SUPPRESSION OF SOMATOSENSORY-EVOKED POTENTIALS BY NITRIC-OXIDE SYNTHASE INHIBITION IN RATS - METHODOLOGICAL DIFFERENCES

We have previously shown that topically applied N-G-nitro-L-arginine ( L-NNA), a nitric oxide synthase (NOS) inhibitor, suppressed both somat osensory evoked potentials (SEPs) and vascular responses during sciati c nerve stimulation in rats. Due to the normal tight coupling between cerebral blood flow and neuronal activity, we surmise that the vascula r response attenuation may be secondary to the SEP decrease. However, a recent study, in which SEPs were recorded with a 'non-contact' elect rode placed longitudinally across the cranial window without touching the cortex, did not find a SEP decrease following NOS inhibition. In t he present study, we compared SEPs recorded with 'contact' and 'non-co ntact' electrodes. Regardless of stimulation methods (sciatic nerve or hindpaw), an electrode in contact with the pial surface overlying the hindlimb somatosensory cortex recorded a steady SEP decline during I- NNA application. In contrast, a 'non-contact' electrode did not detect a significant SEP change in the presence of I-NNA. The present result s thus confirm the attenuation of SEPs by NOS inhibition. (C) 1998 Els evier Science Ireland Ltd.