Exclusively inhibitory action of iontophoretic acetylcholine on single neurones of feline thalamus

Abstract

IN most regions of the mammalian brain only a small percentage of the neurones located with multi-barrelled micro-pipettes are inhibited by iontophoretic acetylcholine (ACh). Indeed, the much more frequent occurrence of cells excited by rather small doses of acetylcholine (see ref. 7 for review), together with the finding that both the inhibitory and excitatory actions of ACh are often antagonised by the same pharmacological agents, has led to the suggestion that the inhibitory action of ACh is mediated indirectly through the excitation of neighbouring cholinoceptive interneurones whose inhibitory transmitter is a substance other than ACh^2,3. Several workers^4–8 have tried to overcome this difficulty by working in the most superficial layers of the cerebral cortex where a strong inhibitory action of ACh predominates and ACh excitation has seldom been reported. We wish to draw attention to the possibility that the nucleus reticularis of the cat thalamus may well prove to be an appropriate area in which to study the depressant action of ACh on central mammalian neurones since almost every cell encountered¹ proved to be inhibited by a short, low amplitude pulse of ACh.