Stimulation of the Spinal Cord of Decerebrated Rat with Double Pulses

Analysis of responses on electrical stimulation is one ofthe experimental paradigms to study the excitability of the nervoussystem. In particular, the technique of recording muscle responsesevoked by electrical epidural stimulation (ES) of the spinal cord(SC) in humans and animals is widely used. In rats decerebratedat 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 pulseswere analyzed. The currents at which the amplitude of the sensorycomponent of the response for a single pulse and one of the pulsesof the pair was maximum were determined. At the minimum of thesecurrents, the ratio of the amplitudes of the sensory component ofthe response to the first and second pulses to the amplitude ofthe sensory component of the response to a single pulse was analyzed.For both muscles, a weakening of the response to both pulses ofthe pair was obtained with TS VL2 and VL4, while when stimulatingVL2, 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 ofthe response to the second pulse was obtained for both muscles.A similar facilitation was qualitatively observed for two othermuscles, mm. iliacus and vastus lateralis. Thus, the use ofdouble pulses during stimulation made it possible to identify thedependence of the response of SC neural networks on the method oftheir activation (TS or ES). The facilitation of the response tothe second pulse during ES is presumably explained by a decreasein presynaptic inhibition due to decerebration.