Lysophosphatidic acid as the initiator of neuropathic pain.

The injury-induced intense stimulation of spinal cord neurons causes lysophosphatidic acid (LPA) biosynthesis. LPA(1) receptor activation causes demyelination and sprouting of dorsal root fibers, leading to an induction of synaptic reorganization underlying allodynia, in which innocuous (tactile) stimuli cause intense pain. The LPA(1) signal also initiates the up-regulation of Ca(v)α2δ1 in dorsal root ganglion and PKCγ in the dorsal horn, underlying mechanisms for characteristic neuropathic hyperalgesia in myelinated sensory (A-type) fibers. On the other hand, the LPA(3) receptor mediates microglia activation at the early stage after nerve injury and LPA-induced LPA biosynthesis. Thus, both the LPA(1) and LPA(3) receptors play key roles in the initiation step using a feed-forward system for neuropathic pain.