Effects of prolactin on in vivo striatal monoaminergic activity are modulated by a previous reproductive experience

Central prolactin (PRL) modulates neuronal activity, which is physiologically relevant and behaviorally meaningful. The stimulatory or inhibitory behavioral effects of exogenous PRL are strongly associated with dose and time of treatment. Central PRL injections produce a dual modulation of striatal dopaminergic responses in males. The activity of the striatal monoaminergic system can be modulated by a previous reproductive experience in females. The objective of the present study was to test in vivo the acute and 5 daytreatment effects of central PRL injections on the striatal dopaminergic and serotoninergic terminals activity in age-matched nulliparous and primiparous females. Seven primiparous and 6 nulliparous rats were stereotaxically implanted with guide cannulas into the lateral ventricle and into the contralateral striatum. Five daily intracerebroventricular injections of ovine prolactin (oPRL;10 mg/5 ml) were performed. On days 1 and 5, females were submitted to striatal microdialysis sessions. The concentrations of dopamine and serotonin metabolites in the dialysate were measured by HPLC-ED. Acute oPRL injection induced a decrease in extracellular levels only for HVA concentrations which was more intense in primiparous than in nulliparous dams. DOPAC concentrations were increased by PRL injection in primiparous compared to nulliparous dams on day 5. On this day DOPAC, HVA and 5HIAA primiparous baseline dialysate concentrations were significantly higher than in nulliparous animals. These data suggest that reproductive experience can modulate in vivo striatal dopaminergic responses to PRL and reveal a relation between striatal dopaminergic and serotoninergic responses that is suggestive of a similar PRL modulation of both neurotransmitter terminals.