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KMID : 0352519830200030017
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Korea Univercity Medical Journal
1983 Volume.20 No. 3 p.17 ~ p.27
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Reflex Effects of Chemically Activated GroupⅢ and GroupⅣ Muscle Afferents upon Gamma Motoneurons in Cat
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Abstract
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In decerebrated cats the effects of fine muscle afferents (groups I and IV) upon gamma motoneurons were studied. The efferent activity was extracellularly recorded from small filaments of ventral roots or from filaments of musole nerves. Fine muscle afferents were selectively activated by bradykinin, potassium and serotonin. For comparison, succinylcholine was administrated to activate muscle spindle afferents. Forty gastrocnemius-soleus gamma
~. motoneurons were recorded. Thirty-six (90%) of them had a tonic background discharge in the absence of intentional stimulation. A high susceptibility to an increased activity in fine muscle efferents was found for the gamma motoneurons. Practically all neurons both to homonymous extensor and antagonistic flexor muscles responded with an excitation to at least one of the algesic substances applied. Only two out of fifteen gamma motoneurons responded to succinylcholine. Thus indicating a weak convergence from muscle spindle aff erents. Control experiments demonstrated that the responses to bradykinin and potassium are entirely due to the nervous outflow from the gastrocnemius-soleus muscle. In contrast, serotonin influencing the gamma motoneurons has unknown additional sites of action. The results indicate that muscular group I and/or group IV units activated by algesic substances evoke excitatory effects upon gamma motoneurons.
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