Influence of D2 Dopamine Receptor Blockade on Extracellular Citrulline Levels in the Nucleus Accumbens during Expression of Conditioned Fear Response

By means of in vivo microdialysis combined with HPLC analysis it was shown that levels of extracellular citrulline (NO co-product) In the rat n. accumbens increased during expression of a conditioned fear response. Intraaccumbal infusions of a D2 receptor antagonist raclopride (10 mu M) decreased the rise of extracellular citrulline produced by expression of the response but did not change behavioral characteristics of conditioned freezing. The raclopride infusions increased exploratory activity inhibited by acquisition of conditioned fear but did not affect the exploration of control rats. These data suo-est that dopaminergic input to the it. accumbens and D2 dopamine receptors regulate activity of the accumbal nitrergic system during conditioned fear response and possibly control fear transfer to another behavioral situation.