Vertebrate circadian and photoperiodic systems: role of the pineal gland and melatonin.
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Animals↗
Biomedical subjects
B D Goldman
Publications and source records attributed to B D Goldman.
Influence of short days on diurnal patterns of serum gonadotrophins and prolactin concentrations in the male Djungarian hamster, Phodopus sungorus.
Exposure to short days for 8 weeks suppressed mean serum concentrations of FSH, LH and prolactin compared to hamsters kept in long days. Hamsters in short days exhibited a small afternoon rise in serum FSH, but serum LH and prolactin did not exhibit 24-h variations. In hamsters under long days, a late afternoon-early evening increase was evident for circulating prolactin but none was detected for the gonadotrophins. A fall in testes weights rapidly occurred by 14-28 days after transfer to short days. This was accompanied or preceded by a decrease in serum gonadotrophins and prolactin. Reductions in serum FSH and LH occurred in short days in blood samples taken at 09:00 h or 15:00 h. However, the nadir in serum prolactin was first achieved (at 09:00 h), at least 7 days before that at 15:00 h (i.e. Day 14 versus Day 21 of short photoperiod, respectively). The ability to secrete gonadotrophins was further tested in hamsters that had undergone gonadal regression. Castration of hamsters exposed to short days or injected with melatonin in the afternoon, a treatment known to mimic short day effects, induced a 3- to 5-fold increase in serum gonadotrophins. However, this rise in FSH and LH was significantly attenuated compared to the 10-fold response in controls in long days. The results indicate that gonadal involution induced by short days may be mediated by the decline in mean gonadotrophin secretion which, in turn, is regulated by responsiveness to steroids, as well as a mechanism independent of the negative feedback action of gonadal steroids.
Animals↗
Activity rhythms and photoperiodism of Syrian hamsters in a simulated burrow system.
Male Syrian hamsters were housed in simulated burrows in order to investigate (a) how these nocturnal, fossorial rodents entrain to the prevailing light:dark cycle in this semi-natural habitat and (b) the response of the reproductive system to environmental illumination. The burrow emergence activity of hamsters housed in simulated burrows was compared to the running wheel activity of animals maintained in standard cage conditions. The activity rhythm was similar in both measuring devices. The data suggested that in a natural environment hamsters are only exposed to light for short amounts of time each day. To determine whether brief photoperiodic stimulation could alter the phase angle of entrainment and/or the reproductive condition, burrow housed animals were exposed to a supplemental 30-second light pulse during specified clock hours of the dark period on a daily basis. These light pulses induced a phase shift and maintained a long day reproductive response in what was otherwise a short photoperiod.
Animals↗
Environmental influences upon circadian periodicity of Syrian hamsters.
The free running period (tau) of male Syrian hamsters, when measured as the circadian rhythm of emergence from simulated burrows, was compared to tau when locomotor activity was measured via running wheels. In constant darkness, the inter-individual variability of the tau s was less among burrow housed hamsters than for running wheel housed hamsters. Hence, access to activity wheels eventually led to more disparate activity onset times among the running wheel animals, as compared to the relative population synchrony observed when animals were housed in simulated burrows. When tau s were contrasted between hamsters housed in standard cages with or without running wheels, it appeared that tau values of hamsters housed in simulated burrows were more similar to those of hamsters housed in standard cages without wheels. The data suggests that the tau of the hamster circadian system may be subject to subtle environmental influences.
Animals↗
Maternal influence on activity rhythms and reproductive development in Djungarian hamster pups.
Photoperiodism and entrainment of the circadian rhythm of locomotor activity were investigated in juvenile Djungarian hamsters. Animals were housed in simulated burrows. Activity was measured as the animal's emergence from a dark nest chamber into an outer box exposed to the room illumination. This burrow emergence activity exhibited marked circadian rhythmicity. Interactions between mother hamsters and their offspring were examined in the simulated burrow system. Male reproductive responses were determined by measuring testicular weights at the time of weaning. It was shown that photoperiodic information received between Days 1 and 15 of life failed to alter the rate of testicular development, but that after Day 15 testicular growth was photoperiod-dependent. The mother, when entrained to a long photoperiod, did not influence the photoperiodic responses of her pups when they were confined to a dark nest box. In contrast, the mother did influence the circadian entrainment patterns of her pups. Pups exhibited a well-developed circadian activity rhythm at weaning with a phase angle roughly similar to that of the mother's activity rhythm. When the maternal rhythms were discrepant with photoperiod information received by the pups directly from the environment, the pups' activity rhythms were synchronized with the light/dark cycle rather than with the rhythm of their mother. Thus, it appears that although pups may first become entrained by maternal cues, they rapidly adjust to the environmental light cycle after leaving the nest.
Animals↗
Maternal transfer of photoperiodic information influences the photoperiodic response of prepubertal Djungarian hamsters (Phodopus sungorus sungorus).
Daylengths during the spring are repeated in reverse order in the autumn. For some photoperiodic species, a given photoperiod may be stimulatory for reproduction in the spring and inhibitory in the autumn. The mechanisms regulating this type of seasonal response have, until recently, remained a mystery. Horton (1984a) showed in Microtus montanus that the photoperiod experienced by the mother influences the gonadal development of her young after weaning. To determine if this phenomenon is characteristic of other photoperiodic rodents, adult Djungarian hamsters were paired on 16L:8D, 14L:10D, or 12L:12D. Young males born from these pairings were killed at 15, 28, and 34 days of age to assess gonadal development (testes weight). At 15 days testicular development was identical in all groups; by 28 days, however, males raised in 16L:8D or 14L:10D exhibited a greater degree of testicular development than those raised in 12L:12D. Next, females maintained on each of the three photoperiods throughout gestation were transferred, with their offspring, to the other two photoperiods at birth. Postnatal exposure to 14L:10D or 12L:12D inhibited testicular development in young that had been gestated on 16L:8D. Both 16L:8D and 14L:10D stimulated testicular growth in animals that had been gestated on 12L:12D or 14L:10D. Therefore, a) 16L:8D stimulates testicular growth in all animals, b) 12L:12D inhibits testicular growth in all animals, and c) the testicular response to 14L:10D depends on the photoperiod experienced by the mother during pregnancy.(ABSTRACT TRUNCATED AT 250 WORDS)
Animals↗
Pineal melatonin rhythms in female Turkish hamsters: effects of photoperiod and hibernation.
Daily rhythms of pineal and serum melatonin content were characterized for adult female Turkish hamsters (Mesocricetus brandti) exposed to long days (16L:8D, 22 degrees C) or after transfer to short days (10L:14D, 22 degrees C). The nocturnal peak of pineal melatonin content was found to be approximately 3 b greater in duration on short than on long days. Changes in levels of serum melatonin closely paralleled those of pineal melatonin. Thus, an effect of photoperiod on synthesis and secretion of pineal melatonin was demonstrated. In a separate experiment, female hamsters were induced to hibernate by exposure to a short-day, cold environment (10L:14D, 6 degrees C). During the 4 to 5-mo hibernation season, Turkish hamsters are known to display 4 to 8-day hours of torpor (body temperature = 7-9 degrees C) alternating with 1 to 3-day intervals of euthermia (body temperature = 35-37 degrees C). Little evidence of nocturnal synthesis or secretion of pineal melatonin was detected in females sampled during torpor. However, animals sampled during the first day after arousal from a torpor bout displayed melatonin rhythms no different in phase or amplitude from those seen in females held at 22 degrees C. Thus, despite the absence of pineal melatonin output during torpor, the pineal gland of hibernating Turkish hamsters produces an appropriately phased, rhythmic melatonin signal during intervals of euthermia.
Aging↗
Reproductive effects of olfactory bulbectomy in the Syrian hamster.
The effects of olfactory bulbectomy on circulating gonadotropin, prolactin and testosterone levels and on the testicular and pituitary responses to shortening of day length were studied in Syrian hamsters. Adult animals maintained on a 14L:10D cycle were sham-operated or sustained bilateral radical olfactory bulbectomies by aspiration to remove the main and accessory olfactory bulbs and the adjacent regions of the anterior olfactory nucleus. They were then maintained either on the long photoperiod or housed on a 10L:14D cycle. Testicular length was measured at weekly intervals over a 5-mo period. Sham-operated controls exhibited the normal pattern of testicular regression and eventual recrudescence on the short photoperiod. Testicular regression was significantly reduced in bulbectomized animals. Many of these animals showed no regression; others exhibited a reduced degree and/or shortened duration of regression. Serum levels of follicle-stimulating hormone (FSH) were substantially elevated in bulbectomized males maintained in long days. Their serum levels of luteinizing hormone (LH), prolactin and testosterone remained within the range for shams on long photoperiod. In short days, the bulbectomized animals showed the normal, pronounced decline in circulating prolactin levels. Serum FSH and LH levels also showed substantial declines, but the FSH levels were not reduced below the range for controls in long days, and the decline in LH levels was not as great as that for controls in short days.(ABSTRACT TRUNCATED AT 250 WORDS)
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Maturation of the pineal melatonin rhythm in long- and short-day reared Djungarian hamsters.
Male Djungarian hamsters, reared under long (16L/8D) or short (10L/14D) days, were sacrificed at various ages during the day or night, or at night following a 30-min light pulse. The pineal melatonin rhythm matured similarly under long and short days by 20 days of age. The results are discussed in context of the hypothesis that melatonin mediates the photoperiod effects which forestall puberty in short-day reared hamsters.
Animals↗
Photic influences on the developing mammal.
In adult mammals, the daily light-dark cycle acts via the retinohypothalamic pathway to entrain the circadian clock in the suprachiasmatic nuclei (SCN) and to communicate information about daylength to photoperiodic species. Studies in rats show that during late fetal and early neonatal life, before the retinohypothalamic pathway has innervated the SCN, the maternal circadian system entrains the timing of the developing clock to prevailing lighting conditions. Although the nature of the maternal output signal(s) used to entrain the developing clock has not been elucidated, the maternal SCN are a necessary component of maternal entrainment during both prenatal and postnatal life. Maternal entrainment of the fetal and neonatal clock thus ensures that the developing circadian system is synchronized to the outside world until maturation of the retinohypothalamic pathway permits direct photic entrainment. The maternal circadian system is not only necessary for entrainment of the developing circadian system, but recent studies suggest it may also provide the immature mammal with important photoperiodic information. In the montane vole (Microtus montanus) and the Djungarian hamster (Phodopus sungorus), the prenatal photoperiod affects postnatal photoperiodic responses, and cross-fostering experiments show that this information about daylength is perceived by the fetus. This prenatal information, in conjunction with postnatal perception of photoperiod, allows the developing animal to determine which way the season is changing and to modify the rate of reproductive maturation accordingly.
Aging↗
Adrenal corticoids in hamsters: role in circadian timing.
The 24-h patterns of circulating cortisol and corticosterone were determined in male hamsters housed under a 14:10 light-dark cycle. Corticoid levels varied significantly over the 24-h sampling period with peak levels of both hormones occurring near the onset of the daily dark phase. The ratio of cortisol to corticosterone changed dramatically during the day. Corticosterone levels were significantly higher than cortisol during the early part of the light phase; however, cortisol levels became significantly higher than corticosterone when both hormones began their daily rise. To examine whether the circadian rhythm of cortisol secretion could be involved in the physiological control of hamster circadian organization, cortisol was infused at approximately physiological levels into adrenalectomized hamsters either continuously or in a 24-h rhythm. No significant differences were observed in the timing of circadian wheel-running rhythms in hamsters housed in LD 16:8, LD 14:10, or LL when cortisol was infused continuously, in a 24-h rhythm that mimicked the cortisol rhythm of intact hamsters, or in a 24-h rhythm several hours out of phase with the rhythm of intact hamsters. Provision of cortisol in a 24-h rhythm appeared to promote the survival of adrenalectomized hamsters since hamsters receiving a 24-h pattern of cortisol survived the experimental protocol significantly longer than those receiving the same dose of cortisol continuously.
Adrenal Cortex Hormones↗
Physiological doses of prolactin stimulate pelage pigmentation in Djungarian hamster.
The Djungarian hamster exhibits a dark agouti pelage during the summer. Under the influence of decreased daylength, this species molts and develops a predominantly white winter coat. After a patch of white fur was plucked from hamsters housed in short photoperiod, chronic infusion of 10 or 20 micrograms ovine prolactin (o-PRL)/day led to the growth of a patch of pigmented fur, thus reversing the effect of the decreased daylength. Circulating o-PRL levels produced by the 10-micrograms/day infusions ranged from 17.9 +/- 4.0 to 35.1 +/- 13.8 (SE) ng/ml and thus approximated the endogenous circulating prolactin levels found in hamsters with the dark summer pelage (6, 9). Infusion of o-PRL stimulated pigmentation of the pelage of castrated as well as intact hamsters, suggesting that the testes do not mediate this effect. Infusion of ovine growth hormone (20 micrograms/day) did not stimulate pigmentation, and infusion of alpha-melanocyte-stimulating hormone (10 micrograms/day) gave inconclusive results.
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Circadian regulation of pineal melatonin and reproduction in the Djungarian hamster.
Gonadal state, pineal melatonin rhythms, and locomotor activity rhythms were examined in juvenile male Djungarian hamsters exposed to non-24-hr light cycles ("T-cycles") or to full photoperiods. At the end of 1 month, hamsters exposed to a 1-hr pulse of light every 24.33 hr (T 24.33) exhibited small testes, whereas those receiving the same amount of light every 24.78 hr (T 24.78) displayed stimulated gonads, ten-fold larger in size. Accompanying the nonstimulatory effect of the T 24.33 cycle were nocturnal peaks in both pineal melatonin content and serum melatonin concentration which were longer by approximately 4 hr than those observed on the photostimulatory T 24.78 cycle. Exposure to an intermediate-length T-cycle (T 24.53) resulted in a mixed gonadal response and in pineal and serum melatonin peaks of intermediate duration. Wheel-running activity was entrained to the T-cycles such that light was present only near the beginning of the subjective night, its phase (relative to activity onset) differing only slightly among T-cycle groups. Hence the durational differences observed in the melatonin peaks were apparently not due to the acute suppressive or phase-advancing effects of morning light on melatonin biosynthesis, but were rather the result of differences in the endogenous control of pineal activity by the circadian pacemaker system. While no strong correlation was detected between gonadal state and the phase of locomotor activity onset relative to the light pulse, a significant correlation was observed between gonadal state and the duration of daily locomotor activity (alpha). These data were compared to similar measures obtained from hamsters exposed to long-versus short-day full photoperiods (LD 16:8 vs. LD 10:14). In summary, the results of this study indicate involvement of the circadian pacemaker system of Djungarian hamsters in the control of pineal melatonin synthesis and secretion, and in photoperiodic time measurement. Furthermore, these data strengthen the hypothesis that it is the duration of nocturnal pineal melatonin secretion that is the critical feature of this neuroendocrine gland's photoperiodic signal.
Animals↗
Testicular function and pelage color have different critical daylengths in the Djungarian hamster, Phodopus sungorus sungorus.
Testicular function and pelage color are regulated by photoperiod in the Djungarian hamster. To investigate the critical daylengths of these functions, adult male hamsters were exposed to one of four photoperiods: 16 h of light, 8 h of darkness (16L:8D), 14L:10D, 12L:12D, or 10L:14D. 10L:14D and 12L:12D induced the winter molt and testicular regression, in contrast to 14L:10D which induced only the latter response, and 16L:8D which maintained the summer pelage and large testes. Melatonin injections administered 4, 2, or 0 h before lights-off to hamsters exposed to 16L:8D mimicked the effects in hamsters exposed to 10:14D, 12L:12D or 14L:10D, respectively, on pelage color and testicular weight. Based on previous observations, the elevated circulating melatonin levels resulting from these injections were expected to extend the endogenous melatonin peak. Thus, this finding suggests that the duration of circadian melatonin elevation is the critical parameter determining its effect not only on the gonads, but also on the pelage. Since 14L:10D induced testicular regression but not the winter molt, this study also investigated whether circulating FSH levels, known to affect testicular function, and PRL levels, which have been shown to affect pelage color, might be affected differently by 14L:10D. Both FSH and PRL levels were found to be suppressed in 14L:10D hamsters compared to those in 16L:8D hamsters, although the interval between the initial decrease and eventual recovery was less than that in 10L:14D hamsters. Thus, the differential responses of the pelage and gonads to 14L:10D do not appear to be based on selective suppression of FSH in this photoperiod. However, different responses to 14L:10D compared to 10L:14D may be related to the shorter period of suppression of both PRL and FSH by the 14L:10D daylengths.
Animals↗
Effects of photoperiod, pinealectomy and castration on body weight and daily torpor in Djungarian hamsters (Phodopus sungorus).
During the autumn and winter Djungarian hamsters (Phodopus sungorus) exhibit regression of the gonads, development of a white winter pelage, loss of body weight and daily torpor. These seasonal events are largely regulated by changes in photoperiod. The present experiments were designed to examine the role of the testes and the pineal gland in photoperiodically induced daily torpor and body weight loss. Hamsters displayed a loss of body weight and daily torpor when exposed to a short-day photoperiod in a cold environment, but these phenomena did not occur in hamsters exposed to long days and cold. Testicular regression is probably a precondition for the display of torpor, since daily torpor was almost totally inhibited in hamsters which were exposed to short days and in which testosterone was administered from subcutaneous silicone elastomer implants. Nevertheless, decreased testosterone secretion alone is not a sufficient condition for induction of daily torpor, since torpor was rarely observed in hamsters exposed to long days, even after castration. In addition to decreased testicular activity, the pineal gland is also involved in establishing conditions for torpor. Thus, pinealectomy prevented the display of torpor by castrated hamsters exposed to short days. Body weight changes were also found to be influenced by both testicular hormone and pineal activity. These observations indicate that the pineal gland is involved, as a part of the photoperiodic mechanism, in regulating a variety of physiological events and that some of these actions of the pineal are independent of its extensively described actions on the reproductive axis.
Adaptation, Physiological↗
Vasopressin injected into the hypothalamus triggers a stereotypic behavior in golden hamsters.
Microinjection of arginine vasopressin into the medial preoptic area of the hypothalamus of male and female golden hamsters triggered a complex, stereotypic behavior--flank marking--a type of scent marking used in olfactory communication. The flank marking was not elicited by saline, oxytocin, neurotensin, or angiotensin II. Vasopressin was ineffective when injected into other areas of the hypothalamus or into the lateral cerebroventricle.
Angiotensin II↗
Avian pancreatic polypeptide phase shifts hamster circadian rhythms when microinjected into the suprachiasmatic region.
The suprachiasmatic nucleus has been identified tentatively as a circadian pacemaker. To examine the functional role of peptides found within suprachiasmatic neurons, avian pancreatic polypeptide and vasopressin were microinjected into the suprachiasmatic region. Avian pancreatic polypeptide, but not vasopressin, shifted the phase of the wheelrunning rhythm as a function of the time of its injection within the circadian cycle. Avian pancreatic polypeptide or a similar peptide may be one component of the neurochemical processes underlying entrainment to the light-dark cycle.
Animals↗
Hormonal regulation of the annual pelage color cycle in the Djungarian hamster, Phodopus sungorus. I. Role of the gonads and pituitary.
The Djungarian hamster exhibits an agouti pelage in the summer and a predominantly white pelage in the winter. This pelage color cycle is known to be regulated by the length of the daily photoperiod probably acting through the pineal gland, as is the seasonal cycle of reproductive function with which it is closely correlated ( Figala et al., '73; Hoffmann, ' 78b ). The possibility of a causal relationship between the decline in gonadal hormone secretion and the coat color change occurring in short photoperiod was examined. Gonadectomized and intact male and female hamsters were exposed to either long (16L:8D) or short ( 10L : 14D ) photoperiod for several months. Gonadectomy neither induced the change to the winter pelage color in long photoperiod-housed animals, nor prevented either the change to the winter pelage or the spontaneous return to summer pelage color in short photoperiod-housed animals. Chronic implants of testosterone in castrated males delayed and attenuated the short photoperiod-induced coat color change. Administration of ovine prolactin (100 micrograms/day) stimulated pigmentation in hamsters with the winter pelage, whereas administration of a alpha MSH (30 micrograms/day) was without effect. These results suggest that changes in pelage color may be regulated largely by changes in pituitary prolactin secretion and modified to some extent by changes in gonadal steroid hormone secretion.
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