Glutamatergic regulation of extracellular citrulline levels in the nucleus accumbens during an emotional conditioned reflex.

Intracerebral microdialysis and high-performance liquid chromatography were used to demonstrate that the acquisition and execution of an emotional conditioned reflex in Sprague-Dawley rats are accompanied by increases in extracellular citrulline (a co-product of nitric oxide synthesis) levels in the nucleus accumbens. Injection of the selective NMDA glutamate receptor antagonist MK-801 (100 microM) into the nucleus accumbens significantly decreased the increase in extracellular citrulline seen in this structure on acquisition of the emotional conditioned reflex and completely blocked the increase induced by execution of the reflex. These data suggest that during the acquisition and execution of an emotional conditioned reflex, the glutamatergic input of the nucleus accumbens acts on NMDA receptors to stimulate nitric oxide production in this part of the brain.