The Journal of Neurophysiology Vol. 88 No. 1 July 2002, pp. 256-264
Copyright ©2002 by the American Physiological Society

Central Sensitization of Nociceptive Neurons in Trigeminal Subnucleus Oralis Depends on Integrity of Subnucleus Caudalis

 ¹Faculty of Dentistry, University of Toronto, Ontario M5G 1G6; and  ²Department of Physiology, Faculty of Medicine, University of Toronto, Ontario M5S 1A8, Canada

Chiang, Chen Yu, Bo Hu, James W. Hu, Jonathan O. Dostrovsky, and Barry J. Sessle. Central Sensitization of Nociceptive Neurons in Trigeminal Subnucleus Oralis Depends on Integrity of Subnucleus Caudalis. J. Neurophysiol. 88: 256-264, 2002. Our recent studies have shown that application to the tooth pulp of the inflammatory irritant mustard oil (MO) produces a prolonged (>40 min) "central sensitization" reflected in neuroplastic changes in the mechanoreceptive field (RF) and response properties of nociceptive brain stem neurons in subnuclei oralis (Vo) and caudalis (Vc) of the trigeminal spinal tract nucleus. In view of the previously demonstrated ascending modulatory influence of Vc on Vo, our aim was to determine whether the Vo neuroplastic changes induced by MO application to the tooth pulp depend on an ascending influence from Vc. In chloralose/urethan-anesthetized rats, MO application to the pulp produced significant increases in Vo nociceptive neuronal orofacial RF size and responses to mechanical noxious stimuli that lasted as long as 40-60 min. These changes were not affected by vehicle (saline) microinjected into Vc at 20 min after MO application, but 0.3 µl of a 5 mM CoCl₂ solution microinjected into the ipsilateral Vc produced a reversible blockade of the MO-induced Vo neuroplastic changes. A similar volume and concentration of CoCl₂ solution injected into subnucleus interpolaris of the trigeminal spinal tract nucleus did not affect the MO-induced neuroplastic changes in Vo. These findings indicate that inflammatory pulp-induced central sensitization in Vo is dependent on the functional integrity of Vc.