Effects of prolactin on sleep in cyclic rats

We previously demonstrated that pregnancy-associated sleep enhancement is correlated with the daily surges of prolactin (PRL). However, in spite of a surge of PRL in the proestrous night, a reduction of nocturnal sleep occurs in phase with proestrus. Therefore, to clarify the physiological role of PRL in sleep regulation during the estrous cycle, time-course changes in sleep were analyzed in bromocriptine (CB-154)-treated and/or PRL-supplemented female rats. Sleep patterns characteristic of proestrus-to-estrus were not affected by the CB-154 treatment. In contrast, nocturnal rapid eye movement sleep (REMS) was significantly increased after the PRL supplementation. The CB-154 treatment diminished the REMS-enhancing effect of PRL. Thus, the results suggest that the endogenous PRL is not crucial for the regulation of sleep during the estrous cycle, while exogenous PRL can enhance REMS.