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, ablocker 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 w a s demonstrated between exploratory behavior on the one hand, and enkephalininduced behavioral activation on the other.