Ethanol reduces motoneuronal excitability and increases presynaptic inhibition of Ia afferents in the human spinal cord.
BACKGROUND
Already low blood concentrations of ethanol acutely impair motor control and coordination. In vitro experiments have given evidence that spinal effects of ethanol contribute to this by reducing spinal excitability and enhancing presynaptic inhibition of Ia fibers. In this study, we investigated the influence of 0.7 g per kilogram of bodyweight ethanol on motoneuronal excitability and presynaptic inhibition in humans.


METHODS
The study was performed in 10 volunteers. Spinal excitability was measured by the maximal H-reflex of the soleus muscle normalized to the maximal muscular response (Hmax/Mmax). Presynaptic inhibition was measured by changes in heteronymous Ia-facilitation of the soleus H-reflex, which is achieved by stimulation of the femoral nerve. A decrease in facilitation can be ascribed to an increase in presynaptic inhibition. Changes of these parameters under the influence of 0.7 g per kilogram of bodyweight ethanol were assessed in comparison to control measurements before ethanol application.


RESULTS
Both parameters, Hmax/Mmax and Heteronymous facilitation, were significantly reduced under the influence of ethanol (Wilcoxon signed-rank test with Bonferroni correction for each, p<0.01).


CONCLUSIONS
The increase in presynaptic inhibition by ethanol is probably caused by an increase in GABAA receptor-mediated Cl-conductance, which has been shown in spinal cord cultures. The role of presynaptic inhibition in movement is assumed to be there to control the afferent input of muscle spindles and tendon organs as a mechanism of specific input-selection. This study demonstrated that ethanol reduces spinal excitability and increases GABAergic presynaptic inhibition on Ia afferent fibers in humans.
von Dincklage
Falk
F
Charité, Universitätsmedizin Berlin, Department of Anesthesiology, Germany. falk.von-dincklage@charite.de
Benzke
Michael
M
Rehberg
Benno
B
Baars
Jan Harald
JH
D000328:Adult; D002492:Central Nervous System Depressants / Q000097:blood / Q000494:pharmacology*; D004558:Electric Stimulation / Q000379:methods; D004576:Electromyography / Q000379:methods; D000431:Ethanol / Q000097:blood / Q000494:pharmacology*; D005260:Female; D005267:Femoral Nerve / Q000187:drug effects / Q000502:physiology; D006801:Humans; D008297:Male; D009046:Motor Neurons / Q000187:drug effects*; D018482:Muscle, Skeletal / Q000187:drug effects / Q000502:physiology; D009433:Neural Inhibition / Q000187:drug effects*; D009475:Neurons, Afferent / Q000187:drug effects*; D010543:Peroneal Nerve / Q000187:drug effects / Q000502:physiology; D012023:Reflex, Monosynaptic / Q000187:drug effects; D013116:Spinal Cord / Q000166:cytology*; D018709:Statistics, Nonparametric