Subregional topography of capillaries in the dorsal vagal complex of rats: I. Morphometric properties

Abstract

Cytoarchitectonic and neurochemical studies of the dorsal vagal complex in the caudal medulla oblongata of rats indicate the existence of distinct anatomical and functional compartments within its components. We applied morphometric methods to discern whether capillary networks differed quantitatively between subregions and zones of area postrema, nucleus tractus solitarii (NTS), and dorsal motor nucleus of the vagus nerve (DMN) of rats. Analysis of 11 subdivisions of area postrema identified both "true" (range in luminal diameter of 3-7.5 microns) and sinusoidal (luminal diameter greater than 7.5 microns) capillaries that, together, made the capillary density for most of area postrema 75% greater than that found in NTS and DMN (526/mm2 vs about 300/mm2). The rank order of true capillary density in area postrema along its rostracaudal axis was caudal greater than central greater than rostral, whereas the reverse order was true for sinusoidal capillaries. Dorsal (periventricular) and medial zones of area postrema throughout its rostrocaudal axis tended to have higher values for capillary density, volume, surface area, luminal diameter, and pericapillary space volume than lateral or ventral zones bordering NTS. Within 200 microns of obex, the ventral zone of rostral area postrema was distinct, having a relatively sparse capillary density that may indicate morphological specializations limiting blood-tissue communication in this subregion. There were no quantitative differences in capillary dimensions between DMN and three subnuclei of NTS. These studies add to extant evidence that the dorsal vagal complex is differentiated for specific functions. Area postrema, especially, has topographical diversity in its capillary organization that likely corresponds to complex roles in neuroendocrine, autonomic, and chemosensory mechanisms.

Quantitative Confocal Imaging of the Retinal Microvasculature in the Human Retina

“…Three-dimensional vascular configurations are believed to increase the efficiency of oxygen transfer and waste removal in metabolically active tissues. 21,23 The variation in retinal capillary network morphology identified in our study demonstrated important parallels to the human cerebral cortex where the microcirculation is adapted in accordance with regional neuronal demands. 24,36,37 Previous researchers have shown that the inner 1 mm of cerebral cortex demonstrates large meshes, the next 2 mm are filled with fine polygonal meshes, and the outer 0.1 mm contains large quadrangular meshes that run parallel to the surface.…”

“…[14][15][16]21 A change in capillary branching pattern 22,23 and projected orientation 14,23,24 was used to distinguish the different capillary networks. Additionally, using the movie-sequence function available on Image J software to view the z-stack sequentially, it was possible to determine if capillary networks displayed a laminar, single-planar orientation that was confined predominantly to a single retinal layer or if they displayed a complex three-dimensional configuration that traversed the z-axis.…”

Aquaporin-1 in blood vessels of rat circumventricular organs

“…All vessels have perivascular spaces, with capillaries and sinusoids sometimes sharing the same perivascular space (Shaver et al 1991). Some, but not all, of the vessels in the area postrema have been found to be AQP1-immunoreactive.…”

“…The area postrema is characterised by a high density of Type I and Type III vessels, which accounts for the high vascular permeability of the area; the vessels include capillaries (<7.5 µm diameter) and larger (>7.5 µm diameter) sinusoids (Shaver et al 1991;Gross 1992). All vessels have perivascular spaces, with capillaries and sinusoids sometimes sharing the same perivascular space (Shaver et al 1991).…”

Systemic administration of leptin potentiates the response of neurons in the nucleus of the solitary tract to chemoreceptor activation in the rat

“…The possibility also exists that the NTS may be involved in monitoring circulating levels of leptin. This is not an unreasonable suggestion as the caudal NTS region, especially the Sg, the dorsal region of Sm, and Com have been suggested to have numerous fenestrated capillaries, enlarged perivascular spaces, and a high capillary permeability to blood-borne substances (Gross et al, 1990;Shaver et al, 1991). The finding that neurons within the Sg, and dorsal Sm, and Com are labeled following the systemic injections of dyes such as horseradish peroxidase and fluorogold (Fox and Powley, 1989;Leong and Ling, 1990;Munzberg, 2008), suggests that the blood-brain barrier in these NTS regions may be such that it allows access of bloodborne substances to gain ready access to neurons.…”