BLOCKADE OF NITRIC-OXIDE SYNTHASE DIFFERENTIALLY INFLUENCES BACKGROUND ACTIVITY AND ELECTRICAL EXCITABILITY IN RAT DORSAL HORN NEURONS

A previous study has shown that inflammation of the gastrocnemius-soleus muscle in rats leads to an increase in excitability of dorsal horn neurones particularly in the spinal segment L3. Here, we have blocked the nitric oxide synthase (NOS) in L3 by spinal cord superfusion with N-G-monomethyl-L-arginine (L-NMMA) to find out if this effect is due to a release of nitric oxide (NO). L-NMMA had no influence on the excitability of L3 neurones but caused a marked increase in background activity. The L-NMMA effect on background activity was also present in rats with intact muscle. The data show that the myositis-induced increase in spinal excitability is not mediated by NO. The background activity, however, appears to be strongly dependent on NO production.