Prolactin-dependent seasonal changes in pelage: role of the pineal gland and dopamine

Neuroendocrine control of brown adipocyte function by prolactin and growth hormone

Growth hormone (GH) is fundamental for growth and glucose homeostasis, and prolactin for optimal pregnancy and lactation outcome, but additionally, both hormones have multiple functions that include a strong impact on energetic metabolism. In this respect, prolactin and GH receptors have been found in brown, and white adipocytes, as well as in hypothalamic centers regulating thermogenesis. This review describes the neuroendocrine control of the function and plasticity of brown and beige adipocytes, with a special focus on prolactin and GH actions. Most evidence points to a negative association between high prolactin levels and the thermogenic capacity of BAT, except in early development. During lactation and pregnancy, prolactin may be a contributing factor that limits unneeded thermogenesis, downregulating BAT UCP1. Furthermore, animal models of high serum prolactin have low BAT UCP1 levels and whitening of the tissue, while lack of Prlr induces beiging in WAT depots. These actions may involve hypothalamic nuclei, particularly the DMN, POA and ARN, brain centers that participate in thermogenesis. Studies on GH regulation of BAT function present some controversies. Most mouse models with GH excess or deficiency point to an inhibitory role of GH on BAT function. Even so, a stimulatory role of GH on WAT beiging has also been described, in accordance with whole-genome microarrays that demonstrate divergent response signatures of BAT and WAT genes to the loss of GH signaling. Understanding the physiology of BAT and WAT beiging may contribute to the ongoing efforts to curtail obesity.

Seasonality of prolactin in birds and mammals

In most animals, annual rhythms in environmental cues and internal programs regulate seasonal physiology and behavior. Prolactin, an evolutionarily ancient hormone, serves as a molecular correlate of seasonal timing in most species. Prolactin is highly pleiotropic with a wide variety of well-documented physiological effects; in a seasonal context prolactin is known to regulate annual changes in pelage and molt. While short-term homeostatic variation of prolactin secretion is under the control of the hypothalamus, long-term seasonal rhythms of prolactin are programmed by endogenous timers that reside in the pituitary gland. The molecular basis of these rhythms is generally understood to be melatonin dependent in mammals. Prolactin rhythmicity persists for several years in many species, in the absence of hypothalamic signaling. Such evidence in mammals has supported the hypothesis that seasonal rhythms in prolactin derive from an endogenous timer within the pituitary gland that is entrained by external photoperiod. In this review, we describe the conserved nature of prolactin signaling in birds and mammals and highlight its role in regulating multiple diverse physiological systems. The review will cover the current understanding of the molecular control of prolactin seasonality and propose a mechanism by which long-term rhythms may be generated in amniotes.

The Chemistry of Cold: Mechanisms of Torpor Regulation in the Siberian Hamster

Siberian hamsters use spontaneous daily torpor, a state of hypometabolism and hypothermia, to save energy during winter. Multiple neuroendocrine signals set the scene for spontaneous torpor to occur, and several brain areas have been identified as potential sites for torpor regulation. Here, we summarize the known mechanisms of a fascinating physiological state in the Siberian hamster.

Evidence for phenotypic plasticity in response to photic cues and the connection with genes of risk in schizophrenia

Numerous environmental factors have been identified as influential in the development of schizophrenia. Some are byproducts of modern life, yet others were present in our evolutionary past and persist to a lesser degree in the current era. The present study brings together published epidemiological data for schizophrenia and data on variables related to photic input for places of residence across geographical regions, using rainfall as an inverse, proxy measure for light levels. Data were gathered from the literature for two countries, the former Yugoslavia and Ireland, during a time in the early 20th century when mobility was relatively limited. The data for Yugoslavia showed a strong correlation between hospital census rates for schizophrenia (by place of birth) and annual rain (r = 0.96, p = 0.008). In Ireland, the hospital census rates and first admissions for schizophrenia (by place of permanent residence) showed a trend for correlation with annual rain, reaching significance for 1st admissions when the rainfall data was weighted by the underlying population distribution (r = 0.71, p = 0.047). In addition, across the years 1921-1945, birth-year variations in a spring quarter season-of-birth effect for schizophrenia in Ireland showed a trend for correlation with January-March rainfall (r = 0.80, p ≤ 0.10). The data are discussed in terms of the effect of photoperiod on the gestation and behavior of offspring in animals, and the premise is put forth that vestigial phenotypic plasticity for such photic cues still exists in humans. Moreover, genetic polymorphisms of risk identified for psychotic disorders include genes modulated by photoperiod and sunlight intensity. Such a relationship between phenotypic plasticity in response to a particular environmental regime and subsequent natural selection for fixed changes in the environmentally responsive genes, has been well studied in animals and should not be discounted when considering human disease.

Pineal and gonadal influences on ultradian locomotor rhythms of male Siberian hamsters

The extent to which changes in ultradian and circadian rhythms (URs and CRs) reflect seasonal variations in pineal melatonin secretion was assessed in male Siberian hamsters transferred from long to short day lengths. The period of the locomotor activity UR increased from 2.5 h in long days to 4.5 h in short day lengths, but this and most other features of the short-day ultradian phenotype were unaffected by pinealectomy; only the short-day increase in UR amplitude was counteracted by pineal extirpation. Virtually all UR components were unaffected by gonadectomy or replacement testosterone or estradiol treatment; changes in testicular hormone secretion appear insufficient to account for seasonal fluctuation in URs. Pinealectomy did not affect activity onsets and offsets or phase angles of CR entrainment in short and long day lengths; the duration of nocturnal activity was equivalently longer in short than long days in both pinealectomized and pineal-intact hamsters. CR robustness of pinealectomized hamsters in short days was intermediate between values of long-day and short-day sham-pinealectomized males. Hourly nocturnal locomotor activity was markedly reduced in SD, and this effect was completely reversed by PINx. We conclude that seasonal transitions in UR and CR waveforms controlled by day length are mediated primarily by melatonin-independent mechanisms, with lesser contributions from melatonin-dependent processes. Most seasonal changes in ultradian and circadian rhythms in males of this species are not influenced by gonadal hormones. URs may allow animals to respond appropriately to changing environmental contingencies. In winter reduced activity combined with temporal restructuring of activity to include longer intervals of rest may be adaptive in maintaining body temperature at lower values and down-regulating energy expenditure when above ground temperatures are extremely low.

Endocrine mechanisms of seasonal adaptation in small mammals: from early results to present understanding

Seasonal adaptation is widespread among mammals of temperate and polar latitudes. The changes in physiology, morphology and behaviour are controlled by the photoneuroendocrine system that, as a first step, translates day lengths into a hormonal signal (melatonin). Decoding of the humoral melatonin signal, i.e. responses on the cellular level to slight alterations in signal duration, represents the prerequisite for appropriate timing of winter acclimatization in photoperiodic animals. Corresponding to the diversity of affected traits, several hormone systems are involved in the regulation downstream of the neural integration of photoperiodic time measurement. Results from recent studies provide new insights into seasonal control of reproduction and energy balance. Most intriguingly, the availability of thyroid hormone within hypothalamic key regions, which is a crucial determinant of seasonal transitions, appears to be regulated by hormone secretion from the pars tuberalis of the pituitary gland. This proposed neuroendocrine pathway contradicts the common view of the pituitary as a gland that acts downstream of the hypothalamus. In the present overview of (neuro)endocrine mechanisms underlying seasonal acclimatization, we are focusing on the dwarf hamster Phodopus sungorus (long-day breeder) that is known for large amplitudes in seasonal changes. However, important findings in other mammalian species such as Syrian hamsters and sheep (short-day breeder) are considered as well.

Seasonal pelage color change: news based on a South American Rodent

Mammalian seasonalmolting and color change are known to be influencedby photoperiod changes. Calomys laucha, a South American rodent, exhibits seasonal pelage color change; however, unlike Northern hemisphere rodents, which present a gray or brown color during summer and a whitish color during winter, C. laucha pelage changes from an orange color during summer to a dark gray color during winter. Animals maintained for over a year in stationary photoperiod (LD 12:12h, 22ºC) presented orange pelage color during the summer corresponding month (January), and gray color during the winter corresponding month (July). Same age animals were evaluated during summer or winter months, and also showed different colors. Animals exposed for 12 weeks to summer or winter artificial conditions displayed color change, not according to the environmental conditions, as expected, but similar to that of animals maintained in stationary photoperiod. These results suggest that pelage color change in C. laucha is controlled by an endogenous circannual rhythm. The adaptive function of C. laucha color change is discussed.

Recurrent flank alopecia in a Tibetan Terrier

Recurrent flank alopecia is described in a 2-year-old, male, neutered Tibetan Terrier with concurrent atopic dermatitis. The diagnosis of recurrent flank alopecia was made after 3 consecutive years of localised, winter-onset alopecia. The diagnosis was based on history, compatible clinical signs and supportive histopathology. The diagnosis was complicated by the presence of concurrent pruritic dermatitis. To our knowledge this is the first report of recurrent flank alopecia in this breed.

An analysis of canine hair re-growth after clipping for a surgical procedure

Hair growth and replacement have been studied extensively in humans, sheep and laboratory rodents, but in dogs and other mammalian species few studies have been published. The objectives of this study were: (1) to determine the time required for the hair to re-grow in dogs after clipping for a surgical procedure; (2) to define whether the season of the year influenced the period of time required for re-growth and; (3) to determine if season might influence the telogen: anagen ratio. Eleven Labrador retrievers were recruited during spring, 10 during summer, six during autumn and 10 during winter. Hairs re-grew to their preclipped length in 14.6 weeks, 14.5 weeks, 13.6 weeks and 15.4 weeks when shaved in the spring, summer, autumn and winter, respectively. The differences in these values were not significant suggesting that season has no effect on the rate of hair re-growth in Labrador retrievers housed indoors (P = 0.12). The mean values for the telogen: anagen ratio in each season were: 5.2 (spring), 6.1 (summer), 9.5 (autumn), and 5.3 (winter). The differences in these values also were not significant (P = 0.89). The percentage of hairs in telogen was over 80% in all four seasons.

Evidence for an endogenous per1- and ICER-independent seasonal timer in the hamster pituitary gland

Most mammals use changing annual day-length cycles to regulate pineal melatonin secretion and thereby drive many physiological rhythms including reproduction, metabolism, immune function, and pelage. Prolonged exposure to short winter day lengths results in refractoriness, a spontaneous reversion to long-day physiological status. Despite its critical role in the timing of seasonal rhythms, refractoriness remains poorly understood. The aim of this study was therefore to describe cellular and molecular mechanisms driving the seasonal secretion of a key hormone, prolactin, in refractory Syrian hamsters. We used recently developed single cell hybridization and reporter assays to show that this process is initiated by timed reactivation of endocrine signaling from the pars tuberalis (PT) region of the pituitary gland, a well-defined melatonin target site, causing renewed activation of prolactin gene expression. This timed signaling is independent of per1 clock gene expression in the suprachiasmatic nuclei and PT and of melatonin secretion, which continue to track day length. Within the PT, there is also a continued short day-like profile of ICER expression, suggesting that the change in hormone secretion is independent of cAMP signaling. Our data thus identify the PT as a key anatomical structure involved in endogenous seasonal timing mechanisms, which breaks from prevailing day length-induced gene expression.

Effects of time of year and reproductive state on the proliferation and keratinisation of bovine hoof cells

Cell proliferation and protein synthesis (keratinisation) were measured in vitro in hoof biopsy samples taken from two groups of seven heifers, the first calving in the winter and the second in the summer. Both parameters were significantly higher in summer than in winter irrespective of the heifers' reproductive state. The mean (se) measure of the rate of protein synthesis was 199 (27) dpm/microg DNA/hour in summer and 4 (1) dpm/microg DNA/hour in winter, and the equivalent values for cell proliferation (measured as DNA synthesis) were 375 (56) dpm/microg DNA/hour and 17 (4) dpm/microg DNA/hour. Changes around parturition depended on the time of the year. In the winter-calving heifers, the rates of proliferation and keratinisation increased significantly after calving from 22.3 (7.2) to 70.4 (16.6) and from 2.1 (0.7) to 12.4 (2.8) dpm/microg DNA/hour, respectively. In the summer-calving heifers, proliferation decreased from 388.2 (91.0) to 66.7 (9.6) dpm/microg DNA/hour but the rate of keratinisation did not change. Lesion scores and locomotion scores deteriorated after parturition, especially in the winter-calving group. The hooves were harder in summer than winter but their hardness was not affected by the heifers' reproductive state.

Photorefractoriness of immune function in male Siberian hamsters (Phodopus sungorus)

Short days induce multiple changes in reproductive and immune function in Siberian hamsters. Short-day reproductive inhibition in this species is regulated by an endogenous timing mechanism; after approximately 20 weeks in short days, neuroendocrine refractoriness to short-day patterns of melatonin develops, triggering spontaneous recrudescence of the reproductive system. It is unknown whether analogous mechanisms control immune function, or if photoperiodic changes in immune function are masked by prevailing photoperiod. In Experiment 1, 3 weeks of exposure to long days was not sufficient to induce long-day-like enhancement of in vitro lymphocyte proliferation in short-day adapted male Siberian hamsters. Experiment 2 tested the hypothesis that immunological photorefractoriness is induced by prolonged exposure to short days. Adult male hamsters were gonadectomized or sham-gonadectomized and housed in long (14 h light/day) or short (10 h light/day) photoperiods for 12, 32 or 40 weeks. Somatic and reproductive regression occurred after 12 weeks in short days, and spontaneous recrudescence was complete after 32-40 weeks in short days, indicative of somatic and reproductive photorefractoriness. In gonad-intact hamsters, 12 weeks of exposure to short days decreased the number of circulating granulocytes and increased the number of B-like lymphocytes. After 32 weeks in short days, these measures were restored to long-day values, indicative of photorefractoriness; castration eliminated these effects of photoperiod. In both intact and castrated hamsters, in vitro proliferation of splenic lymphocytes was inhibited by 12 weeks of exposure to short days. After 40 weeks in short days lymphocyte proliferation was restored to long-day values in intact hamsters, but remained suppressed in castrated hamsters. These results suggest that short-day-induced inhibition of lymphocyte function does not depend on gonadal regression, but that spontaneous recrudescence of this measure is dependent on gonadal recrudescence. In Experiment 3, in vitro treatment with melatonin enhanced basal proliferation of lymphocytes from male hamsters exposed to short days for 12 weeks, but had no effect on lymphocytes of photorefractory hamsters or long-day control hamsters. Lymphocytes of castrated hamsters were unresponsive to in vitro melatonin, suggesting that photoperiodic changes in gonadal hormone secretion may be required to activate mechanisms which permit differential responsiveness to melatonin depending on phase in the annual reproductive cycle. Together, these data indicate that, similar to the reproductive system, the immune system of male Siberian hamsters exhibits refractoriness to short days.

Relationship between norepinephrine release in the hypothalamic paraventricular nucleus and circulating prolactin levels in the Siberian hamster: role of photoperiod and the pineal gland

The impact of norepinephrine (NE) and its metabolite, 3-methoxy4-hydroxyphenylglycol (MHPG), on circulating prolactin (PRL) was evaluated in the paraventricular region of the hypothalamus as a function of photoperiod and integrity of the pineal gland. In Experiment 1, whole tissue content of NE and MHPG was assessed in male and female hamsters that had been pinealectomized or sham-pinealectomized and exposed to long or short photoperiods for 5 weeks. The results revealed a marginal effect of photoperiod in males, but no overall effects of surgery. Because analysis of whole tissue content can be complicated by concurrent changes in synthesis and storage rates, Experiment 2 was conducted using microdialysis to assess extracellular levels of NE and MHPG in female hamsters. Pinealectomy completely prevented the short-day-induced suppression of luteinizing hormone, but it only partially prevented the effects of short days on PRL. Furthermore, both NE and MHPG levels were significantly elevated in short-day-exposed pinealectomized and sham-operated animals. These results suggest that NE release within the paraventricular nucleus inhibits the circulating PRL levels and is one mechanism by which direct photic information can influence the neuroendocrine axis independently of the pineal melatonin signal.

The pars tuberalis: the missing link in the photoperiodic regulation of prolactin secretion?

The endocrine function of the pars tuberalis of the pituitary gland has been an enigma for many years. Recent work suggests that one of its primary functions in seasonal mammals is to mediate photoperiodically regulated changes in prolactin secretion via an unidentified factor called tuberalin.

Role of prolactin in regulating the onset of winter fur growth in mink (Mustela vison): A reconsideration

The objectives of this study were to determine: (1) if the onset of winter hair growth (anagen) in mink could be delayed or inhibited by elevating endogenous PRL concentrations; (2) if bilaterally adrenalectomy (ADX)-induced winter anagen occurs concomitantly with a reduction in serum PRL concentrations, and (3) if exogenous dehydroepiandrosterone (DHEA), an adrenal steroid or Delta(5)-DIOL (a peripherally produced metabolite of DHEA), would delay or inhibit the onset of winter anagen. During early July, while in the resting (telogen) stage of the hair growth cycle, mink were treated with slow release implants containing haloperidol (HAL, a dopaminergic antagonist), melatonin (MEL), deoxycorticosterone (DOC), DHEA and Delta(5)-DIOL. In addition, mink were ADX'd and supplemented with DOC and DHEA. MEL reduced PRL levels to basal levels and induced winter anagen 7 weeks earlier than controls. Surprisingly, HAL initiated winter anagen 7 weeks earlier than controls (P < 0.05), although serum PRL levels were not different between the two groups. Mink that were ADX'd or ADX + DHEA-treated exhibited winter anagen 6 weeks earlier than controls (P < 0.05), but serum PRL concentrations were not different between the three groups. The administration of DHEA or Delta(5)-DIOL to mink with intact adrenals had no effect on the time of onset of winter anagen or serum PRL levels. Our findings suggest that a reduction in circulating PRL levels is not essential for onset of winter anagen in the mink and that the apparent inhibitory effects of the adrenal glands on initiation of winter anagen is not mediated through DHEA or its metabolite Delta(5)-DIOL. J. Exp. Zool. 284:437-444, 1999.

Investigation of the reproductive and growth hormone status of dogs affected by idiopathic recurrent flank alopecia

The reproductive and growth hormone status of a group of 12 neutered dogs affected by idiopathic recurrent flank alopecia was investigated at both maximum and minimum photoperiod using the adrenocorticotrophic hormone (ACTH) stimulation test, the xylazine stimulation test and the insulin-like growth factor I (IGF-I) assay. When compared with a group of nine neutered control dogs, the plasma reproductive hormone concentrations were not significantly different with one exception; a significantly greater post-ACTH plasma progesterone concentration was detected in the affected group at minimum photoperiod (P < 0.05). The significance of this finding in isolation is unclear. Growth hormone response to intravenous xylazine was assessed in the affected group at maximum photoperiod only and was found to be within normal limits in eight of the dogs. Serum IGF-I concentrations were significantly greater in the affected group at maximum photoperiod but the groups were not significantly different at minimum photoperiod. These results suggest that dogs with idiopathic recurrent flank alopecia are of normal reproductive and growth hormone status.

Wool growth rate in vitro is independent of host animal nutrition, season, and the potential mediators of photoperiod, melatonin and prolactin

In most sheep breeds, wool growth varies seasonally and is correlated with changes in photoperiod, temperature, and nutrition. Wool growth regulation by these factors may result from systemic changes, or to a response localized at the wool follicle. Possible roles of systemic and local factors have been examined here by comparison of wool growth responses in vitro and in vitro. Wool follicles were isolated and maintained under conditions facilitating fibre growth for at least 4 days. The wool growth rate by follicles isolated regularly over a 10 month period was invariate (P > 0.10), in contrast to a seasonally varying wool growth rate by follicles from the same animals in vivo (P < 0.001). Although a high energy, high protein diet increased wool growth in vivo (P < 0.05), cultured follicles isolated from these animals showed no change in growth rate (P > 0.10). These observations suggest that the regulation of wool growth by environmental factors is extrafollicular and that there is no carryover of the in vivo growth rate when follicles are isolated and systemic signals are therefore removed. Additional work discussed here examined the regulation of pelage by prolactin and melatonin, potential endocrine mediators of photoperiod. The fibre production rate by isolated follicles maintained in control media was not different to that of prolactin or melatonin supplemented follicles (P > 0.10). It is concluded that selective breeding of domesticated sheep has suppressed the response of follicles to regulation by prolactin and melatonin. Studies currently underway using in situ RT-PCR will provide further characterization of this conclusion.

Effects of N-methyl-D-aspartate (NMDA) on seasonal cycles of reproduction, body weight and pelage colour in the male Siberian hamster

Siberian hamsters (Phodopus sungorus) transferred from stimulatory photoperiods (long days: LD) to inhibitory photoperiods (short days: SD) undergo testicular regression within 8 weeks. This reproductive response to photoperiod was blocked by systemic daily treatment with the glutamatergic agonist N-methyl-D-aspartate (NMDA: 20 mg/kg BW, sc). This powerful effect of NMDA demonstrates the potential for endogenous glutamate to regulate reproductive function. The overall aim of the subsequent studies was to investigate the site and mechanism of action of this glutamatergic agonist in order to identify potential mechanisms through which endogenous glutamate might act. To investigate whether the effect of systemic NMDA was via an effect on the circadian timing system, alterations in gonadal regression and recrudescence, seasonal coat changes (pelage) and body weight (BW) were examined. It would be predicted that long-term cycles of all these seasonal parameters would be affected if the action of NMDA were to perturb the transduction of photoperiodic information. Daily treatments with NMDA, which initially maintained reproductive function in hamsters exposed to SD, did not influence the time course of subsequent testicular recrudescence, nor did they influence long-term cycles of pelage and BW. Moreover, treatment with NMDA induced a dose-dependent increase in serum concentrations of LH within 15 min of systemic injection. These data are consistent with the hypothesis that systemic NMDA exerts it reproductive effects not via an action on the circadian system, but via an action on secretion of GnRH. To investigate potential central sites of action of glutamate, induction of the immediate early gene c-fos, an acute marker of cellular response, was evaluated immunocytochemically (ICC) in brain areas after treatment with NMDA. Although dual-label ICC studies revealed that NMDA did not induce c-fos within GnRH neurons, NMDA did induce c-fos in many cells in the region of the organum vasculosum of the lamina terminalis (OVLT), an area containing a large number of GnRH perikarya, and in the arcuate nucleus, a region close to GnRH secretory terminals in the median eminence. The lack of c-fos induction of GnRH cells argues against a direct effect of NMDA on GnRH neurons. Thus, we examined immunocytochemically the distribution of the common NMDAR1 glutamate receptor subunit to evaluate further the potential sites of glutamatergic action. As expected, NMDAR1-ir was widespread in perikarya throughout the brain, including the region of the OVLT and the arcuate nucleus.(ABSTRACT TRUNCATED AT 400 WORDS)

Bilateral adrenalectomy induces early onset of summer fur growth in mink (Mustela vison)

The purpose of this study was to determine the effects of bilateral adrenalectomy on the time at which growth of the summer pelage begins in mink. Bilateral adrenalectomy of adult female mink between 2 and 11 March 1991, supplemented with deoxycorticosterone (DOC) as a mineralocorticoid, resulted in the onset of the summer fur growth approximately 5 weeks earlier than the controls (P < 0.01). Mink with their adrenal glands intact and treated with DOC, exhibited summer fur growth 2 weeks earlier than the controls (P < 0.01). The duration of time between the first observed hair growth and attainment of maximal guard hair length, was approximately 10 days longer in mink with their adrenal glands intact and supplemented with DOC than the controls (P < 0.05). Adrenalectomized mink treated with DOC exhibited guard hair growth for approximately 13 days longer than controls (P < 0.05). Although exogenous DOC initiated hair growth, the rate of growth appeared to be reduced. These data suggest that adrenal hormones, of undetermined identity, exert a tonic inhibitory effect on the initiation of summer fur growth in mink and may be part of the mechanism through which changes in photoperiod regulate the onset of hair growth cycles.

Seasonal flank alopecia in affenpinschers

Two intact, distantly related, female affenpinschers, belonging to a breeder, were referred in March 1993 for the investigation of bilateral, symmetrical flank alopecia in one bitch and bilateral, symmetrical flank, dorsum and tail alopecia in the other; the alopecia occurred from November to May and January to May, respectively. During that period the bitches were kept in a conservatory without artificial heating or lighting. The owner reported that the mother of one bitch had had bilateral, symmetrical flank alopecia during one winter when kept in the conservatory, but was normal the following winter when kept in the house. Three other females and a male exhibited the same clinical signs when kept in the conservatory during the winter. Seasonal flank alopecia has not previously been reported in affenpinschers.

Ovulated oocytes collected from PMSG/hCG-treated and cycling Djungarian or Siberian hamsters (Phodopus sungorus) are structurally similar with no evidence of polar body formation, indicating arrest in meiosis I

This study was undertaken (1) to devise a method of inducing multiple follicular development and subsequent ovulation in the Djungarian or Siberian hamster (Phodopus sungorus) and (2) to assess the quality of ovulated oocytes collected from PMSG/hCG treated animals in comparison to naturally ovulating animals. Hamsters (4-5 weeks; n = 70) received 5 IU PMSG followed 50-52 hr later by 10 IU hCG. Ovulated oocytes were collected 14-20 hr after hCG injection. Ovulated oocytes were flushed from oviducts of cycling animals (7-12 weeks; n = 30) exhibiting two consecutive estrous cycles. Oocytes were fixed and subjected to triple fluorescence immunostaining using anti-tubulin antibodies, fluorescein phalloidin, and Hoechst 33258. The mean number of ovulated oocytes collected from cycling animals was 4.8 +/- 0.4 (range 1-7). Ovulation occurred in 73% of the PMSG/hCG-stimulated animals. The mean number of oocytes ovulated from stimulated animals was 9.2 +/- 0.8 (range 0-22). The ovaries of animals that did not ovulate or that ovulated few oocytes did respond to PMSG, as indicated by the presence of multiple follicular development and pre-ovulatory stigmata. There was no evidence of a polar body in ovulated oocytes collected from PMSG/hCG-treated or cycling animals, indicating that oocytes were arrested in meiosis I. In the majority (80%) of ovulated oocytes from PMSG/hCG-treated and cycling animals, cortically placed chromosomes were aligned on a metaphase plate equidistant from a bipolar spindle. Sparse f-actin staining was observed in the region of the ooplasm surrounding the chromosomes.(ABSTRACT TRUNCATED AT 250 WORDS)

Chronic administration of sodium valproic acid slows pubertal maturation in inbred DBA/2J mice: skeletal, histological, and endocrinological evidence

Sodium valproic acid (VPA) has been reported to occasionally delay pubertal maturation in children. In the current study, we sought to establish a valid animal model with which to further investigate the neuroendocrinological sequelae of VPA administration. Male and female DBA/2J mice were weaned at 2 weeks of age and administered either VPA (17-20 mg/kg/day) or control solution via drinking water. Animals were weighed and sacrificed via decapitation at 4, 6, or 8 weeks of age. Testes and ovaries were prepared for histological analyses. In addition, the length of the left humerus bone from each animal was obtained as an index of skeletal growth, and trunk blood was assayed for circulating follicle-stimulating hormone (FSH) and prolactin (PRL). For males, testicular weights of the animals receiving VPA were significantly lower than those of control animals at all three sampling ages. No between-group differences were found for body weight at any sampling age, and yet the rate of skeletal maturation (as indexed by humerus length) was decreased significantly for the VPA-treated males at all three sampling periods. Additionally, while hormone levels did not consistently differ, histological analyses of the gonadal tissue demonstrated significantly decreased rats of spermatogenesis at all sampling points for VPA-treated animals. For females, chronic VPA administration led to a significant reduction in uterine weight at the 4 and 6 week sampling periods, and yet by 8 weeks of age the uterine weights for the two groups did not differ.(ABSTRACT TRUNCATED AT 250 WORDS)

Prolactin receptor concentrations in the skin of mink during the winter fur growth cycle

The objectives of this study were to determine: 1) if the skin of mink might be a target organ for prolactin (PRL) by establishing if PRL binding sites (receptors) exist in the cell membranes of skin, and 2) if PRL receptor concentrations change during the onset and progression of the winter fur growth cycle. Skin was collected on October 6, 1992 for characterization of PRL receptors and from July through December 1992 (N = 3 mink/month) to evaluate possible changes in PRL receptor concentrations during the fur growth cycle. PRL receptors were quantified using 125I-oPRL in a validated radioreceptor assay. Scatchard analysis of saturation data revealed a single class of high-affinity (Kd = 5.21 x 10(-11) +/- .84 M), low capacity (Bmax = 27.03 +/- 3.37 fmoles/mg) binding sites. Only oPRL (40% displacement) and to a lesser extent oGH (3% displacement) inhibited the binding of 125I-oPRL to mink skin cell membranes. No inhibition of 125I-oPRL binding to membranes occurred in the presence of a 500-fold excess of bTSH or oLH, indicating that the receptors were hormone specific. Concentrations of 125I-oPRL receptors during the onset and development of winter fur growth (July through November) exhibited no significant change. However, following completion of the winter fur growth cycle (December 1) PRL receptor concentration was significantly higher than all preceding months. The greater binding observed at that time may reflect a change in tissue sensitivity, in preparation for growth of the summer pelage.(ABSTRACT TRUNCATED AT 250 WORDS)

Fiber growth initiation in hair follicles of goats treated with melatonin

The sequence of structural changes in goat hair follicles was investigated using melatonin implants to advance and synchronize spring hair growth. Ten pasture fed cashmere wethers each received a controlled release formulation of 70 mg of melatonin on September 1 1989, and showed plasma melatonin elevated above physiological levels over 14 days post-treatment (914 +/- 154 pg/ml [mean +/- SEM] on day 14). In ten untreated animals, daytime plasma melatonin was 19.9 +/- 4.7 pg/ml. Histological examination of skin biopsies taken over the 14 days from the start of the experiment showed that primary hair follicles of goats with manipulated hormone levels had initiated fiber growth (entered proanagen), whereas primary follicles of untreated goats largely remained in the quiescent phase (telogen). A standardized terminology was used to describe the sequence of events during induced proanagen. Structural reorganization of follicles began in treated animals between days 6 and 12 post-treatment, and emergent fibers grew by day 24. Advancement of spring fiber growth was associated with a suppression of the normal rise in plasma prolactin concentration. Prolactin levels in untreated goats increased from 7.4 +/- 1.8 ng/ml on day 1 to 12.8 +/- 1.6 ng/ml on day 14, but declined in treated goats from 6.3 +/- 2.3 ng/ml to 2.2 +/- 0.8 ng/ml over the same period.

Role of prolactin and the gonads in seasonal physiological changes in the collared lemming (Dicrostonyx groenlandicus)

On a seasonal basis, collared lemmings undergo a number of physiological and morphological changes. Short photoperiod exposure results in a molt to a white pelage, an increase in body weight, a reduction in relative body fat content, an increase in relative water content, and the development of a bifid claw. Treatment with the dopamine agonist, CB-154, resulted in a reduction in serum prolactin and the development of the white pelage in lemmings housed under 16L:8D, while treatment with the dopamine antagonist, sulpiride, prevented the winter molt in animals transferred to 8L:16D. Castration under 16L:8D resulted in an increase in body weight and an enlargement of the bifid claw. Castrated animals also molted more readily when treated with CB-154 and developed a relatively greater carcass water content. Treatment with CB-154 increased relative carcass fat content. These findings suggest that, in the collared lemming, seasonal changes in pelage parameters are regulated by prolactin, with gonadal hormones playing a modulating role. Body weight, water content, and bifid claw size appear to be influenced by gonadal hormones.