Cyclobenzaprine: Effect on segmental monosynaptic and tonic vibration reflexes in the cat

Cyclobenzaprine reduced segmental evoked monosynaptic potentials to a much greater degree in decerebrate as compared with spinal cats. Post-tetanic potentiated responses were also reduced, but to a lesser degree so that the PTP ratio tended to exhibit a dose-related increase, especially in decerebrate preparations. Tonic vibration reflex responses were evaluated in decerebrate and decerbrate-decerebellate cats. In both preparations, reflex contractions elicited by various frequencies of longitudinal muscle vibration appeared equally sensitive to the action of cyclobenzaprine. Consequently, the slope of the line for change in muscle tension, per Hz increase in frequency of vibration in these preparations, exhibited a similar dose-related reduction after cyclobenzaprine. Reflex contractions elicited by vibration amplitudes ranging from 10 to 100μ peak-to-peak were also equally sensitive to drug action. These findings therefore support the concept that the predominant muscle relaxant action of cyclobenzaprine is at the supraspinal level reducing both γ- and α-motoneurone efferent activity. This action does not appear to involve presynaptic mechanisms. It is further suggested that cyclobenzaprine exerts its pharmacologic action upon reticulospinal rather than on vestibulospinal pathways.