Reproductive experience modulates dopamine-related behavioral responses

Reproductive experience (RE), i.e., mating, pregnancy, parturition and lactation, has long-term physiological effects. It reduces the basal levels of circulating prolactin in parous women, decreases the intensity of nocturnal and diurnal prolactin surges in multigravid rats during early pregnancy, as well as the hormonal and neurochemical responses to the dopamine receptor antagonists metoclopramide and haloperidol. In the present study, we evaluated the possible influences of RE on some dopaminergic-related behaviors: (1) acute responses to a new environment represented by an open-field arena plus injection stress; (2) modulation of behavior after a short-term withdrawal subsequent to 7 days amphetamine (AMPH) pretreatment; (3) stereotypy elicited by AMPH and apomorphine (APO); and (4) APO-induced hypothermia. In the 3-min open-field test, there was a decrease in locomotor activity as a function of RE. Behavioral depression was mild and AMPH pretreatment revealed RE alterations. APO-induced stereotyped behavior was slightly more intense in primiparous animals, although no significant differences were found in AMPH-induced stereotyped behavior. No differences were observed between intact and ovariectomized primiparous and nulliparous animals in APO-induced hypothermia. Our data suggest that RE modifies some DA-related behavioral responses. The physiological relevance of the phenomenon is discussed.