MUSCARINIC SUPPRESSION OF THE EVOKED N-WAVE BY OXOTREMORINE-M RECORDED IN THE GUINEA-PIG OLFACTORY CORTEX SLICE

The effect of the muscarinic agonist oxotremorine-M has been studied on the surface-negative field potential (N-wave) evoked by orthodromic stimulation of the lateral olfactory tract in slices of guinea-pig olfactory cortex. Bath-application of oxotremorine-M (5-80 μM) or carbachol (10-300 μM) produced a reversible depression of the N-wave amplitude without affecting the lateral olfactory tract compound action potential, Oxotremorine-M was ∼ 5 times more potent than carbachol in this respect, and the effects of both agonists were competitively blocked by telenzepine (5-100 nM), a selective M1-receptor antagonist. In contrast, methoctramine or AF-DX 116, two 'cardioselective' M2-receptor antagonists, had little or no blocking effect on the agonist responses, it is suggested that oxotremorine-M (like carbachol) inhibits the evoked field potential by activating presynaptic M1-type muscarinic receptors in the olfactory cortex slice. © 1990.