ACTIVITY IN MEDULLA ELICITED BY ELECTRICAL STIMULATION OF POSTERIOR FUNICULUS OF SPINAL CORD IN CAT

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Abstract
Electrical responses were recorded from the nucleus gracilis and cuneatus and from the medial lemniscus in 37 cats by means of the cathode-ray oscilloscope. The responses were induced by stimulation of the posterior funiculus of the cord in the cervical region or the sciatic nerve. Unipolar and bipolar pickup electrodes were placed by means of a stereotactic instrument and their locations detd. later by his to logical examination. "Responses from the nuclei gracilis and cuneatus following stimulation of the posterior funiculus consisted of a direct conduction spike and a slow wave, the latter being increased in amplitude by strychnine. Responses were elicited by posterior funiculus stimulation from the ipsilateral medial lemniscus in the medulla. They were constant and consisted of a direct conduction spike and 3 secondary axon potentials. Responses from the contralateral lemniscus were larger and except for the absence of the 1st spike were similar to the ipsilateral response. A contralateral direct conduction spike was present in the medial lemniscus only when the posterior column nuclei were stimulated. Sciatic nerve stimulation resulted in a bilateral trans-synaptic response in the medial lemniscus 6 to 7 milliseconds after the stimulus. The evidence is in favor of the existence of uncrossed fibers from the posterior columns which enter the ipsilateral medial lemniscus. Various pathways through the posterior column nuclei as suggested by these expts. are discussed.