Danger Signals Inhibit Nitrergic Activation of the Nucleus Accumbens Induced by Exploratory Behavior

Abstract

Studies on male Sprague–Dawley rats using vital intracranial microdialysis and high-performance liquid chromatography showed that exploratory behavior in a novel context was accompanied by increases in extracellular citrulline (a co-product of NO synthesis) in the medial part of the nucleus accumbens, and these were blocked by local administration of the neuronal NO synthase inhibitor 7-nitroindazole (0.5 mM). Presentation during exploratory activity of a tone which had previously been combined with electrocutaneous stimulation decreased exploratory behavior and, secondly, inhibited the increase in the nucleus accumbens citrulline level induced by exploratory behavior. These effects were not seen in control animals in which the tone had not been associated with electrocutaneous stimulation. These data provide the first evidence for the involvement of the medial part of the nucleus accumbens in transferring the effects of fear to exploratory behavior and demonstrate that inhibition of nitrergic transmission may make a contribution to this process.