Step-down inhibitory avoidance training and beta-endorphin-like immunoreactivity of rat hypothalamus and plasma.

A 29 to 35% reduction of beta-endorphin-like immunoreactivity was observed in the hypothalamus of rats 30 min after step-down inhibitory avoidance training. The effect can be attributed to the release and subsequent metabolism of beta-endorphin. Depletion occurred regardless of the size of the platform used for training, and of the intensity and even of the presence of footshocks in the training trial. No changes in beta-endorphin-like immunoreactivity were observed in plasma. These results confirm and generalize previous data on the influence of behavioral training on beta-endorphin-like immunoreactivity.