Examining the role of endogenous opioids in learned odor-stroke associations in infant rats.

Maternal touch profoundly regulates infant neural and behavioral development, and supports learned odor associations necessary for infant attachment. Endogenous opioids are well characterized to mediate the calming and analgesic properties of maternal touch; yet their role in learned odor-touch associations is unknown. We administered naltrexone, an opioid receptor antagonist, before or immediately following classical conditioning with peppermint odor and tactile stimulation (stroking) in rat neonates. Results indicate odor-stroke conditioning produces odor preferences facilitated by endogenous opioids during acquisition and memory consolidation. These results provide additional evidence for the modulatory role of opioids in neonate learning and memory. Disturbances to this system may alter the impact of touch on infant development, particularly in the realm of learning necessary for attachment. Copyright 2005 Wiley Periodicals, Inc.