Estimation of the proportions of dogs and cats that are surgically sterilized.

OBJECTIVE: To determine an estimate of the proportions of dogs and cats in Texas that are surgically sterilized and whether those proportions differed according to species and sex of the animal, level of responsibility of the owner, or geographic location. DESIGN: Cross-sectional study. ANIMALS: 43,831 dogs and cats > or = 6 months old. PROCEDURE: Information on sterilization rates was provided by 14 licensing agencies and 16 animal shelters in diverse regions of Texas. Univariate and multivariate analyses were used to compare sterilization rates among subpopulations of animals (dogs vs cats, males vs females, sheltered vs licensed, rural vs urban location). RESULTS: Overall, 12,893 (29.4%) of the animals (26.9% of dogs and 32.6% of cats) were sterilized. Proportions of animals sterilized were significantly different among subpopulations. CONCLUSIONS AND CLINICAL RELEVANCE: Although the cause of pet overpopulation is multifaceted, failure of owners to spay and castrate their animals is a major contributing factor. Significant differences in sterilization rates among subpopulations of dogs and cats suggest that organizations encouraging spaying and castration should use motivational techniques specific for the pet owners they are targeting.

Electron microscopic evidence for the mechanism of blood-retinal barrier breakdown in diabetic rabbits: comparison with magnetic resonance imaging.

Diabetes leads to a breakdown of the blood-retinal barrier (BRB), which can be demonstrated in experimental models by immunocytochemistry and magnetic resonance imaging (MRI). The present study utilizes these methods to investigate the mechanism of BRB breakdown in diabetic rabbits, a model ideally suited to both procedures. Rabbits were treated with alloxan and examined 2 months, 1 year, and 1.5 years after the development of diabetes to assess BRB breakdown using MRI and immunocytochemical staining for endogenous albumin. Using MRI, an increased incidence of retinal vascular leakage is first evident at 1 year of diabetes. Electron microscopic immunolocalization of albumin suggests that BRB compromise is principally mediated by transendothelial transport of serum proteins in endocytic vesicle-like structures of approximately 0.4-1 micron diameter. Some additional retinal vascular leakage is occasionally demonstrated through the interendothelial cell tight junctions, but only when adjacent vascular endothelial cells show degenerative changes. The similarity of these findings to those previously reported for diabetic humans and rats supports the use of the diabetic rabbit as a model for studying BRB dysfunction. MRI and electron microscopic (EM) immunocytochemistry are complementary methods for evaluating BRB dysfunction. MRI can provide an overall picture of the entire eye without sacrificing the animal. EM immunocytochemistry can provide a more detailed picture of a limited area of interest to gain insight into the mechanisms of extravasation. Together, both methods provide a more complete understanding of BRB breakdown in diabetic rabbits.

Blood-retinal barrier (BRB) breakdown in experimental autoimmune uveoretinitis: comparison with vascular endothelial growth factor, tumor necrosis factor alpha, and interleukin-1beta-mediated breakdown.

Experimental autoimmune uveoretinitis (EAU) induced in Lewis rats by immunization with S-antigen is a model of human uveitis. By using immunocytochemical staining for albumin, relatively minor blood-retinal barrier (BRB) breakdown was initially shown in the peripheral retina 8 days after immunization and in the posterior retina by 10 days. Albumin extravasation appeared to occur by opening of the retinal vascular endothelial (RVE) and the retinal pigmented epithelial (RPE) tight junctions, by transendothelial vesicular transport, and by permeating damaged RVE cells. Each of three anti-inflammatory agents reduced or delayed autoimmune-mediated cell destruction but did not eliminate any particular route of extravasation. Vascular endothelial growth factor (VEGF), tumor necrosis factor alpha (TNF alpha), and interleukin-1beta (IL-1beta) are intimately associated with the development of EAU and are capable of causing BRB dysfunction. A high percentage of RVE tight junctions appeared open ultrastructurally after intravitreal injection of VEGF (26.7%), TNF alpha (35.6%), or IL-1beta (22.1%) compared with saline-injected control (11.4%) or normal, untreated rabbits (4.1%). Heat treatment abolished the effect of IL-1beta on the BRB but only partially reduced the effect of VEGF. By 24 hr after injection, the effect of TNF alpha had reversed, but that of IL-1beta had not; VEGF-mediated BRB dysfunction was partially reversible. In addition, albumin-filled vesicle-like structures were seen in the RVE cytoplasm following treatment with each mediator. This study shows that VEGF, TNF alpha, and IL-1beta each cause BRB breakdown by opening tight junctions between RVE cells and possibly by increasing transendothelial vesicular transport. Each of these agents may contribute to BRB breakdown in EAU and in patients with uveitis.

Blood-aqueous barrier in pseudoexfoliation syndrome: evaluation by immunohistochemical staining of endogenous albumin.

BACKGROUND: Alterations of the integrity of the blood-aqueous barrier (BAB) are frequent findings in eyes with pseudoexfoliation syndrome (PSX). METHODS: Immunohistochemical staining for the demonstration of albumin was used to analyze the BAB in 10 eyes with PSX without previous intraocular surgery and in 10 age-matched normal control eyes. RESULTS: In eyes with PSX, small amounts of albumin were detected along the anterior surface of the iris in 7, in the anterior chamber in 1, along the ciliary epithelium in 4, and in the trabecular meshwork in 9 of 10 eyes. PSX material was also immunoreactive. In the 10 normal control eyes, albumin was detected anterior to the iris stroma in 1 eye, in the anterior chamber in 2 eyes, in the trabecular meshwork in 1 eye, but not internal to the ciliary epithelium. CONCLUSIONS: Our findings indicate that impairment of the BAB in PSX can be localized at the level of the iris and, less frequently or to a lesser extent, at the level of the ciliary body.

Blood-ocular barrier breakdown in eyes with ocular melanoma. A potential role for vascular endothelial growth factor/vascular permeability factor.

A series of 130 eyes with ocular melanomas, 19 normal eyes, and 18 eyes affected with other disorders leading to blood-ocular barrier (BOB) breakdown were immunohistochemically stained for albumin to localize sites of BOB failure within the retina, ciliary body, and iris. Thirty-nine of the eyes containing melanomas and all of the other eyes were also immunohistochemically stained for vascular endothelial growth factor (VEGF), to investigate its potential role as a mediator for BOB failure. Eyes with melanomas showed widespread leakage through the retinal pigment epithelium, and 58% demonstrated leakage from retinal vessels in the proximity of the tumor. BOB failure remote from the tumor also occurred in retina (50%), optic nerve head (77%), ciliary body (51%), and iris (51%), suggesting that a soluble mediator may be involved. VEGF was demonstrated intraretinally in the proximity of (46%) and remote from (24%) melanomas and in eyes affected by other disease processes, particularly those involving neoplasia or retinal detachments, usually within particular cell populations (ie, retinal vessel walls, ganglion cells, inner or outer nuclear layers, retinal pigment epithelium). VEGF localization in retina, ciliary body, and iris often coincided with sites of extravasated albumin. Preincubation of albumin or VEGF antibodies with normal serum or VEGF peptide, respectively, eliminated or markedly reduced all immunoreactivity. Only 1 of 14 normal postmortem eyes and 0 of 5 normal surgically removed eyes showed VEGF positivity in the retina, 5 of 19 normal eyes had weak positivity in the ciliary body, and VEGF was not demonstrated in the iris of normal eyes. VEGF cannot account for all of the BOB failure associated with ocular melanomas, but appears likely to play a contributing role in many cases.

Blood-retinal barrier breakdown in retinitis pigmentosa: light and electron microscopic immunolocalization.

Macular edema can contribute to visual loss in the retinitis pigmentosa (RP), but the sites and mechanism of blood-retinal barrier (BRB) breakdown leading to macular edema are not known. An understanding of the mechanisms involved could lead to the design of effective pharmacologic therapy to prevent or minimize macular edema in RP. To investigate this problem, immunohistochemical staining for albumin was performed on paraffin sections of 22 normal and 29 RP-affected eyes. Specimens were graded for extent of albumin extravasation in different regions of the retina, optic nerve head, ciliary body, and iris. Electron microscopic immunocytochemical staining for albumin was performed on an additional 6 normal and 9 RP-affected eyes. Two-thirds of the eyes from patients with RP and no other ocular disorders demonstrated extravascular albumin in the inner portion of the posterior retina. This was evident even in the absence of cystoid macular edema (CME), but eyes that had CME showed extensive BRB failure. In some cases, passage of albumin from the choroid to the retina was prevented even in the absence of the retinal pigment epithelium (RPE). Electron microscopic immunocytochemistry revealed that albumin permeated retinal vascular endothelial cells and RPE cells that showed degenerative changes in RP.

Isoforms of platelet-derived growth factor and its receptors in epiretinal membranes: immunolocalization to retinal pigmented epithelial cells.

Epiretinal membranes (ERMs) form on the inner surface of the retina in conjunction with various ocular disease processes, but the factors controlling their development are not understood. The predominant cell types involved are retinal pigmented epithelial (RPE) cells and retinal glia. Cultured RPE cells secrete platelet-derived growth factor (PDGF), which is chemotactic and mitogenic for both RPE cells and retinal glia and, therefore, could be involved in the development of ERMs. In the present study, we performed immunohistochemical staining for PDGF A chain (PDGF-A), PDGF B chain (PDGF-B), and both types of PDGF receptors (PDGFr alpha and PDGFr beta) on ERMs associated with various disease processes. PDGF-A is detected in most ERMs, regardless of the associated disease process, and it appears to be localized predominantly in RPE cells, recognized by the presence of pigment and the immunohistochemical demonstration of some or all of the following RPE-associated epitopes: class III beta-tubulin, keratin, the 65-kDa microsomal protein recognized by the RPE9 antibody, and cellular retinaldehyde-binding protein. PDGF-B is found only in minor subpopulations of cells in about half of the ERMs evaluated and, with only occasional exceptions, appears to be localized almost entirely in blood-borne cells found in and around vessels in vascularized ERMs. Both PDGFr alpha and PDGFr beta are demonstrated in most ERMs with neither isotype consistently predominating: they are found predominantly on RPE cells with many cells expressing both receptor types. ERMs with little or no RPE cell component contain little or no PDGF and PDGF receptor, whereas those in which the RPE cell represents the major cell type, have widespread PDGF and PDGF receptor positivity. These findings show that RPE cells in ERMs produce PDGF-A and PDGF alpha and PDGF beta receptors and suggest that autocrine and paracrine stimulation with PDGF may be involved in ERM pathogenesis.

Class III beta-tubulin in human retinal pigment epithelial cells in culture and in epiretinal membranes.

The class III beta-tubulin isotype (beta III) is expressed exclusively by neurons within the normal human retina and is not present in normal retinal pigment epithelial (RPE) cells in situ or in 1 day-old primary cultures; however, beta III is present in RPE cells in 5-day primary cultures and in passaged RPE cells grown in monolayer cultures as determined by immunohistochemistry and Western blotting. beta III-positivity in cultured RPE cells is not affected by cell density or hydroxyurea- or retinoic-acid-mediated growth inhibition, but only a few cells weakly express beta III in cyclohexamide-treated cultures and RPE cells maintained in serum-free medium fail to produce beta III. When monolayer-cultured RPE cells grown in normal, serum-containing medium, are transferred to irradiated bovine vitreous, beta III is undetectable in most cells. Cultured RPE cells coexpress beta III with keratin and cellular retinaldehyde-binding protein (both RPE cell markers), but not with glial fibrillary acidic protein. Some cultured RPE cells also express neuron-specific (gamma) enolase, which is neuron-associated but not neuron-specific, and occasional cells in confluent or super-confluent cultures contain the 200-kDa neurofilament protein. Retinal glia, fibroblasts, endothelial cells, and smooth muscle cells do not express beta III under the same culture conditions. We have detected beta III in 45 of 56 epiretinal membranes, frequently in cells with a bipolar or dedifferentiated morphology, where its expression coincides with other RPE cell-associated antigens. Cells with morphological features resembling normal RPE cells in epiretinal membranes are usually negative for beta III, but RPE cells appearing to be in the early stages of dedifferentiation express the isotype weakly. Electron microscopic immunocytochemistry localizes beta III to microtubules, ribosomes and cytoplasm. beta III may be a useful marker for recognizing the fraction of RPE cells in epiretinal membranes that are no longer identifiable by morphological criteria or other RPE cell markers. These findings demonstrate that mature human RPE cells have the capacity to express a neuron-associated gene in response to conditions that promote dedifferentiation.