Jw. Rudy et al., Isolation reduces contextual but not auditory-cue fear conditioning: A role for endogenous opioids, BEHAV NEURO, 113(2), 1999, pp. 316-323
Isolation for several hours after fear conditioning reduces contextual but
not auditory-cue fear conditioning (J. W. Rudy, 1996). This isolation effec
t is reversed by both centrally and peripherally acting opioid receptor ant
agonists. As in isolation, systemically administered morphine given immedia
tely after conditioning also reduces contextual fear conditioning. Morphine
's effect is also reversed by both centrally and peripherally acting opioid
receptor antagonists. Exposure to the conditioning context has been shown
to eliminate the effect of isolation on contextual fear conditioning (J. W.
Rudy, 1996). Context preexposure also eliminated the effect of morphine on
contextual fear conditioning. These results imply that opioids released in
the periphery play an important role in producing the isolation effect and
that they do so by disrupting the postconditioning memory consolidation pr
ocesses.