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Carolina L. Luna, Susana Quirce, Carlos Belmonte, Juana Gallar, M C. Acosta; Changes Of Corneal Sensory Nerve Activity Induced By Repetitive Allergen Challenge In A Guinea-pig Model Of Allergic Conjunctivitis. Invest. Ophthalmol. Vis. Sci. 2011;52(14):6428.
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To test whether repetitive allergen challenge induced changes in corneal sensory nerve activity in a guinea-pig model of allergic conjunctivitis.
Ovalbumin (OVA) sensitization was evoked by i.p. injection of 100µg OVA+20mg Al(OH)3 in 1ml PBS. On day 14, 10% OVA (10µl) was topically applied to each eye and tearing and blinking rates were measured during 5 min, immediately afterwards. Exposure to the allergen was repeated for 5 consecutive days. Thereafter, nerve activity was recorded from ciliary nerve fibers and from corneal nerve terminals in the whole eye or in the isolated cornea superfused in vitro. Impulse responses of mechano-(n=63) and polymodal (n= 55) nociceptor fibers, and of cold thermosensitive nerve terminals (n=72), to stimulation with thermal changes (exposure to bath temperature variations from the basal temperature of 33ºC, down to 20°C or up to 50°C), mechanical stimulation with calibrated von Frey hairs and chemical stimulation with 98% CO2, 30s gas pulses were recorded in allergen-challenged and in control eyes.
Tearing and blinking rates were significantly increased after allergen challenge (Table 1). In eyes receiving topical OVA, the percentage of nociceptive units with spontaneous activity was higher. Responses to mechanical and chemical stimuli were increased, while response to cooling of cold thermosensitive units was decreased. These changes in nerve activity induced by the allergen increased significantly with repeated exposure to OVA (see table, *p<0.001).
These data suggest that increased sensitivity and discomfort sensations at the eye surface observed under allergic conditions are due to changes in corneal sensory nerve activity induced by allergic challenge that becomes more prominent after repeated exposure to the allergen.
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