A rodent model of trigeminal neuralgia.

Trigeminal Neuralgia (Tic Douloureux) is a neuropathic pain syndrome caused by compression of the trigeminal nerve root and is characterized by severe paroxysms of pain in the face commonly triggered by light mechanical stimulation to the peri-oral area. Trigeminal neuralgia is very difficult to treat in part due to the lack of an suitable animal model for testing novel therapeutic approaches. This chapter describes a model of trigeminal neuralgia in which crystals of a superabsorbent polymer are placed next to the trigeminal nerve root of rats, producing ongoing mechanical compression of the nerve root. The chapter then describes means of behaviorally assessing the robust mechanical hypersensitivity consequent to the compression that can be used to determine the efficacy of potential therapies for this devastating condition.

Thermal nociceptive properties of trigeminal afferent neurons in rats.

BACKGROUND: Although nociceptive afferents innervating the body have been heavily studied form many years, much less attention has been paid to trigeminal afferent biology. In particular, very little is known concerning trigeminal nociceptor responses to heat, and almost nothing in the rat. This study uses a highly controlled and reproducible diode laser stimulator to investigate the activation of trigeminal afferents to noxious skin heating. RESULTS: The results of this experiment demonstrate that trigeminal thermonociceptors are distinct from themonociceptors innervating the limbs. Trigeminal nociceptors have considerably slower action potential conduction velocities and lower temperature thresholds than somatic afferent neurons. On the other hand, nociceptors innervating both tissue areas separate into those that respond to short pulse, high rate skin heating and those that respond to long pulse, low rate skin heating. CONCLUSIONS: This paper provides the first description in the literature of the in vivo properties of thermonociceptors in rats. These finding of two separate populations aligns with the separation between C and A-delta thermonociceptors innervating the paw, but have significant differences in terms of temperature threshold and average conduction velocities. An understanding of the temperature response properties of afferent neurons innervating the paw skin have been critical in many mechanistic discoveries, some leading to new pain therapies. A clear understanding of trigeminal nociceptors may be similarly useful in the investigation of trigeminal pain mechanisms and potential therapies.