Topical instillations of Benzalkonium Chloride alter the extracellular activity of the ciliary nerve

Abstract

Purpose :
Ocular surface diseases are among the most frequent ocular pathologies, with prevalence ranging between 10 and 20% of the general population. Benzalkonium chloride (BAK) as a preservative is a major cause of dry eye in patients treated over the long term like in glaucoma. Here we investigated the effect of an acute exposure of BAK to the cornea on the extracellular ciliary nerve activity using an ex vivo preparation of isolated mouse whole eye.

Methods :
Adult male C57BL/6 mice (8 weeks old) were used. Eye was placed in the two-compartment chamber and the extracellular spontaneous activity of the ciliary nerve was recorded. Two types of BAK application were used: i) ex vivo: BAK instillations were directly performed during the ciliary nerve recording and ii) in vivo: mice received repeated instillations of BAK and after eyes were removed and multiunit ciliary nerve activity was recorded. 0.02% BAK was used for in vivo and ex vivo experiments (15 instillations - 5 min intervals) and 0.2% BAK was used for ex vivo application (3 times - 15 min intervals). The mechanical threshold response was determined using von Frey filament before and after BAK exposure.

Results :
The electrophysiology method to record multiunit ciliary nerve activity in mouse preparations is accurate and reliable. Basal activity of ciliary nerve is 24.6±5.3imp/sec. We showed that ex vivo instillation of 0.02% BAK increased impulse activity of corneal nerve followed by a decreased activity of the ciliary nerve. Importantly, we observed a modified mechanical threshold response following BAK treatment. Similar results were obtained after instillations with 0.2% BAK. A first application of 0.2% BAK significantly increased the ciliary nerve activity (~+50%). A second application 15 min later increased the activity (but less strongly; ~+20% compared to basal activity) and after the third instillation, ciliary nerve activity clearly decreased (~-50%). Interestingly, we observed a higher basal activity of the ciliary nerve after in vivo instillations of 0.02% BAK compared to control eye.

Conclusions :
This work presents the methodology to record the ciliary nerve activity in mouse preparation. Our electrophysiological results provide the first evidence that corneal exposure to BAK altered the ciliary nerve fibers. These experiments constitute a first step to better understand the corneal neurotoxicity of BAK.

This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.