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

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          Abstract

          Background

          Dry eye disease (DED) is a multifactorial disease associated with ocular surface inflammation, pain, and nerve abnormalities. We studied the peripheral and central neuroinflammatory responses that occur during persistent DED using molecular, cellular, behavioral, and electrophysiological approaches.

          Methods

          A mouse model of DED was obtained by unilateral excision of the extraorbital lachrymal gland (ELG) and Harderian gland (HG) of adult female C57BL/6 mice. In vivo tests were conducted at 7, 14, and 21 days (d) after surgery. Tear production was measured by a phenol red test and corneal alterations and inflammation were assessed by fluorescein staining and in vivo confocal microscopy. Corneal nerve morphology was evaluated by nerve staining. Mechanical corneal sensitivity was monitored using von Frey filaments. Multi-unit extracellular recording of ciliary nerve fiber activity was used to monitor spontaneous corneal nerve activity. RT-qPCR and immunostaining were used to determine RNA and protein levels at d21.

          Results

          We observed a marked reduction of tear production and the development of corneal inflammation at d7, d14, and d21 post-surgery in DED animals. Chronic DE induced a reduction of intraepithelial corneal nerve terminals. Behavioral and electrophysiological studies showed that the DED animals developed time-dependent mechanical corneal hypersensitivity accompanied by increased spontaneous ciliary nerve fiber electrical activity. Consistent with these findings, DED mice exhibited central presynaptic plasticity, demonstrated by a higher Piccolo immunoreactivity in the ipsilateral trigeminal brainstem sensory complex (TBSC). At d21 post-surgery, mRNA levels of pro-inflammatory (IL-6 and IL-1β), astrocyte (GFAP), and oxidative (iNOS2 and NOX4) markers increased significantly in the ipsilateral trigeminal ganglion (TG). This correlated with an increase in Iba1, GFAP, and ATF3 immunostaining in the ipsilateral TG of DED animals. Furthermore, pro-inflammatory cytokines (IL-6, TNFα, IL-1β, and CCL2), iNOS2, neuronal (ATF3 and FOS), and microglial (CD68 and Itgam) markers were also upregulated in the TBSC of DED animals at d21, along with increased immunoreactivity against GFAP and Iba1.

          Conclusions

          Overall, these data highlight peripheral sensitization and neuroinflammatory responses that participate in the development and maintenance of dry eye-related pain. This model may be useful to identify new analgesic molecules to alleviate ocular pain.

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          Most cited references64

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          TFOS DEWS II pain and sensation report

          Pain associated to mechanical and chemical irritation of the eye surface is mediated by trigeminal ganglia mechano- and polymodal nociceptor neurons while cold thermoreceptors detect wetness and reflexly maintain basal tear production and blinking rate. These neurons project into two regions of the trigeminal brain stem nuclear complex: ViVc, activated by changes in the moisture of the ocular surface and VcC1, mediating sensory-discriminative aspects of ocular pain and reflex blinking. ViVc ocular neurons project to brain regions that control lacrimation and spontaneous blinking and to the sensory thalamus. Secretion of the main lacrimal gland is regulated dominantly by autonomic parasympathetic nerves, reflexly activated by eye surface sensory nerves. These also evoke goblet cell secretion through unidentified efferent fibers. Neural pathways involved in the regulation of Meibonian gland secretion or mucins release have not been identified. In dry eye disease, reduced tear secretion leads to inflammation and peripheral nerve damage. Inflammation causes sensitization of polymodal and mechano-nociceptor nerve endings and an abnormal increase in cold thermoreceptor activity, altogether evoking dryness sensations and pain. Long-term inflammation and nerve injury alter gene expression of ion channels and receptors at terminals and cell bodies of trigeminal ganglion and brainstem neurons, changing their excitability, connectivity and impulse firing. Perpetuation of molecular, structural and functional disturbances in ocular sensory pathways ultimately leads to dysestesias and neuropathic pain referred to the eye surface. Pain can be assessed with a variety of questionaires while the status of corneal nerves is evaluated with esthesiometry and with in vivo confocal microscopy.
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            Etiology, prevalence, and treatment of dry eye disease

            Purpose: This review article examines the prevalence, etiology, and current therapies of dry eye disease, with special focus on postmenopausal women. Method: A systematic literature search utilizing MEDLINE was conducted to identify peer-reviewed articles related to dry eye published prior to September 2008. The terms “dry eye” and “women” were searched in combination with one or more of the following words or phrases: prevalence, postmenopausal, etiology, risk factors, therapy, medications, surgery, tear film, and quality of life. Articles were selected based on their direct applicability to the subject matter. A manual search was also conducted based on citations in the published literature. Results: Epidemiologic studies identified prevalence rates ranging from 7% in the United States to 33% in Taiwan and Japan. Risk factors include advanced age, female sex, smoking, extreme heat or cold weather conditions, low relative humidity, use of video display terminals, refractive surgery, contact lens wear, and certain medications. Conclusion: The last decade has brought about a better understanding of the etiology of dry eye disease. New therapies that can alleviate the signs and symptoms of dry eye disease and, consequently, improve the quality of life of dry eye patients are available in the market.
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              In Vivo Confocal Microscopy of Corneal Nerves in Health and Disease.

              In vivo confocal microscopy (IVCM) is becoming an indispensable tool for studying corneal physiology and disease. Enabling the dissection of corneal architecture at a cellular level, this technique offers fast and noninvasive in vivo imaging of the cornea with images comparable to those of ex vivo histochemical techniques. Corneal nerves bear substantial relevance to clinicians and scientists alike, given their pivotal roles in regulation of corneal sensation, maintenance of epithelial integrity, as well as proliferation and promotion of wound healing. Thus, IVCM offers a unique method to study corneal nerve alterations in a myriad of conditions, such as ocular and systemic diseases and following corneal surgery, without altering the tissue microenvironment. Of particular interest has been the correlation of corneal subbasal nerves to their function, which has been studied in normal eyes, contact lens wearers, and patients with keratoconus, infectious keratitis, corneal dystrophies, and neurotrophic keratopathy. Longitudinal studies have applied IVCM to investigate the effects of corneal surgery on nerves, demonstrating their regenerative capacity. IVCM is increasingly important in the diagnosis and management of systemic conditions such as peripheral diabetic neuropathy and, more recently, in ocular diseases. In this review, we outline the principles and applications of IVCM in the study of corneal nerves in various ocular and systemic diseases.
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                Author and article information

                Contributors
                annabelle.reaux@inserm.fr
                Journal
                J Neuroinflammation
                J Neuroinflammation
                Journal of Neuroinflammation
                BioMed Central (London )
                1742-2094
                17 December 2019
                17 December 2019
                2019
                : 16
                : 268
                Affiliations
                [1 ]Sorbonne Université, INSERM, CNRS, Institut de la Vision, 17 rue Moreau, F-75012 Paris, France
                [2 ]ISNI 0000 0001 0631 9643, GRID grid.476517.6, R&D Department, , Laboratoires Théa, ; 12 rue Louis Biérot, 63000 Clermont-Ferrand, France
                [3 ]CHNO des Quinze-Vingts, INSERM-DGOS CIC 1423, 17 rue Moreau, F-75012 Paris, France
                [4 ]ISNI 0000 0001 2323 0229, GRID grid.12832.3a, Department of Ophthalmology, Ambroise Paré Hospital, AP-HP, , University of Versailles Saint-Quentin-en-Yvelines, ; 9 avenue Charles de Gaulle, 92100 Boulogne-Billancourt, France
                Article
                1656
                10.1186/s12974-019-1656-4
                6918709
                31847868
                00a2e92b-9fee-494d-92bb-c4206f9466e7
                © The Author(s). 2019

                Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License ( http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver ( http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.

                History
                : 25 July 2019
                : 25 November 2019
                Funding
                Funded by: FundRef http://dx.doi.org/10.13039/100013349, LABoratoires d’EXcellence ARCANE;
                Funded by: Laboratoires Thea ANRT CIFRE
                Award ID: N° 2016/1641
                Award Recipient :
                Categories
                Research
                Custom metadata
                © The Author(s) 2019

                Neurosciences
                dry eye,cornea,pain,electrophysiology,neuroinflammation,synaptic plasticity
                Neurosciences
                dry eye, cornea, pain, electrophysiology, neuroinflammation, synaptic plasticity

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