Ovarian steroids alter dopamine receptor populations in the medial preoptic area of female rats: implications for sexual motivation, desire, and behaviour

Dopamine (DA) transmission in the medial preoptic area (mPOA) plays a critical role in the control of appetitive sexual behaviour in the female rat. We have shown previously that a DA D1 receptor (D1R)‐mediated excitatory state appears to occur in females primed with estradiol benzoate (EB) and progesterone (P), whereas a DA D2 receptor (D2R)‐mediated inhibitory state appears to occur in females primed only with EB. The present experiment employed three techniques to better understand what changes occur to DA receptors (DARs) in the mPOA under different hormonal profiles. Ovariectomized females were randomly assigned to one of three steroid treatment groups: EB + P (10 and 500 μg, respectively), EB + Oil, or the control (Oil + Oil), with hormone injections administered at 48 and 4 h prior to euthanizing. First, the number of neurons in the mPOA that contained D1R or D2R was assessed using immunohistochemistry. Second, the mPOA and two control areas (the prelimbic cortex and caudate putamen) were analysed for DAR protein levels using western blot, and DAR functional binding levels using autoradiography. Ovarian steroid hormones affected the two DAR subtypes in opposite ways in the mPOA. All three techniques supported previous behavioural findings that females primed with EB have a lower D1R : D2R ratio, and thus a D2R‐mediated system, and females primed with EB + P have a higher D1R : D2R ratio, and thus a D1R‐mediated system. This provides strong evidence for a DA‐driven pathway of female sexual motivation, desire, and behaviour that is modified by different hormone priming regimens. Through a series of techniques include immunohistochemistry, Western blotting, and autoradiography, we demonstrated an alteration of dopamine receptors in the medial preoptic area dependent upon the hormonal profile of the female. Specifically, administering estradiol benzoate increases dopamine D2 receptor levels, but the addition of progesterone reverses the receptor ratio by promoting D1 receptor levels. This finding supplements behaviour research demonstrating dopamine's function in the medial preoptic area in the control of sexual motivation in the female rat.