Intra-articular Injection of IL-1beta Facilitated Formalin-induced Temporomandibular Joint Pain in Freely Moving Rats

ABSTRACT

The present study was performed to investigate the effects of intra-articular injection of interleukin-1beta (IL-1beta) on the formalin-induced temporomandibular joint (TMJ) pain. Under anesthesia, a 30-gauge needle was introduced into the right TMJ region for injection of formalin. Microinjection of 50 microliter of 5% formalin significantly produced noxious scratching behavioral response, and the scratching behavior lasted for 40 min. Although the responses produced by formalin injection were divided into two phases, the response of 1st phase did not significantly differ from the scratching behavior response in the saline-treated group. We examined the effects of intra-articular injection of IL-1beta on the number of noxious behavioral responses produced by 50microliter of 5% formalin injection. Intra-articular injection of 100 pg and 1 ng of IL-1beta significantly increased the number of behavioral responses of the 2nd phase, while 10 pg of IL-1beta did not change the formalin-induced behavioral responses. To investigate whether IL-1 receptor was involved in the intra-articular administration of IL-1beta-induced hyperalgesic response, IL-1 receptor antagonist (IL- ra, 50 ng) was administrated together with IL-1beta injection. IL-1beta receptor antagonist blocked IL-1beta- induced hyperalgesic response in the TMJ formalin test. These results suggest that intra-articular injection of IL-1beta facilitated the transmission of nociceptive information in the TMJ area.