Development and characterization of a chronic high intraocular pressure model in New Zealand white rabbits for glaucoma research.

Glaucoma is a neurodegenerative disease characterized by visual field loss associated with optic nerve damage and ocular hypertension. The biological basis for the elevated intraocular pressure (IOP) is largely unknown, such that lowering the IOP is currently the only established treatment. Several animal models have been developed to elucidate the mechanism underlying the increased IOP and for use in drug discovery research, but their utility is often limited by the occurrence of severe intraocular inflammation and by technical challenges. In this study, we developed a rabbit glaucoma model that does not require experimental disease induction. Rabbits were chosen as the model because their eyeballs are similar in size to those of humans, and they are easy to breed. By crossing rabbit strains with inherited glaucoma, as indicated by obvious buphthalmos, we produced a strain that exhibits ocular hypertension. The IOP of the Ocular Hypertension (OH) rabbits was significantly higher than that of the wild type (WT; normal New Zealand white rabbits) from the age of 3 weeks to at least 22 weeks. The significantly larger corneal diameter of the OH rabbits indicated ocular enlargement, whereas there was no significant difference in corneal thickness compared with WT rabbits. Anterior segment ocular coherence tomography and gonioscopic observations revealed an open angle in the OH rabbits. Hematoxylin and eosin (HE) staining together with Masson's trichrome staining showed abnormal collagen accumulation in the angle of the OH rabbit's eyes. Furthermore, aqueous humor (AH) outflow imaging following an intravitreal injection of a fluorescent probe into the anterior chamber for tissue-section analysis revealed retention of the probe in the area of collagen deposition in the OH eyes. The OH rabbits also had a time-dependent increase in the cup/disc ratio. In conclusion, investigations using our newly developed rabbit model of open-angle ocular hypertension showed that abnormal accumulation of extracellular matrix at the angle increased AH outflow resistance in the conventional outflow pathway, leading to a high IOP. Furthermore, the OH rabbits exhibited glaucomatous optic disc cupping over time. These findings suggest the utility of the OH rabbits as a model for open-angle glaucoma (OAG).

A Comprehensive Assessment of Tear-Film-Oriented Diagnosis (TFOD) in a Dacryoadenectomy Dry Eye Model.

Tear film instability is a major cause of dry eye disease. In order to treat patients with short tear film breakup time (TBUT)-type dry eye, the development of tear film stabilizing agents is essential. However, the lack of an appropriate animal model of tear film instability has made drug development difficult. Although rabbit dry eye models have been reported in the past, there are only a few reports that focus on tear film instability. Herein, we assessed the tear film stability of a rabbit dry eye model induced by dacryoadenectomy. A clinical evaluation of the ocular surface, interferometry, and histological assessments of the cornea and conjunctiva were performed. Following the removal of the lacrimal glands, TBUT was shortened significantly, with dimple and random breakup patterns prominently observed. Furthermore, the blink rate in this model increased after dacryoadenectomy, suggesting that this model partially captured the phenotypes of human short TBUT-type dry eye and may be useful as an animal model for investigating potential drug candidates.

Blood biochemistry and hematological changes in rats after administration of a mixture of three anesthetic agents.

Currently, given the concerns regarding animal welfare, it is required that anesthesia or analgesia be used during surgery in experimental animals. Therefore, it is important to understand how anesthesia affects the health conditions of experimental animals. In this study, rat blood biochemistry and hematological changes were examined following administration of a mixture of three anesthetic agents-medetomidine, midazolam and butorphanol (MMB). One of three MMB dose combinations was subcutaneously administered to rats. After 1 hr, rats were treated with atipamezole, to reverse the anesthetic effects. Blood biochemistry and hematological parameters were assessed at 1, 4 and 24 hr post-MMB treatment. We also recorded body weight and food intake at 0, 2, 4, 6 and 24 hr post-MMB administration. Following MMB administration, transient increases were observed in glucose (GLUC) levels, hematocrit (HCT) values and hemoglobin (HGB) levels, whereas transient decreases were observed in total protein (TP) content and white blood cell (WBC) counts. Most of these parameters returned to control values 24 hr following MMB administration. Additionally, body weight and food intake decreased in MMB-treated rats. In conclusion, intermediate and high doses of MMB changed some blood biochemistry and hematological parameters, body weight and food intake. In contrast, low-dose MMB did not cause these effects. Therefore, depending on the experimental design, MMB may influence the results of studies that use laboratory animals. Consequently, anesthetic agents used in laboratory animals should be chosen based on detailed knowledge of their pharmacological effects.

Blood biochemical changes in mice after administration of a mixture of three anesthetic agents.

Currently, from the viewpoint of animal welfare, anesthesia or analgesia is required during experimental procedures in animals that are likely to cause pain. A part of these anesthetics have been reported to influence a blood biochemical level. It is important for us to understand the effect of the anesthetic on blood biochemistry when we choose the anesthetic agent to be used in experiments. In this study, we examined the blood biochemical changes in mice after administration of a new mixture of three anesthetic agents -medetomidine / midazolam / butorphanol (MMB). We subcutaneously administered two dose combinations of MMB (0.45 / 6 / 7.5 and 0.9 / 12 / 15 mg/kg) in mice, followed by administration of atipamezole, for reversal of anesthetic effects, after 1 hr. Thereafter, blood biochemistry was assessed at 1, 4 and 24 hr after MMB administration. We observed that MMB administration caused a transient increase in blood sugar, inorganic phosphorus, potassium and creatine kinase levels. These, however, returned to the reference range 24 hr after MMB administration. In conclusion, MMB changes the levels of some blood biochemical parameters, but not to an extent that would threaten health. However, when using laboratory animals, this effect of MMB may influence the experimental results, depending on the experimental content. Hence, the choice of anesthetic agents used in laboratory animals should be based on detailed knowledge of their pharmacological effects.