Danger-Associated Sound Signals Activate the Nitrergic System of the Medial Part of the Nucleus Accumbens

Abstract

Vital microdialysis and high-performance liquid chromatography were used to show that presentation of conditioned sound signals previously combined with electrocutaneous stimulation in a conditioned reflex chamber to Sprague‐Dawley rats in their home cage led to increases in the extracellular citrulline level (a co-product of nitric oxide synthesis) in the medial part of the nucleus accumbens. This increase was prevented by local administration of the neuronal NO synthase inhibitor 7-nitroindazole (0.5 mM) and was not seen in animals previously presented with sound and pain stimuli with no temporal relationship or in animals with dialysis cannulae located in the lateral part of the nucleus accumbens. These data provide evidence that danger-associated sound signals evoke activation of neuronal NO synthase in the medial part of the nucleus accumbens, leading to increases in the extracellular citrulline level and, probably, enhanced production of nitric oxide in this area of the brain.