Mechanisms of Spinal Cord Plasticity in the Trigeminal System

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Barry J. Sessle

Faculty of Dentistry, University of Toronto Toronto, Canada M5G 1G6

Recent research has identified nociceptive neurones in the V brainstem nucleus that have features indicating their crucial role in our ability to localize an acute orofacial pain and sense its intensity and duration. Many of the nociceptive neurones however receive convergent inputs from afferents supplying not only face or mouth, but also muscle, TMJ or even the neck. These features may be involved in mechanisms underlying the spread and referral of pain and the manifestation of chronic pain. Some of the neurones for example show neuroplastic changes as a result of inflammatory and deafferentation conditions affecting peripheral nerves. Injection into masticatory muscles of the inflammatory irritant mustard oil, a C-fibre stimulant, produces in V brainstem nociceptive neurones increases in their cutaneous receptive field and excitability that may be involved in the spread of pain and hyperalgesia that often result from trauma and inflammation to deep craniofacial tissues. Of further clinical significance are findings that V brainstem neurones can also be altered by therapeutic procedures or trauma associated with deafferentation: endodontic therapy produces pulp deafferentation resulting in expansion of neuronal receptive fields and increased incidence of spontaneous activity and abnormal responses to orofacial stimuli. Since a number of clinical problems manifesting chronic pain may be linked to deafferentation, such changes might be involved in the development of several chronic orofacial pain conditions.

The Canadian Chiropractic Association.

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By Barry J. Sessle

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