The roles of accumbal dopamine D1 and D2 receptors in maternal memory in rats

Female rats show enhanced maternal responsiveness toward their young if they have had maternal experiences before. This kind of maternal experience-based memory is critically dependent on the mesolimbic dopamine (DA) system, especially the nucleus accumbens (NA) shell. However, the relative contributions of the two main DA receptor systems (D-1 and D-2) within the shell have not been delineated. This study investigates the roles of dopamine D-1 and D-2 receptors in maternal memory by infusing a selective D-1 antagonist, SCH-23390; a selective D-2 antagonist, sulpiride; or a combination D-1/D-2 antagonist, cis-Z-flupenthixol, into the NA shell of postpartum female rats. Sulpiride-infused rats showed a significantly longer latency to exhibit full maternal behavior following a 10-day pup isolation period in comparison to the controls that received a vehicle. Cis-Z-flupenthixol disrupted maternal memory to a greater extent, as rats receiving this showed the longest latencies to express maternal behavior. SCH-23390 infusions had only marginal effects. These findings suggest that both the D-1 and the D-2 receptor subtypes play a role in the consolidation of maternal memory and they might do so by mediating the motivational salience of pup stimulation.