title: Changes in sensory activity of ocular surface sensory nerves during allergic keratoconjunctivitis.
abstract: Peripheral neural mechanisms underlying the sensations of irritation, discomfort, and itch accompanying the eye allergic response have not been hitherto analyzed. We explored this question recording the changes in the electrical activity of corneoconjunctival sensory nerve fibers of the guinea pig after an ocular allergic challenge. Sensitization was produced by i.p. ovalbumin followed by repeated application in the eye of 10% ovalbumin on days 14 to 18. Blinking and tearing rate were measured. Spontaneous and stimulus-evoked (mechanical, thermal, chemical) impulse activity was recorded from mechanonociceptor, polymodal nociceptor and cold corneoscleral sensory afferent fibers. After a single (day 14) or repeated daily exposures to the allergen during the following 3 to 4days, tearing and blinking rate increased significantly. Also, sensitization was observed in mechanonociceptors (transient reduction of mechanical threshold only on day 14) and in polymodal nociceptors (sustained enhancement of the impulse response to acidic stimulation). In contrast, cold thermoreceptors showed a significant decrease in basal ongoing activity and in the response to cooling. Treatment with the TRPV1 and TRPA1 blockers capsazepine and HC-030031 reversed the augmented blinking. Only capsazepine attenuated tearing rate increase and sensitization of the polymodal nociceptors response to CO2. Capsazepine also prevented the decrease in cold thermoreceptor activity caused by the allergic challenge. We conclude that changes in nerve impulse activity accompanying the ocular allergic response, primarily mediated by activation of nociceptor's TRPV1 and to a lesser degree by activation of TRPA1 channels, explain the eye discomfort sensations accompanying allergic episodes.
authors.affiliation: Instituto de Neurociencias, Universidad Miguel Hernández-CSIC, Avda. Santiago Ramón y Cajal 2, E-03550 San Juan de Alicante, Spain.
authors.forename: Carmen M
authors.initials: CM
authors.lastname: Acosta
authors.forename: Carolina
authors.initials: C
authors.lastname: Luna
authors.forename: Susana
authors.initials: S
authors.lastname: Quirce
authors.forename: Carlos
authors.initials: C
authors.lastname: Belmonte
authors.forename: Juana
authors.initials: J
authors.lastname: Gallar
mesh_terms: D000818:Animals; D001767:Blinking; D002245:Carbon Dioxide / Q000378:metabolism; D002924:Ciliary Body / Q000503:physiopathology; D003233:Conjunctivitis, Allergic / Q000503:physiopathology*; D003315:Cornea / Q000294:innervation / Q000503:physiopathology; D005071:Evoked Potentials / Q000502:physiology; D005123:Eye / Q000294:innervation*; D005260:Female; D006168:Guinea Pigs; D007637:Keratoconjunctivitis / Q000503:physiopathology*; D008297:Male; D009411:Nerve Endings / Q000502:physiology; D009619:Nociceptors / Q000502:physiology; D011537:Pruritus / Q000503:physiopathology; D011984:Sensory Receptor Cells / Q000502:physiology*; D050053:TRPM Cation Channels / Q000037:antagonists & inhibitors / Q000378:metabolism; D050916:TRPV Cation Channels / Q000037:antagonists & inhibitors / Q000378:metabolism; D013666:Tears / Q000378:metabolism; D013823:Thermoreceptors / Q000502:physiology
chemical_list: D050053:TRPM Cation Channels; D050916:TRPV Cation Channels; C494484:TRPV1 receptor; D002245:Carbon Dioxide
keywords: Allergic conjunctivitis; Cold receptors; Corneal innervation; Nociceptors; TRPA1; TRPV1