MONOARTHRITIS IN THE RAT KNEE INDUCES BILATERAL AND TIME-DEPENDENT CHANGES IN SUBSTANCE-P AND CALCITONIN-GENE-RELATED PEPTIDE IMMUNOREACTIVITY IN THE SPINAL-CORD

Bilateral changes in the spinal cord and dorsal root ganglion content of the sensory peptides substance P and calcitonin gene-related peptid e have been previously reported in animal models of arthritis which af fect many joints within the body. The central nervous system has been implicated in the symmetry of joint involvement in human rheumatoid ar thritis. We aimed to determine whether unilateral inflammation of the knee joint can also induce bilateral changes in the spinal cord. We ha ve induced a monoarthritis in the knee joint of the rat and used quant itative immunocytochemistry to look at changes of these peptides in th e dorsal horn of the spinal cord and the dorsal root ganglia. Furtherm ore we have examined the responses during the acute (three days) and t he chronic (21 days) phases of the model. The data show that in the ac ute phase of the monoarthritis there is both an ipsilateral and contra lateral response which increases the immunoreactive substance P and ca lcitonin gene-related peptide in the L4 level of the dorsal horn of th e spinal cord. In the chronic phase of the monoarthritis, the contrala teral side of the dorsal horn returned to control values whilst the ip silateral side showed reduced amounts of immunoreactive substance P an d calcitonin gene-related peptide compared to controls. We propose tha t the acute response, at three days, to unilateral inflammation is app ropriate and has evolved to protect an organism against the original i nsult ipsilaterally, and the possibility of subsequent insult contrala terally. The loss of substance P and calcitonin gene-related peptide-c ontaining nerves in the chronic phase of the disease may reduce the re gulatory capacity of the system and contribute to the chronicity of th e disease.