A good explanation of capillary action. Make sure your neurologist can answer your questions about how to get your brain capillaries working after a stroke. Don't take, 'I don't know', for an answer. Never mind me, I have no medical training so I can't say anything useful about how the medical world doesn't know what it is doing in regards to stroke rehab. Naked emperor and all.
Bidirectional control of CNS capillary diameter by pericytes
Neural activity increases local blood flow in the central nervous system (CNS), which is the basis of BOLD (blood oxygen level dependent) and PET (positron emission tomography) functional imaging techniques1, 2, 3. Blood flow is assumed to be regulated by precapillary arterioles, because capillaries lack smooth muscle. However, most (65%) noradrenergic innervation of CNS blood vessels terminates near capillaries rather than arterioles4, and in muscle and brain a dilatory signal propagates from vessels near metabolically active cells to precapillary arterioles5, 6, suggesting that blood flow control is initiated in capillaries. Pericytes, which are apposed to CNS capillaries and contain contractile proteins7, could initiate such signalling. Here we show that pericytes can control capillary diameter in whole retina and cerebellar slices. Electrical stimulation of retinal pericytes evoked a localized capillary constriction, which propagated at 
2 
m s-1 to constrict distant pericytes. Superfused ATP in retina or noradrenaline in cerebellum resulted in constriction of capillaries by pericytes, and glutamate reversed the constriction produced by noradrenaline. Electrical stimulation or puffing GABA (
-amino butyric acid) receptor blockers in the inner retina also evoked pericyte constriction. In simulated ischaemia, some pericytes constricted capillaries. Pericytes are probably modulators of blood flow in response to changes in neural activity, which may contribute to functional imaging signals and to CNS vascular disease.
2 m s-1 to constrict distant pericytes. Superfused ATP in retina or noradrenaline in cerebellum resulted in constriction of capillaries by pericytes, and glutamate reversed the constriction produced by noradrenaline. Electrical stimulation or puffing GABA (-amino butyric acid) receptor blockers in the inner retina also evoked pericyte constriction. In simulated ischaemia, some pericytes constricted capillaries. Pericytes are probably modulators of blood flow in response to changes in neural activity, which may contribute to functional imaging signals and to CNS vascular disease.
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