Abstract

Dopamine (DA) in the medial preoptic area (mPOA) mediates the display of solicitational behaviours in the female rat. Previous work from my Masters’ thesis demonstrated that a DA D1 receptor (D1R)-mediated excitatory state appears to occur in females hormonally-primed with both estradiol benzoate (EB) and progesterone (P). Conversely, a DA D2 receptor (D2R)-mediated inhibitory state appears to occur in females primed only with EB. The goals of the current thesis were to understand the mechanisms by which this control occurs, and to incorporate this understanding into the bigger framework of neural control underlying female sexual behaviour. To accomplish this, a variety of techniques were utilized. First, the same behavioural results observed previously were replicated through an endogenous alteration of DA release. It was found that administration of ascorbic acid produced an increase in solicitational, but not consummatory behaviours, in females in both hormonal conditions. Three techniques were then employed to study changes in DA receptors (DAR) in the mPOA under three hormonal profiles. Immunohistochemistry determined the number of neurons in the mPOA containing D1R or D2R, DAR protein levels were analyzed using Western blotting, and DAR functional binding levels were examined using autoradiography. The results from all three techniques supported the previous behavioural findings that EB+P females have a higher D1R/D2R ratio, and thus a D1R-mediated system, and EB-alone females have a lower D1R/D2R ratio, and thus a D2R-mediated system. Finally, fluorescence immunohistochemistry was used to map connections from the mPOA to areas known to regulate female sexual behaviour. These pathways were investigated for neuronal type and presence of DAR under different hormonal conditions. Modifications were found, demonstrating that ovarian steroids alter the mechanisms underlying solicitational behaviour via projections to other areas implicated in female sexual behaviour. A conceptual model is presented here that integrates the data in this thesis along with other known networks that control female sexual behaviour. This model has important implications for the treatment of female sexual desire disorders, and places a central role of DA terminals in the mPOA in the regulation of motivated behaviours in general.