Comparison of behavioral arousal induced by apomorphine and N-n-propylnorapomorphine

A preliminary evaluation of behavioral arousal in mice, as a model system for quantifying activity of presumptive antiparkinsonian and antischizophrenic agents, was made. In experiments not yet published, we have observed stereotypic cage climbing induced by two aporphines (apomorphine, APO; and N-n-propylnoraporphine, NPA) to be specifically dopaminergic. Time of peak effect was found to be 15--30 min and an ED50 of approximately 4 mg/kg was established for both drugs. In the present study we have investigated the activity of APO and NPA on behavioral arousal. As measured by electromagnetic sensors, behavioral arousal reflects several responses including spontaneous locomotor activity and repetitive movements (e.g., grooming and rearing). The procedures which we have employed minimize artifacts due to handling and injection routines while maximizing our ability to observe time of peak effect (based on blood levels). Dose and time response analyses of APO and NPA (i.p.) demonstrated a time of peak effect from 15--30 min and ED50 values of 3.0 and 2.5 mg/kg for APO and NPA, respectively. The results of our experiments show that for a 90 min period over the 1--10 mg/kg dose range employed, APO exhibits a linear dose response relationship whereas that for NPA is sigmoidal. Similarities in time of peak effect and ED50s for the two aporphines in stereotypic cage-climbing and behavioral arousal experiments suggest that the behavioral arousal induced by APO and NPA may be dopaminergically mediated.