The application of capsaicin to the rat TMJ region resulted in an inflammatory reaction illustrated by the expansion of the periarticular tissue and plasma extravasation as demonstrated by Evan’s blue dye staining in this area of interest. Since capsaicin binds to VR1 receptors located on primary sensory afferents innervating the rat TMJ region to produce edema and plasma extravasation, the findings in this study suggest that acute inflammation of the rat TMJ region encompasses a neurogenic component. In addition, sustained and reversible increase in ipsilateral masseter and digastric muscle activities were evoked with the deposition of capsaicin into the rat TMJ region.

Read the rest of this entry »

Among the 64 rats used in this experiment, only data obtained from 48 rats were deemed suitable for analysis. Twelve rats either responded to the injection of saline and the resultant increased EMG activity did not return to baseline levels prior to the injection of capsaicin/ve-hicle, or the application of the preload agent failed to induce a straight lateral movement of the edema measurement needle. In 2 rats, the application of 1% capsaicin to the bupivacaine pretreated TMJ region led to reflex jaw muscle activity, which indicated an unsuccessful nerve conduction blockade. Moreover, there was an absence of blue PE staining in the TMJ region of 2 other rats. Therefore, for the measurement of tissue expansion, each experimental group consisted of 8 rats each, and for the EMG recording of jaw muscle activity, groups 1 and 2 consisted of 6 rats, group 3 consisted of 10 rats, and groups 4-6 consisted of 8 rats each.

Read the rest of this entry »

The University of Toronto Animal Care Committee in accordance with the regulations of the Ontario Animal Research Act (Canada) approved the following protocol. Sixty-four male Sprague-Dawley rats weighing between 225 and 400 g each were prepared for the continuous measurement of one-dimensional tissue expansion, as previously described by Fiorentino et al and Wong et al, and for the acute recording of jaw muscle EMG activity as previously described by Cairns et al. Therefore, only a brief description of the methodology follows.

Read the rest of this entry »

The purpose of this study was to evaluate the effect of local anesthetic blockade of afferent innervation on the development of capsaicin-induced edema in the rat temporomandibular joint (TMJ) region and on reflex jaw muscle activity. Under halo-thane anesthesia, 64 male Sprague-Dawley rats were prepared for monitoring of edema development by lateral movement of a needle overlying the left TMJ region and for acute recording of electromyographic activity in ipsilateral digastric and mas-seter muscles. A double-barrel catheter was inserted into the TMJ region for delivery of saline or 0.5% bupivacaine from 1 needle, followed with the injection of 1% capsaicin, 0.1% capsaicin, or vehicle control from the other needle 5 minutes later. Application of capsaicin into the saline pretreated TMJ region led to dose-dependent edema development and reflex jaw muscle activity; however, only 1% capsaicin solution resulted in significant tissue expansion and muscle activity when compared with the vehicle control. Pretreatment of the rat TMJ region with bupivacaine failed to inhibit capsaicin-induced edema development, although successful blockade of nerve conduction was confirmed with the absence of reflex jaw muscle activity. Capsaicin-induced edema of the rat TMJ region developed independent of axonal conduction, suggesting neurogenic inflammation may arise regardless of functional nerve conduction.

Read the rest of this entry »