NEUROGENIC INFLUENCES ON CONTRALATERAL RESPONSES DURING EXPERIMENTAL RAT MONOARTHRITIS

Many inflammatory conditions show topographically precise symmetrical responses. In this study we assessed vascular and cellular responses o f apparently normal knees following induction of monoarthritis on the opposite side. A strictly localised monoarthritis was induced in the r ight knee of experimental animals using intra-articular latex spheres. In both knee joints bradykinin-induced plasma extravasation was signi ficantly enhanced increasing from 0.52 +/- 0.07 mu g/ml Evans blue to 0.99 +/- 0.07 mu g/ml and 0.88 +/- 0.1 mu g/ml in the injected and uni njected, contralateral, knees respectively (P < 0.05). A bilateral inc rease in cellularity was also apparent with cell counts in the uninjec ted, and apparently normal, knee increasing from 512 +/- 42 cells/mm(2 ) to a maximum of 812 +/- 125 cells/mm(2) on day 10 (P < 0.05). Immuno histological analysis demonstrated that the infiltrating cells in both the ipsilateral and contralateral joints were predominantly macrophag es. Cell counts were not increased in the other peripheral joints. Lev els of the sensory neuropeptide substance P were significantly elevate d in both the ipsilateral and contralateral dorsal root ganglia and pr ior inhibition of small unmyelinated nerve activity inhibited the cell ular infiltrate on the contralateral side, suggesting that the effect was mediated, at least partially, by a specific neurogenic pathway. Th e data suggests the presence of a neurogenic mechanism able to induce a topographically precise response. This may serve to upregulate the c ellular defences of at-risk tissues following a potentially damaging s timulus at another site.