Motoneurone recurrent inhibition is enhanced by L-acetylcarnitine in humans.
Renshaw cells, which mediate the recurrent inhibition of spinal a-motoneurones, are activated by acetylcholine, both through motoneurone collaterals and the reticulo-spinal system. Since it is known that L-acetylcarnitine (L-AC) has central cholinergic effects, we tested in ten normal subjects and three spastic patients the ability of L-AC to induce changes in excitability of the Renshaw cells. These were activated by a conditioning monosynaptic reflex of the soleus muscle, evoked by electrical stimulation of the tibial nerve, and the resulting recurrent inhibition of the motoneurones was assessed by a subsequent monosynaptic reflex (H'). Recurrent inhibition was tested prior to, during and after an intravenous administration of a solution containing 2000 mg of L-AC. L-AC administration proved to be able to induce in all subjects a decrease in the H'-reflex. This effect ensued approximately 30 min after onset of L-AC administration, reached the peak after 40 min and vanished in about one hour. The extent of the decrease in H' varied among subjects, being on the average 22% of the control values. A relationship was found between duration of L-AC administration and time for reaching the maximal effect. These results show that L-AC is able to decrease a-motoneurone excitability by increasing Renshaw cell activity, both in normal and spastic subjects.
Schieppati
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M
Gritti
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I
Mazzocchio
R
R
Rossi
A
A
Mancia
M
M
D000108:Acetylcarnitine / Q000008:administration & dosage / Q000009:adverse effects / Q000494:pharmacology*; D000328:Adult; D002331:Carnitine / Q000031:analogs & derivatives*; D006181:H-Reflex / Q000187:drug effects; D006801:Humans; D007395:Interneurons / Q000187:drug effects / Q000502:physiology; D008875:Middle Aged; D009046:Motor Neurons / Q000187:drug effects / Q000502:physiology*; D009128:Muscle Spasticity / Q000503:physiopathology; D009433:Neural Inhibition / Q000187:drug effects*
D000108:Acetylcarnitine; D002331:Carnitine