Retention enhancement by pre-test beta-endorphin and oxotremorine and its reversal by scopolamine.

The pre-test administration of beta-endorphin (0.05 microgram/mouse), oxotremorine sesquifumarate (5.0 micrograms/mouse), or beta-endorphin plus oxotremorine enhanced retention test performance of a conditioned emotional response in mice. The effects were blocked by scopolamine. Scopolamine had no effect of its own. The data suggest that the retention enhancement caused by beta-endorphin may involve the secondary activation of cholinergic mechanisms.