Dopamine's role in social modulation of infant isolation-induced vocalization: I. Reunion responses to the dam, but not littermates, are dopamine dependent.

Rat pups' vocalization during social separation and the cessation of vocalization upon social reunion (contact quieting) model early life affiliative relationships. The present study examined the roles of dopamine (DA) receptors in regulating contact quieting. Contact quieting to the dam, but not to littermates, was disrupted by either blockade or exogenous stimulation of DA D1-like receptors. The D2 antagonist raclopride also prevented the quieting effect of reunion with the dam and had a lesser effect on the quieting properties of littermates. In contrast, the D2 agonist quinpirole permitted or enhanced contact quieting. Combined systemic and local striatal administration of D2 ligands showed that stimulation of striatal D2 receptors can enhance, but is not necessary for, contact quieting to the dam. These results are consistent with the literature linking the neural mechanisms of affiliation and reinforcement. This is also the first demonstration that the neurochemical substrates of an infant comfort response to dams differ from a behaviorally similar response to siblings.