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The Journal of Neuroscience, January 1, 2001, 21(1):215-220

Nerve Injury Induces a Rapid Efflux of Nitric Oxide (NO) Detected with a Novel NO Microsensor

Shanta M. Kumar¹, D. Marshall Porterfield⁴, Kenneth J. Muller³, Peter J. S. Smith², and Christie L. Sahley¹

¹ Department of Biological Sciences, Purdue University, West Lafayette, Indiana 47907, ² BioCurrents Research Center, Marine Biological Laboratory, Woods Hole, Massachusetts 02543, ³ Department of Physiology and Biophysics and Neuroscience Program, University of Miami School of Medicine, Miami, Florida 33136, and ⁴ Department of Biological Sciences, University of Missouri at Rolla, Rolla, Missouri 65409

An early step in repair of the leech CNS is the appearance of endothelial nitric oxide synthase (eNOS) immunoreactivity and NOS activity, but coincident 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 polarographic NO-selective self-referencing microelectrode that measures NO flux noninvasively was developed to obtain higher spatial and temporal resolution. With this probe, it was possible to demonstrate that immediately after the leech CNS was injured, NO left the lesion with a mean peak efflux of 803 ± 99 fmol NO cm² sec¹. NO efflux exponentially declined to a constant value, as described through the equation f(t) = y_o + ae^t/, with  = 117 ± 30 sec. The constant y_o = 15.8 ± 4.5 fmol cm² represents a sustained efflux of NO. Approximately 200 pmol NO cm² 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 hypothesis that NO acts to stop the migrating microglia at the lesion site.

Key words: nitric oxide (NO); microglia; nerve injury; NO-selective microsensor; NO efflux; endothelial nitric oxide synthase (eNOS); leech CNS; regeneration; nerve repair

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Copyright © 2001 Society for Neuroscience  0270-6474/01/211215-06$05.00/0

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