FUNDAMENTAL ELECTROPHYSIOLOGIC INVESTIGATION OF SPINAL-CORD - REFRACTORY PERIOD OF FELINE CONDUCTIVE SPINAL-CORD EVOKED-POTENTIAL

Refractory periods and recovery curves have been used to investigate t he physiologic importance and disturbance of peripheral nerves, but th e refractory periods of the central nervous system (CNS) have seldom b een investigated. We estimated the refractory periods and the recovery curves of the ascending and descending conductive spinal cord evoked potentials (SCEP) in cats. The absolute refractory period of the first and second potentials of both the ascending and descending SCEP was s imilar to 0.4-0.5 ms. The amplitudes of the first potentials of the as cending and descending SCEP elicited by test stimuli exhibited signifi cant differences, but their latencies did not differ significantly exc ept at the interstimulus interval (ISI) of 1.5 ms, which implies that the same type of fibers was stimulated in the first potentials of the ascending and descending SCEP. The second potential of the descending SCEP elicited by test stimulus showed >100% amplitude and a maximal re covery of 200% when the ISI was 3.0 ms. The third potential was produc ed in the test response more easily when a lower vertebral level (LA) was used as the recording site and the ISI was between 1.0 and 4.0 ms. We consider these phenomena to be the result of elimination of the sy naptic inhibitory influence by the conditioning stimulus of the paired stimuli for the descending SCEP.