Evaluation of an Experimental Model of Dry Eye in the Rat

Abstract

Abstract: : Purpose: Dry eye is defined as a tear film disorder caused by tear deficiency or tear evaporation leading to ocular surface impairment. The use of an animal model is a precious tool to better understand the mechanisms causing dry eye. The purpose of this study was to investigate the feasibility and the clinical relevance of a dry–eye rat model experimentally induced by scopolamine. Methods: Scopolamine was delivered by osmotic pumps implanted subcutaneously in female Lewis rats at different doses: 0, 6, 12.5 or 25 mg/day during 4 weeks. Corneal status was compared in the 4 groups by fluorescein staining. At the end of the experimental period, rats were sacrificed, the conjunctiva was excised and the exorbital lacrymal glands were removed. Mucins expression and inflammatory response reaction were evaluated in the conjunctiva by immunostaining of MUC5AC and MHC class II, respectively. The production of the superoxide anion as a marker of oxidative stress was quantified by DHE/DAPI staining in both structures. Fatty acid composition of the exorbital lacrymal glands was determined by gas chromatography. Results: No staining or minimal scattered punctuate fluorescein staining was observed on the corneas of control and 6 mg/d–group rats. Mild central punctuate staining was seen in rats treated with 12.5 mg/d and diffuse keratitis was observed in rats treated with 25 mg/d. Immunodetections on conjunctival epithelium showed a great number of positive MUC5AC cells in control rats whereas this number decreased progressively with the amount of scopolamine, from 6 mg/d to 25 mg/d. However, no signs of inflammation were observed as evaluated by MHC class II immunostaining, whatever the scopolamine dose. DHE/DAPI staining was increased in lacrymal glands with 25 mg/d (p<0.10). In lacrymal glands, arachidonic acid was increased by up to 50% in the 12 et 25 mg/d scopolamine groups (p<0.01). Conclusions: Altogether these results revealed that a daily scopolamine dose of 12.5 mg/d for 28 days to female rats by osmotic pump, seems to be appropriate to induce a dry eye syndrome, as checked by clinical signs of dryness and histological decrease in mucin production, although no inflammation was detected.

Keywords: immunohistochemistry • lacrimal gland • lipids