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Cerebral Cortex Advance Access published online on December 24, 2007
Cerebral Cortex, doi:10.1093/cercor/bhm232
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© 2007 The Authors
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.0/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

The Expression of Contextual Fear Conditioning Involves Activation of an NMDA Receptor–Nitric Oxide Pathway in the Medial Prefrontal Cortex

Leonardo Barbosa Moraes Resstel, Fernando Morgan de Aguiar Corrêa and Francisco Silveira Guimarães

Department of Pharmacology, School of Medicine of Ribeirão Preto, University of São Paulo, Ribeirão Preto, Av. Bandeirantes 3900, 14049-900, Ribeirão Preto, São Paulo, Brazil

Address correspondence to Dr Leonardo Barbosa Moraes Resstel. Email: leoresstel{at}yahoo.com.br

The ventral portion of medial prefrontal cortex (vMPFC) is involved in contextual fear-conditioning expression in rats. In the present study, we investigated the role of local N-methyl-D-aspartic acid (NMDA) glutamate receptors and nitric oxide (NO) in vMPFC on the behavioral (freezing) and cardiovascular (increase of arterial pressure and heart rate) responses of rats exposed to a context fear conditioning. The results showed that both freezing and cardiovascular responses to contextual fear conditioning were reduced by bilateral administration of NMDA receptor antagonist LY235959 (4 nmol/200 nL) into the vMPFC before reexposition to conditioned chamber. Bilateral inhibition of neuronal NO synthase (nNOS) by local vMPFC administration of the N{omega}-propyl-L-arginine (N-propyl, 0.04 nmol/200 nL) or the NO scavenger carboxy-PTIO (1 nmol/200 nL) caused similar results, inhibiting the fear responses. We also investigated the effects of inhibiting glutamate- and NO-mediated neurotransmission in the vMPFC at the time of aversive context exposure on reexposure to the same context. It was observed that the 1st exposure results in a significant attenuation of the fear responses on reexposure in vehicle-treated animals, which was not modified by the drugs. The present results suggest that a vMPFC NMDA–NO pathway may play an important role on expression of contextual fear conditioning.

Key Words: cardiovascular system • fear conditioning • freezing • glutamatergic system • infralimbic cortex • nitric oxide


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