Biomedical subjects
Publications and source records attributed to I N Pleshchinskii.
The effect of endolumbar dimephosphon perfusion in dogs with spinal cord contusion was studied by means of transcranial magnetic stimulation and stimulation electromyography. Treatment with dimephosphon contributed to preservation of conduction function of the spinal cord and decrease in excitability of spinal motoneurons in the perifocal zone.
Levels of movement activity were used to identify two groups of rats: those with high- and low-activity levels. Blockade of dopamine receptors with haloperidol led to suppression of locomotor activity in both groups of rats; in common snails, haloperidol decreased the rate of locomotion. The excitability of spinal centers in rats decreased 5 min after single i.v. injections, with gradual recovery seen by 30 min. Chronic administration of haloperidol suppressed post-tetanic potentiation of the H response in the gastrocnemius muscle of spinal rats. Prolonged use of haloperidol induced significant hyperpolarization of the membrane potential of command neurons in common snails and increased the action potential generation threshold. Selective pharmacological exclusion of the brain dopamine system was found to lead to decreases in the excitability of defined neurons in snails and the spinal motor centers in rats, also producing impairments in locomotor responses in these animals.
Studies of the electrical characteristics of the command neurons of a defensive reflex showed that the membrane potential showed no significant changes in response to changes in the calcium concentration in the perfusing solution in either intact or trained snails. Increases in the calcium ion concentration in intact snails were accompanied by increases in the threshold potential, from 14 +/- 0.7 mV at 2.5 mM Ca2+ to 21.8 +/- 0.9 mV at 20 mM Ca2+. The threshold potential in trained snails decreased in response to both increases and decreases in calcium concentrations, from 16.8 +/- 0.6 mV (physiological saline containing 10 mM Ca2+) to 13.3 +/- 0.6 mV at 20 mM Ca2+ and 11.8 +/- 0.8 mV at 2.5 mM Ca2+. The critical depolarization level changed correspondingly: in intact snails, this decreased with increases in calcium concentration, while in trained snails it increased in response to both increases and decreases in the calcium concentration.
The effects of unilateral transection of the Achilles tendon (tenotomy) on the electromyographic characteristics of the gastrocnemius muscle on the contralateral side were studied in rats. Motor responses, reflex responses, and motor unit spike activity in the contralateral gastrocnemius muscle were studied in baseline conditions and on afferent stimulation before and 10 days after tenotomy. Changes in the nature of motor unit spike activity and responses to afferent stimulation were observed. The results obtained here demonstrate increases in the excitability of individual motoneurons in the contralateral motor center of the gastrocnemius muscle after exclusion of the symmetrical gastrocnemius muscle from the overall pattern of movement activity.
Constantly firing motor units of the short abductor muscles of the first finger in the human hand and the abdominal wall muscle in immobilized rats responded to afferent stimulation of the median and sciatic nerves respectively with changes in the nature of spike activity. In the first 250 msec of the post-stimulus period, the frequency of motor unit spike activity became unstable and peri-stimulus histograms were individually quite distinct. This was followed by relative stabilization of motor unit discharge frequencies, and the subsequently (750 msec) determined motor unit spike frequency depended on most cases on the background spike frequency.
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