M1 MUSCARINIC RECEPTOR STIMULATION DECREASES ASPARTATE RELEASE IN THERAT NEOSTRIATUM

This study investigates the effects of different muscarinic receptor a gonists on extracellular glutamate and aspartate concentrations in the rat neostriatum. In vivo intracerebral perfusions were undertaken in the conscious rat using a concentric push-pull cannulae system. Amino acid concentrations in samples were determined by HPLC with fluorometr ic detection. The intrastriatal perfusion of arecoline, a M1-M2 muscar inic receptor agonist, produced a significant decrease in extracellula r [ASP] (45% of decrease) but not in extracellular [GLU]. These effect s were blocked by scopolamine, a M1-M2 muscarinic receptor antagonist. McN-A-343, a M1 muscarinic receptor agonist, but not the M2 muscarini c receptor agonist, oxotremorine, produced a significant decrease in e xtracellular [ASP] (40% of decrease) but not in extracellular [GLU]. T he effects of McN-A-343 on extracellular [ASP] were blocked by pirenze pine, a MI muscarinic receptor antagonist. These results suggest that the decrease in extracellular [ASP] could be mediated, at least in par t, by M1 muscarinic receptor activation in the rat neostriatum.