[Spinal cord electrical activity during focal depression of inhibitory processes]

Cord dorsum potentials, dorsal root potentials and field potentials were studied in rats with local depression of inhibitory processes in lumbar spinal segments produced by tetanus toxin. The study was carried out at a stage when excitation of a neuronal population with depressed inhibitory processes (the so-called "determinative dispatch station") evoked generalized excitation of spinal and bulbar motoneurons. In experiments with spinal animals it was shown that the stimulation of a cutaneous nerve on the affected side evokes DRP's P-waves and field potentials of greater amplitude and longer duration than those evoked on the opposite side or in healthy rats. The prolonged P-wave revealed several components which coinsided with prolonged ventral root discharges. This wave could be recorded from an enlarged spinal cord region. The maximal increased and prolonged negative field potentials corresponding in time to the enlarged P-wave were found in the ventral quadrant of the affected side. In this region "spontaneous" rhythmical negative slow waves were recorded. The mechanisms of spreading excitation from the site with depressed inhibitory processes and the localization of this site are discussed.