Influence of Photoperiod on Pineal Melatonin Synthesis, Fur Color, Body Weight, and Reproductive Function in the Female Djungarian Hamster, Phodopus sungorus

Abstract

In order to investigate female Djungarian hamsters’ reactions to changes of the photoperiod, the following two experiments were performed. Experiment I: Age-matched female hamsters were exposed to either short (8L:16D) or long days (16L:8D) for 38 weeks. Initially, the short-day group showed a decline in body weight, associated with changes in gonadal function and fur color. This was not maintained by the short-day group which returned, on the most part, to long-day levels, thus becoming insensitive to this regressive lighting regimen. The time courses of these events compare well with those observed in males, which suggests a common mechanism. Experiment II: Two groups of female hamsters were exposed for 8 weeks to either long days or short days. At the end of the test period, the diurnal variations in pineal content of melatonin, serotonin, hydroxyindole acetic acid, and serum melatonin were estimated, revealing marked differences between the two groups. Not only was there a prolongation of melatonin synthesis observed in the short-day animals, but there was also a significant elevation of the melatonin levels when compared to the long-day animals. Together with recent findings in males, these findings lend support to the hypothesis that, in the Djungarian hamster, the elevation of nocturnal melatonin levels may be of additional significance, with respect to the physiological changes induced by short-day photoperiods.

Enhanced serum oestrogen levels and highly steroidogenic, luteinized atretic follicles in the ovaries of the Djungarian hamster (Phodopus sungorus) kept under a short photoperiod from birth

“…Ebling (6) previously described severe inhibition of gonadal and body growth in immature Djungarian hamsters raised under short days. Short photoperiod also attenuated body growth in adult Djungarian hamsters, but had no significant effect on ovarian weight (21,22); the gonads of these animals contained fewer healthy antral follicles and corpora lutea and more apoptotic antral follicles (21). The different effects of a short daylight regimen on immature and adult hamsters can be attributed to differences in the functioning of the neuroendocrine reproductive system.…”

Phodopus campbelli detect reduced photoperiod during development but, unlike Phodopus sungorus, retain functional reproductive physiology

“…For this reason, the populations studied here are, and have been, maintained at an ambient temperature of 18 8C (Wynne- Edwards & Lisk 1988. This ambient temperature is cooler than 23 8C typically used to house P. sungorus in other laboratories (Lerchl & Schlatt 1993, Gorman 1995, Bilbo et al 2003 and might have slowed developmental trajectories in response to the increased metabolic demands of thermoregulation at the lower ambient temperature.…”

Photoperiod-dependent regulation of inhibin in Siberian hamsters: I. Ovarian inhibin production and secretion

“…In many species, environmental cues are also used to time reproductive effort such that offspring are born at those times of year most conducive to their survival. For example, the Siberian hamster (Phodopus sungorus) uses seasonal changes in day length to time changes in gonadal size and activity, body weight, and pelage color (Hoffmann 1973, Lerchl & Schlatt 1993, Ebling 1994. These changes can be recapitulated in laboratory animal breeding colonies by altering daily light exposure.…”

“…It is possible that additional environmental cues are necessary to promote full reproductive function in this species (Goldman 1991, Ouarour et al 1991, Puchalski & Lynch 1991, Badura & Goldman 1992, Debeljuk & Lasaga 1999, Drazen et al 2001, Horton & Yellon 2001, Pak et al 2001. The LD animals used were 7 weeks old and, based on previous studies, were thought to be sexually mature (Lerchl & Schlatt 1993. However, no vaginal opening was detected, thus contributing to our conclusion that the animals were not cycling.…”

“…These changes can be recapitulated in laboratory animal breeding colonies by altering daily light exposure . Because follicle development can be inhibited by movement of the animals from long to short photoperiods (Lerchl & Schlatt 1993, we predicted that the regulation of inhibin subunit assembly could be readily examined in this animal model. Moreover, given the role of inhibin in FSH regulation, we hypothesized that ovarian inhibin production would differ between long day-exposed (LD) and short day-exposed (SD) animals.…”