CARBACHOL-INDUCED PHOSPHOINOSITIDE METABOLISM IN SLICES OF RAT SUBSTANTIA-NIGRA PARS-RETICULATA

Carbachol produced an approximately 2-fold stimulation, with respect t o basal, of [H-3]inositol monophosphate ([H-3]IP1) accumulation in mic rodissected slices of rat substantia nigra pars reticulata (SNr), meas ured as a percentage of [H-3]inositol incorporation. The response to c arbachol was inhibited by 75+/-7% by 1 muM pirenzepine, consistent wit h a muscarinic M1 receptor-mediated response. Carbachol-induced [H-3]I P1 accumulation was not reduced by pretreatment of the SNr slices with NMDA, in contrast to the 85% inhibition observed in striatal slices. The results suggest that measurement of carbachol-induced phosphoinosi tide hydrolysis may be a feasible approach for studying muscarinic M1 receptor function in slices of SNr.