Subregional topography of capillaries in the dorsal vagal complex of rats: II. Physiological properties.
The differentiated cytoarchitecture, neurochemistry, and capillary organization of the rat dorsal vagal complex prompted this comprehensive investigation of microvascular physiology in 11 subdivisions of area postrema, 5 subnuclei of nucleus tractus solitarii (NTS), the dorsal motor nucleus of the vagus nerve, and 4 other gray matter structures in the dorsal medulla oblongata. Microvascular exchangeable volume (residual plasma volume), capillary blood and plasma flow, and unidirectional transfer constants for a tracer amino acid, [14C]alpha-aminoisobutyric acid (AIB), varied considerably among the structures analyzed. Exchangeable volume, largest in area postrema medial zones (about 29 microliters.g-1) and smallest in medullary gray matter (7-11 microliters.g-1), correlated directly with subregional densities of capillaries and rates of tissue glucose metabolism. Capillary blood flow (range of 1,430-2,147 microliters.g-1.min-1), plasma flow, and tissue glucose metabolism (range of 0.48-0.71 mumol.g-1.min-1) were linearly related in the dorsal vagal complex. The most striking quantitative difference among structures in this brain region were the rates of transcapillary influx and derived permeability X surface area (PS) products of [14C]AIB, which has physicochemical properties resembling those of hormones. PS products for AIB were negligible in most medullary gray matter regions (less than 1 microliter.g-1.min-1, indicative of blood-brain barrier properties), but were 20-59X and 99-402X higher in NTS subnuclei and area postrema, respectively. An extraordinary feature of the microcirculation in area postrema was the long-duration transit of tracer sucrose and blood, a characteristic that would amplify the sensing ability of area postrema as it monitors the composition of the circulation.
Gross
P M
PM
Department of Surgery, Queen's University, Kingston, Ontario.
Wall
K M
KM
Wainman
D S
DS
Shaver
S W
SW
D000818:Animals; D002196:Capillaries / Q000033:anatomy & histology / Q000502:physiology; D003243:Consciousness; D005947:Glucose / Q000378:metabolism; D008297:Male; D008526:Medulla Oblongata / Q000098:blood supply* / Q000378:metabolism / Q000502:physiology; D051381:Rats / Q000033:anatomy & histology* / Q000502:physiology; D011919:Rats, Inbred Strains; D012039:Regional Blood Flow; D014630:Vagus Nerve / Q000502:physiology*
D005947:Glucose