Endogenous opiates and behavioral responses to environmental novelty

Endogenous opiates (endorphins) mediate a variety of motivational and behavioral states. We examined the possible contributions of endorphins to the exploratory behavior of mice. Naloxone, a blocker of opiate receptors, depressed hole board exploratory activity and entry into a novel environment. It also reduced responding for sensory stimulation. Finally, a direct correlation was demonstrated between exploratory behavior on the one hand, and enkephalin-induced behavioral activation on the other.