L-Arginine Potentiates Monosynaptic and Polysynaptic Spinal Reflexes

Abstract

Nitric oxide (NO) is long been known to play a major role in a wide range of physiological functions as a neural messenger and a neurotransmitter. The aim of this study was to investigate the effects of NO precursor L-arginine on monosynaptic and polysynaptic spinal reflexes in anaesthetized and spinalized cats. A polyethylene cannula was placed into the right carotid artery in order to monitor blood pressure and a blood-pressure-clamp was applied between 90-110 mmHg. After a dorsal laminectomy between L5 and S1, monosynaptic and polysynaptic spinal reflexes were evoked by electrical stimulation of gastrocnemius nerves. Following control recordings, administration of NO precursor, L-arginine in 500 μM, 1, 2, 5 mM (local) and 50,100, 200, 500 mg/kg (i.v.) doses significantly increased the monosynaptic and polysynaptic reflex amplitude in a dose dependent manner. L-arginine appears to be more effective on polysynaptic reflexes than on monosynaptic reflexes. D-arginine, an ineffective enantiomer of L-ariginine was also tested as a control substance against L-arginine and it has no effects on the monosynaptic and polysynaptic reflexes. These results suggest that L-arginine may play an excitatory role in modulation of spinal reflexes and this role may be mediated by NO in the cat spinal cord.