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ref: -0 tags: Kleinfeld vasculature cortex review ischemia perfusion date: 01-22-2017 19:40 gmt revision:3 [2] [1] [0] [head]

PMID-25705966 Robust and fragile aspects of cortical blood flow in relation to the underlying angioarchitecture.

  • "The penetrating arterioles that connect the pial network to the subsurface network are bottlenecks to flow; occlusion of even a single penetrating arteriole results in the death of a 500 μm diameter cylinder of cortical tissue despite the potential for collateral flow through microvessels."
  • The pioneering work of Fox and Raichle [7] suggest that there is simply not enough blood to go around if all areas of the cortex were activated at once.
  • There is strong if only partially understood coupling between neuronal and vascular dysfunction [15]. In particular, vascular disease leads to neurological decline and diminished cognition and memory [16].
  • A single microliter of cortex holds nearly one meter of total vasculature length wow! PMID-23749145
  • Subsurface micro vasculature (not arterioles or venules) is relatively robust to occlusion; figure 4.

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ref: -0 tags: David Kleinfeld penetrating arterioles perfusion cortex vasculature date: 10-17-2016 23:24 gmt revision:1 [0] [head]

PMID-17190804 Penetrating arterioles are a bottleneck in the perfusion of neocortex.

  • Focal photothrombosis was used to occlude single penetrating arterioles in rat parietal cortex, and the resultant changes in flow of red blood cells were measured with two-photon laser-scanning microscopy in individual subsurface microvessels that surround the occlusion.
  • We observed that the average flow of red blood cells nearly stalls adjacent to the occlusion and remains within 30% of its baseline value in vessels as far as 10 branch points downstream from the occlusion.
  • Preservation of average flow emerges 350 mum away; this length scale is consistent with the spatial distribution of penetrating arterioles
  • Rose bengal photosensitizer.
  • 2p laser scanning microscopy.
  • Downstream and connected arterioles show a dramatic reduction in blood flow, even 1-4 branches in; there is little reduncancy (figure 2)
  • Measured a good number of vessels (and look at their density!); results are satisfactorily quantitative.
  • Vessel leakiness extends up to 1.1mm away (!) (figure 5).

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ref: -0 tags: David Kleinfeld cortical vasculature laser surgery network occlusion flow date: 09-23-2016 06:35 gmt revision:1 [0] [head]

Heller Lecture - Prof. David Kleinfeld

  • Also mentions the use of LIBS + q-switched laser for precisely drilling holes in the scull. Seems to work!
    • Use 20ns delay .. seems like there is still spectral broadening.
    • "Turn neuroscience into an industrial process, not an art form" After doing many surgeries, agreed!
  • Vasodiliation & vasoconstriction is very highly regulated; there is not enough blood to go around.
    • Vessels distant from a energetic / stimulated site will (net) constrict.
  • Vascular network is most entirely closed-loop, and not tree-like at all -- you can occlude one artery, or one capillary, and the network will route around the occlusion.
    • The density of the angio-architecture in the brain is unique in this.
  • Tested micro-occlusions by injecting rose bengal, which releases free radicals on light exposure (532nm, 0.5mw), causing coagulation.
  • "Blood flow on the surface arteriole network is insensitive to single occlusions"
  • Penetrating arterioles and venules are largely stubs -- single unbranching vessels, which again renders some immunity to blockage.
  • However! Occlusion of a penetrating arteriole retards flow within a 400 - 600um cylinder (larger than a cortical column!)
  • Occulsion of many penetrating vessels, unsurprisingly, leads to large swaths of dead cortex, "UBOS" in MRI parlance (unidentified bright objects).
  • Death and depolarizing depression can be effectively prevented by excitotoxicity inhibitors -- MK801 in the slides (NMDA blocker, systemically)

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ref: -0 tags: histology optical coherence tomography vasculature avoidance date: 01-29-2013 06:46 gmt revision:0 [head]

PMID-9766311 Optical coherence tomography for neurosurgical imaging of human intracortical melanoma.

  • Relevant for our interests: Subsurface cerebral vascular structures could be identified and were therefore avoided.
  • more broadly, could identify subsurface metastatic melanoma due to reflectance changes. nice.

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ref: Bjornsson-2006.09 tags: micro vasculature histology insertion speed tissue shear date: 01-28-2013 03:38 gmt revision:3 [2] [1] [0] [head]

PMID-16921203[0] Effects of insertion conditions on tissue strain and vascular damage during neuroprosthetic device insertion.

  • We have developed an ex vivo preparation to capture real-time images of tissue deformation during device insertion using thick tissue slices from rat brains prepared with fluorescently labeled vasculature.
  • Direct damage to the vasculature included severing, rupturing and dragging, and was often observed several hundred micrometers from the insertion site. (yikes!)
  • Advocate faster insertion of sharp devices. (tatoo needle?).
  • Cortical surface features greatly affected insertion success; insertions attempted through pial blood vessels resulted in severe tissue compression.
    • Thus, avoiding vasculature is useful not only for avoiding hemorrhaging, but also to prevent excessive tissue compression.
  • High degree of variability
    • Indicates that this should be measured! Scientifically interesting!
  • Insertion speeds:
    • Fast 2 mm/sec
    • Medium 500 um/sec
    • Slow 125 um/sec
  • Perhaps there is no need to experiment with multiple insertion speeds?

____References____

[0] Bjornsson CS, Oh SJ, Al-Kofahi YA, Lim YJ, Smith KL, Turner JN, De S, Roysam B, Shain W, Kim SJ, Effects of insertion conditions on tissue strain and vascular damage during neuroprosthetic device insertion.J Neural Eng 3:3, 196-207 (2006 Sep)