Direct regulation of acetylcholine release by N-methyl-D-aspartic acid receptors in rat striatum.

The aziridinium ion of ethylcholine (AF64A), a cholinergic neurotoxin, was injected into the right striatum of a rat. The unilateral injection of 10 nmol AF64A reduced the activity of choline acetyltransferase (CAT) and the tissue content of acetylcholine (ACh) in the striatum. The striatal contents of dopamine (DA), norepinephrine (NE), 5-hydroxyindoleacetic acid (5-HIAA) and gamma-aminobutyric acid (GABA) were unchanged. These results suggest that the cholinospecificity in the striatal lesion was induced by the 10 nmol dose of AF64A. The number of N-methyl-D-aspartic acid (NMDA) receptors in the striatum treated with 10 nmol AF64A was determined by a specific binding assay using 3H-3-(2-carboxypiperazin-4-yl)propyl-1-phosphonic acid ([3H]CPP), a selective ligand for NMDA receptors. The number of the NMDA receptors decreased significantly in the injected area. On the other hand, in a microdialysis using normal rats, the perfusion of 50 microM NMDA into the striatum increased ACh release. The perfusion of 100 microM MK801 which is the specific and non-competitive NMDA receptor antagonist, decreased the basal levels of ACh release and blocked NMDA-elicited ACh release. Taken together, the present results strongly suggest that a population of NMDA receptors exists on cholinergic interneurons within the striatum, and it directly regulates ACh release.