0013-7227/90/1275-2607$02.00/0 Endocrinology Copyright© 1990 by The Endocrine Society
Vol. 127, No. 5 Printed in U.S.A.
MELATONIN RECEPTORS ARE PRESENT IN THE FERRET PARS TUBERALIS AND PARS DISTALIS, BUT NOT IN BRAIN David R. Weaver and Steven M. Reppert Laboratory of Developmental Chronobiology, Children's Service, Massachusetts General Hospital and Department of Pediatrics and Program in Neurosclence, Harvard Medical School Boston MA 02114 USA ABSTRACT; The pineal hormone melatonin regulates reproductive function in seasonally breeding mammals. Recent studies using 1251-labeled 2-iodomelatonin (I-MEL) reveal that the distribution of putative melatonin receptors is species-specific; only the hypophysial pars tuberalis (PT) is a consistent site of I-MEL binding in all photoperiodic species examined. In the present study, we used J[n vitro autoradiography to examine the distribution of I-MEL binding in the ferret brain and pituitary. We report that I-MEL binding is restricted to the PT and pars distalis (PD) of the pituitary; I-MEL binding is absent from brain. I-MEL binds in the PT and PD with high affinity (Kd values ca. 40 pM) and the rank order of potency for inhibition of I-MEL binding (6-chloromelatonin = melatonin > 6-hydroxymelatonin > N-acetylserotonin > serotonin) is the same as that observed for high-affinity melatonin receptors from other species. The consistent presence of high affinity melatonin receptors in the PT of a variety of photoperiodic species suggests that the PT plays a major role in mediating the effects of melatonin on neuroendocrine function. The pineal hormone melatonin regulates the dramatic seasonal changes in physiology that occur in seasonally breeding mammals (for reviews, see 1,2). Melatonin ultimately affects reproduction by altering the activity of the hypothalamic LHRH pulse generator and LHRH release from the median eminence (1-4). The biologically active melatonin analog, 2-[125I]iodomelatonin (I-MEL) is the ligand of choice for studies of putative melatonin receptors (5,6). Autoradiographic studies employing I-MEL show that the distribution of melatonin receptors in the brain varies widely among mammalian species (5). The only consistent site of I-MEL binding in all photoperiodic species examined to date is the pars tuberalis (PT), a part of the pituitary gland that surrounds the median eminence and infundibular stalk (see 5 ) . In this study, we examined the distribution and characteristics of putative melatonin receptors in the ferret brain and pituitary. We report that I-MEL binding in the ferret is restricted to the hypophysial PT and pars distalis (PD), and that the entire ferret brain is devoid of high affinity melatonin receptors. MATERIALS AND METHODS Three female ferret brains with pituitary attached were obtained from Dr. K.D. Ryan, Department of Obstetrics and Gynecology, University of Pittsburgh School of Medicine. Animals were purchased from Marshall Farms (North Rose, NY) at 7 weeks of age and housed in short days (8 h light, 16 h dark, lights on at 0700). At 17 weeks of age, the animals were then placed in long days (16 h light, 8 hr dark, lights on 0700). This paradigm of alternating short and long days synchronizes pubertal development of female ferrets (7). Vulvar swelling occurred in all three females by 22 weeks of age, indicating that they were sexually mature. The animals were killed by decapitation while anesthetized with pentobarbital at 26 weeks of age. Tissues were immediately frozen in 2-methylbutane (-30 C ) , and stored at -80 C. At the time of tissue collection, two of the three ferrets were in full vulvar edema. Vulvar edema in the third ferret had subsided, probably due to ovulation, as 9 weeks of long days is not sufficient to induce photorefractoriness (8,9). Serial coronal sections (20 micron) were cut on a cryostat (-20 C) and stored at -80. ln_ vitro I-MEL autoradiography was performed as previously described Received in Iowa City August 14, 1990
(10). S p e c i f i c I-MEL b i n d i n g i s defined as the difference between t o t a l binding and nonspecific binding (determined on immediately adjacent sections incubated in I-MEL plus 1 uM melatonin). Computer-based image analysis was used to q u a n t i t a t e I-MEL binding r e l a t i v e to 1251 standards included on each film (Amersham 1251 microscales, 20 micron thickness). I-MEL (SA c a . 2000 Ci/mmol) was prepared as previously described (10). 6-Chloromelatonin was provided by Dr. J.A. Clemens (Eli Lilly Corp.). RESULTS The d i s t r i b u t i o n of putative melatonin receptors was determined by examining I-MEL (40 pM) binding in sections at 120 micron i n t e r v a l s throughout the e n t i r e brain from each of the three animals. A low I-MEL concentration was used to minimize non-specific binding, and a long autoradiographic exposure duration (5 weeks) was used to optimize the sensitivity of the autoradiographic procedure. Despite these e f f o r t s , specific I-MEL binding was not detected anywhere in the f e r r e t brain. Specific I-MEL binding was clearly present in the PT and PD of the pituitary in each animal, however (Fig. 1). The entire PT was intensely labeled, while labeling of the PD was less uniform and less intense. Saturation analysis was performed by incubating sections of the PT and PD in a range of I-MEL concentrations (5.5-317 pM), with or without melatonin (1 uM). Specific I-MEL binding increased with I-MEL concentration up to ca. 100 pM and then reached a plateau, suggesting a saturable number of binding site (Fig. 2, upper panel). Scatchard analysis of the data revealed apparent equilibrium dissociation constants (Kd's) of 27.9 +_ 0.6 pM in the PT and 39.2 + 5.8 pM in the PD (mean + SEM, n=3, p > 0.05, paired t - t e s t ; Fig. 2, lower panel). Bmax values for I-MEL binding were significantly higher in the PT (10.9 + 1.2 nCi/mg standard) than in the PD (2.3 +_ 0.84 nCi/mg standard) (p < 0.05, paired t-test). Pharmacologic characterization of I-MEL (25 pM) binding was consistent with the rank order of potency expected for a high affinity melatonin receptor (see 5,6). Melatonin and 6-chlororaelatonin potently inhibited I-MEL binding (half-maximal inhibition, IC-50, ca. 1 nM), while 6-hydroxymelatonin (IC-50 ca. 10 nM), N-acetylserotonin (IC-50 ca. 1 uM) and serotonin (IC-50 > 100 uM) were less potent (data not shown). Results from PT and PD were v i r t u a l l y identical.
2607
The Endocrine Society. Downloaded from press.endocrine.org by [${individualUser.displayName}] on 18 November 2015. at 00:37 For personal use only. No other uses without permission. . All rights reserved.
Endo • 1990 Voll27«No5
RAPID COMMUNICATIONS
2608
O)
c c o • CO
fie
111 Q. O) — E
o
u O) CL W
100
Figure 1. Distribution of I-MEL binding in ferret brain and pituitary. A^ Autoradiogram generated from a section incubated in I-MEL (40 p M ) , representing Bj_ Autoradiogram from an adjacent total binding. section incubated in I-MEL (40 pM) plus 1 uM melatonin, representing nonspecific binding. Note the absence of specific I-MEL binding in the brain. Autoradiographic exposure for A and B, 5 weeks. C. Higher power magnification of an autoradiogram generated by the section in panel A, following 10-day film exposure. At this shorter exposure duration, the film is not saturated and the relative intensity of the images from the pars tuberalis (PT) and pars distalls (PD) can be appreciated. Th_ Adjacent section stained with thionin.
200
300
400
[I-Mel], pM
PT 0.6 n
PT : Kd = 27.3 pM Bmax = 13.2 nCI/mg
0.4-
PD : Kd = 43.6 pM Bmax = 2.8 nCI/mg
•D
C 3 O
m
DISCUSSION We examined I-MEL binding in the ferret brain and pituitary, and report that I-MEL binding is restricted to the PT and PD of the pituitary. I-MEL binding in the ferret PT and PD i s of high affinity and has pharmacologic specificity expected of a high-affinity melatonin receptor (5,6). In PT tissue from hamsters and sheep, occupation of melatonin receptors inhibits forskolin- stimulated cyclic AMP accumulation (11,12), strongly suggesting that I-MEL binding sites in the PT represent functional melatonin receptors. The similarity in I-MEL binding characteristics in the ferret PT and PD, and sheep and hamster PT (11,13) suggests that I-MEL binding sites in the ferret also represent functional melatonin receptors. The apparent absence of melatonin receptors in ferret brain suggests that neural melatonin binding sites are not necessary for photoperiodic regulation of reproduction. The anterior hypothalamus i s a necessary part of the neuroendocrine system ultimately regulated by melatonin, however, as lesions of the anterior hypothalamus disrupt reproductive responses to melatonin in hamsters and skunks (14,15). Thus, i t appears that melatonin acts through the hypothalamus, without necessarily binding within i t . We cannot exclude the possibility that an extremely low density of melatonin receptors exists in neural s i t e s . High-affinity melatonin receptors are consistently present in the PT of all photoperiodic species examined so far, including rodents (10,16), sheep (13), goats (Weaver & Reppert, unpublished),
Figure 2. Saturation curves (upper panel) and Scatchard plots (lower panel) of specific I-MEL binding in the pars tuberalis (PT) and pars d i s t a l i s (PD) from a representative ferret. Values represent means of 2-4 sections at each point. The level of binding and Bmax values are reported in nCi/mg plastic of the 1251 microscale standards.
and rhesus monkeys (Stehle, Weaver & Reppert, unpublished). The consistent presence of melatonin receptors in the PT suggests that the PT plays a major role in mediating the effects of melatonin on the hypothalamic- pituitary- gonadal axis. By virtue of i t s position adjacent to the median eminence, secretory products from the PT would have access to neurosecretory terminals in the external zone of the median eminence. We propose that melatonin may influence hypothalamic function through this indirect, paracrine mechanism involving the PT. Alternatively, an endocrine function of the PT is possible. Further study of the PT as a s i t e of neuroendocrine regulation for melatonin is necessary. The presence of melatonin receptors on the ferret PD suggests that melatonin may also have d i r e c t effects on PD function in the ferret. In adults of other species, however, melatonin does not directly influence PD secretion (1,2,17-20) and melatonin receptors are absent from the PD. It seems unlikely that the PD is a primary site of melatonin action in most species.
The Endocrine Society. Downloaded from press.endocrine.org by [${individualUser.displayName}] on 18 November 2015. at 00:37 For personal use only. No other uses without permission. . All rights reserved.
2609
RAPID COMMUNICATIONS ACKNOWLEDGEMENTS S u p p o r t e d b y NSF g r a n t B N S - 8 9 0 8 5 4 2 (DRW) a n d PHS grant DK42125 (SMR). We t h a n k K.D. Ryan f o r supplying t h e t i s s u e used i n t h i s s t u d y .
REFERENCES 1. Karsch F J , Bittman EL, Foster DL, Goodman RL, Legan SJ, Robinson JE 1984 Neuroendocrine b a s i s of seasonal r e p r o d u c t i o n . Rec Prog Hormone Res 40: 185-232. 2. Tamarkin L, Baird CJ, Almeida OFX 1985 Melatonin: a c o o r d i n a t i n g s i g n a l f o r mammalian reproduction? Science 227: 714-720. 3. Pickard GE, Silverman AJ 1979 E f f e c t s of photoperiod on hypothalamic l u t e i n i z i n g hormone releasing hormone i n t h e male hamster. J Endocrinol 8 3 : 421-428. 4. Glass JD, Knotts LK 1987 A b r a i n s i t e of a c t i o n for t h e antigonadal a c t i o n of melatonin i n t h e white-footed mouse (Peromyscus leucopus): involvement of t h e immunoreactive GnRH neuronal system. Neuroendocrinology 46: 48-55. 5. Weaver DR, Rivkees SA, Carlson LL, Reppert SM 1990 L o c a l i z a t i o n of melatonin receptors i n mammalian b r a i n . I n : Suprachiasmatic n u c l e u s : The M i n d ' s C l o c k . DC K l e i n , RY Moore, SM R e p p e r t (Eds), Oxford U P r e s s , NY ( i n p r e s s ) . 6. Dubocovich ML 1988 Pharmacology and function of melatonin r e c e p t o r s . FASEB J 2: 2765-2773 7. Ryan KD, Robinson SL 1985 A r i s e i n t o n i c luteinizing hormone secretion occurs during p h o t o p e r i o d - s t i m u l a t e d sexual maturation of t h e female f e r r e t . Endocrinology 116: 2013-2018. 8. Ryan KD, Robinson SL 1987 A study of spontaneous sexual maturation of the female f e r r e t . Biol Reprod 36: 333-339. 9. Thorpe PA, Herbert J 1976 Studies on the duration of the breeding season and photorefractorinesss in female ferrets pinealectomized or treated with melatonin. J Endocrinol 70: 255-262. 10. Weaver DR, Rivkees SA, Reppert SM 1989 Localization and characterization of melatonin in rodent brain by in vitro receptors autoradiography. J Neurosci 9: 2581-2590.
11. Carlson LL, Weaver DR, Reppert SM 1989 Melatonin signal transduction in hamster brain: inhibition of adenylyl cyclase through a pertussis toxin-sensitive G protein. Endocrinology 125: 2670-2676. 12. Morgan PJ, Lawson W, Davidson G, Howell HE 1989 Melatonin inhibits cyclic AMP production in cultured ovine pars tuberalis. J Mol Endocrinol 3: R5-R8. 13. Morgan PJ, Williams LM, Davidson G, Lawson W, Howell HE 1989 Melatonin receptors on ovine pars t u b e r a l i s : characterization and autoradiographical localization. J Neuroendocrinol 1: 1-4. 14. Berria M, de Santis M, Mead RA 1989 Lesions of the anterior hypothalamus prevent the melatonin-induced lengthening of delayed implantation. Endocrinology 125: 2897-2904. 15. Bonnefond C, Walker AP, Stutz JA, Maywood E, Juss TS, Herbert J, Hastings MH 1989 The hypothalamus and photoperiodic control of FSH secretion in the male Syrian hamster. J Endocrinol 122: 247-254. 16. Weaver DR, Carlson LL, Reppert SM 1990 Melatonin receptors and signal transduction in melatoninsensitive and melatonin-insensitive populations of white-footed mice (Peromyscus leucopus). Brain Res 506: 353-357. 17. Robinson JE, Kaynard AH, Karsch FJ 1986 Does melatonin a l t e r pituitary responsiveness to gonadotropin-releasing hormone in the ewe? Neuroendocrinol 42: 635-640. 18. Meunier M, Brebion P, Chene N, Servely JL, Martinet L 1988 In vitro secretion of prolactin and growth hormone in the presence of melatonin by pituitary gland from mink kept under long or short days. J Endocrinol 119: 287-292. 19. Martin JE, Sattler C 1979 Developmental loss of the acute inhibitory effect of melatonin on the in vitro pituitary luteinizing hormone and follicle-stimulating
hormone
responses
to
luteinizing hormone-releasing hormone. Endocrinology 105: 1007-1012. 20. Bacon A, Sattler C, Martin JE 1981 Melatonin e f f e c t s on the hamster p i t u i t a r y response to LHRH. Biol Reprod 2 4: 993-999.
The Endocrine Society. Downloaded from press.endocrine.org by [${individualUser.displayName}] on 18 November 2015. at 00:37 For personal use only. No other uses without permission. . All rights reserved.
Vol. 127, No. 5 Printed in U.S.A.
MELATONIN RECEPTORS ARE PRESENT IN THE FERRET PARS TUBERALIS AND PARS DISTALIS, BUT NOT IN BRAIN David R. Weaver and Steven M. Reppert Laboratory of Developmental Chronobiology, Children's Service, Massachusetts General Hospital and Department of Pediatrics and Program in Neurosclence, Harvard Medical School Boston MA 02114 USA ABSTRACT; The pineal hormone melatonin regulates reproductive function in seasonally breeding mammals. Recent studies using 1251-labeled 2-iodomelatonin (I-MEL) reveal that the distribution of putative melatonin receptors is species-specific; only the hypophysial pars tuberalis (PT) is a consistent site of I-MEL binding in all photoperiodic species examined. In the present study, we used J[n vitro autoradiography to examine the distribution of I-MEL binding in the ferret brain and pituitary. We report that I-MEL binding is restricted to the PT and pars distalis (PD) of the pituitary; I-MEL binding is absent from brain. I-MEL binds in the PT and PD with high affinity (Kd values ca. 40 pM) and the rank order of potency for inhibition of I-MEL binding (6-chloromelatonin = melatonin > 6-hydroxymelatonin > N-acetylserotonin > serotonin) is the same as that observed for high-affinity melatonin receptors from other species. The consistent presence of high affinity melatonin receptors in the PT of a variety of photoperiodic species suggests that the PT plays a major role in mediating the effects of melatonin on neuroendocrine function. The pineal hormone melatonin regulates the dramatic seasonal changes in physiology that occur in seasonally breeding mammals (for reviews, see 1,2). Melatonin ultimately affects reproduction by altering the activity of the hypothalamic LHRH pulse generator and LHRH release from the median eminence (1-4). The biologically active melatonin analog, 2-[125I]iodomelatonin (I-MEL) is the ligand of choice for studies of putative melatonin receptors (5,6). Autoradiographic studies employing I-MEL show that the distribution of melatonin receptors in the brain varies widely among mammalian species (5). The only consistent site of I-MEL binding in all photoperiodic species examined to date is the pars tuberalis (PT), a part of the pituitary gland that surrounds the median eminence and infundibular stalk (see 5 ) . In this study, we examined the distribution and characteristics of putative melatonin receptors in the ferret brain and pituitary. We report that I-MEL binding in the ferret is restricted to the hypophysial PT and pars distalis (PD), and that the entire ferret brain is devoid of high affinity melatonin receptors. MATERIALS AND METHODS Three female ferret brains with pituitary attached were obtained from Dr. K.D. Ryan, Department of Obstetrics and Gynecology, University of Pittsburgh School of Medicine. Animals were purchased from Marshall Farms (North Rose, NY) at 7 weeks of age and housed in short days (8 h light, 16 h dark, lights on at 0700). At 17 weeks of age, the animals were then placed in long days (16 h light, 8 hr dark, lights on 0700). This paradigm of alternating short and long days synchronizes pubertal development of female ferrets (7). Vulvar swelling occurred in all three females by 22 weeks of age, indicating that they were sexually mature. The animals were killed by decapitation while anesthetized with pentobarbital at 26 weeks of age. Tissues were immediately frozen in 2-methylbutane (-30 C ) , and stored at -80 C. At the time of tissue collection, two of the three ferrets were in full vulvar edema. Vulvar edema in the third ferret had subsided, probably due to ovulation, as 9 weeks of long days is not sufficient to induce photorefractoriness (8,9). Serial coronal sections (20 micron) were cut on a cryostat (-20 C) and stored at -80. ln_ vitro I-MEL autoradiography was performed as previously described Received in Iowa City August 14, 1990
(10). S p e c i f i c I-MEL b i n d i n g i s defined as the difference between t o t a l binding and nonspecific binding (determined on immediately adjacent sections incubated in I-MEL plus 1 uM melatonin). Computer-based image analysis was used to q u a n t i t a t e I-MEL binding r e l a t i v e to 1251 standards included on each film (Amersham 1251 microscales, 20 micron thickness). I-MEL (SA c a . 2000 Ci/mmol) was prepared as previously described (10). 6-Chloromelatonin was provided by Dr. J.A. Clemens (Eli Lilly Corp.). RESULTS The d i s t r i b u t i o n of putative melatonin receptors was determined by examining I-MEL (40 pM) binding in sections at 120 micron i n t e r v a l s throughout the e n t i r e brain from each of the three animals. A low I-MEL concentration was used to minimize non-specific binding, and a long autoradiographic exposure duration (5 weeks) was used to optimize the sensitivity of the autoradiographic procedure. Despite these e f f o r t s , specific I-MEL binding was not detected anywhere in the f e r r e t brain. Specific I-MEL binding was clearly present in the PT and PD of the pituitary in each animal, however (Fig. 1). The entire PT was intensely labeled, while labeling of the PD was less uniform and less intense. Saturation analysis was performed by incubating sections of the PT and PD in a range of I-MEL concentrations (5.5-317 pM), with or without melatonin (1 uM). Specific I-MEL binding increased with I-MEL concentration up to ca. 100 pM and then reached a plateau, suggesting a saturable number of binding site (Fig. 2, upper panel). Scatchard analysis of the data revealed apparent equilibrium dissociation constants (Kd's) of 27.9 +_ 0.6 pM in the PT and 39.2 + 5.8 pM in the PD (mean + SEM, n=3, p > 0.05, paired t - t e s t ; Fig. 2, lower panel). Bmax values for I-MEL binding were significantly higher in the PT (10.9 + 1.2 nCi/mg standard) than in the PD (2.3 +_ 0.84 nCi/mg standard) (p < 0.05, paired t-test). Pharmacologic characterization of I-MEL (25 pM) binding was consistent with the rank order of potency expected for a high affinity melatonin receptor (see 5,6). Melatonin and 6-chlororaelatonin potently inhibited I-MEL binding (half-maximal inhibition, IC-50, ca. 1 nM), while 6-hydroxymelatonin (IC-50 ca. 10 nM), N-acetylserotonin (IC-50 ca. 1 uM) and serotonin (IC-50 > 100 uM) were less potent (data not shown). Results from PT and PD were v i r t u a l l y identical.
2607
The Endocrine Society. Downloaded from press.endocrine.org by [${individualUser.displayName}] on 18 November 2015. at 00:37 For personal use only. No other uses without permission. . All rights reserved.
Endo • 1990 Voll27«No5
RAPID COMMUNICATIONS
2608
O)
c c o • CO
fie
111 Q. O) — E
o
u O) CL W
100
Figure 1. Distribution of I-MEL binding in ferret brain and pituitary. A^ Autoradiogram generated from a section incubated in I-MEL (40 p M ) , representing Bj_ Autoradiogram from an adjacent total binding. section incubated in I-MEL (40 pM) plus 1 uM melatonin, representing nonspecific binding. Note the absence of specific I-MEL binding in the brain. Autoradiographic exposure for A and B, 5 weeks. C. Higher power magnification of an autoradiogram generated by the section in panel A, following 10-day film exposure. At this shorter exposure duration, the film is not saturated and the relative intensity of the images from the pars tuberalis (PT) and pars distalls (PD) can be appreciated. Th_ Adjacent section stained with thionin.
200
300
400
[I-Mel], pM
PT 0.6 n
PT : Kd = 27.3 pM Bmax = 13.2 nCI/mg
0.4-
PD : Kd = 43.6 pM Bmax = 2.8 nCI/mg
•D
C 3 O
m
DISCUSSION We examined I-MEL binding in the ferret brain and pituitary, and report that I-MEL binding is restricted to the PT and PD of the pituitary. I-MEL binding in the ferret PT and PD i s of high affinity and has pharmacologic specificity expected of a high-affinity melatonin receptor (5,6). In PT tissue from hamsters and sheep, occupation of melatonin receptors inhibits forskolin- stimulated cyclic AMP accumulation (11,12), strongly suggesting that I-MEL binding sites in the PT represent functional melatonin receptors. The similarity in I-MEL binding characteristics in the ferret PT and PD, and sheep and hamster PT (11,13) suggests that I-MEL binding sites in the ferret also represent functional melatonin receptors. The apparent absence of melatonin receptors in ferret brain suggests that neural melatonin binding sites are not necessary for photoperiodic regulation of reproduction. The anterior hypothalamus i s a necessary part of the neuroendocrine system ultimately regulated by melatonin, however, as lesions of the anterior hypothalamus disrupt reproductive responses to melatonin in hamsters and skunks (14,15). Thus, i t appears that melatonin acts through the hypothalamus, without necessarily binding within i t . We cannot exclude the possibility that an extremely low density of melatonin receptors exists in neural s i t e s . High-affinity melatonin receptors are consistently present in the PT of all photoperiodic species examined so far, including rodents (10,16), sheep (13), goats (Weaver & Reppert, unpublished),
Figure 2. Saturation curves (upper panel) and Scatchard plots (lower panel) of specific I-MEL binding in the pars tuberalis (PT) and pars d i s t a l i s (PD) from a representative ferret. Values represent means of 2-4 sections at each point. The level of binding and Bmax values are reported in nCi/mg plastic of the 1251 microscale standards.
and rhesus monkeys (Stehle, Weaver & Reppert, unpublished). The consistent presence of melatonin receptors in the PT suggests that the PT plays a major role in mediating the effects of melatonin on the hypothalamic- pituitary- gonadal axis. By virtue of i t s position adjacent to the median eminence, secretory products from the PT would have access to neurosecretory terminals in the external zone of the median eminence. We propose that melatonin may influence hypothalamic function through this indirect, paracrine mechanism involving the PT. Alternatively, an endocrine function of the PT is possible. Further study of the PT as a s i t e of neuroendocrine regulation for melatonin is necessary. The presence of melatonin receptors on the ferret PD suggests that melatonin may also have d i r e c t effects on PD function in the ferret. In adults of other species, however, melatonin does not directly influence PD secretion (1,2,17-20) and melatonin receptors are absent from the PD. It seems unlikely that the PD is a primary site of melatonin action in most species.
The Endocrine Society. Downloaded from press.endocrine.org by [${individualUser.displayName}] on 18 November 2015. at 00:37 For personal use only. No other uses without permission. . All rights reserved.
2609
RAPID COMMUNICATIONS ACKNOWLEDGEMENTS S u p p o r t e d b y NSF g r a n t B N S - 8 9 0 8 5 4 2 (DRW) a n d PHS grant DK42125 (SMR). We t h a n k K.D. Ryan f o r supplying t h e t i s s u e used i n t h i s s t u d y .
REFERENCES 1. Karsch F J , Bittman EL, Foster DL, Goodman RL, Legan SJ, Robinson JE 1984 Neuroendocrine b a s i s of seasonal r e p r o d u c t i o n . Rec Prog Hormone Res 40: 185-232. 2. Tamarkin L, Baird CJ, Almeida OFX 1985 Melatonin: a c o o r d i n a t i n g s i g n a l f o r mammalian reproduction? Science 227: 714-720. 3. Pickard GE, Silverman AJ 1979 E f f e c t s of photoperiod on hypothalamic l u t e i n i z i n g hormone releasing hormone i n t h e male hamster. J Endocrinol 8 3 : 421-428. 4. Glass JD, Knotts LK 1987 A b r a i n s i t e of a c t i o n for t h e antigonadal a c t i o n of melatonin i n t h e white-footed mouse (Peromyscus leucopus): involvement of t h e immunoreactive GnRH neuronal system. Neuroendocrinology 46: 48-55. 5. Weaver DR, Rivkees SA, Carlson LL, Reppert SM 1990 L o c a l i z a t i o n of melatonin receptors i n mammalian b r a i n . I n : Suprachiasmatic n u c l e u s : The M i n d ' s C l o c k . DC K l e i n , RY Moore, SM R e p p e r t (Eds), Oxford U P r e s s , NY ( i n p r e s s ) . 6. Dubocovich ML 1988 Pharmacology and function of melatonin r e c e p t o r s . FASEB J 2: 2765-2773 7. Ryan KD, Robinson SL 1985 A r i s e i n t o n i c luteinizing hormone secretion occurs during p h o t o p e r i o d - s t i m u l a t e d sexual maturation of t h e female f e r r e t . Endocrinology 116: 2013-2018. 8. Ryan KD, Robinson SL 1987 A study of spontaneous sexual maturation of the female f e r r e t . Biol Reprod 36: 333-339. 9. Thorpe PA, Herbert J 1976 Studies on the duration of the breeding season and photorefractorinesss in female ferrets pinealectomized or treated with melatonin. J Endocrinol 70: 255-262. 10. Weaver DR, Rivkees SA, Reppert SM 1989 Localization and characterization of melatonin in rodent brain by in vitro receptors autoradiography. J Neurosci 9: 2581-2590.
11. Carlson LL, Weaver DR, Reppert SM 1989 Melatonin signal transduction in hamster brain: inhibition of adenylyl cyclase through a pertussis toxin-sensitive G protein. Endocrinology 125: 2670-2676. 12. Morgan PJ, Lawson W, Davidson G, Howell HE 1989 Melatonin inhibits cyclic AMP production in cultured ovine pars tuberalis. J Mol Endocrinol 3: R5-R8. 13. Morgan PJ, Williams LM, Davidson G, Lawson W, Howell HE 1989 Melatonin receptors on ovine pars t u b e r a l i s : characterization and autoradiographical localization. J Neuroendocrinol 1: 1-4. 14. Berria M, de Santis M, Mead RA 1989 Lesions of the anterior hypothalamus prevent the melatonin-induced lengthening of delayed implantation. Endocrinology 125: 2897-2904. 15. Bonnefond C, Walker AP, Stutz JA, Maywood E, Juss TS, Herbert J, Hastings MH 1989 The hypothalamus and photoperiodic control of FSH secretion in the male Syrian hamster. J Endocrinol 122: 247-254. 16. Weaver DR, Carlson LL, Reppert SM 1990 Melatonin receptors and signal transduction in melatoninsensitive and melatonin-insensitive populations of white-footed mice (Peromyscus leucopus). Brain Res 506: 353-357. 17. Robinson JE, Kaynard AH, Karsch FJ 1986 Does melatonin a l t e r pituitary responsiveness to gonadotropin-releasing hormone in the ewe? Neuroendocrinol 42: 635-640. 18. Meunier M, Brebion P, Chene N, Servely JL, Martinet L 1988 In vitro secretion of prolactin and growth hormone in the presence of melatonin by pituitary gland from mink kept under long or short days. J Endocrinol 119: 287-292. 19. Martin JE, Sattler C 1979 Developmental loss of the acute inhibitory effect of melatonin on the in vitro pituitary luteinizing hormone and follicle-stimulating
hormone
responses
to
luteinizing hormone-releasing hormone. Endocrinology 105: 1007-1012. 20. Bacon A, Sattler C, Martin JE 1981 Melatonin e f f e c t s on the hamster p i t u i t a r y response to LHRH. Biol Reprod 2 4: 993-999.
The Endocrine Society. Downloaded from press.endocrine.org by [${individualUser.displayName}] on 18 November 2015. at 00:37 For personal use only. No other uses without permission. . All rights reserved.
