Ke. Edmonds et Mh. Stetson, PHOTOPERIOD AND MELATONIN AFFECT TESTICULAR GROWTH IN THE MARSH RICE RAT (ORYZOMYS PALUSTRIS), Journal of pineal research, 17(2), 1994, pp. 86-93
Reproduction in rice rats is subject to photoperiodic control and the
pineal gland mediates this effect. We examined the effects of the pine
al gland hormone melatonin on testicular weight when administered via
implants, injections, and infusions. Testicular weight was modified by
photoperiod and the size of the melatonin implant. Twenty-millimeter
implants suppressed testicular weight in rice rats housed on 12- and 1
6-hr photoperiods, while those housed on a 14-hr photoperiod were more
sensitive to melatonin; in these animals 10- and 20-mm implants inhib
ited testicular weight. Melatonin implants also prevented rice rats fr
om responding to a change in photoperiod with the appropriate alterati
on of testicular growth. Melatonin injections inhibited testicular gro
wth when administered before lights out on LD 14:10, but not on LD 16:
8. Morning injections had no effect on either photoperiod. Finally, 12
-hr duration melatonin infusions inhibited testicular growth in pineal
ectomized rice rats on LD 16:8, while 6-hr duration infusions were wit
hout effect. These data show that the pineal, through the secretion of
melatonin, is a phototransducing organ intimately involved in testicu
lar growth in rice rats.