Restoration of Dorsal Root Potential by Strychnine after Abolition by Partial Sectioning of Spinal Cord

Abstract

According to the interpretation of Barron and Matthews 1 the primary site of origin of the spinal cord potential as led electrotonically from the dorsal root is in the dorsal root terminations. Bonnet and Bremer 2 and Eccles, 3 however, think that the dorsal root potential more probably originates in the internuncial neurones. That internuncial neurones can be the origin of the dorsal root potential can be simply demonstrated with the aid of strychnine in the following type of experiment (Fig. 1).

Toads were used. The spinal cord with its roots was exposed and the brain severed from the cord just below the medulla under ether anesthesia, care being taken to preserve the blood supply of the cord. Between the discontinuance of the ether and the beginning of the observations there was an interval of at least 40 min. Curare was given to eliminate movements of the animal. The stimulus was applied on the 9th dorsal root while the leading electrodes were on the ipsilateral 3rd root. With the toads used the points of entrance of these two roots into the cord were usually 7-8 mm apart. After ascertaining the presence of the potential and its size, a partial cut of the spinal cord was made midway between the two roots. The cut was sometimes a transverse dorsal one, of a depth corresponding roughly to about 1/4 of the thickness of the spinal cord, calculated to sever the fiber tracts in both dorsal columns; sometimes it was limited to the ipsilateral dorsal half of the cord, severing the dorsal column on one side only. Either procedure invariably abolished the potential. A 1/20,000-1/10,000 solution of strychnine nitrate was then irrigated repeatedly on the spinal cord. Within about 10 min. the stimulation of the 9th root was found again to produce large potential in the 3rd root.