Increased sensitivity of dopamine systems following reproductive experience in rats

Several studies have suggested that alterations in forebrain dopamine activ ity during the postpartum period may result in the onset of postpartum psyc hosis in women [J. Psychosom. Obstet. Gynecol. 19 (1998) 104; Prog. Neuro-P sychopharmacol. Biol. Psychiatry 17 (1993) 571; J. Clin. Psychiatry 51 (199 0) 365.]. The present study investigated whether increased dopamine activit y in these forebrain regions is a normal consequence of reproductive experi ence in rodents. Both intact and ovariectomized parous and nulliparous fema les were tested for their responses to the dopamine agonist apomorphine usi ng two behavioral measures, prepulse inhibition (PPI) and oral stereotypy. In addition, dopamine and DOPAC levels were measured in tissue from the str iatum and nucleus accumbens together with circulating plasma prolactin leve ls. The results of the behavioral studies demonstrate an increased response to apomorphine in parous females. Parous subjects also hail increased leve ls of dopamine and DOPAC hi striatal tissue and lower levels of circulating prolactin. Ovariectomy in nulliparous females resulted in a potentiated re sponse to apomorphine with regard to the disruption of PPI, as well as a si gnificant decrease in the plasma prolactin levels, as compared with intact nulliparous females. These data suggest that increased dopamine activity in forebrain regions occurs as a consequence of parity, which persists for a minimum of several weeks postpartum. These findings support the hypothesis that increased dopamine sensitivity in forebrain dopamine regions may be on e potential mechanism underlying the development of postpartum psychosis in women. (C) 2001 Elsevier Science Inc. All rights reserved.