Pathological
chronic pain, which is frequently associated with prolonged tissue damage,
inflammation, tumour invasion, and
neurodegenerative diseases, gives rise to
hyperalgesia and
allodynia. We previously reported that intrathecal administration of
nociceptin/orphanin FQ (N/OFQ), an endogenous
ligand for the orphan
opioid receptor-like receptor, in the femtomole range induces touch-evoked
allodynia. N/OFQ has been implicated in multiple signalling pathways, such as inhibition of cAMP production and Ca(2+) channels, or activation of K(+) channels and
mitogen-activated protein kinase, although the signalling pathways of N/OFQ-induced
allodynia remain unclear. To address these issues, we developed an ex vivo
mitogen-activated protein kinase assay by using intact slices of mouse spinal cord. N/OFQ markedly increased the phosphorylation of
c-Jun N-terminal kinase (JNK) in the superficial dorsal horn of the spinal cord. The N/OFQ-stimulated JNK phosphorylation was significantly inhibited by
pertussis toxin, the
phospholipase C inhibitor
U73122, and the
inositol trisphosphate receptor antagonist
Xestospongin C. Intrathecal administration of the JNK inhibitor
SP600125 inhibited N/OFQ-evoked
allodynia. The N/OFQ-induced increase in JNK phosphorylation was observed in astrocytes that expressed
glial fibrillary acidic protein. N/OFQ also induced
monocyte chemoattractant protein-1 (MCP-1) release via the JNK pathway, and N/OFQ-induced JNK phosphorylation was observed in MCP-1-immunoreactive astrocytes. Intrathecal administration of the
MCP-1 receptor antagonist RS504393 inhibited N/OFQ-evoked
allodynia. These results suggest that, in the spinal dorsal horn, N/OFQ induces
allodynia through activation of JNK via the
phospholipase C-
inositol trisphosphate pathway, which is coupled to
pertussis toxin-sensitive
G-protein, and following the release of MCP-1 from astrocytes.