Effects of cyclobenzaprine on brainstem motor systems

Cyclobenzaprine, a new centrally acting skeletal muscle relaxant, was compared with diazepam as to their effects on several brainstem motor systems. Precollicular decerebrate cats were used to investigate intervestibular, vestibulo-spinal and reticulo-spinal effects. Both cyclobenzaprine and diazepam were without significant effect at less than high doses on the vestibular system as assessed by the monosynaptic response recorded in the median longitudinal fasciculus to vestibular nerve stimulation. The effects on brainstem reticular formation was assessed by the vestibulo-reticulo-spinal, spinal-bulbo-spinal and reticulo-spinal responses. In every case cyclobenzaprine had a strong blocking effect on reticular-produced inhibition of the spinal cord monosynaptic reflex. Diazepam was without effect or enhanced the inhibition. The evidence supports the notion that cyclobenzaprine depresses spinal cord interneurone activity by disfacilitation from a reticulo-spinal pathway.