Nerve injury induces a rapid efflux of nitric oxide (NO) detected with a novel NO microsensor

An early step in repair of the leech CNS is the appearance of endothelial n itric oxide synthase (eNOS) immunoreactivity and NOS activity, but coincide nt generation of NO at the lesion after injury has not been shown. This is important because NO can regulate microglial cell motility and axon growth. Indirect measurement of NO with the standard citrulline assay demonstrated that NO was generated within 30 min after nerve cord injury. A polarograph ic NO-selective self-referencing microelectrode that measures NO flux nonin vasively was developed to obtain higher spatial and temporal resolution. Wi th this probe, it was possible to demonstrate that immediately after the le ech CNS was injured, NO left the lesion with a mean peak efflux of 803 +/- 99 fmol NO cm(-2) sec(-1). NO efflux exponentially declined to a constant v alue, as described through the equation f(t) = y(o) + ae-t/tau, with tau = 117 +/- 30 sec. The constant y(o) = 15.8 +/- 4.5 fmol cm(-2) represents a s ustained efflux of NO. Approximately 200 pmol NO cm(-2) is produced at the lesion (n = 8). Thus, injury activates eNOS already present in the CNS and precedes the accumulation of microglia at the lesion, consistent with the h ypothesis that NO acts to stop the migrating microglia at the lesion site.