Effects of d-amphetamine, WIN 35,428, pentobarbital and morphine on schedule-controlled responding in two inbred rat strains that differ in locomotor stimulatory effects of cocaine

Abstract

Behavioral effects of d-amphetamine, the cocaine analog, WIN 35,428, morphine, and pentobarbital were compared in NBR/NIH and F344CR1BR rats. Either nose-poke or lever-press responding was maintained under 3-min fixed-interval schedules of food presentation. The effects of morphine, WIN 35,428 and pentobarbital depended upon the rat strain studied: morphine increased nose-poke responding in NBR but not F344 rats; significant strain x dose interactions were observed with WIN 35,428; and pentobarbital was more potent in decreasing nose-poke responding in NBR than in F344 rats. No strain differences were observed in the behavioral effects of d-amphetamine. There were also prominent differences in the effects of drugs that were related to the nature of the response requirement. In both rat strains, nose-poke responding was affected differently than lever-press responding by morphine, d-amphetamine, and WIN 35,428. Pentobarbital produced effects that were independent of the specified response topography. A global underlying difference in these rat strains cannot be identified at present to account for the diversity of findings. The behavioral effects of these drugs appear to be influenced by a host of interactive factors including the drug, strain of animal, the baseline response rate and physical dimensions of the response.