Abstract
Purpose :
To test whether exposure of one eye of the guinea-pig to ultraviolet radiation (UVR) induced changes in corneal sensory nerve activity of the contralateral, non-exposed unaffected eye.
Methods :
Guinea pigs (both sexes, 2-4 months old) were anesthetized and UVR (254 nm; 1000 mJ/cm2) was delivered to one eye of the animal. Tearing rate was measured before and 48 h after UVR using phenol-red threads. 48 h after UVR, nerve activity was recorded from corneal nerve terminals and from single ciliary nerve fibers in irradiated (IRE) and contralateral eyes (CLE) superfused in vitro at 34°C. Thermal stimulation was performed changing the temperature of the bath from 34°C down to 20°C (cooling ramp) or up to 50°C (heating ramp). Mechanical stimulation was applied with calibrated von Frey hairs. Chemical stimulation was performed applying for 30s, gas jets of 98% CO2 in air. The characteristics of the spontaneous and stimulus-evoked activity recorded in IRE, CLE and in intact eyes were analyzed.
Results :
Tearing rate was not modified after UVR in IRE or CLE. Mechanical threshold of mechanonociceptors decreased significantly in IRE and slightly in CLE compared with naïve eyes (Table 1). The proportion of spontaneously active polymodal nociceptors and the value of the mean firing frequency evoked by chemical stimulation increased after UVR in both eyes (Table 1). Spontaneous and cold-evoked activity of cold thermoreceptors decreased significantly in IRE and slightly in CLE (Table 1).
Conclusions :
Inflammation in one eye evoked sensitization of nociceptors and desensitization of cold thermoreceptors in the directly inflamed eye but also in a lesser degree, in the contralateral eye. This effect may be caused by spreading to the contralateral side of the changes in immune cells and/or central synaptic connections developed along the ipsilateral sensory pathway.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.