Cholinergic mechanisms in the rat somatosensory cerebral cortex.

1. The responses of identified cells in the rat cerebral cortex to cholinomimetic and anticholinergic substances has been investigated.2. Acetylcholine and muscarinic agonists have an excitatory action on 80% of pyramidal tract cells. This response is found especially on cells responding to specific thalamic stimulation and the burst of spikes evoked from this site can sometimes be blocked by the iontophoresis of atropine. This strongly suggests an excitatory transmitter function for acetylcholine in a specific thalamocortical pathway.3. Experiments on non-pyramidal tract cells have detected a muscarinic depression of some cells, and a nicotinic excitation of some cells above a depth of 600 mu in the cortex.4. It is suggested that the increased release of acetylcholine from the cortex produced by atropine administration may be due to an excess of muscarinic inhibitory over excitatory synapses in the cortex.