Two Methods of Modeling of Spinal Superreflexia in Rats

Abstract

We studied the relations between conditions of induction and quantitative characteristics of abnormally amplified monosynaptic reflex discharges (MSD) in ventral roots (VR) observed in two experimental situations: (i) 5 days after simultaneously performed denervation (transection of the sciatic nerve) and spinalization at the L 1 level, and (ii) 5 days after preliminary denervation and with systemic injection of 4-aminopyridine (4-AP) in the course of the acute experiment. In both situations, the amplitude of the MSD conducted via the VR was close to the threshold of excitation of fibers in this root or even exceeded this value (a superreflexia phenomenon). Under both (i) and (ii) conditions, we observed generation of the second component of MSD in the VR, which was probably related to transition of excitation from excited to "silent" fibers in the VR. The latter of the above variants of induction superreflexia (5 days after denervation and with the effect of 4-AP in the acute experiment) is preferred because there is practically no death of the experimental animals in the course of the chronic experiment, there are no negative post-spinalization changes in the spinal cord, and the possibility of supraspinal activation of motoneurons is preserved.

Extrapyramidal descending influences on neurons of the spinal cord in a superreflexia state

“…The second component of the VR MR observed under superreflexia conditions is a derivative of the first component, which is dramatically intensified (probably, the second component of the discharge results from ephaptic excitation of the fibers in the VR [1][2][3]). Thus, the nature of inhibition of this component (Fig.…”

“…This is quite natural because the maximum absolute amplitudes of the responses recorded from the VR at vestibular and cortical stimulations were in these cases about 3 and 2 mV. No doubt, such amplitudes are insufficient to initiate effective electrical interaction between excited and "silent" fibers in the VR (we would like to repeat that an amplitude of response providing such interaction should be about 15 to 20 mV) [1][2][3].…”

“…This state was formed according to the earlier described technique [3], by preliminary denervation of the hindlimb (transection of the n. ishiadicus) and systemic introduction of 4-aminopyridine in the course of the acute experiment; the dose of 4-AP was selected in such a way that it still did not initiate intensive constant discharges of spinal neurons (1.5 mg/kg). A severalfold increase in the amplitude of monosynaptic reflex discharges (MRs) in the VR L 4 (which in many cases reached 16 to 20 mV), the arrival of an additional component in the VR MRs (related to direct electrical interaction between fibers in the VR), and an increase in the MR duration served as the indices of development of the state of spinal superreflexia.…”

“…Unfortunately, in this situation it was impossible to study supraspinal effects on the segmental reflex arcs because preliminary chordotomia was one of the factors inducing the above state. In the present study, we used a new model of spinal superreflexia where this state is formed with no injury of the spinal cord [3]. This technique allows us to study both segmental and descending influences on neuronal systems of the spinal cord that are in the state of exclusively increased excitability.…”

“…Responses were evoked by vestibular stimulation and cortical stimulations (A and B, respectively) in intact animals (1), in rats after preliminary (5 days) isolated transection of the sciatic nerve(2) and after systemic injection of 1.5 mg/kg aminopyridine(3).…”