Short day lengths affect perinatal development of the male reproductive system in the Siberian hamster, Phodopus sungorus.

The Siberian hamster, Phodopus sungorus, breeds seasonally. In the laboratory, seasonal breeding can be controlled by photoperiod, which affects the duration of nightly melatonin secretion. Winterlike, short day lengths induce gonadal regression in adult animals, and pups born and maintained in short days undergo pubertal gonadal development later than animals born into long days. However, to date there have been no reports of gestational photoperiod affecting fetal development of reproductive systems. The spinal nucleus of the bulbocavernosus (SNB) and its target muscles, the bulbocavernosus (BC) and levator ani (LA), compose a sexually dimorphic, androgen-sensitive neuromuscular system involved in male reproduction. The SNB neuromuscular system was studied in male Siberian hamsters maintained from conception in short-day (8 h light, 16 h dark; 8L:16D) versus long-day (16L:8D) conditions. On the day of birth, and at postnatal (PN) days 2 and 18, the BC/LA muscles of hamsters gestated and raised in the short photoperiod were significantly reduced relative to those of their long-day counterparts. Testes weights were not significantly different between groups until day 18. Thus, photoperiod exposure during gestation and after birth affects perinatal development of the SNB system in this species, and these effects can be seen as early as the day of birth. Because photoperiod did not significantly affect testes weights until PN18, these results suggest that either perinatal photoperiod affects fetal androgen production without affecting testes weight or it influences BC/LA development independently from androgen.