Effects of corneal injury on ciliary nerve fibre activity and corneal nociception in mice: A behavioural and electrophysiological study

Abstract

Background Ocular surface diseases are among the most frequent ocular pathologies. Ocular pain following corneal injury is frequently observed in clinic. Corneal sensory innervation is supplied by ciliary nerves derived from ophthalmic division of the trigeminal ganglion. Methods & Results Extracellular activity of the mouse ciliary nerve was first used to investigate the corneal responsiveness to chemical, mechanical and thermal stimulations in order to specifically study the responses of polymodal nociceptors, mechano‐nociceptors and cold thermoreceptor in a control cornea. Then, in two models of corneal injury (repeated instillations of 0.02% benzalkonium chloride and corneal scraping), we first measured the corneal sensitivity to chemical (eye‐wiping test) and mechanical (von Frey filaments) stimulation. Thereafter, we evaluated whether these corneal injuries modified the spontaneous and chemical stimulation‐evoked activity of the ciliary nerve. Both models of injury induced a significant corneal chemical hypersensitivity correlated with an increase of the spontaneous activity of the ciliary nerve and a faster response of the ciliary nerve after a chemical stimulation. Conclusions Overall, this study provides new insights into the functional aspects of corneal nerve fibre activity in mice after corneal injury. The increase in ciliary nerve activity may thus contribute to the development of ocular pain after corneal damage. Significance This study highlights the parallel increase in ciliary nerve activity and corneal sensitivity after corneal injury in mice. The strategy of combining ex vivo electrophysiological recordings of the ciliary nerve in mice and corneal sensitivity measurements therefore helps to uncover the functional aspects of corneal pain.

Chronic dry eye induced corneal hypersensitivity, neuroinflammatory responses, and synaptic plasticity in the mouse trigeminal brainstem

“…We next investigated whether DED-induced corneal hypersensitivity was accompanied by an increase in the spontaneous electrical activity of the ciliary nerve at d0, d7, d14, and d21 (Fig. 8a) by extracellular recording of the ciliary nerve fiber activity [34] of naïve, sham, and DED mice. We found no difference in spontaneous ciliary nerve fiber activity between the naïve mice at d0 and sham mice at d7 (43.2 ± 4.7 vs 34.1 ± 4.5 P > 0.05; Fig.…”

“…An in vivo laser confocal microscope (IVCM, Heidelberg Retina Tomography (HRT) II/Rostock Cornea Module (RCM; Heidelberg Engineering GmbH, Heidelberg, Germany)) was used to examine the entire cornea of anesthetized mice [34]. The images covered an area of 400 × 400 μm with a transversal optical resolution of 2 μm and an axial optical resolution of 4 μm (Heidelberg Engineering).…”

“…Mechanical corneal sensitivity was monitored using von Frey filaments [34]. Various forces of calibrated von Frey filaments (0.008–0.04 g) were applied to the center of the cornea of immobilized mice as previously reported.…”

“…Spontaneous ciliary nerve fiber activity was determined at d0, d7, d14, and d21 as previously reported [34]. Briefly, mice were euthanized and the eye placed in a two-compartment chamber [34].…”

“…Spontaneous ciliary nerve fiber activity was determined at d0, d7, d14, and d21 as previously reported [34]. Briefly, mice were euthanized and the eye placed in a two-compartment chamber [34]. The cornea was continuously superfused at a rate of 3 mL/min at 33 ± 1 °C with a physiological saline solution (133.4 mM NaCl, 4.7 mM KCl, 2 mM CaCl 2 , 1.2 mM MgCl 2 , 16.3 mM NaHCO 3 , 1.3 mM NaH 2 PO 4 , and 7.8 mM glucose) saturated with O 2 and adjusted to pH 7.4 by bubbling with 95% O 2 and 5% CO 2 .…”