Constance S. Campbell

The interaction of photoperiod and testosterone on the development of copulatory behavior in castrated male hamsters

Abstract Castrated adult male golden hamsters were maintained on either a stimulatory (LD 14:10) or a nonstimulatory (LD 6:18) light cycle for 10 weeks, and then were implanted subcutaneously with empty or testosterone-filled Silastic capsules of various lengths. Animals were tested for copulatory behavior prior to capsule implantation and 10, 20 and 40 days after implantation. Androgen-treated LD 14:10 hamsters showed a higher incidence of ejaculation on the final trial than did similarly treated LD 6:18 animals. When serum androgen levels were maintained at physiological levels (about 3 ng/ml, from a 20 mm capsule), significantly greater numbers of LD 14:10 hamsters intromitted and ejaculated compared to LD 6:18 animals. Examination of the development of copulation over trials revealed an interaction of photoperiod and androgen: LD 14:10 animals showed significant improvement over trials if stimulated with 8,20 or 100 mm long testosterone capsules, while LD 6:18 animals showed increased copulation over trials only if they were implanted with 100 mm capsules. These results indicate that exposure to short days for 10 weeks renders copulatory behavior of the castrate male hamster less responsive to the stimulatory effects of testosterone. This alteration in sensitivity to androgen may be one way in which the photoperiod acts to decrease copulation in seasonally breeding animals.

Changes in social behavior of the male golden hamster accompanying photoperiodic changes in reproduction

Abstract Testicular regression and decreased serum testosterone levels result when male hamsters are placed in a short-day photoperiod, and these changes are reversed after reexposure to long-days. The present study was undertaken to determine whether these physiological changes lead to modifications in social behavior in the male hamster. Animals in a nonstimulatory short-day (LD 6:18) or a stimulatory long-day (LD 14:10) photoperiod were observed every 3 weeks for 21 weeks. After 9 weeks, half of the LD 6:18 males were returned to LD 14:10 and showed rapid testicular recrudescence. The other half remained in LD 6:18 and showed a slower rate of testicular recrudescence. Assessment of aggression was accomplished by placing an intruder in the home cage of a test animal and recording latency to attack, decisive encounters, number of attacks, and number of aggressive postures. Dominance was evaluated in a neutral arena with opponents of different weights, using the same parameters. Scent-marking was recorded in response to both bedding from an intact male and bedding from an ovariectomized female in a clean cage. Short-day animals undergoing testicular regression showed heightened levels of aggression and an upward shift in their dominance status. Alteration of the photoperiod did not affect the pattern or number of scent marks. As animals underwent testicular recrudescence, there was a return to lower levels of aggression and to a lower dominance status. Males undergoing rapid testicular recrudescence also showed the most rapid decline in aggressive behaviors. These results suggest that levels of agonistic behavior in the male hamster are inversely related to serum testosterone levels. Scent-marking appears to be unreleated to androgen levels in the male hamster and its role in hamster social behavior remains unclear.

Entrainment of the female hamster to reversed photoperiod: Role of the pineal ☆

Abstract The effects of pinealectomy and photoperiod reversal on locomotor activity and behavioral receptivity rhythms were investigated in the hamster. Activity rhythms of the control animals required 7.3 days to reentrain to the reversed photoperiod, while pinealectomized animals showed a precocious reentrainment of running activity. Behavioral receptivity reentrained to the new photoperiod within the first estrous cycle after photoperiod reversal in all animals. Thus there was a dissociation between the rhythms of activity and behavioral receptivity following photoperiod reversal, suggesting that two circadian thythms that are thought to be regulated by a common circadian system can become uncoupled from each other. The estrous cycle rhythms of estradiol, progesterone, FSH and uterine wet weight all appeared to be reentrained by at least the third estrous cycle after photoperiod reversal. This suggests that sex hormone rhythms are more rapidly reentrained than had been previously thought possible from studies on reentrainment of ovulation.

Interaction of estradiol and photoperiod on activity patterns in the female hamster

Abstract The extent of the effects of estradiol on the locomotor rhythm in hamsters is unknown. This study was designed to determine the ability of estradiol alone and in combination with the photoperiod to alter activity patterns. Intact animals displayed higher levels of activity in LD 16:8 than in LD 6:18. Ovariectomy without estradiol treatment caused a sharp decline in activity in LD 16:8; estradiol treatment prevented this. In LD 6:18, activity levels were unaffected by either estradiol or ovariectomy. Estradiol altered the temporal distribution of activity only in LD 6:18, advancing peak activity towards lights-off. Estradiol decreased the variability in day to day onsets of activity in LD 6:18, but did not affect onsets in LD 16:8. The data suggest that the activity rhythm of the hamster is comprised of discrete components; the response of each component to estradiol is differentially altered by photoperiod. Furthermore, estradiol is vital for the expression of high activity levels in the LD 16:8 female.

Steroid feedback regulation of luteinizing hormone and follicle‐stimulating hormone secretion rates in male and female rats

The long‐accepted dogma of feedback control of luteinizing hormone (LH) and follicle‐stimulating hormone (FSH) secretion by gonadal steroids is reconsidered in this article in light of recent investigations in the rat, using radioimmunoassay measurements of both the steroids and the gonadotropins. The negative feedback control of gonadotropin secretion in the female rat has been studied by many approaches; in every case, LH and FSH appear to respond differently to either removal or administration of gonadal steroids. Serum FSH increases rapidly after removal of one or both ovaries, but its secretion cannot be completely suppressed by any combination of exogenous gonadal steroids. LH secretion shows a delayed increase after ovariectomy or hemiovariectomy, but serum levels are readily suppressed by estradiol administration. Furthermore, the delayed increase in LH after ovariectomy corresponds more closely to the delayed drop in estradiol levels than does the rapid increase in FSH. Serum FSH secretion in the...

Small effect of brown adipose tissue and major effect of photoperiod on body weight in hamsters (Mesocricetus auratus)

It has been suggested that brown adipose tissue plays a special role in the control of body weight. This hypothesis was investigated by measuring the body weight of female hamsters over a two month period following removal of interscapular brown adipose tissue. Two groups of animals were used, one maintained on a short day (10:14 light: dark ratio) and the other on a long day (16:8 light: dark ratio) photoperiod. Under both photoperiod conditions hamsters with interscapular brown adipose tissue removed gained somewhat more weight than their corresponding sham operated controls. Photoperiod, however, had a much larger effect on body weight. Hamsters maintained on short days increased their body weight by about 60 percent during the two months of the experiment whereas the hamsters maintained on long days increased their body weight by only about 17 percent. It was concluded that brown adipose tissue plays a small non special role in the control of body weight in the female hamster, but that the light-dark ratio is quantitatively much more important under these experimental conditions.

Induction of maternal behavior in nulliparous golden hamsters (Mesocricetus auratus).

The purposes of this study were to determine: (1) if naive hamsters could be induced to behave maternally through exposure to pups (i.e., to become “sensitized”); (2) if previous exposure to pups had any effect on the latency to sensitize; and (3) the differences in the latency to sensitize between males and females. Naive females sensitized with a mean latency of 18 hr; previously sensitized females, 28 hr; and males 72 hr. The female groups did not differ from each other, and naive females differed significantly from naive males.

Relation of fatty acids to feeding behaviour: effects of palmitic acid infusions, lighting variation and pent 4 enoate, insulin or propranolol injection

Intravenous infusion of palmitic acid in the day or in the night was found neither to inhibit nor to facilitate feeding in the rat. The results showed only a night-phase inhibition when infusion approached a calorically substantial rate and this effect was produced both by the palmitic acid-albumin complex and by the albumin vehicle alone. The well-known increase in rate of feeding at light offset was closely controlled by lighting, rather than by duration of the daytime fat mobilizing phase. Pent-4-enoic acid, an inhibitor of fat oxidation, did not increase food intake during the day. Insulin increased food intake not only by day when it would prevent fat mobilization, but also at night, when no mobilization normally occurs. Propranolol, a blocker of beta adrenergic fat mobilization, had only inhibitory effects on feeding. Under isolation conditions, propranolol injection shortened the latency of meal by day, but so did saline injection. It is concluded that, although fat no doubt ultimately enters into the caloric control of feeding, there is as yet no evidence that circulating fatty acids have large short-term effects on food intake. Relation of fatty acids to feeding behaviour: Effects of palmitic acid infusions, lighting variation and Pent4-enoate, insulin or propranolol injection1 - ResearchGate.

Weaning in the female hamster: effect of pup age and days postpartum

It has been previously demonstrated that female golden hamsters (Mesocricetus auratus) housed with 4- to 6-, 6- to 10-, or 10- to 14-day-old foster pups did not maintain normal growth in those pups past 24 days postpartum (Rowell, Zool. Soc. London, 135, 165–282, 1960). The purpose of this study was to examine more closely the behavior associated with the maintenance of maternal behavior and behavioral weaning in the golden hamster. Litters of 3-day-old pups were fostered to experimental females which had been lactating for 12 days. Control females raised their own litters. The amount of time spent nursing was recorded each morning and evening. Females raising foster pups continued to nurse for 14 days longer than did controls. However, foster pups gained weight much more slowly than did control pups. It appears that the female hamster behaviorally weans her litter according to the pup characteristics rather than according to the time elapsed since parturition. In addition, the results suggest that lactation and milk production may cease before nursing behavior ends and behavioral weaning occurs.

Cyclic Function of the Mammalian Ovary

The maturation and release of eggs from the mammalian ovary occur at regular and predictable intervals that are species-specific. This cyclicity of the ovary has been the subject of intensive interdisciplinary investigation in the past several decades. At base, the ovarian cycle is a product of the interaction of a number of components of the neuroendocrine system. Tonic secretion of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) from the pituitary is stimulated by the tonic release of luteinizing-hormone-releas-ing hormone (LH-RH) from the ventromedial arcuate region of the hypothalamus (Figure 1). In addition to this tonic component, there is a complex of trophic hormones (LH, FSH, and prolactin) released in large quantities from the pituitary on a regular, periodic basis in most mammals; this rhythmic component is dependent on the integrity of the preoptic-suprachiasmatic area of the hypothalamus. The tonic release of gonadotropins stimulates maturation of ovarian follicles and secretion of ovarian steroid hormones, notably estradiol. The cyclic release of gonadotropins results in ovulation and the secretion of more ovarian steroid hormones, notably progesterone. These ovarian steroids act both alone and in synergy in complex positive and negative feedback relationships to ensure the periodic release of gonadotropins.