Lack of experience-mediated differences in the immunohistochemical expression of blood-brain barrier markers (EBA and GluT-1) during the postnatal development of the rat visual cortex.

The development of the cortical vascular tree depends on functional development. External inputs are an essential requirement in the modeling of the visual cortex, mainly during the critical period, when congruous blood supply is needed. The blood brain barrier (BBB) function regulates the passage of substances between the blood and the brain parenchyma, which is one of the main differential features of central nervous system (CNS) microvessels. The endothelial barrier antigen (EBA) has been reported as a specific marker for the BBB physiological function in rats. We studied the postnatal development of EBA expression in the visual cortex of rats reared under opposite paradigms of visual experience, e.g., standard laboratory conditions, dark rearing, and enriched environment at 14, 21, 28, 35, 42, 49, 56, and 63 days postnatal (dpn). Parallel sections were immunohistochemically processed for endothelial barrier antigen (EBA) and glucose transporter-1 (GluT-1). Total vasculature was quantified by Lycopersicon esculentum (LEA) lectin histochemistry. No differences in EBA expression were found between groups, although quantitative differences were recorded paralleling differences in vascular density. Paradoxically, there was no expression in certain cortical vessels which were GluT-1 immunopositive and positivity was consistent in non-barrier areas such as the pineal gland. These findings were completely independent of age or experimental conditions. Therefore, the role of the EBA antigen in the BBB remains unclear: it has been undeniably linked to vascular permeability, but its presence in non-barrier vessels suggests another vascular function. Although visual experience modifies vascular density in the visual cortex, it has not been shown to have an influence on the maturation of the BBB function.