Experiential constraints on the development of tolerance to amphetamine hypophagia following sensitization of stereotypy: instrumental contingencies regulate the expression of sensitization

In previous research, sensitization of stereotypy induced by injections of 2.5 mg/kg amphetamine did nor interfere with subsequent tolerance developme nt to the hypophagic effect of 2 mg/kg. This study examined the effect of a higher sensitizing dose. Rats given intermittent injections of 5 mg/kg amp hetamine and then challenged with various doses of amphetamine showed focus ed head scanning at 2 mg/kg and oral stereotypy at 4 mg/kg. In contrast, sa line controls showed diffuse sniffing and head scanning at 2 and 4 mg/kg. S ubgroups from each condition were then given daily injections of either amp hetamine (2 mg/kg) or saline and access to milk for 30 min. Dose-response t ests revealed that both drugged groups learned to suppress stereotypy in or der to feed at 2 mg/kg, but only the non-sensitized group could do so at 4 mg/kg. These results demonstrate that (1) rats learn to suppress only those stereotyped movements that they experience in the context of feeding and ( 2) instrumental contingencies can influence the expression of behavioral se nsitization.