The purpose of this study is to assess with spectral-domain optical coherence tomography (OCT) the interspecies variation of outer retinal morphology and identification of choriocapillaris in four research animal species. METHODS. Spectralis HRAþOCT images acquired from locations dorsal, central, and ventral to the optic disc in healthy, anesthetized animals were evaluated by two independent readers. First, the number of OCT B-scans on which a choriocapillaris layer could clearly be identified was determined and quantified, and B-scans were correlated with histology. Second, B-scans demonstrating the highest number of discernable individual outer retinal bands (ORBs) were defined as ideal presentation and quantified. Interrater agreement was evaluated. RESULTS. Five-hundred seventy-four B-scans from 96 subjects were evaluated. The choriocapillaris layer was identified in 100.0% of minipig, 70.8% of rabbit, 75.4% of pigmented rat, 77.7% of albino rat, 56.5% of pigmented mouse, and 50.8% of albino mouse OCT scans. The percentage of ideal ORB presentation in B-scans was 11.7% in minipigs, 73.8% in rabbits, and 80.0%, 91.0%, 28.5%, and 62.5% in pigmented rats and mice and albino rats and mice, respectively. The interrater evaluation for both attributes showed substantial to perfect agreement in all species. CONCLUSIONS. The choriocapillaris is an easy and valid marker for identification of the outer retinal margin. ORB presentation likely varies due to differences in retinal anatomy and pigmentation between animal species and strains and between anatomic locations. Proper and consistent outer retinal margin and ORB identification are essential for research result reproducibility and translation.
Analysis of the angioarchitecture and quantification of the conduit vessels and microvasculature is of paramount importance for understanding the physiological and pathological processes within the central nervous system (CNS). Most of the available in vivo imaging methods lack penetration depth and/or resolution. Some ex vivo methods may provide better resolution, but are mainly destructive, as they are designed for imaging the CNS tissues after their removal from the skull or vertebral column. The removal procedure inevitably alters the in situ relations of the investigated structures and damages the dura mater and leptomeninges. µAngiofil, a polymer-based contrast agent, permits a qualitatively novel postmortem microangio-computed tomography (microangioCT) approach with excellent resolution and, therefore, visualization of the smallest brain capillaries. The datasets obtained empower a rather straightforward quantitative analysis of the vascular tree, including the microvasculature. The µAngiofil has an excellent filling capacity as well as a radio-opacity higher than the one of bone tissue, which allows imaging the cerebral microvasculature even within the intact skull or vertebral column. This permits in situ visualization and thus investigation of the dura mater and leptomeningeal layers as well as their blood supply in their original geometry. Moreover, the methodology introduced here permits correlative approaches, i.e., microangioCT followed by classical histology, immunohistochemistry and even electron microscopy. The experimental approach presented here makes use of common desktop microCT scanners, rendering it a promising everyday tool for the evaluation of the (micro)vasculature of the central nervous system in preclinical and basic research.
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