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 th e rat brain during pregnancy, a physiologically unique and important n aturally occurring state. We are particularly interested in changes in the dopamine receptor complement of the brain during pregnancy becaus e these receptors might support some components of the immediate postp artum onset of normal maternal behavior. Quantitative in vitro recepto r autoradiography was applied particularly focusing on brain areas tha t control maternal behavior. The D-1 dopamine receptor selective antag onist [H-3]SCH23390 and the D-2 dopamine receptor selective antagonist [H-3]spiperone were used as the ligands. We examined the levels of bi nding 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 pregna ncy. In addition, brains from females on diestrus-1 and from males pro vided reference points to the existing literature. Late in pregnancy f emales had significantly 18-27% lower levels of binding to D-1 dopamin e receptors in the lateral striatum, the medial striatum, and the nucl eus accumbens when compared to all other groups. Late in pregnancy, fe males had also significantly 11-25% lower levels of binding to D-2 dop amine receptors in the lateral striatum, the anterior striatum, the nu cleus accumbens and the olfactory tubercle compared to all other exper imental groups. We examined all of the brain regions already establish ed to be important for maternal behavior, and found that dopamine rece ptor binding changed across pregnancy only in one such region, the nuc leus accumbens. Thus pregnancy, perhaps the hormones of pregnancy, red uces the levels of D-1 and D-2 dopamine receptors in the striatum, and the nucleus accumbens, but not in other brain regions.