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In rodents ongoing maternal behaviour requires activation of dopamine receptors. Therefore, it is possible that some motor components of maternal behaviour might be mediated by concurrent dopaminergic stimulation. It has been previously demonstrated that peripheral injections of some antipsychotic drugs such as pimozide have disruptive effects on maternal behaviour. The present experiments were designed to verify the effects of pharmacological blockade of limbic dopamine receptors on ongoing maternal behaviour in lactating rats. The hypothesis that central injections of the drug pimozide would have an effect on maternal behaviour was tested. We investigated the effects of central bilateral intraaccumbens microinjections of the dopamine D2 receptor antagonist pimozide (1.5 and 3.0 mg) on maternal behaviour. Animals treated with 3.0 mg of pimozide showed significantly longer latencies for all parameters of maternal behaviour compared to controls. These results suggest that dopamine receptors in the nucleus accumbens play a role in ongoing maternal behaviour.

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Reproductive experience influences basal and pregnancy profiles of circulating prolactin levels in women and female rats, respectively. Endocrine responses to dopaminergic antagonists are modified by reproductive experience as well. Striatal extracellular dopamine metabolites were measured in vivo by HPLC-ED in perfusates obtained by microdialysis in non-anaesthetized, freely moving, intact and ovariectomized, nulliparous and primiparous rats. Data were collected for at least 7 h. This period always included the light-dark shift at 18:00 h. In a second experiment, microdialysis was performed in ovariectomized nulliparous and primiparous rats treated with haloperidol (1.0 mg/kg s.c.). During the 1 h before and after the onset of the light-dark shift, HVA concentrations in the perfusates increased in nulliparous compared with primiparous rats. The haloperidol-induced increase in DOPAC and HVA was less intense in primiparous rats than that in nulliparous ovariectomized rats. These data revealed a different pattern of striatal dopaminergic anticipation and response to the shift in the light-dark cycle in nulliparous as compared with primiparous intact females. In addition, a distinct striatal dopaminergic response to haloperidol was observed in primiparous as compared to nulliparous ovariectomized rats. The results suggest that reproductive experience can modulate the activity of dopaminergic terminals in the striatum.

Background/Aim: Prolactin (PRL), a hormone produced by the pituitary gland, has multiple physiological functions, including immunoregulation. PRL can also be secreted in response to stressful stimuli. During stress, PRL has been suggested to oppose the immunosuppressive effects of inflammatory mediators. Therefore, the aim of the present study was to analyze the effects of short- and long-term hyperprolactinemia on the inflammatory response in rats subjected to acute or chronic cold stress. Methods: Inflammatory edema was induced by carrageenan in male rats, and hyperprolactinemia was induced by injections of the dopamine receptor antagonist domperidone. The volume of inflammatory edema was measured by plethysmography after carrageenan injection. Additionally, the effects of hyperprolactinemia on body weight and serum corticosterone levels were evaluated. Results and Conclusion: Five days of domperidone-induced hyperprolactinemia increased the volume of inflammatory edema. No differences in serum corticosterone levels were observed between groups. No significant differences were found among 30 days domperidone-induced hyperprolactinemic animals subjected to acute stress and the inflammatory response observed in chronic hyperprolactinemic animals subjected to chronic stress. The results suggest that short-term hyperprolactinemia has pro-inflammatory effects. Because such an effect was not observed in long-term hyperprolactinemic animals, PRL-induced tolerance seems likely. We suggest that short-term hyperprolactinemia may act as a protective factor in rats subjected to acute stress. These data suggest that hyperprolactinemia and stress interact differentially according to the time period.

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