Quantitative autoradiographic analysis of D-1 and D-2 dopamine receptors in rat brain in early and late pregnancy

This study examined the levels of D-1 and D-2 dopamine receptors in the rat brain during pregnancy, a physiologically unique and important naturally occurring state. We are particularly interested in changes in the dopamine receptor complement of the brain during pregnancy because these receptors might support some components of the immediate postpartum onset of normal maternal behavior. Quantitative in vitro receptor autoradiography was applied particularly focusing on brain areas that control maternal behavior. The D-1 dopamine receptor selective antagonist [H-3]SCH23390 and the D-2 dopamine receptor selective antagonist [H-3]spiperone were used as the ligands. We examined the levels of binding to D-1 and D-2 dopamine receptors in brains in females on day 2 (early pregnancy) and day 21 (late, but prepartum pregnancy) of pregnancy. In addition, brains from females on diestrus-1 and from males provided reference points to the existing literature. Late in pregnancy females had significantly 18-27% lower levels of binding to D-1 dopamine receptors in the lateral striatum, the medial striatum, and the nucleus accumbens when compared to all other groups. Late in pregnancy, females had also significantly 11-25% lower levels of binding to D-2 dopamine receptors in the lateral striatum, the anterior striatum, the nucleus accumbens and the olfactory tubercle compared to all other experimental groups. We examined all of the brain regions already established to be important for maternal behavior, and found that dopamine receptor binding changed across pregnancy only in one such region, the nucleus accumbens. Thus pregnancy, perhaps the hormones of pregnancy, reduces the levels of D-1 and D-2 dopamine receptors in the striatum, and the nucleus accumbens, but not in other brain regions.