Lecture 6 Mechanisms and Mediators of Neurovascular Coupling Flashcards
Briefly overview the first neurovascular ideas/research
Around 1880, Angelo Mosso Balance Board
1890 Roy and Sherrington conducted research on dogs from which they concluded vascular supply in brain can be varied locally in correspondence with functional activity
describe what makes Murine models, good models in NV research
- we have a good understanding of anatomy (barrel cortex). With preserved anatomy from snout to barrelletes in the hindbrain, to barreloids in the VPN thalamus to barrels in the somatosensory cortex- similar to human trigeminal projections. With a good topographic map of murine model visible on cortex.
- easy to stimulate - whisking
- easy to access barrel cortex for measurements- thinning skull
advantages of anaesthetised animals
- high levels of control
- able to be invasive
- a good anaesthetic can mimic quiet awake state in brain activity
disadvantages of anaesthetised animals
- animals aren’t awake so difficult to compare to human fMRI
- Anaesthetic can alter NV coupling
advantages of awake animals
- looking at more natural behaviour
- more comparable to human fMRI
disadvantages of awake animals
- behaviour can confound results
- more resources required e.g. money and time to train
- welfare implications
- more high risk- if animals die, data is lost
advantages of ex-vivo slice research
- good spatial precision (can isolate single cells)
- accurate pharmacology experiments- can see how drugs are acting
- have been vital in showing role of pericytes
disadvantages of ex-vivo slice research
lack of active blood flow (major issues of performing NV research)
- time scale responses different- usually much slower
- questions about how healthy the slice is
3 key cells of NV unit
astrocytes
pericytes
endothelial cells
where are astrocytes found
between neurons and vessels- with feet on BVs
where are pericytes found
around blood vessels
where are endothelial cells found
lining blood vessels
Zonta et al 2003 (astrocytes)
slice work with electrode stimulatiom, found that electrode stimulation to neurons, activated nearby astrocytes to increase Ca2+ , causing vasodilation of nearby vessels
describe the prostaglandin pathway
astrocytes uptake glutamate from synapses, causing an increase in Ca2+ which activates the prostaglandin pathway where phospholipase transform phospholipids into prostanoids, via COX 1 and 2, prostanoids dilate blood vessels
what do COX inhibitors do?
inhibit vasodilation
how do we know that astrocytes are unlikely wholly responsible for NV coupling?
when COX is inhibited or metabotropic glutamate receptor antagonists are given, there’s 50% reduction in dilation- suggesting other mechanisms (for other 50%)
Takano 2006 (astrocytes)
used in-vivo 2 photon calcium imaging in anaesthetised mice. Photolysis of caged calcium, led to vasodilation. Also showed how close to veins and arteries astrocytes were. They found COX inhibitors only reduced vasodilation 50%
Nizar et al 2013 (astrocytes)
found astrocyte calcium increase was occurring after vasodilation- but dismissed fast responses as artefacts
Lind et al. (astrocytes)
found that astrocyte Ca2+ does elevate before vasodilation- did not dismiss fast responses
who has conducted much research on pericytes?
David Atwell
discuss David Atwell’s Labs work on pericytes
found that pericyte activation caused vasocontriction and that pericytes seem to regulate blood flow in health and disease, however, this work was all done ex vivo slices and responses were very slow
discuss work in conflict to David Atwell’s
Work at Yale suggested that it was actually arteriolar smooth muscle cell contractility causing these changes in blood flow- recorded in live animals
what did Zlokovic find 2017 (pericytes)
that pericyte degeneration leads to NV uncoupling and limits O2 in brain- due to disease such as AD
what is the issue with much pericyte research
generally done ex vivo, so lacking in vivo work
what does Nitric Oxide (NO) do?
vasodilation
what enzyme produces NO?
nitric oxide synthase
what are the 3 isoforms of NOS?
iNOS (inducible)
eNOS (endothelial)
nNOS (neurons)
draw the basic pathway for NO
check book
what are the 2 types of inhibitors of NOS?
general and specific
what are the 2 types of NOS general inhibitors?
L-NNA and L-NAME
what do L-NNA and L-NAME do?
inhibit both eNOS and nNOS
name the specific NOS inhibitor
7-NI
what does 7-NI do?
inhibits nNOS only
what is the issue with 7-NI
difficult to dissolve to cross BBB so has to be injected (neuroinflammation consequences)
what’s the issue wit general inhibitors?
target both eNOS and nNOS so difficult to seperate when focussing on NV coupling
Lindaver 1999 (NO)
found NO to be a modulator not mediator of NV coupling in rat cortex- when SNAP/cGMP were present to make NO available, blood flow was still increased with inhibitor- thought to be involved in basal floow flow
Stefanovic 2017 (NO)
NOS inhibitors reduced BOLD response by 50% suggesting role of NO in NV coupling from nNOS interneurons
discuss variation of nNOS throughout the brain
found at varying levels e.g. high in the cerebellum, this may mean different regions have differing mechanisms involving NV
each may be main modulator in cerebellum
discuss research into the role of endothelium in NV coupling
research suggests that upstream dilation is propagated along vessel wall via gap junctions between smooth muscle cells .
Hillman found when light was used to disrupt vascular endothelium, backward dilation stopped suggesting separate mechanisms for capillaries and surface vessels
