The glutamatergic regulation of cortical and striatal cholinergic neurons was investigated by measuring ACh output from the parietal cortex and striata of freely moving rats after administration of the competitive NMDA-receptor antagonist 3-((RS)-2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid (CPP). It has been shown that intracerebroventricular administration of 5 nmol of CPP brings about a long lasting 100% increase in ACh output from the parietal cortex but does not affect ACh output from the striatum. Conversely, local perfusion of the striata with 50 microM CPP results in a 45% decrease in ACh output from the striatum but has no effect on parietal ACh output. The decrease in striatal ACh output induced by CPP is antagonized by concurrent perfusion with NMDA. In conclusion, glutamate may exert both inhibitory and excitatory modulatory effects on ACh output, through NMDA receptors, according to the neuronal circuitry existing in different brain regions.