Ocular nociception and neuropathic pain initiated by blue light stress in C57BL/6J mice

Abstract

Abstract To elucidate the physiological, cellular, and molecular mechanisms responsible for initiating and sustaining ocular neuropathic pain, we created a blue light exposure model in C57BL/6 mice. Mice were exposed to 12 hours of blue or white light followed by 12 hours of darkness. Before blue light exposure, baseline tear secretion, stability, and ocular hyperalgesia were assessed by measuring hyperosmotic or hypoosmotic solution-induced eye wiping, wind-induced eye closing, and cold-induced eye blinking. At 1 day after blue light exposure, alterations in hypotonic or hypertonic-induced eye wiping and tear film abnormalities were observed. Eye-wiping behaviors were abolished by topical anesthesia. The cold-stimulated eye blinking and wind-stimulated eye closing behaviors began after day 3 and their frequency further increased after day 9. Blue light exposure reduced the density of nerve endings and increased their tortuosity, the number of beadlike structures, and the branching of stromal nerve fibers, as assessed by whole-mount confocal microscopy. Blue light exposure also increased TRPV1, but not TRPV4 staining intensity of corneal-projecting neurons in the trigeminal ganglia, as detected by FluoroGold retrograde labeling and immunohistochemistry. TRPV1 and substance P expression was increased, whereas CGRP expression deceased at the mRNA level in isolated corneal projecting neurons. Hence, our blue light exposure B6 mouse model for assessing tearing and ocular hyperalgesia is useful for studying ocular pain and its underlying mechanisms. Blue light–induced alterations in tearing and ocular hyperalgesia may be related to the elevated expression of TRPV1, substance P, or the suppressed expression of CGRP at the ocular surface.