J Orofac Pain
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Previous work suggests that hyperexcitability of central nociceptive neurons may play a role in the pain of temporomandibular disorders (TMD). The aim of this study was to test this theory by assessing differences, between myalgic TMD patients and pain-free controls, in temporal summation of mechanically evoked pain and aftersensations following repetitive noxious stimulation. ⋯ A generalized hyperexcitability of central nociceptive processing in this TMD patient group is indicated by their more pronounced temporal summation of pain and greater aftersensations following repetitive noxious digital stimulation versus controls. Such hyperexcitability may contribute to the pathophysiology of TMD pain.
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To investigate changes in calcitonin gene-related peptide (CGRP)-like immunoreactivity (CGRP-LI) in the rat masseter muscle and brain after the unilateral experimental induction of masseter myositis. ⋯ The results of this study demonstrate that CGRP may play an important role both peripherally and centrally in masseter muscle myositis in association with presumed nociceptive behavior.
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Peripheral nerve injury produces a hyperexcitability of primary afferents and neurons in the spinal cord that is considered important in the development of nerve injury-induced pain. The authors recently developed a nerve injury model in the trigeminal region of the rat to study the neuronal mechanism of neuropathic pain in the trigeminal system. The escape thresholds to mechanical stimulation applied to the whisker pad area were significantly lower in rats with an inferior alveolar nerve (IAN) transection than those evoked from the contralateral, sham-operated whisker pad. ⋯ The incidence of licking behavior in response to noxious radiant heat stimulation of the hind paw was lower in the aged rats than in younger adults, but paw withdrawal latency was shorter and the activities of spinal dorsal horn neurons were higher in the aged rats. Furthermore, the descending inhibitory systems were impaired in the aged rats. These observations suggest that the changes in neuronal activity in the aged rats likely corresponded to the changes observed in the rat model of peripheral nerve injury.
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Neuropathic pain in the orofacial region poses a difficult challenge to the treating physician. In some cases diagnosis is far from easy. ⋯ In addition, the discussion includes idiopathic trigeminal neuralgia (tic douloureux), a neuropathic pain syndrome that is nearly unique to the trigeminal distribution (very rarely, it has also been reported in the glossopharyngeal region). Brief summaries of major research problems and successes are also provided.