Joint inflammation is reduced by dorsal rhizotomy and not by sympathectomy or spinal cord transection.

OBJECTIVES To investigate the role of primary afferents, sympathetic postganglionic efferents and descending systems on the central control of peripheral inflammation. METHODS Acute inflammation was induced by intra-articular injection of kaolin and carrageenan into the knee joint cavity of the rat. Before the induction of the arthritis, a unilateral dorsal rhizotomy, a chemical (phentolamine) and/or surgical sympathectomy, or a spinal transection was performed. Joint inflammation (joint circumference and thermographic readings) and behavioural signs were assessed. RESULTS Only arthritic animals with a dorsal rhizotomy showed a significant reduction of the inflammatory response compared with control arthritic animals. No significant differences in the inflammatory response occurred following sympathectomy or spinal transection. The animals who received sympathectomy showed similar behavioural manifestations to the arthritic animals. CONCLUSIONS The central terminals of primary afferents are important in the development of acute joint inflammation since dorsal rhizotomy attenuated the inflammatory response in the knee joint. The sympathetic nervous system is not involved in the acute inflammatory phase of this arthritis model. The central processes controlling acute inflammation involve a local spinal circuit since spinal cord transection at T9 has no effect on the inflammation.