Burstein and collaborators55 found that sensory neurons in the rat posterior thalamus that were activated and sensitized by chemical stimulation of the cranial dura exhibited long-lasting hyperexcitability
to innocuous (brush, pressure) and noxious (pinch, heat) stimulation of the paws. Innocuous, extracephalic skin stimuli that did this website not produce neuronal firing at baseline (such as brush) became as effective as noxious stimuli (such as pinch) in eliciting large bouts of neuronal firing after sensitization was established. In migraine patients, functional MRI with BOLD analysis showed that brush and heat stimulation at the skin of the dorsum of the hand produced larger BOLD responses in the posterior thalamus of subjects undergoing a migraine attack with extracephalic allodynia than the corresponding responses registered when the same patients that were free of migraine and allodynia. The authors suggested that the spreading of multimodal allodynia and hyperalgesia beyond the locus of migraine headache is mediated by sensitized thalamic neurons that process nociceptive information from the cranial meninges together with sensory information from the skin of
the scalp, face, body, and limbs. The transformation of episodic migraine into chronic, daily headache has been attributed frequently to the excessive use buy LEE011 of abortive medication. Patients with this type of chronic headache (medication-overuse headache, MOH) exhibit abnormal glucose metabolism in brain areas belonging to the “pain network.”56 Fluorodeoxyglucose (FDG) PET data were obtained by Fumal and colleagues57 in patients during an analgesic-overuse headache and 3 weeks after withdrawal of the overused medication. Before withdrawal, several areas of abnormal metabolic activity were detected in association with MOH (ie, hypometabolism
in the bilateral thalamus, orbitofrontal cortex, anterior cingulate cortex, insula/ventral striatum, and right inferior parietal lobule; and hypermetabolism in the cerebellar vermis). Interestingly, the cerebellum displays an increased Adenosine triphosphate blood flow during migraine ictus. In addition, altered serotonergic transmission, decreased grey matter volume, reduced activity, and increased functional connectivity with dorsal anterior cingulate cortex were evidenced in the orbitofrontal cortex of migraineurs.58 In MOH, glucose uptake in dysmetabolic areas, recognized as being involved in pain processing, recovered to almost normal levels after the medication was withdrawn. The metabolic activity of the orbitofrontal cortex, however, was further reduced after medication withdrawal, indicating a role for this structure in the predisposition to analgesic overuse. Interestingly, this area also has been implicated in drive and compulsive behavior, including drug dependence and gaming addiction.59 In addition, PET studies using 18F-FDG demonstrated increased metabolism in the brainstem of patients with chronic migraine.