The Journal of Neuroscience, November 1, 1999, 19(21):9201-9208
Neuronal Nitric Oxide Synthase mRNA Upregulation in Rat Sensory
Neurons after Spinal Nerve Ligation: Lack of a Role in Allodynia
Development
Z. David
Luo1,
S. R.
Chaplan1,
B. P.
Scott1,
D.
Cizkova1,
N. A.
Calcutt2, and
T. L.
Yaksh1
Departments of 1 Anesthesiology-0818 and
2 Pathology-0612, University of California, San Diego, La
Jolla, California 92093
Pharmacological evidence suggests a functional role for spinal
nitric oxide (NO) in the modulation of thermal and/or inflammatory hyperalgesia. To assess the role of NO in nerve injury-induced tactile
allodynia, we examined neuronal NO synthase (nNOS) expression in the
spinal cord and dorsal root ganglia (DRG) of rats with tactile
allodynia because of either tight ligation of the left fifth and sixth
lumbar spinal nerves or streptozotocin-induced diabetic neuropathy.
RNase protection assays indicated that nNOS mRNA (1) was
upregulated in DRG, but not spinal cord, neurons on the injury
side beginning 1 d after nerve ligation, (2) peaked (~10-fold
increase) at 2 d, and (3) remained elevated for at least 13 weeks.
A corresponding increase in DRG nNOS protein was also observed and
localized principally to small and occasionally medium-size sensory
neurons. In rats with diabetic neuropathy, there was no significant
change in DRG nNOS mRNA. However, similar increases in DRG nNOS mRNA
were observed in rats that did not develop allodynia after nerve
ligation and in rats fully recovered from allodynia 3 months after the
nerve ligation. Systemic treatment with a specific pharmacological
inhibitor of nNOS failed to prevent or reverse allodynia in
nerve-injured rats. Thus, regulation of nNOS may contribute to the
development of neuronal plasticity after specific types of peripheral
nerve injury. However, upregulation of nNOS is not responsible for the
development and/or maintenance of allodynia after nerve injury.
Key words:
neuronal nitric oxide synthase; nerve injury; spinal
cord; dorsal root ganglia; sensory neurons; mRNA regulation; diabetic
neuropathy; allodynia
Copyright © 1999 Society for Neuroscience 0270-6474/99/19219201-08$05.00/0