Temporomandibular joint innervation in rats: a horseradish peroxidase study

In the present study, we have used the horseradish peroxidase (HRP) retrograde transport technique to map the trigeminal primary afferent and motor neurons that innervate the temporomandibular joint (TMJ) and the lateral pterygoid muscle (LPM). One to 3.0 microL of 4% wheatgerm agglutinin conjugated horseradish peroxidase (HRP-WGA) solution was introduced unilaterally into the joint cavity of twelve Sprague-Dawley rats. Injections were made from the above, following trephining of the zygomatic arch with a dental bur. Seventy-two hours after surgery, the animals were sacrificed via perfusion-fixation through the left ventricle. The TMJ, both trigeminal ganglia and brain stem were removed, sectioned serially at 50 microns, and reacted according to the tetramethyl benzidine (TMB) technique of Mesulam. Tissues were then examined at the light microscopic level. The injection site showed that the HRP-WGA filled the upper chamber of the TMJ cavity and extended anteriorly to include the LPM. HRP injected into the joint cavity was transported retrogradely to the ipsilateral trigeminal ganglion, where numerous HRP labeled neurons were found. The greatest number of cells were localized in the dorsolateral posterior portion of the ganglion. In the brain stem, numerous labeled cells representing the motor innervation of the LPM were found in a crescent-shaped array on the ventral side of the trigeminal motor nucleus. No labeled cells were found in the mesencephalic nucleus. The results show substantial trigeminal sensory innervation of the TMJ and LPM with no central projection to the mesencephalic nucleus.