Effects of cyclobenzaprine on spinal synaptic transmission

The effects of cyclobenzaprine on spinal synaptic transmission were studied in spinal unanesthetized cats. The drug, in cumulative doses up to 20 mg/kg, depressed monosynaptic reflexes evoked by stimulation at 0.2 Hz to a moderate degree. Polysynaptic reflexes were depressed to a similar extent. Monosynaptic reflexes evoked repeatedly at 5 and 10 Hz were depressed even after 5 mg/kg of cyclobenzaprine. Maximum potentiation of monosynaptic responses after tetanization was not affected. Neither direct postsynaptic nor recurrent inhibition was influenced by the drug. Presynaptic inhibition was slightly reduced. It is suggested that direct effects of cyclobenzaprine at the spinal level do not represent the primary site of action responsible for its antispastic activity.