Pretest beta-endorphin and epinephrine, but not oxotremorine, reverse retrograde interference of a conditioned emotional response in mice.

CD-1 mice were trained in a classically conditioned emotional response paradigm and tested 24 hr later. Exposure to an open field 0 or 1, but not 3 hr after training retroactively interfered with retention of the conditioned emotional response. The retroactive interference was counteracted by the pretest IP administration of beta-endorphin (0.05 microgram/mouse) or epinephrine (1 microgram/mouse), but not by that of oxotremorine (5 micrograms/mouse). The three drugs were able to enhance retention test performance in animals not exposed to the open field after training. In view of evidence in the literature that beta-endorphin and epinephrine are released during training in an aversive task like this, it seems likely that these two agents were able to overcome the effect of retroactive interference by reinstating neurohumoral attributes of the conditioned emotional task at the time of testing.