The development of
pain after peripheral nerve and tissue injury involves not only neuronal pathways but also immune cells and glia. Central sensitization is thought to be a mechanism for such persistent
pain, and
ATP involves in the process. We examined the contribution of glia to neuronal excitation in the juvenile rat spinal dorsal horn which is subjected to neuropathic and inflammatory
pain.
RESULTS: In rats subjected to
neuropathic pain, immunoreactivity for the microglial marker OX42 was markedly increased. In contrast, in rats subjected to inflammatory
pain, immunoreactivity for the astrocyte marker
glial fibrillary acidic protein was increased slightly. Optically-recorded neuronal excitation induced by single-pulse stimulation to the dorsal root was augmented in rats subjected to neuropathic and inflammatory
pain compared to control rats. The bath application of a glial inhibitor
minocycline and a
p38 mitogen-activated protein kinase inhibitor
SB203580 inhibited the neuronal excitation in rats subjected to
neuropathic pain. A specific P2X1,2,3,4 antagonist
TNP-ATP largely inhibited the neuronal excitation only in rats subjected to
neuropathic pain rats. In contrast, an astroglial toxin L-alpha-aminoadipate, a gap junction blocker
carbenoxolone and
c-Jun N-terminal kinase inhibitor
SP600125 inhibited the neuronal excitation only in rats subjected to inflammatory
pain. A greater number of cells in spinal cord slices from rats subjected to
neuropathic pain showed Ca2+ signaling in response to puff application of
ATP. This Ca2+ signaling was inhibited by
minocycline and
TNP-ATP.
CONCLUSIONS: