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Ariadna Diaz-Tahoces, Enrique Velasco, Carolina Luna García, Fernando A. Carrera, Carlos Belmonte, Juana Gallar, M Carmen Acosta; Coding of small temperature changes by high-background cold thermosensitive trigeminal neurons innervating the ocular surface. Invest. Ophthalmol. Vis. Sci. 2018;59(9):155. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Typically, studies characterizing the response of cold thermoreceptor neurons use high-intensity cooling stimuli, far from the normal range of temperature oscillation under physiological conditions. In the present work, we studied the changes in impulse activity of cold thermosensitive trigeminal ganglion (TG) neurons in response to small temperatures changes of the ocular surface.
In anesthetized adult Wistar rats of both sexes placed in a stereotaxic frame, impulse activity of TG neurons was recorded extracellularly with tungsten electrodes (1-2MΩ) and stored for off-line analysis (Spike2 software, CED). A microprobe thermometer was placed on the corneal surface for simultaneous temperature recording. Receptive field (RF) of high-background cold neurons (HBCs) innervating cornea and conjunctiva was mapped. Spontaneous and stimulus-evoked activity (thermal stimulation from 34°C down to 20° or up to 45°; chemical stimulation with 10µl drops of hyperosmolar solutions or 50µM menthol; mechanical stimulation with von Frey hairs) were evaluated. After characterization, the response to a temperature reduction of 1.5°C at a rate of -0.11°C/s was explored.Simultaneously, video images of the ocular surface were obtained with an infrared thermal camera (InfRec R300SR, Nippon Avionics) for further analysis of the temperature values over time at the neuron RF.
Thirteen HBCs with RF located at the peripheral cornea or the near conjunctiva were recorded. In basal conditions, baseline activity of HBC was 5.58±0.81 imp/s with a RF temperature of 34.06±0.04°C. Temperature reduction of the receptive field to 32.88±0.24°C evoked in HBC a sustained increase in firing rate up to 8.21±1.03 imps/s (p<0.01, n=6). Cold thermosensitive neurons signaled RF temperature changes over -0.24°C with an increase in firing rate proportional to the temperature decrease. There was a significant correlation between RF temperature values and mean firing rate of HBC neurons (Pearson coefficient = -0.98, p<0.001).
High-background cold thermoreceptor neurons innervating the cornea and conjunctiva are able to encode small temperature changes of the ocular surface, increasing their basal frequency proportionally to the temperature of their receptive field.Support: SAF2014-54518-C3-1-R and SAF2017-83674-C2-1-R, Spanish Ministry of Economy and Competitiveness and European Union.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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