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Morphology and function of capillary networks in subregions of the rat tuber cinereum

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The differentiated cytology, cytochemistry, and functions within subdivisions of the tuber cinereum prompted this morphometric and physiological investigation of capillaries in the median eminence and arcuate nucleus of albino rats. Morphometric studies established that the external zone of the median eminence had 3–5 times the number and surface area of true and sinusoidal capillaries than the internal or subependymal median eminence zones, or either of two subdivisions examined in the arcuate nucleus. Type-I true capillaries, around which Virchow-Robin spaces comprise 1% of arcuate tissue area, were situated proximally to the median eminence border. This finding is consistent with a premise that confluent pericapillary spaces enable infiltration of arcuate neurons by factors from capillary blood from the median eminence or Virchow-Robin spaces. Physiologically, the rate of penetration across the median eminence capillaries by blood-borne [14C]α-aminoisobutyric acid (a neutral amino acid used as a capillary permeability tracer) was 142 times greater than for capillaries in the distal arcuate nucleus within 12 s of tracer administration. A new finding was that the proximal arcuate nucleus had a permeability x surface area product of 69 μl g−1 min−1, 34 times greater than that in more distal aspects of the tuber where blood-brain barrier properties exist. We also found that the microcirculatory transit time of a plasma space marker, [14C]sucrose, was considerably longer (1.2 s) in the median eminence and proximal arcuate nucleus than in the distal arcuate or ventromedial nucleus (0.4 s). By virtue of its high capillary permeability and extensive blood-tissue surface area, including the wide Virchow-Robin spaces, the median eminence external zone could be a gateway for flooding other tuberal compartments with blood-borne factors. This effect may be compounded by capillary bed specializations in the proximal arcuate nucleus where Type-I true capillaries, Type-III sinusoids, and pericapillary spaces are confluent with those in the median eminence. The results indicate that the proximal arcuate parenchyma could be exposed to circulating neuroactive substances on a moment-to-moment basis.

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Authors and Affiliations

  1. Neurosurgical Research Unit, Department of Surgery, Queen's University, K7L 3N6, Kingston, Ontario, Canada

    Steven W. Shaver, Judy J. Pang, Dan S. Wainman, Katharine M. Wall & Paul M. Gross

  2. Department of Physiology, Queen's University and Kingston General Hospital, K7L 3N6, Kingston, Ontario, Canada

    Steven W. Shaver, Judy J. Pang, Dan S. Wainman, Katharine M. Wall & Paul M. Gross

  3. Kingston General Hospital, K7L 3N6, Kingston, Ontario, Canada

    Steven W. Shaver, Judy J. Pang, Dan S. Wainman, Katharine M. Wall & Paul M. Gross

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  1. Steven W. Shaver
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  2. Judy J. Pang
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  3. Dan S. Wainman
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  4. Katharine M. Wall
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  5. Paul M. Gross
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Dedicated to Dr. Milton W. Brightman of Bethesda, Maryland, USA on the occasion of his 67th birthday and tribute as Craigie scholar at the First Craigie Conference on Brain Capillaries, Toronto, Ontario, June 24, 1990

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Shaver, S.W., Pang, J.J., Wainman, D.S. et al. Morphology and function of capillary networks in subregions of the rat tuber cinereum. Cell Tissue Res 267, 437–448 (1992). https://doi.org/10.1007/BF00319366

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  • DOI: https://doi.org/10.1007/BF00319366

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