Cyclobenzaprine: effect on tonic vibration reflexes in local tetanus cat preparations

Local tetanus was induced by the injection of toxin into the gastrocnemius-soleus muscle of cats. After 48 hr, longitudinal vibration of the muscle was used to elicit a reflex contraction (tonic vibration reflex, TVR). In other experiments, electrical stimulation of various regions of the central nervous system served to elicit contraction of the muscle alone or to facilitate a vibration (150 mu at 300 Hz)-induced tonic vibration reflex. In contrast with normal animals, tonic vibration reflex responses in local tetanus preparations of decerebrate cats were augmented after transection of the spinal cord at Cl. In decerebrate local tetanus preparations, a dose-related reduction of tonic vibration reflex responses, induced at all frequencies and amplitudes of muscle vibration, was observed after doses of 0.5 to 3.5 mg/kg (i.v.) of cyclobenzaprine. Muscle contractions induced by stimulation of the medial reticular formation and facilitation of tonic vibration reflex responses were more sensitive to the action of cyclobenzaprine than were similar responses activated through stimulation of Deiters' lateral vestibular nucleus. In spinal preparations, tonic vibration reflex responses were only moderately reduced after similar doses of cyclobenzaprine. Contractions induced by stimulation of the spinal cord (T6) and facilitated tonic vibration reflex responses were only moderately reduced, whereas the post-stimulus-induced facilitations were considerably attenuated. Thus, experiments in local tetanus preparations support further the concept that the major site of action of cyclobenzaprine is supraspinal, whereas its action upon spinal structures contributes to its overall skeletal muscle-relaxant activity.