Dopamine D1 receptors regulate the extracellular citrulline level in the nucleus accumbens during performance of a conditioned reflex fear reaction.

Intracerebral microdialysis studies on Sprague-Dawley rats using HPLC showed that performance of a conditioned reflex fear reaction was accompanied by an increase in the extracellular citrulline (a co-product of nitric oxide synthesis) level in the nucleus accumbens. Administration of the selective D1 receptor antagonist SCH-23390 (100 microM) into the nucleus accumbens had no long-lasting effect on the extracellular citrulline level in this structure, but reduced the magnitude of the increase in the citrulline level seen on performance of the conditioned reflex fear reaction. These data suggest that the dopaminergic input of the nucleus accumbens acts via D1 receptors to increase NO synthase activity and nitric oxide production during performance of the conditioned reflex fear reaction.