A possible neural mechanism for photosensitivity in chronic pain. Issue 4 (April 2016)

• Record Type: Journal Article
• Authors: Martenson, Melissa E.; Halawa, Omar I.; Tonsfeldt, Karen J.; Maxwell, Charlene A.; Hammack, Nora; Mist, Scott D.; Pennesi, Mark E.; Bennett, Robert M.; Mauer, Kim M.; Jones, Kim D.; Heinricher, Mary M.
• Is Part Of: Pain. Volume 157:Issue 4(2016)
• Publication Date: 2016-04
• Subjects: Pain-modulation -- Descending control -- Rostral ventromedial medulla -- Multisensory hypersensitivity -- Fibromyalgia; Pain -- Periodicals; Douleur -- Périodiques; Anesthésie -- Périodiques; Pain; Electronic journals; Periodicals; Electronic journals; 616.0472
• DOI: 10.1097/j.pain.0000000000000450
• Languages: English
• ISSNs: 0304-3959

Abstract

Abstract : Abstract: Patients with functional pain disorders often complain of generalized sensory hypersensitivity, finding sounds, smells, or even everyday light aversive. The neural basis for this aversion is unknown, but it cannot be attributed to a general increase in cortical sensory processing. Here, we quantified the threshold for aversion to light in patients with fibromyalgia, a pain disorder thought to reflect dysregulation of pain-modulating systems in the brain. These individuals expressed discomfort at light levels substantially lower than that of healthy control subjects. Complementary studies in lightly anesthetized rat demonstrated that a subset of identified pain-modulating neurons in the rostral ventromedial medulla unexpectedly responds to light. Approximately half of the pain-facilitating "ON-cells" and pain-inhibiting "OFF-cells" sampled exhibited a change in firing with light exposure, shifting the system to a pronociceptive state with the activation of ON-cells and suppression of OFF-cell firing. The change in neuronal firing did not require a trigeminal or posterior thalamic relay, but it was blocked by the inactivation of the olivary pretectal nucleus. Light exposure also resulted in a measurable but modest decrease in the threshold for heat-evoked paw withdrawal, as would be expected with engagement of this pain-modulating circuitry. These data demonstrate integration of information about light intensity with somatic input at the level of single pain-modulating neurons in the brain stem of the rat under basal conditions. Taken together, our findings in rodents and humans provide a novel mechanism for abnormal photosensitivity and suggest that light has the potential to engage pain-modulating systems such that normally innocuous inputs are perceived as aversive or even painful. Abstract : An unexpected finding of photosensitivity in pain-modulating neurons in the brain stem could contribute to multisensory hypersensitivity in patients with fibromyalgia, who demonstrated profound photosensitivity compared to healthy control subjects.