EFFECTS OF A CARRAGEENAN-INDUCED INFLAMMATION IN RABBIT LUMBAR FACET JOINT CAPSULE AND ADJACENT TISSUES

The effects of experimentally induced inflammation of the lumbar facet joint capsule and adjacent tissues were investigated electrophysiolog ically and histologically. Type II carrageenan was injected into the r eceptive fields innervated by identified mechanosensitive afferent uni ts. The multi-unit spontaneous background discharge rate showed increa ses that consisted of two phases over a time period of 150 min: the fi rst phase (0-30 min) and the second phase (45-150 min). The time cours e of single units, identified as groups II, III and IV, and silent uni ts, was also investigated. The silent unit discharge rates displayed a gradual increase in the first 15 min and persisted beyond 75 min. His tological examination revealed inflammatory changes in carrageenan inj ected tissues. In contrast, in isotonic saline injected control experi ments there were no changes observed in the electrophysiological or hi stological studies. This study shows the effects of inflammation in ra bbit lumbar facet joint capsule and adjacent tissues. The electrophysi ological results show that inflammation of the facet joint and deep ba ck muscles causes (1) increases in multi-unit discharge rate, (2) sens itization to mechanical stimuli and (3) recruitment of previously sile nt units. Inflammatory changes were also demonstrated histologically.