Abstract
Those neurons in the sensorimotor cortex of cats which fired orthodromic discharges in response to stimulation of the peduncular pyramidal tract showed a similar excitability to microiontophoretically applied acetylcholine as did other neurons not giving such a response. Atropine and scopolamine antagonized this acetylcholine effect, but neither of these muscarinic cholinolytics nor the nicotinic acetylcholine antagonist, d-tubocurarine, blocked the orthodromic responses to pyramidal stimulation even though the former agents blocked the excitatory responses to stimulation of the mesencephalic reticular formation in some acetylcholine-excited neurons. A depressant effect of acetylcholine was uncommon and unrelated to the depression commonly seen after the pyramidal stimulus. These results suggest that acetylcholine is not a synaptic transmitter of the orthodromic response to pyramidal stimulation, presumably mediated through recurrent collaterals, but that acetylcholine may transmit the excitation of some cortical neurons by reticular stimulation.
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