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B.J. Tripathi, R.C. Tripathi, K.V. Chalam, A. Haddad; Extravascular Smooth Muscle Cell System in the Choroid . Invest. Ophthalmol. Vis. Sci. 2006;47(13):5621.
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To investigate the morphologic organization of extravascular smooth muscle (EVSM) cells in the choroid.
Whole mounts of the choroid from 13 young male albino rabbits, fixed by intracardic perfusion and stained with a FITC–conjugated antibody against α–actin of smooth muscle, were examined by stereomicroscopy and confocal microscopy. The contralateral eye was processed for light microscopy and sections stained with a monoclonal anti–smooth muscle α–actin antibody and horseradish peroxidase or for transmission electron microscopy (TEM).
Stereomicroscopy of choroidal whole mounts revealed the presence of cord–like structures that, by confocal microscopy, were identified as blood vessels partially enveloped by bundles of spindle–shaped cells oriented parallel to the vessel lumen and exhibited green fluorescence of the FITC–labeled anti–α–actin antibody. The smooth muscle cells of the tunica media of the arteries and arterioles also fluoresced green but were oriented circumferentially around the vessel walls. The EVSM cell system extended from the optic nerve to the ciliary body where it fused with the ciliary muscles. In places, this extravascular mantle was up to 20 cell layers thick and strongly immunopositive for smooth muscle cell α–actin. Ultrastructurally, the EVSM cells had fine cytoplasmic filaments, irregularly shaped electron–dense areas, frequent glycogen granules, as well as endoplasmic reticulum and mitochondria in the vicinity of the nucleus. Based on these features, these cells were distinguishable from isolated myofibroblasts.
While the smooth muscle cells in the adventitia of the vessels control the caliber of the lumen, the extensive system of EVSM cells, being organized along the choroidal vessels, probably regulate the axial length to increase or decrease the tortuosity and hence the volume of the choroidal blood flow. This finding may provide an anatomic basis for the myogenic autoregulation of choroidal blood flow that has been postulated in human and non–human eyes.
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