Dopamine autoreceptor agonists attenuate spontaneous motor activity but not spontaneous fighting in individually-housed mice

The present study was conducted to determine whether or not two behavioral characteristics of individually-housed mice, hyperactivity in a novel environment and intermale fighting, are attenuated by the dopamine (DA) agonists, apomorphine, (+)- and (−)-3-(3-hydroxyphenyl)-N-n-propylpiperidine (3-PPP). Autoreceptor-activating doses of these drugs which reduced spontaneous activity in a novel environment did not inhibit spontaneous fighting with conspecific olfactory bulbectomized males. Individually-housed mice were more active in a novel environment and showed a significant reduction of activity at lower doses of apomorphine, (+)- and (−)-3-PPP than group-housed mice. However, the ED 50 's for the inhibition of spontaneous activity in a novel environment in group- and individually-housed mice were similar: apomorphine, o.02 vs. 0.012 mg/kg, SC; (+)-3-PPP, 0.50 vs. 0.51 mg/kg, SC; and (−)-3-PPP, 1.0 vs. 0.56 mg/kg, SC, for group- and individually-housed mice respectively. A significant proportion of individually-housed mice, but not group-housed mice, displayed catalepsy in response to high doses of (−)-3-PPP. These data suggest that DA autoreceptor agonists can modulate the hyperactivity syndrome but not spontaneous fighting behavior in individually-housed mice.