Kinesthetic Mechanisms in the Trigeminal System

Capra, Norman

Abstract

Physiological studies suggest that sensory receptors located in the temporomandibular joint (TMJ), the muscles of mastication, and the periodontal ligament (PDL) are involved in the perception of jaw position and jaw movements (mandibular kinesthesia). The proposed studies will address several important anatomical and functional issues related to the organization of sensory receptors and the primary afferent neurons that innervate these structures. Using the techniques of anterograde and transganglionic transport of wheat germ agglutinin conjugated horseradish peroxidase (WGA-HRP), injections will be made into the spinal tract of the trigeminal nerve and into the trigeminal mesencephalic nucleus and tract of adult cats. Selected masticatory muscles and the TMJ capsule will be processed using HRP histochemistry to unequivocally identify, categorize, and map the types of receptors located in these structures. The location of the somata and the central terminations of primary afferent neurons that innervate receptors in the muscles of mastication and the PDL will be determined in the studies mentioned above and by a series of """"""""double label"""""""" experiments involving injections of retrogradely transported fluorescent dye and WGA-HRP in selected masticatory muscles and the PDL. Combined anatomical and physiological studies will be performed to identify neurons in the brainstem that receive primary afferent information from receptors in orofacial structures and that respond to experimentally imposed movements of the jaw. The receptive fields of movement sensitive neurons will be determined by electrical or natural stimulation in the periphery. Angular and rate sensitivity of identified neurons will be measured using an angular position transducer. Physiological methods will be used to determine whether the identified cells receive direct input from primary afferent neurons (e.g., latency measurements and following characteristics to high frequency electrical stimulation). Antidromic stimulation techniques will be used to determine whether the identified neurons project to the ventrobasal thalamus. After physiological characterization, WGA-HRP will be iontophoretically injected from the recording electrode. HRP histochemistry will allow the identification of brainstem nuclei that contain movement sensitive neurons and also central neurons that project to these regions. These central neurons may be important in the modulation of kinesthetic input. These data will further our overall goal of characterizing the anatomical and functional properties of neurons involved in mandibular kinesthesis.