Angioarchitecture of the CNS, pituitary gland, and intracerebral grafts revealed with peroxidase cytochemistry

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Abstract
Blood vessels of the fetal, neonatal, and adult subprimate and primate CNS, including circumventricular organs (e.g., median eminence, pituitary gland, etc.), and of solid CNS and nonneural (anterior pituitary gland) allografts placed within brains of adult mammalian hosts were visualized with peroxidase cytochemistry applied in three ways: (1) to tissues from animals injected systemically with native horseradish peroxidase (HRP) or peroxidase conjugated to the lectin wheat germ agglutinin (WGA) prior to perfusion fixation; (2) to tissues from animals infused with native HRP into the aorta subsequent to perfusion fixation; and (3) to tissues from animals fixed by immersion and incubated for endogenous peroxidase activity in red cells retained within blood vessels. In neonatal and adult animals receiving native HRP intravascularly, non‐fenestrated vessels contributing to a blood‐brain barrier were outlined with HRP reaction product when tetrarnethyl‐benzidine (TMB) as opposed to diaminobenzidine (DAB) was used as the chromogen; fenestrated vessels of circumventricular organs were not discernible due to the density of extravascular reaction product. Fenestrated and nonfenestrated cerebral and ext racer ebral blood vessels exposed to blood‐borne WGA‐HRP were visible when incubated in TMB and DAB solutions. Native HRP infused into the aorta of fixed animals likewise labeled nonfenestrated vessels throughout the brain upon exposure to TMB or DAB but obscured fenestrated vessels of the circumventricular organs. Endogenous peroxidase activity of red cells, seen equally well with TMB and DAB, outlined blood vessels throughout the cerebral gray and white matter and all circumventricular organs in fetal, neonatal, and adult animals.Application of the three peroxidase cytochemical approaches to study the development or absence of a blood‐brain barrier in intracerebral allografts demonstrated that the vascularization of day 16–19 fetal/1 day neonatal. Placement of the grafts. CNS allografts secured from donor sites expected to possess a blood‐brain barrier exhibited blood vessels that were not leaky to HRP injected intravenously in the host. Fenestrated blood vessels associated with anterior pituitary allografts were evident prior to 3 days posttransplantation within the host brain and permitted blood‐borne HRP in the host to enter the graft and surrounding host brain parenchyma.The three peroxidase cytochemical approaches are useful for visualizing CNS blood vessels that contribute or do not contribute to a blood‐brain barrier in fetal, neonatal, and adult laboratory animals; the three approaches have potential application to cerebrovascular studies of stroke, trauma, and neoplasia.