Exploratory response habituation and the attenuating effect of an amphetamine-barbiturate mixture

Mutual potentiation between dl-amphetamine (0.75 mg/kg) and amylobarbitone (15.0 mg/kg) can occur, measured as a marked increase in locomotor exploratory responses in the rat (Rushton and Steinberg, 1963). Experiment 1 confirms the potentiation between amphetamine and amylobarbitone, and extends the finding to a distinctly different type of exploratory behaviour (the 'head-poke' response). However, the same amphetamine-barbiturate mixture did not affect the preference for responses rewarded by a light-onset contingency (Expt. 1), and also did not affect the threshold of a response elicited by aversive footshock (Expt. 2). The mixture may facilitate the occurrence of exploratory responses by a direct attenuation of the rate of habituation of the exploratory responses, and not secondarily by altering the reward or aversion of external stimuli, or by changing the animal's level of arousal.