Maternal transfer of photoperiodic information in Siberian hamsters. vi. effects of time-dependent 1-hr melatonin infusions in the mother on photoperiod-induced testicular development of her offspring.

We tested in Siberian hamsters the nature of the maternal signal that relays photoperiodic information to the developing fetuses. As previous investigations have identified maternal hormonal and circadian components in this process, the specific goal of this presentation is to determine quality of the signal that connotes daylength when it is imparted to the fetus. Does the function of the signal received by the fetus best support the coincidence or duration hypotheses of photoperiodic induction? Pregnant hamsters received 1 or 8 hr melatonin or vehicle infusions everyday. Juveniles of intact mothers gestated on 16 hr of light per day (16L) experienced maximal suppression of testicular development when reared on 14L. However, when intact mothers gestated on 10L received a 1-hr melatonin infusion daily at 20:00-21:00 hr, their young responded to 14L with greatly accelerated testicular development. In the absence of the maternal pineal gland (and, therefore, the maternal melatonin signal), the effects of maternal melatonin infusions were reversed. Here, only the juveniles of 16L-gestated females infused at 20:00-21:00 hr daily responded to 14L with enhanced testicular development. All other groups showed the same extent of gonadal development, independent of the time or type of infusion their mothers received. Testicular development on 14L of all juveniles from pinealectomized mothers gestated on 10L was of the same magnitude, regardless of the type and time of infusion their mothers received during pregnancy. The results suggest that the maternal signal transferred to the fetuses during gestation consists not only of the daily melatonin signal, but also some circadian-based component that greatly affects the effect of the former. The timing, and not the duration, of the maternal melatonin signal with respect to the animals' (mother and fetus) circadian day is of crucial importance in the transfer of photoperiodic information from mother to fetus.

Development of rhythmic melatonin secretion from the pineal gland of embryonic mummichog (Fundulus heteroclitus).

The pineal gland of vertebrates produces and secretes the hormone melatonin in response to changes in the light-dark cycle, with high production at night and low production during the day. Melatonin is thought to play an important role in synchronizing daily and/or seasonal physiological, behavioral, and developmental rhythms in vertebrates. In this study, the functional development of the pineal melatonin-generating system was examined in the mummichog, Fundulus heteroclitus, an euryhaline teleost. In this species, the pineal gland contains an endogenous oscillator, ultimately responsible for timing the melatonin rhythm. Oocytes from gravid females were collected and fertilized in vitro from sperm collected from mature males. Skull caps containing attached pineal glands were obtained from F. heteroclitus embryos at different embryonic stages and placed in static or perfusion culture under various photoperiodic regimes. Rhythmic melatonin secretion from pineal glands of embryonic F. heteroclitus embryos exposed to a 12L:12D cycle in static culture was observed at five days post-fertilization. The ontogeny of circadian-controlled melatonin production from F. heteroclitus pineal glands exposed to constant darkness for five days was also seen at day five post-fertilization. These data show that early development of the pineal melatonin-generating system in this teleost occurs prior to hatching. Pre-hatching development of the melatonin-generating system may confer some selective advantage in this species in its interactions with the environment.

Food availability and photoperiod affect reproductive development and maintenance in the marsh rice rat (Oryzomys palustris).

To examine whether photoperiod and food availability interact to influence reproductive development (Experiment 1), we exposed juvenile male and female rice rats to 16L:8D or 14L:10D and to ad lib, 80% of ad lib, or 60% of ad lib food intake from 3 to 8 weeks of age and recorded body and reproductive organ masses. Absolute paired testis masses were similar in ad lib and 80% of ad lib groups but significantly different than the 60% of ad lib group in both photoperiods. Relative paired testis masses were significantly different in the 80% and 60% of ad lib groups on 16L:8D only. Absolute seminal vesicle masses (SVM) were directly dependent upon the level of food restriction in both photoperiods, but relative SVMs were different only in the 60% of ad lib group. Terminal body masses were also directly dependent upon the level of food restriction and were greater on 16L:8D than on 14L:10D at most levels of food availability. In juvenile females, absolute uterine mass was only affected in the 60% of ad lib group on 14L:10D, while absolute paired ovary masses were affected on both photoperiods in the 60% of ad lib groups only. There was no effect of photoperiod or food on relative uterine and paired ovary masses. Terminal body mass was affected by food intake in both photoperiods. Lastly, in adult males (Experiment 2), photoperiod and food restriction affected reproductive function. Within a photoperiod, there was no effect of food restriction (75% of ad lib) on the testes, seminal vesicles, or testosterone levels in animals housed on 16L:8D, but terminal body mass was significantly reduced. On 12L:12D, however, food restriction significantly decreased testes and SVMs relative to ad lib-fed controls. Testosterone levels were reduced regardless of food availability. There was no effect of food restriction on terminal body mass. These results suggest that multiple potential environmental cues can be utilized to affect gonadal status in both juvenile and adult marsh rice rats.