Photoinhibited Hamsters Research Articles

Transcriptome analysis during photostimulated recrudescence reveals distinct patterns of gene regulation in Siberian hamster ovaries†.

In Siberian hamsters, exposure to short days (SDs, 8h light:16h dark) reduces reproductive function centrally by decreasing gonadotropin secretion, whereas subsequent transfer of photoinhibited hamsters to stimulatory long days (LDs, 16L:8D) promotes follicle stimulating hormone (FSH) release inducing ovarian recrudescence. Although differences between SD and LD ovaries have been investigated, a systematic investigation of the ovarian transcriptome across photoperiod groups to identify potentially novel factors that contribute to photostimulated restoration of ovarian function had not been conducted. Hamsters were assigned to one of four photoperiod groups: LD to maintain ovarian cyclicity, SD to induce ovarian regression, or post transfer (PT), where females housed in SD for 14-weeks were transferred to LD for 2-days or 1-week to reflect photostimulated ovaries prior to (PTd2) and following (PTw1) the return of systemic FSH. Ovarian RNA was extracted to create RNA-sequencing libraries and short-read sequencing Illumina assays that mapped and quantified the ovarian transcriptomes (n=4/group). Ovarian and uterine masses, plasma FSH, and numbers of antral follicles and corpora lutea decreased in SD as compared to LD ovaries (P<0.05). When reads were aligned to the mouse genome, 18 548 genes were sufficiently quantified. Most of the differentially expressed genes noted between functional LD ovaries and regressed SD ovaries; however, five main expression patterns were identified across photoperiod groups. These results, generally corroborated by select protein immunostaining, provide a map of photoregulated ovary function and identify novel genes that may contribute to the photostimulated resumption of ovarian activity.

The Use of Lectin Histochemistry for Detecting Apoptotic Cells in the Seminiferous Epithelium.

Lectin histochemistry is commonly used to characterize the pattern of glycoconjugates in cells and tissues. Recent studies show that alterations in these glycoconjugates are associated with the entry of cells into apoptosis. A widely used technique for the detection of apoptotic cell death is TUNEL. In this chapter, we study the sensitivity of both techniques to identify apoptotic cells in the testis of photo-inhibited Syrian hamster.

Peripheral kisspeptin reverses short photoperiod-induced gonadal regression in Syrian hamsters by promoting GNRH release

In seasonal breeders, reproduction is synchronised by day length via the pineal hormone melatonin. In short winter days (short day, SD), the Syrian hamster displays a complete gonadal atrophy together with a marked reduction in expression of kisspeptins (Kp), a family of potent hypothalamic stimulators of GNRH neurons. Both central and peripheral acute injections of Kp have been reported to activate the gonadotropic axis in mammals. The aim of this study was to determine if and how peripheral administration of Kp54 could restore gonadal function in photo-inhibited hamsters. Testicular activity of hamsters kept in SD was reactivated by two daily i.p. injections of Kp54 but not by chronic subcutaneous delivery of the same peptide via mini-pumps. Acute i.p. injection of Kp54-induced FOS (c-Fos) expression in a large number of GNRH neurons and pituitary gonadotrophs together with a strong increase in circulating testosterone. The activation of pituitary cells by Kp was inhibited by preadministration of the GNRH receptor antagonist acyline. Altogether, our results demonstrate that peripheral Kp54 activates the gonadotropic axis by stimulating GNRH release and indicate that an appropriate protocol of long-term systemic Kp administration can recrudesce a photo-inhibited reproductive axis.

Apoptosis and Molecular Pathways in the Seminiferous Epithelium of Aged and Photoinhibited Syrian Hamsters (Mesocricetus auratus)

Aging and short photoperiod exposure induce germ cell apoptosis in the Syrian hamster; however, the specific germ cells affected and the molecular pathways triggered have not been elucidated. We analyzed germ cell apoptosis and the expression of the Fas/Fas-L system, Bcl-2 family, and p53 in aged and photoinhibited hamsters and compared with those young maintained in natural photoperiod. Aging increased apoptosis in spermatogonia and spermatocytes, but in photoinhibited hamster testes only an increase in apoptotic spermatocytes was observed. Apoptosis was higher in aged hamsters in stages I-IV, V-VI and VII-VIII. Aging increased apoptosis of spermatogonia in stages I-IV and V-VI. Apoptotic pachytene spermatocytes were significantly higher in stages I-IV, V-VI, and VII-VIII in aging. Apoptotic preleptotene and pachytene spermatocytes were higher in aging, but no differences were observed in leptotene-zygotene. Fas-L was expressed by Sertoli cells, of young, aged, and photoinhibited hamsters. Bcl-x(L) was strongly expressed in germ cells on young hamsters and slightly in aging and after short photoperiod exposure. Spermatocytes of photoinhibited hamsters were intensively stained with Fas, Bax, Bcl-xs/L, and p53. In conclusion, aging increases apoptosis in spermatogonia and spermatocytes, depending on the stage of the seminiferous epithelium cycle, whereas after a short photoperiod exposure only an increase in apoptotic spermatocytes is observed. The results suggest that Fas, Bcl-x(L), Bax, and p53 participate in germ cell apoptosis induction after short photoperiod exposure, whereas only Bcl-x(L) is involved in aging.

Kisspeptin Mediates the Photoperiodic Control of Reproduction in Hamsters

The KiSS-1 gene encodes kisspeptin, the endogenous ligand of the G-protein-coupled receptor GPR54. Recent data indicate that the KiSS-1/GPR54 system is critical for the regulation of reproduction and is required for puberty onset. In seasonal breeders, reproduction is tightly controlled by photoperiod (i.e., day length). The Syrian hamster is a seasonal model in which reproductive activity is promoted by long summer days (LD) and inhibited by short winter days (SD). Using in situ hybridization and immunohistochemistry, we show that KiSS-1 is expressed in the arcuate nucleus of LD hamsters. Importantly, the KiSS-1 mRNA level was lower in SD animals but not in SD-refractory animals, which spontaneously reactivated their sexual activity after several months in SD. These changes of expression are not secondary to the photoperiodic variations of gonadal steroids. In contrast, melatonin appears to be necessary for these seasonal changes because pineal-gland ablation prevented the SD-induced downregulation of KiSS-1 expression. Remarkably, a chronic administration of kisspeptin-10 restored the testicular activity of SD hamsters despite persisting photoinhibitory conditions. Overall, these findings are consistent with a role of KiSS-1/GPR54 in the seasonal control of reproduction. We propose that photoperiod, via melatonin, modulates KiSS-1 signaling to drive the reproductive axis.

Follicle-Stimulating Hormone Regulates Both Sertoli Cell and Spermatogonial Populations in the Adult Photoinhibited Djungarian Hamster Testis1

The hormones that regulate spermatogonial development are ill defined, in part due to lack of appropriate experimental models. The photoinhibited hamster model provides a rich source of spermatogonia, thus making it an ideal model to study their control. This study aimed to assess the effects of FSH, in the absence of testosterone, on the reinitiation of Sertoli cell and spermatogonial development in the photosensitive adult Djungarian hamster. Hamsters raised under long photoperiods (LD, 16L:8D) were exposed to short photoperiods (SD, 8L:16D) for 11 wk, leading to suppression of gonadotropins and regression of testicular function. Groups of 10 animals then received FSH alone or in combination with the antiandrogen, flutamide, for 7 days. Two control groups maintained either under long or short photoperiods were treated with vehicle. Sertoli and germ cell number were then determined using the optical disector (sic) stereological technique. The number of Sertoli cells, type A spermatogonia, type B spermatogonia/preleptotene spermatocytes, and leptotene/zygotene spermatocytes were suppressed in SD controls to 66%, 34%, 19%, and 10% (all P < 0.01) of long-day control values, respectively. Later germ cell types were not detected. FSH treatment, with or without flutamide, increased Sertoli cell number (P < 0.01) to normal long-day values. Similarly, FSH treatment in the absence/presence of flutamide increased type A spermatogonia, type B spermatogonia/preleptotene spermatocytes, and leptotene/zygotene spermatocytes to approximately 85%, 69%, and 80% (all P < 0.01) of long-day controls, respectively. Our data demonstrate that the reinitiation of spermatogonial maturation in this model is dependent on FSH in the presence of an antiandrogen. Surprisingly, the adult Sertoli cell population in this model is also hormone dependent. This naturally occurring model provides a unique opportunity to understand the mechanisms (apoptotic and/or proliferative) by which FSH regulates Sertoli and germ cell development in the adult animal.

311. Adult Sertoli cells proliferate in response to exogenous follicle stimulating hormone in the adult photo-inhibited Djungarian hamster

Sperm production relies on nutritional and structural support from Sertoli cells. Sertoli cells undergo maturational changes (e.g. cessation of proliferation and formation of the blood–testis barrier) around the onset of puberty in higher mammals1 and maturational failure has been associated with some infertility syndromes and testicular malignancies2. The Sertoli cell population is considered to be stable and unmodifiable by hormones after puberty in mammals, although recent data using the adult Djungarian hamster showed that Sertoli cell numbers decreased by 35% in the absence of serum gonadotrophins, and returned to control levels by short-term replacement of follicle stimulating hormone (FSH)3. Therefore, the aims of this study were to (i) quantify the proliferative activity of Sertoli cells in the hormonally manipulated Djungarian hamster, and (ii) examine the localisation of several tight junction proteins as markers of the blood–testis barrier. Long day (LD) photoperiod (16L : 8D) adult hamsters were exposed to short day (SD) photoperiod (8L : 16D) for 11 weeks to suppress gonadotrophins and then received FSH for up to 10 days. Sertoli cell proliferation was assessed immunohistochemically by the colocalisation of GATA-4 and PCNA, and quantified by stereology. Tight junction proteins (occludin and ZO-1) were colocalised using confocal microscopy. Sertoli cell proliferation in both the LD and SD controls was minimal; however, in response to FSH treatment proliferation was upregulated within 4 days compared with SD controls (98% v. 2%, P &lt; 0.001, respectively). Tight junction proteins colocalised at the blood–testis barrier in LD hamsters, but were disorganised within the Sertoli cell cytoplasm in SD animals. FSH treatment restores colocalisation in a time-dependent manner. It is concluded that FSH contributes to the regulation of Sertoli cell proliferation and tight junction formation in the adult Djungarian hamster. This data provides definitive evidence that the adult Sertoli cell population in this model is modifiable by hormones. (1)Meachem et al. (2005). Biol Reprod 72, 1187.(2)Allan et al. (2004). Endocrinol 145, 1587.(3)Russell and Peterson (1985). Int Rev Cytol 94, 177.

Histochemical study of glycoconjugates in active and photoperiodically-regressed testis of hamster (Mesocricetus auratus)

The objective of the present study was to characterize glycoconjugates of hamster testis in gonadally-active and -inactive states by lectin histochemical methods. Thirteen HRP- or digoxigenin-labeled lectins were used in samples obtained from fertile and photoinhibited hamsters. In gonadally-active hamsters, spermatozoa tails were stained with Con-A, HPA, PNA, UEA-I, LTA, AAA, WGA and LFA and weakly with GNA and RCA-I. Spermatozoa acrosomes were labeled with HPA, SBA, WGA and PNA. Spermatid acrosomes were labeled with SBA, RCA-I, PNA, and WGA. Staining with GNA and Con-A was found in the Golgi phase and HPA staining was found in the Golgi phase and maturated spermatids. Cytoplasm of spermatocytes was labeled with Con-A, GNA, LTA, AAA, RCA-I, HPA, WGA and LFA, whereas spermatocyte membranes were stained with Con-A, LTA and AAA. Spermatogonia were strongly labeled with Con-A and moderately labeled with AAA, WGA and LFA. Sertoli cells were positive after staining with Con-A, AAA, WGA, and LFA. The lamina propria was positive after staining with UEA-I, LTA, AAA and LFA. Leydig cells showed strong labeling with SBA, Con-A, GNA, SNA and MAA, moderate labeling with WGA, weak labeling with RCA-I, AAA and LFA. In gonadally-inactive hamsters, spermatocytes showed increased staining with HPA, PNA and AAA, whereas staining with Con-A, GNA and LTA had disappeared. Spermatogonia showed an increased labeling with AAA and WGA, but labeling with Con-A and LFA had disappeared. Sertoli cells were strongly labeled with GNA. Con-A and GNA staining was decreased in Leydig cells of gonadally-inactive hamsters but PNA and HPA staining was increased. The lamina propria in regressed testes showed intense labeling with PNA. These results suggest that histological, morphological and hormonal changes occurring in hamster testis during exposure to a short photoperiod are reflected in altered patterns of expression and distribution of N- and O-linked glycans.

Proliferation and apoptosis in the seminiferous epithelium of photoinhibited Syrian hamsters (Mesocricetus auratus).

In the hamster, male reproductive quiescence is accomplished via testicular atrophy and the germinal epithelium is regressed to spermatogonia and spermatocytes after 8-14 weeks of short photoperiods. However, the cellular mechanisms involved in this process have not been elucidated. As it is suggested that the regulation of seasonal testicular activity is characterized by coordinated shifts in the relationships between mitosis, meiosis and apoptosis, the changes in the proliferative and apoptotic activity in the seminiferous epithelium of photoinhibited Syrian hamster were examined and compared with those maintained in natural photoperiod. The proliferative activity was studied using BrdU immunostaining, and germ cell apoptosis was assessed by in situ TUNEL labelling and transmission electron microscopy. A significant increase in the rate of apoptosis (percentage of TUNEL-positive spermatogonia + spermatocytes) was observed in photoinhibited animals (2.84 +/- 0.16) compared with those exposed to natural photoperiod (0.77 +/- 0.03, p < 0.05). The majority of apoptotic germ cells were spermatocytes and in some occasions spermatogonia. Germ cell apoptosis was confirmed by morphological characteristics: condensation of the chromatin and nuclear fragmentation. The rate of proliferation (percentage of BrdU-positive spermatogonia + preleptotene spermatocytes) was significantly higher in photoinhibited hamsters (42.7 +/- 2.6) compared with animals exposed to natural photoperiod (31.1 +/- 1.6, p < 0.05). After the exposure to a short photoperiod the apoptotic index positively correlated with the proliferative index (r = 0.8150, p < 0.05). In conclusion, the seminiferous epithelium of photoinhibited Syrian hamsters is characterized by an increased rate of apoptosis associated to an enhanced rate of proliferation.

Manipulations of glutamatergic (N-methyl-D-aspartate receptor) neurotransmission alter the rate of photoperiodically regulated sexual maturation in the male Siberian hamster.

This study investigated whether central glutamatergic pathways are involved in sexual maturation in the Siberian hamster, a species in which puberty is regulated by photoperiod. The aim of the initial experiments was to determine whether exogenous activation of N-methyl-D-aspartate (NMDA) receptor-mediated glutamatergic pathways could induce premature testicular development in photoinhibited hamsters. Male hamsters raised in an inhibitory short-day photoperiod (8L:16D) received systemic injections of the glutamate agonist NMDA. Twice-daily treatment with 20 or 40 mg/kg BW caused significant increases in testicular weight within 4 wk, but this was not accompanied by a significant increase in circulating testosterone. Subsequent experiments revealed that the degree of testicular development induced by NMDA was comparable to that induced by daily treatment with GnRH (1 microg). This study demonstrates the potential for increased glutamatergic activity to induce testicular development. The aim of the second series of experiments was to determine whether blockade of endogenous NMDA receptor-mediated glutamatergic pathways could prevent testicular development in photostimulated hamsters. Males were transferred from short (SD) to long days (LD; 16L:8D) at 80-100 days of age to induce rapid testicular growth and were concurrently treated with MK801, a noncompetitive NMDA receptor antagonist (2 mg/kg BW per day), or CGP40116, a competitive NMDA receptor antagonist (5 or 10 mg/kg BW per day) for 4 wk. LD photoperiod caused a rapid increase in testicular weight in vehicle-treated hamsters within 4 wk. Both antagonists significantly reduced the LD-stimulated testicular growth. MK801 treatment induced a degree of sedation and a loss of body weight, suggesting that the reduced testicular development in this group may have been secondary to decreased growth rates; but no behavioral changes or loss of body weight was observed in the hamsters treated with CGP40116. These observations in a photoperiodic species provide support for the hypothesis that activation of NMDA receptor-mediated glutamatergic pathways contributes to sexual maturation.

In vitro fertilizing capacity of sperm from FSH-treated photoinhibited Djungarian hamsters (Phodopus sungorus).

In hypogonadal male Djungarian hamsters FSH alone can induce normal spermatogenesis. However, for the induction of mating behavior, supplementation with testosterone is necessary. We have here investigated, by in vitro fertilization, whether sperm produced by photoinhibited hamsters treated with FSH alone can fertilize without testosterone. Photoinhibited hypogonadal male Djungarian hamsters were injected daily with human FSH (10 IU; Fertinorm) for 5-7 weeks. The hormone stimulated regrowth of the testes. Neither body weight nor the weights of the androgen-dependent organs-epididymides, prostates, accessory glands-showed significant differences from photoinhibited controls; furthermore FSH treatment did not raise intratesticular or serum testosterone levels. In eleven out of the twelve FSH-treated photoinhibited hamsters, elongated spermatids were found in the testes; in five out of nine epididymides, sperm was found by histological examination. In two out of the twelve FSH-treated hamsters, the amount of sperm in the caudal part of the epididymis was sufficient for in vitro fertilization with oocytes collected from superstimulated females. These spermatozoa fertilized 16-29% of the oocytes. Spermatozoa from photostimulated controls produced similar levels of fertilization.

Gonadal Growth and Hormone Concentrations in Photoregressed Siberian Hamsters: Pinealectomy Versus Photostimulation1

In Siberian hamsters, long and short durations of nightly melatonin secretion are associated with testicular regression and development, respectively; surprisingly, the absence of a nightly melatonin signal induced by pinealectomy is less effective than a short (4-6 h) melatonin duration for promoting gonadal development. We compared the patterns of serum FSH and prolactin concentrations underlying pinealectomy-induced and photostimulated testicular growth in juvenile hamsters. Pinealectomy in photoinhibited hamsters on Day 18 produced significant gonadal development compared to that in short-day controls by Day 23. By Day 28, however, testes weights of pinealectomized hamsters were significantly lower than those of intact hamsters transferred to a long photoperiod. Pinealectomy was associated with significant elevations in serum FSH and prolactin concentrations over baseline by Day 21, but peak values were attenuated compared with those induced by exposure to long days. FSH titers of pinealectomized animals were significantly lower than those of photostimulated animals between Days 21 and 30 but were significantly greater on Days 35 and 40; prolactin values were comparable in pinealectomized and photostimulated hamsters between Days 21 and 25 but were significantly lower in the former group thereafter. Blunted elevation of FSH and prolactin secretion may underlie the slower rates of gonadal maturation observed in pinealectomized, juvenile hamsters. The neuroendocrine systems of pinealectomized hamsters appear to be in a state intermediate between those characteristic of hamsters kept in long and in short day lengths.

Photoperiodic responses in Djungarian hamsters (Phodopus sungorus): importance of light history for pineal and serum melatonin profiles.

Male Djungarian hamsters with previous light experience of long photoperiods of 16 h of light per day (16L:8D) or short photoperiods (8L:16D) were transferred either to the opposite photoperiods or to intermediate photoperiods (14L:10D). It was demonstrated that the same intermediate photoperiod could exert inhibitory or stimulatory effects on coat color, body weight, and the reproductive system, dependent on the previous light history. The response was graduated in accordance with the degree of change in day length. Despite opposite responses to the same photoperiod, diurnal patterns of melatonin in the pineal glands were identical. However, the circadian melatonin pattern in serum of photoinhibited hamsters had a more pronounced nighttime elevation than that found in the serum of photostimulated animals. In hamsters nonresponsive to short photoperiods, no proper short-day pattern was found. Melatonin production is a highly dynamic process, causing concentration shifts in the pineal gland and changes in the serum amplitude during prolonged exposure to short photoperiods. The different reactions to identical photoperiods are associated with different serum melatonin patterns, as shown here for the first time.

Photoperiod regulates the LH response to central glutamatergic stimulation in the male Syrian hamster.

This study investigated central glutamatergic function in relation to photoperiodically-induced changes in the secretion of luteinizing hormone (LH). The experimental approach was to compare the central effects of glutamate agonists on LH secretion in reproductively active hamsters kept in long days (LD) with those in photoinhibited hamsters kept in short days (SD) for 6 weeks and having regressed testes. Agonists were delivered via a cannula into the III ventricle of freely moving hamsters, and blood samples collected 10 to 15 min after the start of the infusion. A high dose (3.0 nmole) of N-methyl-D-L-aspartate (NMDA) induced significant (P<0.01) increases in serum concentrations of LH in hamsters in both photoperiods, though the NMDA-induced increase relative to endogenous LH concentrations was greater in SD than in LD. However, a lower dose of NMDA (0.3 nmole revealed a difference in sensitivity. This dose significantly increased serum LH (P<0.05) in hamsters in SD but had no effect in those in LD. The seasonal difference in response to NMDA was compared with the response to an equimolar dose of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA), a non-NMDA agonist. This dose of AMPA (0.3 nmole) induced a two-fold increase (P<0.05) in serum concentrations of LH in hamsters in both photoperiods, relative to vehicle-treated controls. In a third experiment the dose-response effects of central AMPA on LH secretion were examined more closely. The sensitivity of LH secretion to stimulation with AMPA did not differ between SD- and LD-housed hamsters. Thus the photoperiod-related difference in sensitivity to stimulation with glutamate agonists is specific for NMDA receptor-mediated activation, rather than a passive reflection of differences in the capacity to secrete GnRH/LH in SD and LD photoperiods. To investigate the site of action of NMDA, the expression of the c-fos immediate-early gene, as assessed by immunocytochemistry for its protein product Fos, was used as a marker of neuronal activation, because previous studies in rodents indicate that a high proportion of GnRH neurons express c-fos at the time of the mid-cycle LH surge. NMDA induced widespread expression of c-fos in many periventricular regions including the medial preoptic area (POA) and ventromedial hypothalamic nucleus. However, dual ICC revealed that in neither photoperiod was Fos present in GnRH-positive neurons 1 h after infusion of 3 nmole of NMDA, despite the increases in LH secretion induced by the infusion. AMPA injected icv at doses which released LH did not enhance expression of c-fos in the hypothalamus. Thus, in the male, enhanced expression of c-fos cannot be detected in GnRH neurons at the time of increased secretion of this hormone induced by glutamate agonists. In conclusion, these results show that both NMDA and non-NMDA glutamatergic pathways potentially regulated LH secretion in the Syrian hamster. The increased sensitivity to NMDA but unaltered sensitivity to AMPA in photoinhibited hamsters in SD is consistent with the view that changes in photoperiod might induce specific alterations in NMDA-mediated pathways that ultimately regulate GnRH neurosecretory activity.

Pattern of pineal melatonin concentrations during prolonged exposure to short photoperiods in photosensitive and photoinsensitive Djungarian hamsters.

In the Djungarian hamster (Phodopus sungorus) there is strong evidence that the nightly decompression or lengthening, respectively, of the pineal melatonin pattern is involved in conveying the inhibitory influence of short photoperiods. Some hamsters, however, are insensitive to photoinhibitory influences; other late-responding hamsters show a delayed reaction of several months. The daily pattern of pineal melatonin proves that the mechanisms determining long- or short-day patterns become effective in the morning and evening hours when melatonin concentrations of photoinhibited hamsters are clearly elevated, while those of long-day hamsters are reduced to negligible low values. At two decisive time points in the morning and evening, male and female early-responding photosensitive hamsters were killed after 5, 10, 15, and 20 weeks in short photoperiods, nonresponding hamsters after 10 and 20 weeks, and late-responding after 20 weeks. In all early-responding hamsters changes in gonadal stage, body weight, and pelage color corresponded to the decompression of the nightly melatonin pattern. During prolonged exposure to short photoperiods a decrease of mean melatonin concentrations in the morning and an increase of evening concentrations was observed in both sexes. The lengthening of nightly elevated melatonin concentrations was missing in photoinsensitive hamsters. In late-responding hamsters this decompression seems to be delayed, as melatonin concentrations of female late responders indicate. In conclusion, the lengthening of the melatonin pattern seems to predict a photoperiodic reaction of the effector system. The lengthened pattern of photosensitive hamsters may not be unchangeable, as it may be subjected to modifications during prolonged exposure to short photoperiods.

Differential Effects of Follicle-Stimulating Hormone and Luteinizing Hormone on Leydig Cell Function and Restoration of Spermatogenesis in Hypophysectomized and Photoinhibited Djungarian Hamsters (Phodopus Sungorus)

Effects of pure human follicle-stimulating hormone (hFSH) and ovine luteinizing hormone (oLH) on testicular function were investigated in long-term hypophysectomized or photoinhibited Djungarian hamsters. hFSH (5 IU) or oLH (5 micrograms) or a combination of FSH and LH (5 IU and 5 micrograms, respectively) were injected s.c. twice daily for 7 days to hypophysectomized and photoinhibited hamsters. Other photoinhibited hamsters were treated for 14 and 21 days with FSH and LH (3 IU and 3 micrograms, respectively) in a similar way. LH alone had little, if any, effect on testicular weights; FSH, when injected alone or in combination with LH (FSH/LH), caused a significant increase in testes weights at each time point. On the other hand, LH or FSH/LH, but not FSH alone, caused a significant increase in the accessory organ weights. FSH had no effect on intratesticular testosterone (T) or on 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD) activity but enhanced the in vitro response of interstitial cells to hCG. LH and FSH/LH had pronounced effects on intratesticular T, 3 beta-HSD activity, and in vitro response of interstitial cells to human chorionic gonadotropin. Treatment with FSH or FSH/LH caused regrowth of the testis and restoration of tubular lumen and tubular diameter and restored complete spermatogenesis. However, LH had little effect on spermatogenesis in spite of increased intratesticular and peripheral T levels. These results indicate that although LH can cause a full redifferentiation of Leydig cells in photoinhibited hamsters, it has only minor effects on tubular function. On the other hand, FSH alone induces full restoration of tubular function in these animals and has no direct effect on Leydig cell steroidogenesis, but may enhance the Leydig cell responsiveness to LH.

The effects of castration, testosterone replacement and photoperiod upon hypothalamic β-endorphin levels in the male syrian hamster

Syrian hamsters kept in long day-lengths have active gonads and high circulating levels of gonadal steroids. Under the influence of the pineal gland, animals exposed to short photoperiods undergo testicular regression, have low circulating levels of testosterone and gonadotrophins and elevated levels of β-endorphin within the hypothalamus. This paper describes the interaction between testosterone and photoperiod in the regulation of β-endorphin levels in three regions of the hypothalamus. Hypothalamic β-endorphin levels were measured by a combination of high-performance liquid chromatography and radioimmunoassay techniques that allows separation of the β-endorphin (1–31) peptide from its metabolites and precursors. All of the β-endorphin-like immunoreactivity in the hypothalamus of the male hamster, in both photoinhibited and photostimulated conditions, was found to represent the 31-aminoacid peptide. In photostimulated hamsters, chronic castration was associated with a significant increase of β-endorphin levels in the anterior hypothalamus and mediobasal hypothalamus, which was reversed by treatment with exogenous testosterone. Castration prevented the ability of naloxone, an opiate receptor antagonist, to release luteinizing hormone, and this effect was also reversed by exogenous steroid. In photoinhibited hamsters, however, castration had no effect upon β-endorphin levels in the preoptic area or mediobasal hypothalamus, and there was only a small increment in the anterior hypothalamus. Significantly, β-endorphin levels in all areas of the hypothalamus of photoinhibited castrates were not decreased by testosterone treatment. In addition, administration of exogenous testosterone did not restore sensitivity to naloxone in these animals. These results show that inhibitory photoperiods uncouple the functional interaction between testosterone and the hypothalamic β-endorphin system, and reinforce the proposition that a change in the activity of β-endorphin neurons is a component of the central mechanism which mediates the environmental control of reproduction.