Delayed onset of the amnestic effect of posttraining beta-endorphin: effects of propranolol administered prior to retention testing.

Mice were trained in a 1-trial inhibitory avoidance task (0.7 mA FS) and tested for retention at 1, 3, or 6 h following training. Posttraining beta-endorphin (0.1 micrograms/mouse i.p.) administration impaired retention at 6 h, but not 1 or 3 h after training. Propranolol (0.3 mg/mouse i.p.), but not naloxone (0.1 mg/mouse i.p.) administered prior to retention testing at 1 or 3 h accelerated the onset of amnesia in mice given posttraining beta-endorphin. Neither propranolol nor naloxone affected retention when given alone. These findings suggest that the delayed onset of the amnesia produced by posttraining beta-endorphin is due to the activation of a beta-adrenergic system.