Sensitization elicited by directly and indirectly acting dopaminergic agonists: comparison using neural network analysis.

The major aim of this work was to compare sensitized responses to amphetamine with those of apomorphine. This was done using both a univariant analysis of locomotor activity and a multivariant neural network analysis of five different behaviors. The neural network analysis compares the pattern of behaviors from a treated group to a set of patterns from control conditions and estimates the dose of drug in control conditions that best matches the pattern of behaviors of the treated group. Both methods indicated that repeated administration of 2.0 mg/kg amphetamine but not 0.5 mg/kg amphetamine resulted in sensitization to the administration of a 0.5 mg/kg amphetamine challenge given 10 days following the end of the sensitizing regimen. Both analyses indicated sensitization following repeated administration of 5 mg/kg apomorphine. Studies of cross sensitization were done using a neural network analysis that could distinguish patterns of behavior elicited by amphetamine from those elicited by apomorphine. Such studies indicated that apomorphine elicits an apomorphine-like response in animals sensitized to either apomorphine or amphetamine. In contrast, amphetamine produces an amphetamine-like response in animals sensitized to amphetamine and an apomorphine-like response in animals sensitized to apomorphine. The results indicate that neural network analysis may be a useful tool for analyzing drug effects on patterns of behavior.