Adult Djungarian Hamsters Research Articles

Torpor expression in juvenile and adult Djungarian hamsters (Phodopus sungorus) differs in frequency, duration and onset in response to a daily cycle in ambient temperature

In addition to morphological and physiological traits of short-day acclimatisation, Djungarian hamsters (Phodopus sungorus) from Central Asia exhibit spontaneous daily torpor to decrease energy demands during winter. Environmental factors such as food scarcity and low temperatures have been shown to facilitate the use of this temporal reduction in metabolism and body temperature. We investigated the effect of a daily cycle in ambient temperature on short-day acclimation and torpor expression in juvenile and adult Djungarian hamsters. The animals were exposed to a cold dark phase (6°C) and a warmer light phase (18°C) and were compared with control hamsters kept at a constant ambient temperature of 18°C. Under constant conditions, torpor expression did not differ between adult and juvenile hamsters. Although the daily temperature cycle evoked an increased metabolic rate in adult and juvenile hamsters during the dark phase and strengthened the synchronization between torpor entrance and the beginning of the light phase, it did not induce the expected torpor facilitation. In adult hamsters, torpor expression profiles did not differ from those under constant conditions at all. In contrast, juvenile hamsters showed a delayed onset of torpor season, a decreased torpor frequency, depth and duration, as well as an increased number of early torpor terminations coinciding with the rise in ambient temperature after the beginning of the light phase. While the temperature challenge appeared to be of minor importance for energy balance and torpor expression in adult hamsters, it profoundly influenced the overall energy saving strategy of juvenile hamsters, promoting torpor-alleviating active foragers over torpor-prone energy-savers. In addition, our data suggest a more efficient acclimation in juvenile hamsters under additional energy challenges, which reduces the need for torpor expression.

Co-localization of serine/threonine kinase 33 (Stk33) and vimentin in the hypothalamus

We investigate the immunoreactivity of serine/threonine kinase 33 (Stk33) and of vimentin in the brain of mouse, rat and hamster. Using a Stk33-specific polyclonal antibody, we show by immunofluorescence staining that Stk33 is present in a variety of brain regions. We found a strong staining in the ependymal lining of all cerebral ventricles and the central canal of the spinal cord as well as in hypothalamic tanycytes. Stk33 immunoreactivity was also found in circumventricular organs such as the area postrema, subfornical organ and pituitary and pineal glands. Double-immunostaining experiments with antibodies against Stk33 and vimentin showed a striking colocalization of Stk33 and vimentin. As shown previously, Stk33 phosphorylates recombinant vimentin in vitro. Co-immunoprecipitation experiments and co-sedimentation assays indicate that Stk33 and vimentin are associated in vivo and that this association does not depend on further interacting partners (Brauksiepe et al. in BMC Biochem 9:25, 2008). This indicates that Stk33 is involved in the dynamics of vimentin polymerization/depolymerization. Since in tanycytes the vimentin expression is regulated by the photoperiod (Kameda et al. in Cell Tissue Res 314:251-262, 2003), we determine whether this also holds true for Stk33. We study hypothalamic sections from adult Djungarian hamsters (Phodopus sungorus) held under either long photoperiods (L:D 16:8h) or short photoperiods (L:D 8:16h) for 2months. In addition, we examine whether age-dependent changes in Stk33 protein content exist. Our results show that Stk33 in tanycytes is regulated by the photoperiod as is the case for vimentin. Stk33 may participate in photoperiodic regulation of the endocrine system.

Regulation of testicular tight junctions by gonadotrophins in the adult Djungarian hamster in vivo

This study aimed to assess the effect of gonadotrophin suppression and FSH replacement on testicular tight junction dynamics and blood-testis barrier (BTB) organisation in vivo, utilising the seasonal breeding Djungarian hamster. Confocal immunohistology was used to assess the cellular organisation of tight junction proteins and real-time PCR to quantify tight junction mRNA. The effect of tight junction protein organisation on the BTB permeability was also investigated using a biotin-linked tracer. Tight junction protein (claudin-3, junctional adhesion molecule (JAM)-A and occludin) localisation was present but disorganised after gonadotrophin suppression, while mRNA levels (claudin-11, claudin-3 and occludin) were significantly (two- to threefold) increased. By contrast, both protein localisation and mRNA levels for the adaptor protein zona occludens-1 decreased after gonadotrophin suppression. FSH replacement induced a rapid reorganisation of tight junction protein localisation. The functionality of the BTB (as inferred by biotin tracer permeation) was found to be strongly associated with the organisation and localisation of claudin-11. Surprisingly, JAM-A was also recognised on spermatogonia, suggesting an additional novel role for this protein in trans-epithelial migration of germ cells across the BTB. It is concluded that gonadotrophin regulation of tight junction proteins forming the BTB occurs primarily at the level of protein organisation and not gene transcription in this species, and that immunolocalisation of the organised tight junction protein claudin-11 correlates with BTB functionality.

The effect of testosterone, dihydrotestosterone and oestradiol on the re-initiation of spermatogenesis in the adult photoinhibited Djungarian hamster

The roles of testosterone (T) and its metabolites on hamster spermatogenesis are poorly defined. This study assessed the effects of T, dihydrotestosterone (DHT) and oestradiol (E) on the re-initiation of spermatogenesis in the adult Djungarian hamster. Hamsters raised under long photoperiods (LD, 16 h light:8 h darkness) were exposed to short photoperiods (SD, 8 h light:16 h darkness) for 11 weeks to suppress gonadotrophins. Groups of eight animals then received T, DHT and E for 5 weeks. Cell numbers were determined using the optical disector (sic). The number of Sertoli cells was suppressed in SD controls to 48% (P<0·001) of LD control and restored either fully or partially by exogenous DHT and E (2·6- and 1·8-fold above SD levels) respectively, corresponding with a twofold elevation of serum FSH. The number of germ cells in SD animals was reduced (all P<0·001) to levels reported. The number of type A spermatogonia increased in line with the rise in Sertoli cell number, by 2·6-fold (P<0·01) and 1·8-fold (NS) above SD controls after DHT and E treatments respectively. DHT increased the number of type B spermatogonia/preleptotene spermatocytes, leptotene/zygotene and pachytene spermatocytes by 3·5-, 5·7- and 21-fold above SD (all P<0·01) respectively, compared with a 2·2-fold (P<0·01), 2·4-fold (not significant, NS) and 6-fold (NS) in E-treated animals respectively. Exogenous T had little effect on cell numbers or serum FSH compared with SD controls. Spermatids were rarely observed after steroid treatment. We believe this study suggests that steroids can regulate the re-initiation of early spermatogenic cells via a mechanism which includes FSH.

Adult Sertoli Cells Are Not Terminally Differentiated in the Djungarian Hamster: Effect of FSH on Proliferation and Junction Protein Organization1

Sertoli cell number is considered to be stable and unmodifiable by hormones after puberty in mammals, although recent data using the seasonal breeding adult Djungarian hamster (Phodopus sungorus) model challenged this assertion by demonstrating a decrease in Sertoli cell number after gonadotropin depletion and a return to control levels following 7 days of FSH replacement. The present study aimed to determine whether adult Sertoli cells are terminally differentiated using known characteristics of cellular differentiation, including proliferation, junction protein localization, and expression of particular maturational markers, in the Djungarian hamster model. Adult long-day (LD) photoperiod (16L:8D) hamsters were exposed to short-day (SD) photoperiod (8L:16D) for 11 wk to suppress gonadotropins and then received exogenous FSH for up to 10 days. Sertoli cell proliferation was assessed by immunofluorescence by the colocalization of GATA4 and proliferating cell nuclear antigen and quantified by stereology. Markers of Sertoli cell maturation (immature, cytokeratin 18 [KRT18]; mature, GATA1) and junction proteins (actin, espin, claudin 11 [CLDN11], and tight junction protein 1 [TJP1, also known as ZO-1]) also were localized using confocal immunofluorescence. In response to FSH treatment, proliferation was upregulated within 2 days compared with SD controls (90% vs. 0.2%, P < 0.001) and declined gradually thereafter. In LD hamsters, junction proteins colocalized at the basal aspect of Sertoli cells, consistent with inter-Sertoli cell junctions, and were disordered within the Sertoli cell cytoplasm in SD animals. Exogenous FSH treatment promptly restored localization of these junction markers to the LD phenotype. Protein markers of maturity remain consistent with those of adult Sertoli cells. It is concluded that adult Sertoli cells are not terminally differentiated in the Djungarian hamster and that FSH plays an important role in governing the differentiation process. It is proposed that Sertoli cells can enter a transitional state, exhibiting features common to both undifferentiated and differentiated Sertoli cells.

Trans‐pineal microdialysis in the Djungarian hamster (Phodopus sungorus): a tool to study seasonal changes of circadian clock activities

The Djungarian hamster is a highly seasonal small mammal. The rhythmic secretion of melatonin by the pineal gland is under control of the circadian clock, conveying the photoperiodic message to the organism. Trans-pineal microdialysis permits the in vivo study of this well-defined and precise clock output by measuring melatonin release directly in the pineal gland. The aim of this study was to adapt this method to the Djungarian hamster in order to monitor clock properties during photoperiodic changes. Male adult Djungarian hamsters were kept in a long photoperiod (LD 16:8) and melatonin release was measured hourly during the dark period for several weeks. Melatonin showed a regular secretion between ZT 17 and ZT 23.5 whereas the amplitude became stable only after the third day of perfusion. To test how quickly changes in melatonin profile can be measured, 15-min light pulses were given at different time points throughout the scotophase. Light-pulses immediately interrupted melatonin secretion at any time point during the scotophase and the temporal resolution for measurement could be reduced to 30 min. In accordance with studies in the rat, long-term effects of light on the clock could only be observed when a light pulse was administered in the second half of the night. For the first time we established a method to measure precisely a direct and reliable clock-output in a highly seasonal species which allows us now to study the circadian and seasonal properties of the clock in detail.

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.

002.Sertoli cell terminal differentiation: doing a 'U' turn on a one way street

The concept of terminal differentiation of Sertoli cells has been challenged and this new information has important implications for male fertility. The mammalian Sertoli cell has two distinct functions: (i) formation of the seminiferous cords and (ii) provision of nutritional and structural support to the developing germ cells. For these to occur successfully, Sertoli cells must undergo numerous maturational changes between foetal and adult life, the main switches occur around the onset of puberty, coincident with the rise in serum gonadotrophins. These switches include the loss of proliferative activity and the formation of the blood testis barrier. Follicle stimulating hormone (FSH) plays a key role in supporting Sertoli cell proliferation in early postnatal life and thus is critical in establishing sperm output in adulthood. After puberty, the size of the Sertoli cell population is considered to be stable and unmodifiable by hormones. This accepted view has been contested as data shows that the size of the adult Sertoli cell population is modifiable by hormone suppression, and that Sertoli cells can regain proliferative activity when stimulated by FSH in the Djungarian hamster1. The molecular mechanism(s) by which Sertoli cells re-enter proliferation are not known in this model however a study demonstrated that helix-loop-inhibitor of differentiation proteins can induce terminally differentiated Sertoli cells to re-enter the cell cycle and proliferate2. Thyroid hormone and testosterone may be involved in the cessation of Sertoli cell proliferation. Gonadotrophin suppression in the adult Djungarian hamster also results in the disruption of the blood testis barrier and spatial organisation of the inter Sertoli cell tight junction proteins and as a consequence the loss of all germ cells that reside inside the blood testis barrier. FSH restores the organisation of these tight junction proteins, which is associated with the appearance of more mature germ cells. It is expected that the integrity of the blood testis barrier is also re-established. It is suggested that this demonstrated plasticity of the adult Sertoli cell may be relevant in clinical settings, particularly to some types of infertility and testicular malignancies where Sertoli cells have failed to undergo these important maturational switches. (1)Chaudhary et al. (2005) Biol. Reprod. 72, 1205. (2)Meachem et al. (2005) Biol. Reprod. 72, 1187.

51. FSH regulates Sertoli cell and spermatogonial populations in the adult Djungarian hamster

Reproduction, Fertility and Development is an international journal publishing original research , review and comment in the fields of reproduction and developmental biology in humans, domestic animals and wildlife

Effect of various acute 60 Hz magnetic field exposures on the nocturnal melatonin rise in the adult Djungarian hamster.

Acute exposure to a 1 Gauss 60 Hz magnetic field for 15 min beginning 2 hr before darkness delays and blunts the nighttime melatonin rhythm in some but not all studies. To determine whether other exposure parameters (dose, mode, or time) influence the nocturnal melatonin rise, adult Djungarian hamsters reared in long days (16L:8D, lights off at 1000-1800 hr) were acutely exposed to a 60 Hz continuous magnetic field (15 min of 1 or 0.1 Gauss) beginning 4 hr before or 4 hr after lights off. Other hamsters were exposed to a 60 Hz intermittent magnetic field (15 or 60 min of a 1 Gauss field, 1 min on then 1 min off) between 1 and 2 hr before lights off. In sham-exposed controls, i.e., hamsters simultaneously placed in an adjacent coil system but without current, pineal and serum melatonin concentrations increased from a low baseline (1 hr after lights off) to concentrations that were typical of the nighttime peak by 3 hr after darkness. Acute exposure to the 0.1 or 1 Gauss continuous magnetic field for 15 min at either 4 hr before or 4 hr after lights off did not disrupt the nocturnal rise in pineal or serum melatonin. Similarly, onset of the melatonin rhythm was not suppressed by intermittent magnetic field exposures compared to that in sham controls. Thus, several magnetic field exposure paradigms failed to alter the rising phase of the melatonin rhythm in pineal gland content or in circulation. These findings indicate that the biological clock mechanism that mediates photoperiodic time measurement in this seasonally breeding rodent is resistant to a variety of acute continuous or intermittent magnetic field exposures.

60-Hz magnetic field exposure effects on the melatonin rhythm and photoperiod control of reproduction.

Adult Djungarian hamsters in long (16 h of light) or short (10 h of light) days for 6 wk were acutely exposed to a 1-G 60-Hz magnetic field (MF) for 15 min 2 h before dark. The nighttime rise in melatonin was delayed and duration reduced in MF-exposed hamsters in both photoperiods compared with sham controls. In a second replicate experiment, MF effects on melatonin rhythm duration were repeated in hamsters in short but not long days, and amplitudes at some clock times differed between the same treatment groups in the two studies. To test the hypothesis that daily MF abbreviates melatonin rhythm duration and induces a long-day reproductive response, adults in shot days were exposed daily to MF. After 3 wk, pineal and serum melatonin rhythms were the same in MF and sham groups; reproduction remained suppressed. Irrespective of acute MF exposure effects on the melatonin rhythm, daily MF treatment does not alter photoperiodic time measurement or the clock mechanism controlling reproduction. Adaption to environmental MF exposures may be part of a normal physiological mechanism that maintains photoperiodic responsiveness in individuals and a seasonal pattern of reproduction.

Daily Melatonin Treatments Regulate the Circadian Melatonin Rhythm in the Adult Djungarian Hamster

The present study tested the hypothesis that daily melatonin treatments influence the biological clock mechanism controlling the circadian melatonin rhythm. Adult male and female Djungarian hamsters in light:dark = 16L:8D (lights on 0300-1900 h) were administered melatonin subcutaneously (s.c.) each day (5 micrograms/0.2 ml saline) in the morning at 1000 h (AM) or late afternoon at 1700 h (PM); controls received a vehicle injection (CON). After 14 days, pineal and serum melatonin concentrations were determined at various times on the last day of treatment and the next day in constant darkness (no treatment). The rhythm in pineal gland melatonin content was similar in each of the three groups on the last day of treatment (about 6 h duration). On the next day in constant dark, the rising phase was advanced and duration extended by 2 h or more in melatonin-treated hamsters compared to that in CONs (ANOVA). In circulation, the melatonin rhythm in AM and PM groups was phase advanced (onset and peak) on both days of the study. Thus duration was extended by up to 4.5 h compared to that in saline-treated controls. Moreover, amplitude of the nighttime serum melatonin rise was elevated up to fivefold relative to that in the CON group (ANOVA and Accumulated Sums analysis). The effects of repeated melatonin treatments on amplitude and phase of the serum melatonin rhythm raise the possibility that the circadian clock that controls pineal gland production of melatonin may also regulate melatonin secretion. From this and another study, the apparent half-life of melatonin in circulation was estimated to be 7.5 min; the melatonin injection initially produced pharmacological concentrations that were followed by low serum melatonin levels within 2 h. Thus, in both melatonin treatment groups, the data suggest that two distinct periods of elevated serum melatonin were present each day. The cellular mechanism for melatonin action must take into consideration how a brief interruption in elevated melatonin in circulation (about 1 h in the PM group) is recognized as a continuous duration (short daylength), whereas a more extended baseline period is transduced as an abbreviated or long daylength (about 7 h in the AM group). These data further suggest that the biological clock mechanism that generates the circadian melatonin rhythm is responsive to the influence of daily melatonin treatments and presumably to the feedback action of endogenous melatonin on its own rhythm in the Djungarian hamster in long days.

Direct effects of the pineal hormone melatonin on testosterone synthesis of Leydig cells in Djungarian hamsters ( Phodopus sungorus) in vitro

Leydig cells of adult Djungarian hamsters, stimulated with luteinizing hormone (LH), were co-incubated with melatonin at various concentrations in a primary culture system. Testosterone secretion was only affected by melatonin when cells were stimulated with LH. Maximal suppression was observed at low doses of LH (0.5 ng/ml). These effects are at least partially mediated through the adenylate cyclase system, since melatonin was able to reduce forskolin-stimulated testosterone secretion. These results indicate that the time between pulses of LH can be considered to be most highly effective for tonic melatonin actions.

Diurnal Variations of Serum and Testicular Testosterone and Dihydrostestosterone (DHT) in Djungarian Hamsters (Phodopus sungorus): Testes Are the Main Source for Circulating DHT

Testes and sera of adult Djungarian hamsters kept in a light:dark cycle of 16L:8D were collected every 1.5-3 hr for 24 hr. The concentrations of testosterone (T) and its metabolite 5α-dihydrotestosterone (DHT) were estimated by HPLC separation of the steroids followed by radioimmunoassay. Both testicular and serum concentrations of T and DHT exhibited strong diurnal variations (P < 0.001) with highest levels at the end of the light phase, while both hormones declined drastically during the dark period. The ratios of DHT/T, as an indicator of the activity of the enzyme 5α-reductase, were on average 0.39 in the testes and 0.29 in serum. Comparisons of individual data revealed highly significant correlations between testicular and serum concentrations of the hormones (T:r = 0.87; P < 0.0001; DHT:r = 0.69, P < 0.0001). Likewise, the individual values of testicular and serum DHT/T ratios correlated highly significantly (r = 0.60; P < 0.001). The results indicate that in Djungarian hamsters the main source of DHT is the testes, while the peripheral conversion of T to DHT seems to be negligible.

Acute 60 Hz magnetic field exposure effects on the melatonin rhythm in the pineal gland and circulation of the adult Djungarian hamster.

Adult male and female hamsters in long days (16 hr of light) were exposed to a 1 gauss 60 Hz magnetic field for 15 min starting 2 hr before lights off. Sham-exposed controls were placed in an adjacent exposure system but current was not applied. Hamsters were decapitated at 0.5-2 hr intervals from 1 hr before lights off to 1 hr after lights on (n = 4-6/clocktime/group); sera were harvested and pineal glands obtained for melatonin radioimmunoassay. In controls, pineal melatonin significantly increased from an average daytime baseline of less than 0.3 ng/gland to 3 ng/gland by 3 hr after lights off (P < 0.05, ANOVA). This increase was sustained for the duration of the night and returned to baseline within 1 hr after lights on. A similar melatonin rhythm was found in serum; concentrations ranged from 30 to 50 pg/ml at night and returned to a baseline of 12 pg/ml or less by 1 hr before lights on. The single magnetic field exposure reduced the duration and blunted the rise in the nocturnal melatonin rhythm. The study was then repeated in its entirety 6 months later. The same magnetic field treatment significantly suppressed pineal melatonin content at 5 hr after lights off and reduced serum melatonin concentrations at 3 and 5 hr after dark onset compared to sham-exposed controls. Thus, the acute magnetic field exposure was again found to blunt the increase and suppress the duration of the nighttime melatonin rise.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of acute melatonin treatment and light on the circadian melatonin rhythm in the Djungarian hamster.

The present study tested the hypothesis that acute melatonin treatment affects the biological clock mechanism controlling the circadian melatonin rhythm. Adult Djungarian hamsters were raised in LD 16:8 (lights-on from 0300 to 1900 hr). Pineal and serum melatonin concentrations were assessed at specific clock times during the subsequent LD cycle (day 1) and afterwards in hamsters that remained in constant darkness (day 2), to assess the effects of treatment on the circadian melatonin rhythm. In untreated controls (n = 76), melatonin increased in the pineal and in circulation within the first hour after lights-off (day 1) or subjective night (day 2); melatonin concentrations remained elevated for up to 7 hr. A single melatonin injection (5 micrograms/0.2 ml saline, s.c.), administered in the morning (0900 hr, n = 80) or late afternoon (1600 hr, n = 74), transiently increased in circulation but not in the pineal gland. In constant darkness (day 2), the circadian melatonin rhythm in both the pineal gland and circulation was the same as that in untreated controls. No significant differences were found among the three groups in the mean concentration during the day or night; the rise, fall, peak time, peak amplitude, and duration of increased melatonin were also unchanged. The ability of melatonin to override the effect of a light pulse on the circadian melatonin rhythm was also tested. The 5-min light pulse at night (2300-2305 hr of day 1, n = 64) delayed the rise and shortened the duration of increased melatonin in both pineal gland and serum by as much as 3 hr (day 2); these light effects were more pronounced on the pineal than on the serum melatonin rhythm. Injection with melatonin prior to the light pulse (5 micrograms/0.2 ml saline at 2245 hr, n = 64) failed to alter the inhibitory effects of light on the circadian melatonin rhythm. These data suggest that the biological clock mechanism controlling the circadian melatonin rhythm in the Djungarian hamster in long days is responsive to the phase-shifting effects of light, but resistant to the influence of acute melatonin treatment.

Assessment of the Role of Follicle-Stimulating Hormone and Prolactin in the Control of Testicular Endocrine Function in Adult Djungarian Hamsters (Phodopus Sungorus) Exposed to Either Short or Long Photoperiod1

Exposure of adult male Djungarian hamsters (Phodopus sungorus) to a short photoperiod induces testicular atrophy. To evaluate the role of FSH and prolactin (PRL) in the control of testicular endocrine function, adult Djungarian hamsters were exposed to either a long photoperiod (16L:8D per day) or a short photoperiod (6L:18D per day) for 11 wk. After 11 wk, hamsters housed in each of these photoperiods were placed into three groups and treated s.c. daily for 7 days with 50% polyvinylpyrrolidone in saline (SAL-PVP), rat FSH (10 micrograms/hamster/day) in SAL-PVP, or ovine PRL (100 micrograms/hamster/day) in SAL-PVP. On Day 8, animals in each of these groups received i.p. injections of saline or ovine LH (0.3 microgram/g BW); 1 h later, blood was obtained by cardiac puncture under ether anesthesia. Plasma FSH, LH, PRL, androstenedione (A-dione), and testosterone levels were measured by validated RIAs. In hamsters kept in the short photoperiod, testicular weight was decreased (p < 0.001). In these animals, FSH treatment increased (p < 0.001) testicular weight, whereas PRL injections had no effect. Testicular weight in animals kept in the long photoperiod was unaffected by FSH or PRL treatment. After 12 wk of exposure to the short photo-period, circulating PRL levels were undetectable; plasma levels of FSH (p < 0.001), LH (p < 0.05), A-dione (p < 0.005), and testosterone (p < 0.001) were significantly reduced. Administration of either FSH or PRL had no influence on plasma A-dione levels in hamsters exposed to either photoperiod.(ABSTRACT TRUNCATED AT 250 WORDS)

Antigonadal effects of two novel melatonin analogues in adult Djungarian hamsters

This study examined the effects of two novel melatonin analogues in adult Djungarian hamsters housed under long photoperiod (LD 16:8). Daily injection (10 micrograms, s.c.) of either melatonin, 5-methoxy N-butanoyltryptamine (bMT), or 5-methyl N-butanoyltryptamine (5-MebT) 3 hr before lights off for 8 weeks led to a significant decrease in paired testis weight compared to vehicle-injected controls. The reduction in testis weight was of similar magnitude with melatonin and bMT, but 5-MebT was not as effective. The affinity of the analogues was determined in competition experiments using chicken brain membranes and 2-[125I]iodomelatonin (2-[125I]aMT). Replacing the N-acetyl side-chain of melatonin with an N-butanoyl group increased affinity for the chicken brain 2-[125I]aMT binding site, but exchanging the 5-methoxy group of melatonin for a 5-methyl group reduced affinity. These studies show that these analogues not only inhibit 2-[125I]aMT binding in vitro but also mimic melatonin's antigonadal activity in vivo.

Cycle of the seminiferous epithelium in the Djungarian hamster (Phodopus sungorus sungorus).

In this study, spermatogenesis in the adult Djungarian hamster is described. Undifferentiated spermatogonia topographically arranged as Asingle (A(s)), Apaired (Apr), and Aaligned (Aal) spermatogonia were observed, as were six generations of differentiating spermatogonia (A1, A2, A3, intermediate, B1, and B2). The differentiating spermatogonia divided at regular intervals during the cycle of the seminiferous epithelium. Mitosis of these cells was observed at the transition from stage IX to stage X (mitosis of A1 into A2 spermatogonia), at the transition from stage XII to stage I, at the transition from stage II to stage III, at the transition from stage IV to stage V, at the end of stage VI, and at approximately the middle of stage VII. Cellular associations in the cycle of the seminiferous epithelium are described. The seminiferous epithelium was divided into 12 stages, based upon the developmental steps in spermiogenesis, and the frequency of these stages was determined. The duration of the cycle of the seminiferous epithelium, determined by [3H]thymidine incorporation, was shown to be 7.90 +/- 0.01 (mean +/- SEM) days.