ACETYLCHOLINE AND SOMATICALLY EVOKED INHIBITION ON PERIGENICULATE NEURONES IN THE CAT

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Abstract
1 Perigenicuiate neurones in cats were found to be inhibited by iontophoretically applied acetylcholine (ACh) and some of them by somatic sensory stimulation under certain experimental conditions. 2 Under chloralose anaesthesia, perigenicuiate neurones could be divided into two groups with regard to their spontaneous activity, sensitivity to glutamate and reaction to sensory inputs. Somatic sensory stimulation clearly inhibited the glutamate discharges of those perigenicuiate neurones which were characterized by a high sensitivity to glutamate and the absence of spontaneous activity. ACh had no clear inhibitory effect. 3 Under fluothane and urethane anaesthesia, no somatic sensory influence was noticed but ACh depressed almost all perigenicuiate neurones. 4 In an unanaesthetized midpontine pretrigeminal preparation, the inhibitory effect of ACh was confirmed. 5 No conditions were found under which the inhibitory influences of ACh and those of somatic sensory stimulation could be observed simultaneously on the same neurone. Therefore, it could not be established whether ACh mediates the somatic sensory influences on perigenicuiate cells.