Spontaneous Recrudescence Research Articles

Spontaneous Recrudescence of Spermatogenesis in the Photoinhibited Male Djungarian Hamster, Phodopus Sungorus1

Photosensitive rodents exposed to inhibitory short photoperiods become insensitive to this environmental factor after prolonged exposure. During the following process of spontaneous recrudescence, the animals that have adapted to the winter season show a return of all seasonal parameters. In the Djungarian hamster, obvious photoperiod-dependent changes are reinitiation of the reproductive organs, a 20-30% increase in body weight, and a moult from whitish fur into brown summer fur. This study was designed to analyze the morphological and endocrinological changes occurring during spontaneous testicular recrudescence in male Djungarian hamsters under prolonged short photoperiods. Two experiments were performed 1) to analyze the time-dependent changes in groups of hamsters exposed to short photoperiods and 2) to observe testicular and humoral changes in individual animals during spontaneous recrudescence. Regrowth of the testes and seminal vesicles did not begin before Week 18 in short photoperiods. While serum testosterone did not increase before Week 24, serum FSH had already returned to normal values from Week 18 onwards. Individual analysis by enzyme histochemistry revealed that 3 beta-hydroxysteroid-dehydrogenase activity in Leydig cells was not restored before testicular weights of more than 400 mg were observed and the first wave of spermatogenesis had reached the stage of elongated spermatids. This indicates that the testicular testosterone production was low until a status of testicular recrudescence had been achieved, at which point the testis showed complete qualitative spermatogenesis and a restoration of the Sertoli cell actin filaments. These data suggest that the process of early spontaneous recrudescence in male Djungarian hamsters appears to be initiated by the restoration of serum FSH rather than by testosterone.

Dissociation of the Reproductive and Prolactin Photoperiodic Responses in Male Golden Hamsters1

The response of prolactin (PRL) and that of the pituitary-testicular axis to inhibitory photoperiods were compared in immature and young adult hamsters. In the first experiment, 14-day-old hamsters were transferred from 14L:10D to 12L:12D or 8L:16D. At 21, 28, 35, and 49 days of age, body weights, testes weights, and plasma LH were similar in all groups. In contrast, the levels of PRL were lower in animals on 8L:16D or 12L:12D than in those on 14L:10D and 49 days of age. In a second experiment, 80-day-old hamsters were transferred from 14L:10D to either 12L:12D or 8L:16D. At 5-wk intervals, they were weighed and bled by cardiocentesis and the length of the testes was measured. Photoperiods of 12L:12D and 8L:16D induced testicular regression, which was complete by 15 wk. Thereafter, augmented levels of FSH preceded spontaneous recrudescence of the testes in animals on both photoperiods. Serum PRL levels were significantly depressed within 5 wk after transfer to either 8L:16D or 12L:12D. After 15 wk as the testes were increasing in size in both groups, circulating PRL levels increased in animals exposed to 8L:16D, whereas in animals exposed to 12L:12D, PRL remained at or below the sensitivity of the assay. In a final experiment, on the day before parturition, pregnant hamsters were transferred to either 6L:18D, 6L:30D, 6L:42D, or 6L:54D or were held on 14L:10D. There were no differences in testicular weights, plasma LH, or plasma thyroxine (T4) of the pups from these dams at 21, 36, or 48 days of age.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of short photoperiods on reproductive organs and estrous cycles of normal and pinealectomized female Djungarian hamsters, Phodopus sungorus.

This study was designed to analyze morphological changes in the reproductive organs and endocrine changes in the serum and pituitaries of female Djungarian hamsters during regression, the period of involution and early spontaneous recrudescence in response to short photoperiods. In addition, the involvement of the pineal gland on the inhibitory response to short photoperiods was investigated. In the first study, 63 adult female hamsters were divided into five groups, which were either pinealectomized at the time of transfer or 11 wk after transfer into short photoperiods, or exposed to different light regimens. The estrous cycles of these hamsters were recorded by vaginal smears for a period of 34 wk. In a second study, 156 adult female hamsters were divided into 14 groups and maintained under the influence of long or short photoperiods for 0-33 wk. The animals were killed by decapitation at 3-wk intervals and analyzed for changes in body weight and morphology of the vagina, ovary, and uterus. A loss of cyclic activity and complete involution of uterus and vagina were observed between Week 9 and Week 27 after transfer into short photoperiods. During this time period, no corpora lutea were observed in the ovaries. Under the influence of short photoperiods, the numbers of medium and antral follicles declined continuously until Week 15, and afterwards gradually recovered to maximal numbers in Week 27. This biphasic response to short photoperiods was not observed in the number of small follicles. These morphological changes were accompanied by changes in serum and pituitary FSH concentrations. Pinealectomy prevented the loss of estrous cyclicity after transfer into short photoperiods.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Photoperiodic regulation of body mass, food intake, hibernation, and reproduction in intact and castrated male European hamsters, Cricetus cricetus.

A group of sexually active male European hamsters were raised either in short-photoperiod conditions (SP; LD 8:16) or in long-photoperiod conditions (LP; LD 16:8) from their capture at the end of the hibernation period. Another group of hamsters was castrated in April and gonadectomized animals were maintained in SP and cold (7 degrees C) or in a succession of SP and LP plus cold. Another group, castrated in May or in September and raised in LP conditions, was transferred in September to SP conditions and cold. 1. Normal hamsters raised in continuous SP or LP apparently did not show signs of rhythmic behavior, except possibly in gonadal activity. 2. Body weight increased continuously, plasma testosterone levels oscillated between 1.5 and 2.5 ng/ml, and animals raised in SP and in cold did not enter hibernation. 3. Similar results were also found in castrated animals kept in SP conditions and cold. 4. The sequence LP-SP induced a decrease in food intake and body weight and a decrease in plasma testosterone levels and triggered entry into hibernation in both intact and castrated animals. 5. After 6 months continuously in SP and with exposure to cold spontaneous recrudescence in food intake and body weight occurred and hibernation ended in both intact and castrated animals. 6. In normal animals a spontaneous increase in plasma testosterone levels was observed. 7. In both normal and gonadectomized animals the phase of refractoriness could be broken by exposure to LP conditions. 8. The critical photoperiod lies between 15 and 15.5 h. These results demonstrate that the European hamster is a photoperiodic species.(ABSTRACT TRUNCATED AT 250 WORDS)

Spontaneous testicular recrudescence of Syrian hamsters: Role of stimulatory photoperiods

The gonads of hamsters maintained in short photoperiods first undergo regression and then spontaneous recrudescence. The latter is indicative of refractoriness of the neuroendocrine axis to short day lengths. We tested the hypothesis that the absence of long-day stimulation contributes to the development of refractoriness to short photoperiods. Male Syrian hamsters were maintained for 26 weeks in a short-day photoperiod (8 hr light/day). Testicular regression was confirmed in all animals at week 10; thereafter different groups of hamsters were stimulated with one long day (16 hr light) every 10, 15, 20 or 30 days until week 26. Control groups were maintained continuously in long or short photoperiods, respectively. The rate of gonadal recrudescence of short-day hamsters was not affected by intermittent stimulation with long photoperiods. After 26 weeks, testes in all short-day groups had undergone recrudescence. Refractoriness to short day lengths is not counteracted by long photoperiods. The role of the pineal gland in the development of refractoriness is considered.

Role of short photoperiod and cold exposure in regulating daily torpor in Djungarian hamsters.

1. Male and female Djungarian hamsters (Phodopus sungorus) were gonadectomized or sham-operated after 12 weeks of exposure to short photoperiods (10L:14D). Half of the animals were single housed and transferred to a cold environment (7 degrees C) at week 13 of short days and half were transferred to cold at week 21. The time courses of short photoperiod induced seasonal changes in body weight, pelage color stage, and daily torpor were monitored periodically until the experiment was terminated after 34 weeks of short days. 2. The total duration of short photoperiod exposure was of primary importance compared to the duration of cold exposure in regulating seasonal changes in the frequency of daily torpor, body weight and pelage color exhibited by male and female Djungarian hamsters; that is, the change from long to short days was much more effective as a seasonal time cue than was the onset of cold exposure. 3. Gonadectomy did not prevent the occurrence of seasonal torpor in hamsters of either sex, indicating that these cycles are regulated by a time measuring mechanism (seasonal clock) that is largely independent of the gonadal cycle. However, castration did influence certain aspects of the body weight and torpor cycles exhibited by male hamsters. 4. Some castrated animals showed a delay in terminating the torpor season lending further support to the hypothesis that the spontaneous recrudescence of the testes which occurs toward the end of the torpor season may play a role in the termination of torpor in males.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of external factors on hibernation of golden hamsters

1. Hibernation of golden hamsters begins after about 2 months exposure to cold and dark, occurs repeatedly for a further 6 months and then ceases. Constant light reduces the frequency of hibernation only slightly. 2. There is an inverse relation between occurrence of hibernation and gonadal activity. Continuous exposure to dark or cold or both induces gonadal involution within 30–60 days and spontaneous recrudescence of gonads occurs after about 7 months under these conditions. Application of testosterone prevents hibernation. 3. Gonadal functions are not the only factor involved in the control of hibernation. Castration has a slightly positive effect on hibernation and in castrated individuals hibernation ceases after several months in the cold, similar to controls. 4. Application of melatonin to golden hamsters exposed to cold and dark does not influence hibernation pattern. The effect of cold on gonadal involution and on hibernation is not mediated by the pineal because pinealectomized animals exposed to cold, and intact hamsters kept in continuous light and cold, undergo gonadal involution and hibernate. 5. Under controlled laboratory conditions hibernation of golden hamsters can be induced at any time of the year, providing that gonadal activity is maintained at a low level. No strict adherence of hibernation to a circannual rhythm was detected. Exogenous cues are required to establish seasonality of hibernation.

Role of the pineal and its hormone melatonin in the termination of photorefractoriness in golden hamsters.

Continuous exposure of male hamsters to short day lengths induces testicular regression. This is followed many weeks later by spontaneous recrudescence of the testes with reinitiation of spermatogenesis and function of the accessory sexual glands. Hamsters at this stage of the annual reproductive cycle are refractory to short photoperiods--even continuous darkness will not induce another bout of testicular regression. Animals refractory to short days are also refractory to the pineal hormone melatonin and a number of investigators attribute spontaneous recrudescence and photo and melatonin refractoriness to a developed target cell insensitivity to endogenous melatonin from the pineal. Refractoriness is terminated by exposure to long days for at least 11 weeks. The pineal gland is reported to be essential for this process. We report here the effects of pinealectomy, daily melatonin injections, and constant-release melatonin implants on the ability of male hamsters to recover from the refractory state. In the absence of the pineal gland, refractory male hamsters did not discriminate (count?) 15 weeks of long days to terminate refractoriness. Daily melatonin injections at 1900 h, but not at 1200 h (lights 0600-2000 h) during the 15 weeks of long-day exposure blocked the recovery from refractoriness. Constant-release melatonin implants abolished the animals ability to measure 12 and 15 weeks of long days to terminate refractoriness. These results demonstrate that general target tissue insensitivity to melatonin cannot account for the refractory state in hamsters, that a multiplicity of target tissues may exist for melatonin to account for its varied roles throughout the annual reproductive cycle in hamsters, and that the pineal gland is intimately involved in the animals' ability to measure a prescribed duration of long days to terminate refractoriness.

Alterations in neuroendocrine function during photoperiod induced testicular atrophy and recrudescence in the golden hamster.

Transfer of golden (Syrian) hamsters from a 14L:10D (Light:dark) to a 5L:19D photoperiod causes profound changes in the reproductive axis. Testicular weight fell within 7 weeks of short photoperiod exposure and remained low until 19 weeks, at which time spontaneous recrudescence began. Plasma LH, FSH, and Prl levels were undetectable at 7.5 weeks of exposure, but LH and FSH returned to basal levels by 15 weeks and Prl by 20.5 weeks. Hypothalamic LHRH levels increased concurrently with the fall in LH and FSH, suggesting that LHRH release was decreased. Increasing plasma gonadotropin levels and testicular recrudescence were associated with decreases in hypothalamic LHRH content. Hypothalamic norepinephrine (NE) turnover was low at 10 weeks, suggesting that decreased LH and FSH levels were ultimately due to decreased adrenergic activity. At 15 weeks, plasma LH levels and hypothalamic NE turnover were both increased over values seen at 10 weeks. Hypothalamic dopamine turnover, possibly reflecting decreased Prl feedback, was decreased between 0 and 10 weeks, but returned to control level by 15 weeks. It, therefore, appears that the endocrine changes associated with photoperiod induced testicular regression and recrudescence are secondary to changes in hypothalamic function.

Plasma prolactin concentrations and testicular human chorionic gonadotropin binding sites during short photoperiod-induced testicular regression and recrudescence in the golden hamster.

Experiments were conducted in the golden hamster to determine temporal relationships and statistical correlations between plasma PRL concentrations and unoccupied testicular hCG binding sites during short photoperiod-induced testicular regression and spontaneous recrudescence. Although two experiments provided statistically significant (P<O.02) correlations between plasma PRL concentrations and testicular hCG binding, variability in onset of increased plasma PRL during recrudescence prevented any definite conclusions concerning a possible cause-and-effect relationship. Hence, the data do not indicate that a period of increased PRL secretion either initiates, or is initially necessary for, spontaneous recrudescence or changes in testicular hCG binding occurring during spontaneous recrudescence. Time of initiation of spontaneous testicular recrudescence was variable, but was always associated with increases in plasma concentrations of LH, FSH, and PRL. Testes from hamsters maintained in either short or long photoperiod had a single class of high affinity hCG binding sites with an average equilibrium association constant (Ka) of 3.06 × 1010 M−1. During the first 4 weeks of short photoperiod, when no changes in testicular weights were found, there were significant decreases in both concentration (fmol/mg protein) and total content (fmol/testes) of testicular hCG binding sites. However, after 10 weeks of short photoperiod and continuing through 16–18 weeks, the concentration of hCG binding sites was increased, while total content remained depressed, in regressed testes when compared with testicular hCG binding found in long photoperiod hamsters. Use of either [125I] iodo-hCG or [125I] iodo-hLH gave identical results. This increased concentration of unoccupied hCG/hLH binding sites may represent 1) an increase in binding sites per Leydig cell; 2) decreased occupancy or decreased loss of testicular hCG binding sites commensurate with decreased plasma LH concentrations; or 3) a relative increase in numbers of Leydig cells compared with other testicular components as testes undergo regression.

Photoperiodic regulation of the testes of adult white-footed mice (peromyscus leucopus).

Exposure to short daylengths (10 h of light per day) for 12 weeks caused the gonads to regress and inhibited spermatogesis in most P. leucopus; however, in approximately 30% of mice the testes did not regress, and spermatogenesis was maintained despite 20 weeks exposure to short photoperiods. The pattern of entrainment of circadian rhythms to the short-day photoperiod did not correlate with the degree of gonadal regression. Mice whose gonads regressed after 12 weeks manifested testicular recrudescence and resumption of spermatogenesis after 30 weeks of short-day treatment. Spontaneous recrudescence, a feature common to a number of photoperiodic rodents, ensures viability of the reproductive system in the early spring in advance of the advent of long days. It is proposed that recrudescence reflects development of refractoriness of the neuroendocrine axis to pineal antigonadal factors and that individuals whose gonads do not regress in short days are permanently refractory to pineal antigonadal products. Other interpretations also are considered.

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

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.

Hypothalamic-Pituitary-Gonadal Interactions during Spontaneous Testicular Recrudescence in Golden Hamsters

Golden hamsters exposed to short days (<12.5 h Iight/24 h) show a decrease in serum FSH and LH resulting, after 10-12 weeks, in testicular regression. This is followed by a spontaneous rise in serum FSH and LH (weeks 15-23) and a concomitant maturation of the reproductive system. In this study, we examined the interaction of negative feedback mechanisms and photoperiodic effects during the period of spontaneous recrudescence in hamsters exposed to continual short day treatment (LD 6 h:18 h). After 2 weeks, animals were divided into 4 groups. One group served as intact controls. Another group of intact males received 5 mm testosterone implants (in Silastic tubing). The others were castrated; half of these received testosterone implants. Five animals were sacrificed every 2 weeks in the control group and every week in the treatment groups. Spontaneous testicular recrudescence occurred between weeks 15-27 in control animals and weeks 20-29 in animals with testosterone implants. Analysis of serum gonadotropins in each treatment group revealed a temporal difference in the peak of FSH and LH that appears to correlate with circulating levels of testosterone. These data suggest that alternations in gonadotropin release during spontaneous testicular recrudescence may be controlled by a gradual change in the set point of the sensitivity of the hypothalamic-pituitary axis to testosterone.

Prolonged Exposure of Castrated Male Hamsters to a Nonstimulatory Photoperiod: Spontaneous Change in Sensitivity of the Hypothalamic-Pituitary Axis to Testosterone Feedback*

ABSTRACT. Maintenance of male golden hamsters on nonstimulatory short days for 8-10 weeks induces testicular atrophy, while prolonged exposure (18-30 weeks) results in a refractoriness to the inhibitory effects of short days, and a spontaneous recrudescence of the testes. In view of recent reports that photicinduced changes in the reproductive axis involve an alteration in sensitivity of the gonadotropin control center to steroid feedback, the present investigation was designed to determine if spontaneous changes in the reproductive axis may also involve a change in the responsiveness of the hypothalamic-pituitary system to steroid feedback. Hamsters were castrated and exposed to short days [6 h of light/(LD 6:18)] for 8 weeks. Castrates were then implanted with either empty or testosterone-filled Silastic capsules which were 2, 4, 8, or 20 mm long, and maintained on LD 6:18 for another 18 weeks. Blood samples were obtained by cardiac puncture before capsule implantation and after 11, 14, 18, 22, and 26 w...

Photoperiodic influences on testicular regression in the golden hamster: termination of scotorefractoriness.

Hamsters whose testes have regressed and recrudesced during the animals’ exposure to short photoperiods are insensitive to short days (scotorefractoriness). To restore sensitivity to short days, hamsters must first experience many weeks of long days (Reiter, 1972). The precise photoperiodic requirements for the termination of scotorefractoriness were investigated. Animals with spontaneously recrudesced testes were subjected to different durations and patterns of long day exposure to test the hypothesis that a restricted long day-sensitive period exists. Twenty weeks of photostimulation uniformly allowed regression to occur upon return of the animals to short days; hamsters exposed to 10 weeks of photostimulation were generally rendered sensitive to short days, but their testes did not regress as rapidly nor as consistently. This effect was obtained regardless of the pattern of photostimulation after spontaneous recrudescence. There was some indication that episodes of photostimulation can summate over intervals of 1, but not 10 weeks of short days or darkness. The results indicate that scotorefractoriness is not an all-or-none phenomenon; photostimulation during the refractory period acts principally to alter the rate of regression upon reexposure to short days. It is unlikely that a restricted long day-sensitive phase exists in the golden hamster.

Effect of Short Days in the Photoperiodic Testicular Response of Japanese Quail

Avian gonadal activity is known to be controlled by photoperiods. In male Japa-nese quail, testicular activity is stimulated by long days and inhibited by short days. However, the photoperiodic testicular response of the quail is not completely under-stood. Thus, I investigated it under various photoperiodic conditions.When birds were reared under continuous light (LL) after hatching, they reached maturation in 6 weeks and maintained large testes as long as they were kept under LL. When birds were transferred from LL to a short photoperiod (8L : 16D), their testes showed considerable involution within 2 weeks. However, when birds received the short day treatment for 5 weeks or longer period prior to the long day treatment, their testes showed resistance to involution in the subsequent short day treatment of both young and old birds. Further, when birds were continuously kept under a short photoperiod, they showed spontaneous growth of their testes 12 weeks after hatching. Adult birds, which experienced sexual maturation under the long photoperiod, also showed spontaneous recrudescence of their testes under a short photoperiod after several weeks in the involuted state. These results clearly indicate that a short photoperiod does not always act to inhibit the testes of the Japanese quail. They also suggest that there is a kind of photorefractoriness against short days.

Why Don't Boblinks Breed in Brazil?

The Bobolink, Dolichonyx oryzivorus, experiences two sets of "long" and "short" days each year during the transequatorial migration between North and South America. Increasing daylength normally stimulates gametogenesis in birds, and thus it is perplexing that Bobolinks do not also respond to the southern summer and attempt to breed in Brazil. Previous hypotheses regarding transequatorial migration are discussed; four experiments relating to these hypotheses are presented and evaluated. The testis cycle, moult pattern, body weight fluctuations, and beak color of male birds were followed on simulated natural daylength cycles for 15 months at 20—day intervals. Body weight and testis cycles appeared normal on this simulated natural cycle; beak color patterns and moult desynchronized. Absolute insensitivity to light terminates by late October; thereafter the birds are sensitive to "long days" for 6 months, yet they do not respond to an increasing daylength cycle comparable to 20° S latitude. Birds were also exposed to 17 months of continuous bright light: body weight cycles were regular for 6 months, then desynchronized; the testes regressed but spontaneous recrudescence was observed in 3 of 13 birds; recrudescence was not synchronous. Bobolinks did not respond to the 6L—30D lighting cycle that indicates a circadian control mechanism in other birds. A summarization of the photoperiodic responses of the Bobolink is included.