Intracellular preoptic and striatal monoamines in pregnant and lactating rats: possible role in maternal behavior

In many mammals, hormonal fluctuations during pregnancy and parturition produce neurochemical events that are necessary for the transition from a non-maternal state to a maternal state that occurs when infants are born. However, the nature of these events is mostly unknown. We investigated whether changes in dopamine (DA) and serotonin (5-HT) activity within the preoptic area (POA) and striatum, neural sites important for some maternal behaviors, could be part of this process. Female rats were sacrificed as either diestrus virgins, on pregnancy day 10 or 20, on the day of parturition, or on day 7 or 17 of lactation. Bilateral tissue punches from the POA, dorsolateral striatum (ST(dl)), and nucleus accumbens (NA) were obtained and levels of intracellular DA and 5-HT analyzed with high-performance liquid chromatography with electrochemical detection (HPLC-EC). In the POA, DA was high in virgins and during early pregnancy, lowest on the day of parturition, and very high during lactation. Although there were no changes in the DOPAC to DA ratio (i.e., turnover), DOPAC levels also followed this pattern. 5-HT turnover in the POA was lower in virgins compared to other groups. In the ST(dl), DA turnover was highest during late pregnancy and on the day of parturition, while no changes in 5-HT measures were found. No significant effects were found in the NA. Therefore, decreased DAergic activity in the POA and increased DAergic activity in the ST(dl) occurs around parturition, the time when maternal behavior emerges, and may influence its onset.