Effects of capsaicin in the motor nerve.
The injection of capsaicin into the lateral gastrocnemius (LG) muscle of the rat induced an immediate and sustained reduction in the A delta and C components of the compound action potential (CAP) of the LG motor nerve. Conversely, the drug did not immediately affect the CAP wave belonging to fast-conducting fibers or the motor responses to LG nerve stimulation. It seems that capsaicin only affects the group III and IV afferents of LG nerve. However, a week after the injection the capsaicin also altered the motor responses, as shown by the threshold enhancement and amplitude reduction of the muscle twitch and by the decrease of the A alpha-beta CAP components. This late motor impairment was attributed to a central depression following a reduction of capsaicin-sensitive neuron input into the CNS. However, this motor effect was transient since the LG nerve regained the preinjection excitability level in a week and the muscle twitch amplitude reached the control value in a month.
Pettorossi
V E
VE
Institute of Human Physiology, University of Perugia, Italy.
Bortolami
R
R
Della Torre
G
G
Brunetti
O
O
D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D002211:Capsaicin / Q000494:pharmacology*; D009046:Motor Neurons / Q000187:drug effects*; D009119:Muscle Contraction / Q000187:drug effects; D009132:Muscles / Q000294:innervation*; D009420:Nervous System / Q000187:drug effects; D009424:Nervous System Physiological Phenomena; D051381:Rats; D013997:Time Factors
D002211:Capsaicin