The content of dopamine, serotonin, and their metabolites in the neural circuit that mediates maternal behavior in juvenile and adult rats.

Continuous exposure of non-parturient rats to pups can induce maternal behavior similar in most aspects to that found in the postpartum rat. Surprisingly, young juvenile rats (20-24 days of age) only require 1-3 days of exposure to pups, while adults require 4-8 days before maternal behavior emerges. Dopamine (DA) and possibly serotonin (5-HT) may mediate the expression of adult maternal behavior. We hypothesize that postnatal changes in DA and 5-HT within the neural circuit that supports maternal behavior including the medial preoptic area (MPOA), medial and cortical amygdala (MCA), and nucleus accumbens (NAC), may underlie these differences in responsiveness across juveniles and adults. We measured DA, 5-HT, and their metabolites in postmortem samples of these regions in maternal and non-maternal juvenile and adult females. The only difference found across behavioral groups was that the MPOA of adults induced into maternal behavior by pup exposure had more DA than did that of isolated adult females or maternal juveniles. However, when adults versus juveniles were compared, the content of DA and 3,4-dihydroxyphenylacetic (DOPAC) was higher in the adult than in the juvenile NAC and MCA; the content of 5-HT and 5-hydroxyindoleacetic acid (5-HIAA) in these structures did not vary across the age groups. In contrast, higher levels of 5-HT and 5-HIAA were found in the MPOA in juveniles compared to adults. We propose that these region-specific age differences in DA and 5HT may underlie differences in juvenile-adult responses to pups.