Extrapyramidal descending influences on neurons of the spinal cord in a superreflexia state |
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Authors: | E A Makii A G Rodinskii |
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Institution: | (1) Dnepropetrovsk State Medical Academy, Ministry of Public Health of Ukraine, Ukraine |
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Abstract: | The spinal superreflexia state was modeled in experiments on rats using preliminary transection of the spinal cord and injection
(in the course of the acute experiment) of 4-aminopyridine. An extremely high (reaching 15–20 mV) amplitude of monosynaptic
reflex discharges (MRs) evoked by stimulation of the dorsal root and recorded from the ventral root (VR) L
4 and the presence of an additional component in the above discharges were phenomena indicative of the development of the above
state. Under such conditions, the amplitudes of the discharges evoked in the VR by electrical stimulation of the round window
of the labyrinth (vestibular stimulation) and of the discharges elicited by stimulation of the motor cortex under conditions
of bilateral transection of the pyramids increased several times. Thresholds of the VR responses to vestibular and cortical
stimulations demonstrated an about threefold drop; latencies of the mass responses and responses of single spinal moto-and
interneurons decreased about twofold, on average. The pattern of vestibular conditioning effects on the VR MRs changed: in
intact animals vestibular stimulation induced inhibition of the VR MRs, while in animals with superreflexia such stimulation
led to facilitation of the MRs. Cortical stimulation under conditions of pyramidotomy in both intact animals and animals with
superreflexia resulted in facilitation of the VR MRs of a nearly the same intensity. The levels of convergence of the segmental
and supraspinal effects on interneurons and motoneurons of the rat spinal cord dramatically increased under superreflexia
conditions. The possible mechanisms of augmentation of the descending influences on spinal neuronal systems under the above
conditions are discussed.
Neirofiziologiya/Neurophysiology, Vol. 38, No. 2, pp. 140–149, March–April, 2006. |
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Keywords: | spinal superreflexia corticofugal extrapyramidal and vestibular influences monosynaptic reflex discharges interneurons motoneurons convergence |
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