later, five birds were sacrificed ae initial controls, and each of 13 others was subjected to iatracerebral implantation (7) of a 24-gauge, atainlasa-steal tube (o .d . ~ 0.56 ma ; i .d . ~ 0.30 mn) containing 459 t 41 ug corticosteroas (4-pregnea-118,21-dio1-3,20-dione) nixed homogeneously with cocoa butter (1 :1 w/w) . Corticoeterone-implanted birds were held 3 additional weeks on 20L. Control sad corticostarona-implanted birds were sacrificed at "dawn" by ezsanguiaation (5) . Plasmas were made approzimataly O.lx is sodium nude and stored at -7° until ahippad via air mail to Hangor, Wales, whore they ware aa sagad for LH according to Follatt et al . (14) . Teems and adrenal glands were fund 5 days is 95x ethaaol :glacialâcatic acid :foroalin :watnr (3 :1 :1 :5), déBrains of corticostarona-implanted birds bridnd in 70x ethanol, sad weighed. ware fund 3-4 days in Bouin's fluid, sectioned at 10 um, stained with paraldehyda-fuchsia, and examined microscopically to determine implantation sites . Data ware subjected to one-way analysis of variance after that' were transformed logarithmically to reduce lutsroganaity of variance . Multiple compariSignificance was desons ware by Student-Newmaa-Rains' multiple range test . fined as P < 0 .05 . Results Five birds were sacrificed on day 21 of photostimulatioa to estimate testicular weight and concentration of plasma LH at implantation . Aa indicated in Table 1, there was considerable variation among initial controls : Testicular TABLE 1 Effects on Plasma L8, Testicular Weight, and Adrenal Weight of Corticostsroaa Dnplaatad Intracnrabrally is Photostimulated Trae Sparrows Groupl
Days on 20L
Plasma LH 2 z ng/ml t SD
Testicular wt 2 z mg ± SD
Adrenal wt z mg t SF1~!
IC (5) EC (5) TC (8)
21 42 42
3.38 t 1 .46a 1.31 ± 0.36b 3.07 t 0.90a
28 .99 t 29 .60b 18 .54 t 26 .40b 296 .2 t 138 .9a
1 .29 _ " 0.05 1 .26 ± 0 .11 1 .35 ± 0.05
IIC, initial controls ; EC, birds with effective implanta ; TC, birds with iaaffactivs iaplaata (terminal controls) . Number of birds in each group is indicated in par~thsaaa . Corticosterona was implanted is birds of groups EC sad TC on day 21 . ZBasad on logarithmically tranaformad data, groups sharing a common auperacript do not differ significantly (P > 0 .05) .
Vol . 17, No . 9
Corticosterone-induced Gonadosuppreesion
1453
weight ragged from 9 to 80 mg, and plasma LH concentration ranged from 1 .5 to 5.4 ng/ml . Teatea of five corticoataroae-implanted birds sacrificed 21 days later fell within or below the range of weights of initial controls, gad plasma LH was significantly below the control level (Table 1) . Gonadosuppresaiva (effnctiva) lmplanta were confined to the aatnrobaaal infundibular nucleus of the hypothalamus or its common border with the anterior median eminence and optic chiasma or tracts (Fig . 1) . Teatea of eight other corticoataroae implanted
FIG. 1 Schematic parasagittal section through the basal hypothalamus showing locations of corticoataroae implants in photostimulatad tree sparrows . e effective implant (testicular growth arrested gad plasma LH reduced) ; o ineffective implant ; BIN banal iafuadibular nucleus ; EM madiaa emiaaace ; C optic chiaeva/tract ; NL neural lobe . Carrier tubas aztanded aatarodorsally (parallel to caudal margin of optic chiasma) from implantation sites . birds were significantly heavier than those of either initial controls or effectively implanted birds, gad plasma LH was at the control level (Table 1) . With one azception, inaffective implante were confined to the optic chiasma oz tracts (Fig . 1) . Adrenal weight was unaffected by corticoataroae implanted in any location (Table 1 ; Fig . 1) . Diacusaion This study shows that chronic intrahypothalamic implanutioa of 24-gauge tubes coatainiag corticoeterone gad cocoa butter can inhibit testicular growth in photostimulated tree sparrows . The possibility that implants ware gonado suppraseive because of tissue elimination or damage or because of a noaspacific chemical effect is unlikely : Ia earlier studios on tree sparrows, empty or cholesterol filled 27-gauge tubes (o .d . ~ 0 .41 mm ; i.d . ~ 0.20 mm) implanted in or sear the corticoataroae-seasitlve cone defined here did got block testicular growth (7), nor did cholesterol gad cocoa butter in 27-gauge tubes induce testicular regreaeioa (B) . Therefore, ttse gonadosuppression observed in this study was probably corticoeterone dependent . Moreover, it was probably due to local affects of the hormone on the hypothalamohypophyeeal a=ia . If corticoeterone had acted systemically, peripheral to the hypothalamohypophyseal azie, all intracerebral Implants should have base inhibitory or, üternativüy, iahibitlon should have been unrelated to implant location : With affective implants clustered is the tuberoinfuadibular region of the hypothalamus gad ineffective implante confined, with one azception, to the optic chiasma or tracts, the data argue comrincingly for regional corticoeterone sensitivity . That effective corticoeterone implanta induced goasdotropic iaaufficieacy was confirmed by the observation that plasma LH concentration was suppressed 3 weaka after implaata-
145 4
Corticostarone-Induced Conadosuppresaion
vol . 17, No . 9
tioa . Ia view of the recently damonatratad fuactione of avian FSH (15-17), the plasma lwnl of that gonadotropia probably was reduced ae well . Although the basis of the aatigonadotropic affect of corticoeterona is unknown, there are several poasibla e>plaaations : 1) Corticoetaronn might hwa activated the hypothalamohypophysaal inhibitory feedback mechanism ahovn by intracerebral implantation of androgen (7,8, 18-21) and bq castration (5,22) to influence gonadotropin secretion in photore aponsivs birds . The findiage that (a) corticosterone and testosterone propionate have similar postimplantatioa effacta on photoperiodic tnaticular growth (cf . 8), and (b) the basal hypothalamic zone sensitive to corticoeterona is virtually identical with the basal hypothalamic zoaa sensitive to androgen in several apscias, including tree sparrows, support that view . Ia a recent study on castrated ring doves, Stern (23) showed that cozticoatarone inhibited accumulation by both hypothalamus and pare diatalis of a 3H-tastoatarona metabolite having the chromatographic mobility of dihydrotastoatarona, an androgaa with pronouacnd antigoaadotropic prapartias (24) . Corticosteroae also reduced uptake bq pare diatalis, but not by hypothalamus, of 3 H-testosterone . The functional significance of Stern's observations is uakaown, but they, too, suggest that corticostaroas and androgaa may compete for nonspecific antigonadotropic receptors along the hypothalamohypophysnal a:ie . A similar conclusion was reached by Smith et al . (11), who reported that chronic intrahypothalamic implantation of cortisol acetate inhibited dwelopmeat of the reproductive syatams of immature rats . Aa is our study, the corticoataroid-sanaitiva region was the msdial basal hypothalamus, a region pravioualy implicated is inhibitory feedback control of gonadotropia secretion is mammals . Further widenca for as aatigonadotropic affect of corticoetaroids was scantly provided by Baldwin and Sawyer (12), who showed that systemic injections of the synthetic glucocorticoid daa:amethasona blocked the praovulatory aurgs of LH in rats, possibly by acting dirsctly on the pats diatalis . 2) Supported by widenca that adrenal ataroids era important synchroaizara of daily rhythms, Maier et al . (13) poatulatad that a unique temporal synergism of corticoeterona and prolactin, fazed by their daily rhythms of secretion, accounts for reproductive photosensitivity in soma birds . Seasonal changes in the relationship between the daily rhythms of hormone eecration, they argued, control the annual cycle of photosensitivity and photorefractorineas . If their position is valid, abolishing the daily rhythm of corticoeterona availability at some, as yet unknown, target in photosenaitiva birds ought to iaduca gonadosuppraesion daapita continued photoatimulation . Reaulta of this study am conaiataat with that prediction, for it can be assumed that goaadosuppresaive implants released corticosterone continuously is amouata sufficient to mask, at least at the hypothalamohypophysaal level (targat4), daily fluctuations is endogenous corticosterone (25) . Altarnativaly, gonadosuppresalva implants, by ezartiag as aatiadrenocorticotropic effect, might have eliminated an ACTH-dependaat daily rhythm of corticoeterona secretion (9) . This ezplanatioa lacks strong support, however, as affective implants usually lay outside hypothalamic zones that affect corticosteroidoganeais in chickens (26) and pigeons (27) . [That adrenal weights of effectively implanted birds did not differ from those of initial or terminal controls supports neither interpretation, for adrenal weight and function correlate poorly (26,27) .] 3) Corticoatarona might have been gonadosupprasaive because of effects oa gonadotropin secretion of corticosterone-induced alterations in thyroid function . Tha thyroid-gonad relationship in birds is complaz and poorly understood (9), but raceat data, showing that testosterone eecration was inhibited in both hypo- and hyperthyroid drakes, suggest that normal gonadal, poasiblq gonadotropic (28), function requires thyroid hormones in precisely regulated amouata
Vol. 17, No . 9
Corticosterone-InBuced Gonadosuppreasion
1455
(29) . Even less clear is the avian adrenal-thyroid relationship . Ia mammals, however, corticoateroide, iacludiag dexamathasoae, reportedly affect thyroid function indirectly by acting on both hypothalamus and pituitary (11,30) . It seems unlikely, though, that thyroid function was modified by as affect of corticosteroae on the hypothalamus, for hypothalamic areas knows to regulate TSH aecratioa is birds (31) are anterior sad dorsal to the corticosteroae-seaeitive cone demonstrated in tree sparrows . 4) Inasmuch ae adrenal steroids inhibit eacretlon of most pituitary tropic hormones (e .g ., ACTH (32) ; TSH (11,30) ; GH (33) ; LH (12)] and altar firing rates of hypothalamic aeurona (34), corticoatarona might have impaired LH re lease by exerting a nonspecific deprsasaat affect on aaurona coataiaiag LH-relnaeiag hormone or by affacti.ng the activity of "ordinary" neurons that interact with them . Support for this visa+ stems from the observation that the basal hypothalamic region shown by ablation to control gonadotropin secretion 1a several species of birds (35) iacludea the tuberoinfuadibular sons ssasitive to corticosteroae is tree sparrows . The data preaentad here make mars credible the speculation that corticosteroae might have iaactivatsd the LH-control mechanism in chronically photostimulated castrated tree sparrows (5) . But whether control of gonadotropia secretion is a physiologically significant function of the principal adrenal steroid of birds remains unresolved, as does the mechanise by which increased local concentrations of corticosteroae in the basal hypothalamus iaducsd gonadotropic iasufficieacy . Ackaowlsdgmeate This is contribution ao . 1265, Diviaioa of Biology, Keaaas Agricultural Ezperimsat Station, Manhattan 66506. We era grateful to A. D. Dayton for atatiatical advice and to C. L. Chen, A. P . Labhsetwar, and A. H. Meier for read ing the manuscript . This investigation was aupportsd in part by grants from the Biology Research Fund sad the Agricultural Research Council (AB18/1) . Refersacas 1. 2. 3. 4. 5. 6. 7. 8. 9. 10 . 11 . 12 . 13 . 14 .
B. LOFTS and R . K. MIIRTO~N, J. Zool ., Lond . 155 327-394 (1968) . F. GREELEY and R. R. MEYER, Auk 70 350-358 (1953) . J. R. RING, B. R. FOLLETT, D . S.FARMER, sad M. L. MORTON, Condor 68 476-487 (1966) . M. H. ST$TSO~i and J . E. ERICKSON, Gea . ÇOm~ . Endocrinol . 17 105-114 (1971) . F. E. WILSON and B. R. FOLLETT, _Gee . Comp . Endocrinol . 23 82-93 (1974) . B. R. FOLLETT, D . S . FARMER, and P. W. MATTOCKS, JR ., Gea. Comp . 8ndocriaol . 26 126-134 (1975) . F . E. WILSON, Aspects of Neuroeadocrinology (Ed . W. Bergmann and B. Scharrer), pp . 274-286 Springar-Verlag, Berlin (1970) . E. R. CUSICR and F . E . WILSON, Gee. Com . Eadocrinol . 19 441-456 (1972) . I . ASSENMACHER, Avisa Biology (Ed. D . S . Ferner and J. R. Ring ), vol. III, pp . 183-286 Academic Press, New York (1973) . - om~. Endocrinol . 20 144-149 S. W. C . CHAN and J. G. PHII.LIPS, Gea. C (1973) . E . R. SMITH, J . JOHNSON, R . F. WEICR, S . LSVIIJE, and J . M. DAVIDSOQi, Nauroendocrinology 8 94-106 (1971) . D. M. BALDWIN and C. H. SAWYBx, Endocrinology 94 1397-1403 (1974) . A. H. MEIER, D . D. MARTIN, sad R . MACGREGOR, III, Science 173 1240-1242 (1971) . B. R. FOLLETT, C . G. SCANES, sad F. J. CONNINGHAM, J . Eadocr . 52 359-378 (1972) .
1456 15 . 16 . 17 . 18 . 19 . 20 . 21 . 22 . 23 . 24 . 25 . 26 . 27 . 28 . 29 . 30 . 31 . 32 . 33 . 34 . 35 .
Corticrosterona-Induced Gônadoaupprssaion
Vol . 17, No . 9
S . ISHII and T . FURUYA, G~a . -C~ . Eadocriaol . 25 1-8 (1975) . . FOLLETT, Cell Tiss . Rea . N . L . BROWN, J . D . BAYLE, C . G . SCANES, and B. R 156 499-520 (1975) . W. S. FARMER, H. PAPROFF, and P . LICHT, Biol . Reprod . 12 415-422 (1975) . F . GOGAN, Gea . ~. Endocrinol . 11 316-327 (1968) . M. H . STETSON, Gee . Com . Endocrincl . 19 37-47 (1972) . M . WADA, _Z . Zollforsch . 124 507-519 (1972) . H . R . FOLLETT, Breading Biology of Birds (Ed . D . S . Farnar), pp . 209-243 National Academy of Sciaacas, Washington, D .C . (1973) . W . R . GIBBON, B . R. FOLLEPT, and B . GLEDHILL, J . Sadocr . 64 87-101 (1975) . J . M . STERN, Gaa . Cow. Endocrinol . 18 439-449(1972) . H . H . FIER, Éadocr J. . 51 241-252 (1971) . J . W . DUSSBAIJand A . H . MBIER, Cwn . Comp . Eadocriaol . 16 399-408 (1971) . A . I . FRANREL, J . W . GRASER, and A . 0 . NALBANDOfi, Gee . Comte. Eadocrinol . 8 387-396 (1967) . C . BOUILLE and J . D . SAYLE, Neuroandocriaology 11 73-91 (1973) . M . JALLAGFAS, I . ASSBlQlACHER, and B . & . FOLLEIT, GQn . CootP . Endocrinol . 23 472-475 (1974) . M . JALLAiGEAS and I . ASSEI~IIlACHF.R, Gan . COm~. Endocriaol . 22 13-20 (1974) . T . RANTA, HndocrinologY .96 1566-1570 (1975) . H . ROBAYASHI and M . WADÂ, Avian Biology (Ed . D . S . Farnar and J . R . Ring), vol . III, pp . 287-347 Acadanic Press, Now York (1973) . G . MAIiGILI, M . MOZTA, and L . MARTIITI, Nauroaadocrinology (Ed . L . Martini and W. F . Ganoag), vol . I, pp . 297-370 Acadaotic Presa, New York (1966) . S . M . GLICR, Frontiers is Nauroandocrinology , 1969 (Ed . W . F . Ganong and L . Martini), pp " 141-182 Ôzford University Praaa, Nev York (1969) . C . BEY~ and C . H . SAWYER, Frontiers _in Nauroandocriaology , 1969 (Ed . W . F . Ganoag and L . Martini), pp " 255-287 Ozford IInivnraitq Prass, New York (1969) . F . E . WILSON, The Sun 1n the Saryicn of Mankind , B16-15 UNESCO House, Paris (1973) .
1451-1456
Pergamon Press
CORTICOSTERONE-INDUCED GONADOSUPPRESSION IN PHOTOSTIMULATED TREE SPARROWS Fred E . Wilson and Brian K . Follett Division of Biology, Ransae State Uaiversity, Manhattan, Ransas 66506, and Department of Zoology, Uaiversity College of North Wales, Bangor, Gwynedd, U .K . (Received in final form October 9, 1975) Summary To explore the possibility that adrenal hormones play a role is the natural termination of testicular function in chronically photostimulated tree sparrows, corticoeterone, the principal adrenal ster oid of birds, was implanted intracerebrally in photoresponaive tree sparrows 3 weeks after they were transferred to a gonadostimulatory photoragime . Three weeks later, plasmas were assayed for immuaoreactive luteiaizing hormone (LH), testes were weighed, sad implantation sites ware determined . When implanted in a region of the basal hypothalamw known to be androgen sensitive, corticoeterone reduced the concentration of plasma LH and blocked testicular growth . Control implants is the optic chiasma or tracts ware not gonadoinhibitory . Thasa results confirm the potnatial for inhibition of goaedotropia secretion by as effect of corticoeterone on the hypothalapohypophyseal aais, but the physiological significance and mechanism of corticoaterona's antigonadotropic effect remain to be established . The annual breeding seasons of many photopariodic species of birds and in summer, while dagleagths are still long (1) . Collapse of the gonads appears to be a manifestation of goaadotropic insufficiency (2-6), but despite conslder able study, the etiology of the insufficiency remains unkaowa . Some data on male tree sparrows (7,8) suggest that feedback of androgen onto the hypothalamohypophyaeal axis triggers the seasonal reduction in gonadotropia sacrstioa, yet the observation that chronically photostimulatad castrates have a cycle is plasma LH concentratioa temporally similar to that of intact melee (5) indicates that testicular steroids are not obligatory determinants of the annual cycle of goasdotropin secretion . To e:plaia the nearly ayachroaow LH cycles of castrated sad intact males, Wilson and Follett (5) speculated that castrates might become refractory to photostimulatioa about the same time as intact males if corticoeterone, the principal adrenal steroid hormone of birds (9), could activate the aadrogea fnadbaek mechanism that inhibits gonadotropia secretion . Adrenal-gonad interrelations is birds are poorly understood, but caatratioa in some species reportedly eahaaces adrenal steroid ascretion (9,10), an affect that can be reversed by androgen raplacemeat therapy . Moreover, in mammals, activation of the hypothalamohypophyseal-adrenal axis ie thought to inhibit goaadotropin secretion (11,12), possibly by a nonspecific effect of corticoateroids oa the goaadal feedback mechanism (11) . The possibility that adrenal function influences the reproductive cycles of photopariodic species of birds had been emphasized earlier by Meier et al . (13), who attributed the seasonal conditions of photosensitivity and photorafractoriness to seasonal changes in the relation between the daily rhgthms of corticoeterone sad prolactin secretion . 1451
1452
Corticosterone-Induced Goaadosuppreasion
Vol . 17, No . 9
To clarify whether adrenal etaroida affect the avian hypothalamohypophyseal-gonadal azia, wa implanted corticosteroas intracerabrally in photostimulated tree sparrows . Implantation sites ware regions above in earlier azperi mnata (7,8) to ba androgen seaaitiva or androgen insaneitive . The data, the first to show that corticosteroas can inhibit gonadotropin (LH) secretion in birds by an effect on the hypothalamohypophyeaal azia, confirm the potential for a role of adrenal steroids in the natural termination of testicular function in photoperiodic species . Methods Male tree sparrows (Spizalla arboraa , captured between November 25 and December 15, 1973, near Manhattan, Raasas, ware bald on 8-hr (0830-1630) daily photopariods (BL) until mid-April, 1974, when they were transferred to a gona [For maintenance conditions, indoatimulatory photoregimn (20L (0830-0430)) . cluding source sad intensity of illumination, sea (8) .) Three weeks later, five birds were sacrificed ae initial controls, and each of 13 others was subjected to iatracerebral implantation (7) of a 24-gauge, atainlasa-steal tube (o .d . ~ 0.56 ma ; i .d . ~ 0.30 mn) containing 459 t 41 ug corticosteroas (4-pregnea-118,21-dio1-3,20-dione) nixed homogeneously with cocoa butter (1 :1 w/w) . Corticoeterone-implanted birds were held 3 additional weeks on 20L. Control sad corticostarona-implanted birds were sacrificed at "dawn" by ezsanguiaation (5) . Plasmas were made approzimataly O.lx is sodium nude and stored at -7° until ahippad via air mail to Hangor, Wales, whore they ware aa sagad for LH according to Follatt et al . (14) . Teems and adrenal glands were fund 5 days is 95x ethaaol :glacialâcatic acid :foroalin :watnr (3 :1 :1 :5), déBrains of corticostarona-implanted birds bridnd in 70x ethanol, sad weighed. ware fund 3-4 days in Bouin's fluid, sectioned at 10 um, stained with paraldehyda-fuchsia, and examined microscopically to determine implantation sites . Data ware subjected to one-way analysis of variance after that' were transformed logarithmically to reduce lutsroganaity of variance . Multiple compariSignificance was desons ware by Student-Newmaa-Rains' multiple range test . fined as P < 0 .05 . Results Five birds were sacrificed on day 21 of photostimulatioa to estimate testicular weight and concentration of plasma LH at implantation . Aa indicated in Table 1, there was considerable variation among initial controls : Testicular TABLE 1 Effects on Plasma L8, Testicular Weight, and Adrenal Weight of Corticostsroaa Dnplaatad Intracnrabrally is Photostimulated Trae Sparrows Groupl
Days on 20L
Plasma LH 2 z ng/ml t SD
Testicular wt 2 z mg ± SD
Adrenal wt z mg t SF1~!
IC (5) EC (5) TC (8)
21 42 42
3.38 t 1 .46a 1.31 ± 0.36b 3.07 t 0.90a
28 .99 t 29 .60b 18 .54 t 26 .40b 296 .2 t 138 .9a
1 .29 _ " 0.05 1 .26 ± 0 .11 1 .35 ± 0.05
IIC, initial controls ; EC, birds with effective implanta ; TC, birds with iaaffactivs iaplaata (terminal controls) . Number of birds in each group is indicated in par~thsaaa . Corticosterona was implanted is birds of groups EC sad TC on day 21 . ZBasad on logarithmically tranaformad data, groups sharing a common auperacript do not differ significantly (P > 0 .05) .
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Corticosterone-induced Gonadosuppreesion
1453
weight ragged from 9 to 80 mg, and plasma LH concentration ranged from 1 .5 to 5.4 ng/ml . Teatea of five corticoataroae-implanted birds sacrificed 21 days later fell within or below the range of weights of initial controls, gad plasma LH was significantly below the control level (Table 1) . Gonadosuppresaiva (effnctiva) lmplanta were confined to the aatnrobaaal infundibular nucleus of the hypothalamus or its common border with the anterior median eminence and optic chiasma or tracts (Fig . 1) . Teatea of eight other corticoataroae implanted
FIG. 1 Schematic parasagittal section through the basal hypothalamus showing locations of corticoataroae implants in photostimulatad tree sparrows . e effective implant (testicular growth arrested gad plasma LH reduced) ; o ineffective implant ; BIN banal iafuadibular nucleus ; EM madiaa emiaaace ; C optic chiaeva/tract ; NL neural lobe . Carrier tubas aztanded aatarodorsally (parallel to caudal margin of optic chiasma) from implantation sites . birds were significantly heavier than those of either initial controls or effectively implanted birds, gad plasma LH was at the control level (Table 1) . With one azception, inaffective implante were confined to the optic chiasma oz tracts (Fig . 1) . Adrenal weight was unaffected by corticoataroae implanted in any location (Table 1 ; Fig . 1) . Diacusaion This study shows that chronic intrahypothalamic implanutioa of 24-gauge tubes coatainiag corticoeterone gad cocoa butter can inhibit testicular growth in photostimulated tree sparrows . The possibility that implants ware gonado suppraseive because of tissue elimination or damage or because of a noaspacific chemical effect is unlikely : Ia earlier studios on tree sparrows, empty or cholesterol filled 27-gauge tubes (o .d . ~ 0 .41 mm ; i.d . ~ 0.20 mm) implanted in or sear the corticoataroae-seasitlve cone defined here did got block testicular growth (7), nor did cholesterol gad cocoa butter in 27-gauge tubes induce testicular regreaeioa (B) . Therefore, ttse gonadosuppression observed in this study was probably corticoeterone dependent . Moreover, it was probably due to local affects of the hormone on the hypothalamohypophyeeal a=ia . If corticoeterone had acted systemically, peripheral to the hypothalamohypophyseal azie, all intracerebral Implants should have base inhibitory or, üternativüy, iahibitlon should have been unrelated to implant location : With affective implants clustered is the tuberoinfuadibular region of the hypothalamus gad ineffective implante confined, with one azception, to the optic chiasma or tracts, the data argue comrincingly for regional corticoeterone sensitivity . That effective corticoeterone implanta induced goasdotropic iaaufficieacy was confirmed by the observation that plasma LH concentration was suppressed 3 weaka after implaata-
145 4
Corticostarone-Induced Conadosuppresaion
vol . 17, No . 9
tioa . Ia view of the recently damonatratad fuactione of avian FSH (15-17), the plasma lwnl of that gonadotropia probably was reduced ae well . Although the basis of the aatigonadotropic affect of corticoeterona is unknown, there are several poasibla e>plaaations : 1) Corticoetaronn might hwa activated the hypothalamohypophysaal inhibitory feedback mechanism ahovn by intracerebral implantation of androgen (7,8, 18-21) and bq castration (5,22) to influence gonadotropin secretion in photore aponsivs birds . The findiage that (a) corticosterone and testosterone propionate have similar postimplantatioa effacta on photoperiodic tnaticular growth (cf . 8), and (b) the basal hypothalamic zone sensitive to corticoeterona is virtually identical with the basal hypothalamic zoaa sensitive to androgen in several apscias, including tree sparrows, support that view . Ia a recent study on castrated ring doves, Stern (23) showed that cozticoatarone inhibited accumulation by both hypothalamus and pare diatalis of a 3H-tastoatarona metabolite having the chromatographic mobility of dihydrotastoatarona, an androgaa with pronouacnd antigoaadotropic prapartias (24) . Corticosteroae also reduced uptake bq pare diatalis, but not by hypothalamus, of 3 H-testosterone . The functional significance of Stern's observations is uakaown, but they, too, suggest that corticostaroas and androgaa may compete for nonspecific antigonadotropic receptors along the hypothalamohypophysnal a:ie . A similar conclusion was reached by Smith et al . (11), who reported that chronic intrahypothalamic implantation of cortisol acetate inhibited dwelopmeat of the reproductive syatams of immature rats . Aa is our study, the corticoataroid-sanaitiva region was the msdial basal hypothalamus, a region pravioualy implicated is inhibitory feedback control of gonadotropia secretion is mammals . Further widenca for as aatigonadotropic affect of corticoetaroids was scantly provided by Baldwin and Sawyer (12), who showed that systemic injections of the synthetic glucocorticoid daa:amethasona blocked the praovulatory aurgs of LH in rats, possibly by acting dirsctly on the pats diatalis . 2) Supported by widenca that adrenal ataroids era important synchroaizara of daily rhythms, Maier et al . (13) poatulatad that a unique temporal synergism of corticoeterona and prolactin, fazed by their daily rhythms of secretion, accounts for reproductive photosensitivity in soma birds . Seasonal changes in the relationship between the daily rhythms of hormone eecration, they argued, control the annual cycle of photosensitivity and photorefractorineas . If their position is valid, abolishing the daily rhythm of corticoeterona availability at some, as yet unknown, target in photosenaitiva birds ought to iaduca gonadosuppraesion daapita continued photoatimulation . Reaulta of this study am conaiataat with that prediction, for it can be assumed that goaadosuppresaive implants released corticosterone continuously is amouata sufficient to mask, at least at the hypothalamohypophysaal level (targat4), daily fluctuations is endogenous corticosterone (25) . Altarnativaly, gonadosuppresalva implants, by ezartiag as aatiadrenocorticotropic effect, might have eliminated an ACTH-dependaat daily rhythm of corticoeterona secretion (9) . This ezplanatioa lacks strong support, however, as affective implants usually lay outside hypothalamic zones that affect corticosteroidoganeais in chickens (26) and pigeons (27) . [That adrenal weights of effectively implanted birds did not differ from those of initial or terminal controls supports neither interpretation, for adrenal weight and function correlate poorly (26,27) .] 3) Corticoatarona might have been gonadosupprasaive because of effects oa gonadotropin secretion of corticosterone-induced alterations in thyroid function . Tha thyroid-gonad relationship in birds is complaz and poorly understood (9), but raceat data, showing that testosterone eecration was inhibited in both hypo- and hyperthyroid drakes, suggest that normal gonadal, poasiblq gonadotropic (28), function requires thyroid hormones in precisely regulated amouata
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(29) . Even less clear is the avian adrenal-thyroid relationship . Ia mammals, however, corticoateroide, iacludiag dexamathasoae, reportedly affect thyroid function indirectly by acting on both hypothalamus and pituitary (11,30) . It seems unlikely, though, that thyroid function was modified by as affect of corticosteroae on the hypothalamus, for hypothalamic areas knows to regulate TSH aecratioa is birds (31) are anterior sad dorsal to the corticosteroae-seaeitive cone demonstrated in tree sparrows . 4) Inasmuch ae adrenal steroids inhibit eacretlon of most pituitary tropic hormones (e .g ., ACTH (32) ; TSH (11,30) ; GH (33) ; LH (12)] and altar firing rates of hypothalamic aeurona (34), corticoatarona might have impaired LH re lease by exerting a nonspecific deprsasaat affect on aaurona coataiaiag LH-relnaeiag hormone or by affacti.ng the activity of "ordinary" neurons that interact with them . Support for this visa+ stems from the observation that the basal hypothalamic region shown by ablation to control gonadotropin secretion 1a several species of birds (35) iacludea the tuberoinfuadibular sons ssasitive to corticosteroae is tree sparrows . The data preaentad here make mars credible the speculation that corticosteroae might have iaactivatsd the LH-control mechanism in chronically photostimulated castrated tree sparrows (5) . But whether control of gonadotropia secretion is a physiologically significant function of the principal adrenal steroid of birds remains unresolved, as does the mechanise by which increased local concentrations of corticosteroae in the basal hypothalamus iaducsd gonadotropic iasufficieacy . Ackaowlsdgmeate This is contribution ao . 1265, Diviaioa of Biology, Keaaas Agricultural Ezperimsat Station, Manhattan 66506. We era grateful to A. D. Dayton for atatiatical advice and to C. L. Chen, A. P . Labhsetwar, and A. H. Meier for read ing the manuscript . This investigation was aupportsd in part by grants from the Biology Research Fund sad the Agricultural Research Council (AB18/1) . Refersacas 1. 2. 3. 4. 5. 6. 7. 8. 9. 10 . 11 . 12 . 13 . 14 .
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Corticrosterona-Induced Gônadoaupprssaion
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