Compression neuropathy is one of the most common lesions of the peripheral nervous system. In our view, it is interesting to explore the dynamic changes of bioelectrical activity in monosynaptic reflex arcs of spinal cord because they determine the ability of nerve regeneration and are most sensitive to disturbances reverse afferentiation. In experiments on rats the activity of spinal cord motoneurons was investigated for intact rats and rats with experimental compression neuropathy during 1, 3, 5, 7, 10 days after sciatic nerve ligation.

The monosynaptic answers of ventral root (MA VR) was performed by using bipolar electrodes with the registration on personal computer and analog-to-digital converter. We analyzed the following parameters of MA VR: threshold, chronaxia, latent period, amplitude and duration of the MA VR. Analysis of excitability was carried out by applying stimuli of increasing intensity to sciatic nerve (from 1.1 threshold to 2 threshold). Phenomenon of refractory was investigated by applying paired stimuls at intervals from 2 to 20 ms.

The investigation of this dynamics can give probability about neurophysiological mechanisms of compression neuropathy complications.

We showed increasing spinal motoneurons excitability on the early period after sciatic nerve ligation. The threshold was decreased in the experimental group (by 10,38 % as compared to intact rats) on the 7th day after compression. Significant decrease of chronaxia MA VR by 22 % caused of deafferentation of spinal motor neurons and decrease number of inhibitory synapses on the motor neuron membrane. the growth of MA VR amplitude on 10th day of the experiment was noted.

In analyzing the dynamics of excitability using the electrophysiological method of spinal dorsal root stimulation by increasing intensity of stimulus (from 1,1 to 2 thresholds) it was discovered that on the 10th day after compression neuropathy there was significant increase in amplitude MA VR (n = 6, p < 0,01) at stimulation force 1,8–1,9 thresholds. Increase of MA VR amplitude at the application of paired stimuli, probably due to the violation of the afferent and braking phenomenon is a consequence of the extended motor neuron activity that occurs in neuropathies of various origins.

The investigaton of experimental compression neuropathy showed changes of the segmental structures of spinal cord (more in the motoneurons pool). We find a significant decrease of chronaxie MA VR by 22 % and this can be explained by deaferentation of spinal cord motor neurons and reduction in the number of brake synapses on motor neurons cell membrane. Revealed changes in amplitude MA VR also indicated the presence of hyperexcitability and possibly related to the biochemical effects of restructuring membrane of motor neurons in the background compression of the sciatic nerve. The described effects of changes in permeability of motor neurons membrane can be interesting for further studies since they can be used in pharmacology to study the stimulators and inhibitors of synthesis cell membrane channels.

Article Received 08.12.2016

Keywords: spinal cord motoneurons, compression neuropathy, hyperreflexia

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