Discharge behaviour of feline gamma-motoneurones following induction of an artificial myositis.
The study was undertaken to test the widely held hypothesis that a painful lesion of the skeleto-motor system leads to an increase in the neuromuscular component of muscle tone by activating gamma-motoneurones in the affected region. In chloralose-anaesthetized cats, artificial myositis was induced in the lateral gastrocnemius-soleus (LGS) muscle and several hours later the impulse activity was recorded from single gamma-motoaxons supplying the medial gastrocnemius (MG) muscle. Under the conditions of the study, the majority of the fusimotor neurones had a resting activity and could be readily excited by natural stimuli. In contrast to the assumptions of the working hypothesis, the gamma-motoneurones in the myositis animals were not activated but showed a strong inhibition; both resting activity and excitability by electrical and natural stimuli were decreased. Additional recordings from fusimotor neurones of a flexor muscle (tibialis anterior, TA) demonstrated that in the preparation used, the behaviour of the flexor gamma-motoneurones was different from extensor ones in that the former usually had no resting activity and did not respond to natural stimuli. The only discernible effect of a myositis of the LGS muscle on the TA gamma-motoneurones was a decrease in their electrical reflex threshold. The results of the study do not support the assumption that a painful muscle lesion is followed by an activation of the gamma-loop that leads to an increase in muscle tone. Instead, the data may offer an explanation for the weakness and--in chronic cases--the reflex atrophy of lesioned muscles.
Mense
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S
Institut für Anatomie und Zellbiologie, Universität Heidelberg, D-6900 HeidelbergF.R.G.
Skeppar
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D000161:Acoustic Stimulation; D000818:Animals; D001794:Blood Pressure / Q000502:physiology; D001831:Body Temperature / Q000502:physiology; D001920:Bradykinin / Q000494:pharmacology; D002245:Carbon Dioxide / Q000378:metabolism; D002351:Carrageenan / Q000633:toxicity; D002415:Cats; D004558:Electric Stimulation; D005260:Female; D006982:Hypertonic Solutions / Q000494:pharmacology; D008297:Male; D009047:Motor Neurons, Gamma / Q000502:physiology*; D009133:Muscular Atrophy / Q000503:physiopathology; D009220:Myositis / Q000139:chemically induced / Q000503:physiopathology*; D009431:Neural Conduction / Q000187:drug effects / Q000502:physiology; D011189:Potassium Chloride / Q000494:pharmacology; D051381:Rats; D012018:Reflex / Q000502:physiology; D013268:Stimulation, Chemical
D006982:Hypertonic Solutions; D002245:Carbon Dioxide; D011189:Potassium Chloride; D002351:Carrageenan; D001920:Bradykinin