| Abstract: | In experiments on spinal cats changes in the second negative postsynaptic component (N2) of the dorsal surface potential (DSP) of the spinal cord recorded in the region of segment L7 was used as the index of inhibition of segmental dorsal horn interneurons. Conditioning and testing stimuli were applied at increasing time intervals to the popliteal and superficial peroneal nerves respectively. Changes in the N2 component were compared with changes in the N1 component of the DSP, reflecting mainly activity of nonsegmental ascending dorsal horn interneurons. After an initial short facilitation a conditioning volley of pulses evokes prolonged (over 500 msec) inhibition of the N2 component, characterized by the presence of two maxima (on the average at the 16th and 80th milliseconds) which indicate that two systems with different latent periods play a role in this inhibition. In its shape and temporal characteristics the curve of inhibition of the N2 component corresponds to the two-component dorsal root potential (DRP) recorded in spinal animals in response to stimulation of flexor afferents (FRA) 8, 19]. Together with other features, this similarity is evidence of the presynaptic nature of this inhibition. Intravenous injection of hexobarbital has a stronger action on inhibition of the N2 component, leading to a marked increase in its depth and duration. Suggestions are made regarding the functional organization of systems responsible for presynaptic inhibition of segmental dorsal horn interneurons.Deceased.Dnepropetrovsk State University. Translated from Neirofiziolgiya, Vol. 4, No. 1, pp. 75–82, January–February, 1972. |
