[Sound signals of danger activate the nitrergic system of the medial nucleus accumbens]

It was shown in Sprague-Dawley rats by means of in vivo microdialysis combined with HPLC analysis that presentations to the animals in a home cage of a tone previously paired with a footshock in an experimental chamber produced an increase in extracellular levels of citrulline (an NO co-product) in the medial n. accumbens. The increase was prevented by intraaccumbal infusions of 7-nitroindasole (0.5 mM), a neuronal NO synthase inhibitor and was not observed in rats previously exposed to unpaired tone and footshock presentations and in controls with microdialysis probes implanted into the lateral n. accumbens. The results indicate that sound signals of danger produce a neuronal NO synthase activation within the medial n. accumbens, which leads to citrulline formation and, very likely, to NO production in this brain area.