Our previous study showed that intrathecal (i.t.) injection of
platelet-activating factor (PAF) induced
tactile allodynia, suggesting that spinal PAF is a mediator of
neuropathic pain. The present study further examined the spinal molecules participating in PAF-induced
tactile allodynia in mice. I.t. injection of
L-arginine, NO donor (5-amino-3-morpholinyl-1,2,3-oxadiazolium (SIN-1) or 3,3-bis(aminoethyl)-1-hydroxy-2-oxo-1-triazene (NOC-18)) or cGMP analog (8-(4-chlorophenylthio)-
guanosine 3',5'-cyclic monophosphate; pCPT-cGMP) induced
tactile allodynia. PAF- and
glutamate- but not SIN-1- or pCPT-cGMP-induced
tactile allodynia was blocked by an
NO synthase inhibitor. NO scavengers and
guanylate cyclase inhibitors protected mice against the induction of
allodynia by PAF,
glutamate and SIN-1, but not by pCPT-cGMP.
cGMP-dependent protein kinase (PKG) inhibitors blocked the
allodynia induced by PAF,
glutamate, SIN-1 and pCPT-cGMP. To identify signalling molecules through which PKG induces
allodynia,
glycine receptor alpha3 (
GlyR alpha3) was knocked down by spinal transfection of
siRNA for
GlyR alpha3. A significant reduction of
GlyR alpha3 expression in the spinal superficial layers of mice treated with
GlyR alpha3 siRNA was confirmed by immunohistochemical and Western blotting analyses. Functional targeting of
GlyR alpha3 was suggested by the loss of PGE(2)-induced
thermal hyperalgesia and the enhancement of
allodynia induced by
bicuculline, a
GABA(A) receptor antagonist in mice after
GlyR alpha3 siRNA treatment. pCPT-cGMP, PAF,
glutamate and SIN-1 all failed to induce
allodynia after the knockdown of
GlyR alpha3. These results suggest that the
glutamate-NO-cGMP-PKG pathway in the spinal cord may be involved in the mechanism of PAF-induced
tactile allodynia, and
GlyR alpha3 could be a target molecule through which PKG induces
allodynia.