[Influence of local administration of apomorphine on citrulline extracellular level in the striatum: participation of the dopamine D1 and D2 receptors].

By means of in vivo microdialysis combined with HPLC analysis, we have shown that local infusions of 1 mM N-nitro-L-arginine (NO-synthase inhibitors) in the rat striatum reduced, and infusions of 100 microM apomorphine (agonists of the dopamine receptors) increased the level of citrulline (a NO co-product) in extracellular space of this structure. The apomorphine-induced increase in citrulline extracellular levels in the striatum was completely prevented by infusions of N-nitro-L-arginine in this structure, and 10 microM raclopride (dopamine D2 receptor blocker), but not by infusions of 50 microM SCH-23390 (dopamine D1 receptor blocker). The data obtained suggest that the increase in citrulline extracellular levels in striatum resulted from local activation of NO-synthase, and this effect is mediated by D2 rather than D1 dopamine receptors.