IDENTIFICATION OF RELAY CELLS AND INTERNEURONS IN THE CUNEATE NUCLEUS

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Abstract
147 cuneate neurons of the anesthetized cat have been recorded from extracellularly and investigated by the spike responses that are evoked by 3 different kinds of input: by afferent volleys in the ipsilateral forelimb; by stimulation of the medial lemniscus; by stimulation of the contralateral sen-sori-motor cortex. The selectivity and the characteristics of the responses to these inputs have been used in classifying the neurons. The 78 neurons antidromically invaded from the medial lemniscus and ortho-dromically activated by 1 or 2 afferent nerves were classified as the cuneo-thalamic relay (CTR) neurons. No CTR neuron so specified was activated by cortical stimulation. The remaining 69 neurons that were not antidromically invaded by volleys from the medial lemniscus were classified as interneurons. They were further subdivided according to whether they were excited from the cortex (56) and/or from peripheral nerves. The responses evoked both CTR neurons and interneurons by afferent volleys were depressed by an antecedent afferent volley in the same or a different afferent nerve or by descending volleys from the sensori-motor cortex.