[SOUND SIGNALS OF DANGER ACTIVATE THE NITRERGIC SYSTEM OF THE MEDIAL PREFRONTAL CORTEX]

In Sprague-Dawley rats by means of in vivo microdialysis, we have shown that presentation to rats-during conditioned fear expression of a sound conditioned stimulus previously paired with footshock (CS+) produces an increase in extracellular levels of citrulline (an NO co-product) in the medial prefrontal cortex. Presentation to the same rats of a different sound stimulus (not associated with footshock) (CS-) causes a very small increase in extracellular citrulline level. CS+ induced citrulline increase is prevented by infusions into the medial prefrontal cortex of Nomega-propyl-L-arginine (1 mM), a neuronal NO synthase inhibitor and it is not observed in control rats (same procedure, no footshock). These data indicate for the first time that sound signals of danger, but not safety signals activate nitrergic system of the medial prefrontal cortex.