D1 dopamine receptors and the reversal of isolation-induced behaviors in mice.

In a previous study, it was demonstrated that the high rates of social reactivity exhibited by isolated male mice in a dyadic encounter were mediated, at least in part, by an increased sensitivity of the D1 dopamine receptors. The present research was guided by the hypothesis that the behavioral effects of isolation are reversible, and that changes in dopaminergic function support this reversibility. To this end, mice selectively bred for high and low levels of aggression were reared in isolation from weaning (21 days) to puberty (45 days), at which point they were either assigned to groups or left in isolation until day 69. By comparison to the continuous isolation condition, mice that eventually formed groups exhibited significantly less reactivity in a dyadic test conducted on day 69, showed a reduced response to dihydrexidine (DHX), and a decreased density of D1 dopamine receptors. This experiment provided evidence for the plasticity of the neurobiological system supporting reactive responses, and confirmed the view that its functional organization is open to experientially-induced changes.