Background : We designed this study to evaluate the anitinociceptive effect and
changes in amounts of substance P in the spinal cord after perineural application of
capsaicin to the injured nerve in rats in neuropathic pain.
Methods : Male Sprague-Dawley rats (200-250 g) were prepared with the tight
ligation of the left L5, 6 spinal nerves of with the sham operation. They were divided
into 3 groups according to the solution treated to the left sciatic nerve and pre-treated
condition, group I(capsaicin treatment after ligation ; n = 10), group Ⅱ(solvent treatment
after ligation ; n = 10), group Ⅲ(capsaicin treatment after sham operation; n = 10). The
withdrawal threshold to touch with von Frey filaments and the withdrawal time to
thermal stimulus by plantar tester were measured and percent maximum possible effects
(%MPE) were calculated, respectively, at 1, 2, 3 and 4 weeks after treatment. The area
and integrity optical density (IOP) of substance P stained immunohistochemically in the
lumbar dorsal horn were quantified with an image analyzer in group I.
Results : In the capsaicin-treated groups (I, Ⅲ), withdrawal time to thermal stimulus
was prolonged significantly during the 4 weeks as compared with baseline values before
treatment (p < 0.05), but withdrawal time to touch didn't change. The %MPE of
capsaicin to thermal stimulus in group I was significantly higher than that in group Ⅲ(p
< 0.05). In group Ⅱ, withdrawal responses to touch and thermal stimulus didn't change.
The area and IOP of substance P in the left lumbar dorsal horn at the 1st and 4th
week didn't change, compared with the baseline before capsaicin treatment, except for
the
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