Genotype-dependent modulation of LY 171555-induced defensive behavior in the mouse.

The selective D2 dopamine receptor agonist LY 171555 increased defensive behavior dose dependently, decreased social investigation and activity, and increased immobility in mice of the C57BL/6 (C57) strain interacting with non-aggressive mice of the same strain. In the same test situation, DBA/2 (DBA) mice did not present any increase in defensive behavior following injection of the same doses of LY 171555, while exhibiting a marked decrease in activity and increased immobility. Mice of the BALB/c strain were less responsive than C57 mice as far as defensive behavior was concerned, and showed decreased activity and social investigation and increased immobility. These results point to a major genetic role in the modulation of social behavior by D2 receptors.