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Modulation of the tonic stretch reflex by monoamines
European Journal of Pharmacology
|July 15, 1979
Summary
L-DOPA enhances the tonic stretch reflex (TSR) in rats, primarily by increasing gamma motoneuron sensitivity. This effect is mediated by dopamine, not serotonin, and is blocked by pimozide.
Area of Science:
- Neuroscience
- Motor Control
- Pharmacology
Background:
- The tonic stretch reflex (TSR) is crucial for maintaining posture and muscle tone.
- Understanding the neurochemical modulation of the TSR is key to deciphering motor control mechanisms.
Purpose of the Study:
- To investigate the effects of L-DOPA and 5-hydroxytryptophan (5-HTP) on the TSR in decerebrate rats.
- To elucidate the roles of dopamine (DA) and serotonin (5-HT) in modulating the TSR.
Main Methods:
- Electromyography (EMG) was used to record single motor unit discharges in decerebrate rats.
- Dose-dependent administration of L-DOPA and 5-HTP.
- Pharmacological blockade with pimozide and depletion of 5-HT.
Main Results:
- L-DOPA dose-dependently facilitated the TSR, an effect blocked by pimozide.
- EMG data indicated increased gamma motoneuron sensitivity relative to alpha motoneuron sensitivity during L-DOPA facilitation.
- 5-HTP inhibited the TSR dose-dependently.
- L-DOPA's facilitation persisted even after 5-HT depletion.
Conclusions:
- Dopamine, not serotonin, mediates L-DOPA's facilitation of the TSR.
- Gamma motoneuron activation plays a more significant role than alpha motoneuron activation in L-DOPA-induced TSR facilitation.