Effects of propranolol on conditioned suppression, discriminated punishment and discriminated non-reward in the rat

Abstract

In Experiment I, two groups of rats were rewarded for lever-pressing under RI 64. During signalled 3-min intrusion periods shocks were delivered response-contingently (on RI 64) for the Punishment group and non-contingently (on RT 64) for the Conditioned Suppression group. d,l-Propranolol (2, 5 mg/kg) released intrusion responding to a similar extent in the two groups. Experiment II comprised two distinct experiments: two groups of rats were trained in parallel on signalled multiple schedules in which responding during the baseline component was rewarded on RI 20. For the second component responding was extinguished in Experiment IIa; it continued to be rewarded but was also punished by electric shock in Experiment IIb. Shock levels were adjusted individually so as to produce similar levels of response suppression in these two groups. d,l-Propranolol released non-rewarded responding (2-5 mg/kg; Expt IIa) but had no effect on punishment (2-10 mg/kg; Expt IIb). l-Propranolol (2.5 mg/kg) but not d-propranolol (2.5 mg/kg) also released non-rewarded responding in Expt IIa. In a further trial d,l-propranolol (5 mg/kg) released punished responding in Expt IIb in a group of animals in which response suppression had been partially relieved by reducing shock intensity. It is hypothesized that beta-adrenergic stimuli may influence response suppression to the extent that the unconditioned aversive event causing suppression is not salient.