Stimulation of the Spinal Cord of Decerebrated Rat with Double Pulses

Abstract

Analysis of responses on electrical stimulation is one of the experimental paradigms to study the excitability of the nervous system. In particular, the technique of recording muscle responses evoked by electrical epidural stimulation (ES) of the spinal cord (SC) in humans and animals is widely used. In rats decerebrated at the precollicular level, responses of mm. tibialis anterior (TA) and gastrocnemius medialis (GM) on ES of the L2, L4, L6 spinal segments and transvertebral stimulation (TS) of the VL2, VL4, VL6 vertebrae with single and double pulses were analyzed. The currents at which the amplitude of the sensory component of the response for a single pulse and one of the pulses of the pair was maximum were determined. At the minimum of these currents, the ratio of the amplitudes of the sensory component of the response to the first and second pulses to the amplitude of the sensory component of the response to a single pulse was analyzed. For both muscles, a weakening of the response to both pulses of the pair was obtained with TS VL2 and VL4, while when stimulating VL2, the TA response to the second pulse was lower than to the first. On the contrary, with ES of all segments of interest, a facilitation of the response to the second pulse was obtained for both muscles. A similar facilitation was qualitatively observed for two other muscles, mm. iliacus and vastus lateralis. Thus, the use of double pulses during stimulation made it possible to identify the dependence of the response of SC neural networks on the method of their activation (TS or ES). The facilitation of the response to the second pulse during ES is presumably explained by a decrease in presynaptic inhibition due to decerebration.