A comparative study of the behavioral effects of d-amphetamine and apomorphine in the rat.

A wide range of doses of d-amphetamine and apomorphine were injected into rats, in order to better characterize and compare dopaminergic agonist-induced behavioral effects. The study was carried out using a computerized technique for the quantification and analysis of various behavioral elements. Although both drugs increased motor activity and provided dose-dependent stereotyped responses, the whole pattern of behavior in the open field showed a different structure. d-Amphetamine in doses that did not produce stereotyped responses induced a wide range of varied behavioral elements with increased frequency but decreased mean duration, while apomorphine induced a more restricted behavioral profile. Furthermore, a higher frequency of freezing reaction was observed after d-amphetamine treatment in low doses but not after apomorphine treatment. Both drugs in high doses elicited a similar stereotyped syndrome characterized by repetitive movements of great duration, but at low doses the behavioral pattern was completely different. The apomorphine-induced syndrome was characterized mainly by moving and sniffing, interrupted by rearing, while the amphetamine-induced syndrome by sniffing and moving, interrupted by standing and freezing.