Biphasic effects of propranolol on a temporal generalization gradient in the rat

Rats were trained on a fixed interval (FI 20 s) schedule of food reinforcement, then subjected to drug trials on an ABBA design. Responses, recorded in 2 s post-reinforcement bins, formed a temporal generalization gradient. d,l-propranolol (7.5 mg/kg, intraperitoneally) decreased responding in bins two to four, in which control response rates were relatively low, but increased responding in bins five to eight, in which control response rates were higher. The effect was weaker at 5 mg/kg, non-significant at 2.5 mg/kg and absent at 1 and 10 mg/ kg. A similar effect was seen in a single trial of d,l-propranolol (7.5 mg/kg) on FI 40. I- propranolol (3.75 mg/kg) reproduced this effect in part, whereas d-propranolol (7.5 mg/kg) and the peripherally acting beta-blocker, atenolol (10, 20 mg/kg), were without any effect.