Termination of gonadal refractoriness in Turkish hamsters, Mesocricetus brandti

The Turkish hamster (Mesocricetus brandti) is a photoperiodic species. In this investigation, we characterized the photoperiodic requirements for termination of gonadal refractoriness, defined as the inability of the animal to respond to short-day treatment with gonadal regression. Paired testes weights were reduced to less than 20% of their original weight by 10 wk of 12L:12D treatment. This was followed by spontaneous testicular recrudescence (completed by Week 25 of 12L:12D treatment), the overt indication of refractoriness to short photoperiods. Next, the period of long-day exposure sufficient for termination of refractoriness was determined. Refractory males were exposed to 16L:8D for 5 to 20 wk. Ten weeks of 16L:8D treatment was enough for the animals to regain the sensitivity to a second challenge of 12L:12D treatment. Fifteen weeks of 20L:4D or 16L:8D terminated refractoriness in female Turkish hamsters; 20L:4D therefore was not interpreted as a short day by refractory hamsters. This was unexpected because in photosensitive animals this photoperiod acts like a short day, causing gonadal regression. These results suggest that Turkish hamsters are similar to Syrian hamsters in that both species require two or more months of long days in summer to recover sensitivity to the short days of the following fall.     

The pachytene chromomere map of the oocyte of the Turkish hamster (Mesocricetus brandti)

A study of the chromomere maps of the sex and twenty autosomal bivalents of Turkish hamster pachytene oocytes was carried out. The average total number of chromomeres in early/mid pachytene autosomes was 280 with 91 on the p (short arm) and 189 on the q (long arm). The submetacentric X1 chromosome had 20 chromomeres and the metacentric X2 had 27. Comparisons of the number and location of oocyte chromomeres are made with the pachytene spermatocyte chromomere maps of this species.     

The chromomere map of the pachytene spermatocyte of the Turkish hamster (Mesocricetus brandti).

The chromomere map of the early to mid pachytene spermatocyte of the Turkish hamster (Mesocricetus brandti) is described. Each autosomal bivalent was identified and a total of 304 chromomeres was found. A sex bivalent with a despiralized Xq protruding from the sex vesicle and a small number of the polymorphic 16q bivalents were observed.     

Patterns of immunocytochemically detected Z-DNA in the recrudescing testicular epithelium of the Turkish hamster (Mesocricetus brandti)

Z-DNA has been considered a labile but essential structural form of DNA in recombination and gene expression, two significant activities in mammalian seminiferous epithelium. The present study has utilized the recrudescing testes of Mesocricetus brandti to study in detail the potential Z-DNA sites in specific testicular cell types as detected by an immunoprobe. Testicular regression was physiologically induced by modifying environmental photoperiods and/or temperature. Partial atrophy of seminiferous epithelium occurred in all experimental groups but Sertoli cells persisted throughout regression. Recrudescence of testicular activity was marked in all experimental groups by characteristic sequences of reappearance of potential Z-DNA sites to a final positive or negative mature state of the cell type. It is suggested that Z-DNA is a functionally important from of DNA in many cell types of the active seminiferous epithelium of the Turkish hamster, and perhaps other mammals.     

The circadian system of the Turkish hamster, Mesocricetus brandti: responses to light

The circadian system of the Turkish hamster controlling wheel-running activity responded to single 1-hr light pulses and to repeated 1-hr pulses in a similar way as that of Syrian hamsters studied previously. At constant light of 100 lx, the period length (tau) of the freerunning activity rhythm of Turkish hamsters was longer and the activity time (alpha) was shorter than that of Syrian hamsters. Among individuals, the ability of the system to be entrained by one 1-hr light pulse per cycle was related to the range (advance plus delay amplitude) of the phase response curve (PRC) derived from single light pulses and to the compression of alpha caused by the pulse Zeitgeber. The data support the hypothesis derived from experiments on Syrian hamsters that the range of the PRC is functionally related with alpha, possibly reflecting the phase relations (coupling) between two oscillators.     

The Cycle of the Seminiferous Epithelium of the Turkish Hamster (Mesocricetus brandti)

The Turkish hamster ( Mesocricetus brandti ) has become a desirable species for experimentation in testicular function, photoperiod, reproductive hormones and hibernation. Basic data on the kinetics of the seminiferous epithelium have not yet been published. In the present study, the cycle of the seminiferous epithelium was divided into eight stages based on the overall cellular associations of 1540 cross sections of tubules. The mean relative frequencies for stages 1 through 8 were 5.9, 3.3, 11.7, 6.7, 7.2, 28.5, 21.6 and 15.1%, respectively. The absolute duration of the cycle of the seminiferous epithelium was determined by administration of ³H-thymidine, removal of testes at intevals after injection and autoradiography. The mean duration of one cycle was estimated at 8.0 days and the duration of stages 1 through 8 was 0.5, 0.3, 0.9, 0.5, 0.6, 2.3, 1.7 and 1.2 days, respectively. The duration of meiotic prophase was 11.5 days and of spermiogenesis was 13.8 days. The life span of preleptotene cell was estimated at 1.21 days, leptotene, 0.73 days, zygotene, 0.94 days and pachytene, 7.37 days. The total cycle length of spermatogenesis as usually calculated was 32.0 days.     

Uterine steroid hormone receptors during the estrous cycle and during hibernation in the Turkish hamster (Mesocricetus brandti)

The Turkish hamster is a long-day breeder that hibernates for 4-5 mo if exposed to a short-day, cold environment. The objective of this study was to assess the uterine responsiveness of the hibernating animal to ovarian steroids. Our approach was 1) to characterize and determine uterine estrogen (E) and progesterone (P) receptors (R) during hibernation as compared to the levels observed in cycling females that had terminated hibernation, and 2) to assess the responsiveness of the uterus to E during hibernation by its ability to induce uterine P receptor. Females were exposed to short days (10L:14D) for 2 mo and then were placed in a cold-room (10L: 14D, 6 +/- 1 degrees C). After 2 or 4 mo in the cold, hibernating animals were killed and uterine steroid receptors were determined by 3H-steroid binding assay. Uterine receptors were also determined in cycling Turkish hamsters on each morning of the estrous cycle. Values for uterine receptors (pmol/g tissue, n = 4-6) during the estrous cycle (estrus, diestrus I, diestrus II, proestrus) were: 4.3 +/- 0.78, 3.9 +/- 0.19, 4.1 +/- 0.25, 3.7 +/- 0.5 for cytosolic ER; 36.6 +/- 5.8, 32.2 +/- 6.8, 36.3 +/- 1.5, 54.4 +/- 1.9 for cytosolic PR; 0.59 +/- 0.11, 0.54 +/- 0.07, 1.06 +/- 0.05, 1.42 +/- 0.17 for nuclear ER. Hibernating (torpid) animals sampled after 2 mo in the cold showed a significant (p less than 0.05) depression of cytosolic ER (2.6 +/- 0.12, n = 5) and cytosolic PR (19.0 +/- 2.6, n = 8) as compared to any day of the estrous cycle.(ABSTRACT TRUNCATED AT 250 WORDS)     

The effects of day length, hibernation, and ambient temperature on incisor dentin in the Turkish hamster (Mesocricetus brandti)

Dentin is deposited on a circadian basis, and daily layers manifest as bands on the medial surfaces of rodent incisors. Hibernation alters dentin deposition, and a distinct hibernation mark has been described on incisor surfaces of several rodent species; the factors that influence the morphology of this mark are poorly understood. We tested the effects of day length, torpor expression, and ambient temperature on incisor surface morphology in Turkish hamsters housed in one of four conditions: long days (LDs) at 22 °C, short days (SDs) at 22 °C, SDs at 5 °C, and SDs at 13 °C. Body temperature was monitored continuously with implanted radio transmitters, and teeth examined postmortem. Teeth of SD hamsters had narrower, less distinct circadian increments than those of LD hamsters, but the width of ultradian increments was similar in both photoperiods. Hibernation at both 5 and 13 °C was associated in most specimens with very narrow, sharply defined dentin increments and increased tooth heterogeneity. Hamsters in SDs at 5 °C that did not hibernate lacked characteristic hibernation increments. At 5 °C, but not 13 °C, the number and cumulative width of hibernation increments were related to number and cumulative duration of periodic arousals. Our results suggest that incremental deposition of dentin in rodent incisors may be a useful trait for characterizing hibernation behavior in both evolutionary and historical contexts.     

Predictors of social dominance in the adult female golden hamster (Mesocricetus auratus)

Adult female golden hamsters exhibit smaller and less pigmented flank glands than do males. Nevertheless, as has been found in male hamsters, variations in these parameters of the flank glands correlate highly (r_s=0·78) with social rank attained in a group of four females. Ovariectomy and subsequent replacement with a graded series of testosterone propionate doses produces a directly related response in the flank gland and in the social rank attained in all-female groups (r_s=0·72). Body weight of females also correlates directly with social status (r_s=0·74), but, when body weight is held constant, social rank can still be predicted from measures of the flank gland. Oestrous-related fluctuations in aggressive behaviour of females did not alter dominance relationships.     

Effects of gonadal steroid hormones on hibernation in the Turkish hamster (Mesocricetus brandti)

Summary The Turkish hamster (Mesocricetus brandti) is a photoperiodic species in which exposure to a short day photoperiod induces gonadal atrophy. When hibernating male Turkish hamsters were administered testosterone via subcutaneous silastic capsules hibernation was abruptly terminated. The threshold serum testosterone level required to prevent hibernation was intermediate between the levels observed in males with fully-regressed and fully-functional testes. Dihydrotestosterone was as effective as testosterone in blocking hibernation. Estradiol had a partial inhibitory effect. Progesterone and corticosterone implants had no effect on hibernation. Similar results were obtained in female hamsters. The total period of hibernation for untreated males under laboratory conditions was usually 5–6 months. In most animals testicular growth began to occur toward the end of that period. As gonadal growth continued bouts of torpor decreased in frequency and duration, and hibernation was terminated when the testes approached reproductive size. Castrated males continued to hibernate much longer than intact animals. These observations suggest that in nature decreasing day length in the fall initiates gonadal regression which is followed by cold-induced hibernation. In the spring spontaneous recrudescence of the testes may lead to termination of the dormancy period. This mechanism may enable the species to prepare for the reproductive season with maximum efficiency.Supported by NIH Research Grant HD-10478 and by a grant from the Connecticut Research FoundationThe data in this paper were presented in part at the Annual Meeting of the American Society of Zoologists, Toronto, December 26–30, 1977     

Elimination of short-day melatonin signaling accelerates gonadal recrudescence but does not break refractoriness in male Turkish hamsters

Long days stimulate and short days (SDs) inhibit the reproductive axis of photoperiodic rodents. In long-day Turkish hamsters, unlike most other rodents, elimination of pineal melatonin secretion by constant light or pinealectomy initiates a cycle of gonadal involution and recrudescence outwardly similar to that induced by short days. The present study assessed whether short days and constant light induce the seasonal reproductive cycle via common or different interval timing mechanisms. Male hamsters that had undergone gonadal involution in SDs for 8 or 14 weeks were treated with LL for 14 and 8 weeks, respectively. If SDs and LL act via independent mechanisms, then gonadal quiescence of SD-regressed males, which normally lasts 10 weeks, might be extended by LL treatment; alternatively, if SDs and LL act on the same timer, or the timer cannot be retriggered, then LL will not extend the duration of reproductive quiescence. Neither of these outcomes materialized. Instead, male hamsters exposed to LL while reproductively quiescent exhibited accelerated gonadal recrudescence. Extended LL treatment did not restore responsiveness to SDs in photorefractory hamsters. In Turkish hamsters, photoperiodic history determines whether constant light inhibits or stimulates the hypothalamic-pituitary-testicular axis.     

Knife cuts lateral but not dorsal to the hypothalamic paraventricular nucleus abolish gonadal responses to photoperiod in female hamsters (Mesocricetus auratus)

Horizontal and parasagittal knife cuts in the hypothalamus of female hamsters (Mesocricetus auratus) were employed to investigate the neural pathways that mediate gonadal responses to photoperiod. Bilateral horizontal knife cuts placed dorsal to the paraventricular nucleus (PVN) did not prevent short-day-induced acyclicity and uterine regression. On the other hand, regardless of photoperiod, animals with bilateral parasagittal knife cuts placed lateral to the PVN continued to exhibit regular 4-day estrous cycles and stimulated uteri. Thus, parasagittal cuts prevented the effects of short days on reproductive physiology. This finding suggests that the lateral efferent projections from the PVN represent an important component of the neural pathway mediating reproductive photoperiodism in female hamsters.     

Chromosome replication in fibroblasts of the Syrian hamster (Mesocricetus auratus)

The BrdU/Hoechst 33258/Giemsa method for sub-dividing S-phase in asynchronous cell populations has been re-evaluated and modified to give better definition and more even distribution of sub-phases. A reference pattern of early-relicating euchromatic bands is given for all chromosomes at Sk2 in primary cultures of skin fibroblasts. The overall band patterns at each sub-phase have allowed more objective definitions of early and late replication for these cells, and show that in both classes of chromatin light G-bands preceed dark G-bands. Asynchrony between homologous bands is observed at all stages of S, albeit with a variable frequency. The observed in vitro replication patterns and programme for the chromosomes of skin fibroblasts does not appear to be affected by the age or sex of the source.     

Cytological sub-division of S-phase in the Syrian hamster (Mesocricetus auratus)

Using BrdU/Hoechst 33258/Giemsa methods for detecting replicating chromosome bands, a method is described by which the DNA synthesis phase may be sub-divided on the basis of distinctive patterns displayed by certain chromosomes. — Applied to asynchronous populations successively sampled through one cell cycle, cells in S can be unscrambled and replaced in their correct time sequence. — This helps to overcome the sampling-time variable inherent in such populations, and allows a clearer picture of the progression of events both qualitatively and quantitatively.