Effect of various behavioral training and testing procedures on brain beta-endorphin-like immunoreactivity and the possible role of beta-endorphin in behavioral regulation.

Beta-Endorphin-like immunoreactivity is reduced in the rat diencephalon after the animals are exposed for the first time to any of the following behavioral situations: 50 tones (habituation), 50 tone-footshock shuttle avoidance trials, one step-down inhibitory avoidance trial, simple exposure to the avoidance apparatus with no footshocks, or inescapable shock. The effect is not observed when animals are exposed to any of these situations for a second time. The reduction of brain beta-endorphin-like immunoreactivity is attributable to release and subsequent metabolism of the substance, and correlates with the novelty inherent in the diverse training or test situations. The role of beta-endorphin in behavior is discussed in the light of these and previous results which showed that it causes both retrograde amnesia and a facilitation of retrieval. The substance would appear to serve an adaptive function when animals are exposed to a new experience, by inducing a temporary forgetting of the experience together with (or leading to) a state of alertness or preparedness for what may happen next.