REARING CONDITIONS ALTER SOCIAL REACTIVITY AND D-1 DOPAMINE-RECEPTORSIN HIGH-AGGRESSIVE AND LOW-AGGRESSIVE MICE

As a result of selective breeding, NC900 mice exhibit isolation-induce d attacks in a social interaction test, whereas NC100 mice do not atta ck but freeze instead. Administration of the D-1 receptor agonist dihy drexidine was previously shown to reduce aggression in NC900 mice and nonagonistic approaches in NC100 mice. This resulted from induction of a marked social reactivity in both selected lines. Because isolation rearing also induces social reactivity, the present experiment was des igned to test the hypothesis that D-1 dopamine receptors mediate isola tion-induced social reactivity. Isolation was expected to potentiate t he effects of a D-1 agonist and to increase D-1 dopamine receptor dens ity. Thus, isolated and group-reared mice were administered dihydrexid ine, and their social behavior was compared to vehicle-injected contro ls. Dihydrexidine induced higher levels of reactivity among isolated t han among group-reared animals, especially in NC900 mice. In independe nt experiments, increased densities of D-1 dopamine receptors in the s triatum of isolated animals were found, with no change in affinity. Th ese studies suggest an important role for the D-1 dopamine receptor as a mediator of isolation-induced social reactivity.