Effects of acute and chronic interactions of diazepam and d-amphetamine on punished behavior of rats.

Abstract

Drinking of water-deprived rats was punished by delivery of either 0.03 or 0.1 mA shocks through the drinking tube during the last 5 of 7-s tone components during a 15-min daily exposure to water. These sessions consisted of 66 alternating components marked by the presence or absence of a tone. Drinking was not punished during the 33 components without tones or during the first 2 s of each tone. The baseline number of shocks accepted by the rats at 0.1 mA was less than half that at 0.03 mA. Acute diazepam markedly increased shocks delivered from the baseline values for both shock intensities, while acute d-amphetamine either had no effect or decreased the number of shocks accepted. The combination of acute diazepam and d-amphetamine caused a decrease in shock rates as compared to diazepam alone. Daily treatment with the combination of 10 mg/kg diazepam and 1 mg/kg d-amphetamine caused a gradual increase in punished responding over 25 days under either shock intensity. Gross observation of these rats after daily treatments indicated the development of hyperreactivity and a pattern resembling stereotyped behavior. At the end of the chronic treatment with the drug combination the shock rates were significantly greater than those caused by diazepam alone. Nevertheless, neither the effect of diazepam nor that of d-amphetamine, when administered singly after the period of chronic treatment with the combination, differed significantly from initial effect of the respective drugs on punished responding.