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.
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.
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