Influence of prenatal photoperiods on postnatal reproductive responses to daily infusions of melatonin in the Siberian hamster (Phodopus sungorus).

Prepubertal reproductive development in juvenile male Siberian hamsters can be strongly influenced by photoperiod information received during gestation. Information transmitted from the mother hamster to her fetuses appears to modify the photoperiodic mechanism of the developing hamsters so that they may respond differently to certain intermediate day lengths [i.e. 14 h of light and 10 h of darkness/day (14L)] experienced after birth depending on whether gestation occurred in longer or shorter day lengths. In adult and juvenile hamsters, the duration of the nocturnal elevation of pineal and serum melatonin (MEL) is an important component of the photoperiodic system coding for day length. In the present study, we investigated whether the photoperiod in effect during gestation could influence the responsiveness of developing male hamsters to daily MEL infusions of fixed durations administered after weaning. The results indicated that hamsters gestated under 16L or 10L did not differ from each other with respect to testicular growth in response to any of the fixed duration MEL infusions. Thus, target tissue responsiveness to fixed duration MEL infusions (over a range of 6-10 h) was the same regardless of the gestation photoperiod to which the animals had been exposed.