EFFECTS OF CAPSAICIN IN TEMPOROMANDIBULAR-JOINT ARTHRITIS IN RATS

Temporomandibular joint (TMJ) arthritis was induced in female Lewis ra ts by unilateral injection of a suspension of heat-killed Mycobacteriu m butyricum in paraffin oil into the TMJ. Control rats received paraff in oil by the same route. Arthritic and control rats were pretreated e ither with capsaicin or denervation of the mandibular branch of the tr igeminal nerve. Tissues were collected for neuropeptide extraction and analysed by radioimmunoassay and reverse-phase high-performance liqui d chromatography. In all groups, the levels of substance P- (SP), calc itonin gene-related peptide- (CGRP) and neuropeptide Y- (NPY) like imm unoreactivity (LI) were higher in the trigeminal ganglia than in the T MJs. In control rats, capsaicin significantly lowered the levels of SP -LI in the trigeminal ganglia and TMJ, but not CGRP-LI and NPY-LI. In the arthritic rats, capsaicin pretreatment significantly lowered the S P-LI and CGRP-LI in the trigeminal ganglia and TMJ; but not the NPY-LI . In the trigeminal ganglia the unilateral denervation significantly l owered SP-LI in control rats, and in arthritic rats SP-LI and CGRP-LI. On the denervated side of the arthritic TMJ, NPY-LI, SP-LI and CGRP-L I were significantly lowered as compared to the arthritic control rats and to the contralateral side. In this rat model, pretreatment with c apsaicin and surgical denervation decreased the neuropeptide content i n the trigeminal ganglia and the TMJ. The results clearly demonstrate a close interaction between increased neuropeptide release from sensor y and sympathetic neurones after induction of arthritis in the rat. (C ) 1997 Elsevier Science Ltd. All rights reserved.