MATERNAL TRANSFER OF PHOTOPERIODIC INFORMATION IN RODENTS

In many photoperiodic rodents the maternal system transmits photoperiodic information to the young in utero. The young then use this information in an integrated reproductive response to prevailing photoperiodic conditions at the time they leave the nest. Thus it is quite common for weaned young of the same species to respond differently to the same photoperiod, the response dependent on the photoperiod perceived by the dam during gestation. The precise mechanism by which transfer of photoperiodic information from mother to young is accomplished is not entirely known. Central to successful transmission of photoperiodic information is the maternal pineal gland and its hormone, melatonin; in the absence of these no information is transferred to the young, while daily treatment of the pregnant pinealectomized mother with exogenous melatonin has led to successful transmission from mother to young of short-day, but not long-day, information. Reproductive development of newly weaned young, rendered incapable (by pinealectomy) of responding directly to ambient photoperiod, or functionally pinealectomized by exposure to continuous illumination (LL). directly reflects gestational photoperiod seen by the mother; pinealectomized or LL-exposed weanlings gestated on short (inhibitory) days experience a slow rate of reproductive development while similarly treated weanlings that were gestated on long (stimulatory) days undergo rapid gonadal and sex accessory gland growth. Many questions remain about the mechanism of maternal transfer of photoperiodic information to her young. Answers to these questions can only be determined after attaining a thorough knowledge of the basic properties of the photoperiodic time measurement system of the species being investigated.