Modulation of the tonic stretch reflex by monoamines. |
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Authors: | J W Commissiong E M Sedgwick |
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Affiliation: | School of Biochemical and Physiological Sciences, Medical and Biological Sciences Building, Basset Crescent East, Southampton S09 3TU, U.K. |
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Abstract: | The effects of L-DOPA and 5-HTP on the tonic stretch reflex (TSR) in the decerebrate rat were studied. L-DOPA facilitated the TSR in a dose-dependent manner. The facilitation of the TSR was blocked by pimozide. A sensitive electromygraphic (EMG) technique capable of recording single motor unit discharges was used. The EMG results suggest that gamma motoneuron sensitivity was increased to a greater degree than alpha motoneuron sensitivity during the facilitation by L-DOPA. The L-DOPA-induced facilitation persisted in animals partly depleted of 5-hydroxytryptamine (5-HT) by reserpine, p-chlorophenylalanine or 5,6-dihydroxytryptamine. 5-HTP inhibited the TSR in a dose-dependent manner. It is concluded that DA not 5-HT is the amine which normally mediates facilitation of the TSR after L-DOPA and that gamma motoneuron activation is more likely to be involved to a greater degree than alpha motoneuron activation in the neural mechanisms of the facilitation. |
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Keywords: | L-DOPA 5-HTP Pimozide Tonic stretch reflex Electromyography |
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