Complement and clusterin in the spinal cord dorsal horn and gracile nucleus following sciatic nerve injury in the adult rat.

We provide evidence for activation of the complement cascade in the dorsal horn of the spinal cord and in the gracile nucleus in the brainstem following sciatic nerve transection in the adult rat. Immunocytochemical analyses showed immunoreactivity for endogenous immunoglobulin G as shown by immunostaining with F(ab')2 antibodies, as well as complement factors C1, C1q, C3, C3d and C9 in the appropriate central termination areas of the injured sciatic nerve. Results from double labelling immunocytochemistry showed a strong association between immunoglobulin and complement factors on the one hand and reactive microglia on the other. However, some complement immunoreactivity was also found in the neuropil, possibly representing secreted complement. In situ hybridization with an oligonucleotide probe showed a marked increase in C3 messenger RNA, indicating local synthesis of C3 protein. In parallel with activation of complement, there was an increased immunoreactivity for the putative complement inhibitor clusterin, which co-localized with glial fibrillary acidic protein-positive astrocytes. In situ hybridization showed an increased labelling of clusterin messenger RNA. These findings indicate that complement activation and up-regulation of complement inhibitors are prominent central responses to peripheral sensory nerve injury. These responses may therefore be important elements underlying so-called transganglionic degenerative changes in primary sensory axons and terminals.