Class 7: Ischemia-Reperfusion

Question 1

Evaluate brain energy metabolism

Answer 1

• Glu=essential(Or lactate)
• brain req’s continuous circulation
• excitatory/inhibitory neurons consume = energy
• brain=inefficient..50-70% O2 use and only 10% glucose extracted.
• includes: glycolysis, gluconeogenesis, pentose phosphate shunt, malate aspartate shuttle, TCA cycle.

Question 2

Apply various techniques to IMAGE ischemia reperfusion

Answer 2

1. PET: positron emission tomography. Uses analogs of glu. (2-flouro-deoxyglucose). Quantitative intracellular trapping of phosphorylated DG-6-phosphate, enables assays of the hexokinase reaction.
2. MRS: magnetic resonance spectroscopy. Uses glu labeled w/ radioactive or stable isotope. NMR spectrum obtained- determine metabolism of precursors via specific neuronal/glial pathways.

Question 3

Distinguish btw Focal vs. global ischemia

Answer 3

Focal cerebral ischemia: focal disruption of blood flow to a part of the brain-majority of CVAs, thanks to collateral circulation.

Global cerebral ischemia:transient impairment of blood flow to whole brain, penumbra is area of reduced blood flow. Necrosis w/in 3 hours.

Question 4

Explain the cellular mechanisms of brain injury in ischemia-reperfusion

Answer 4

Disruption-blood flow->reduction/absence of O2/glu supply->impaired metabolism->reduced ATP levels->Ion pump dysfunction->membrane depolarization->opening of voltage-gated channels->cascade of subsequent signaling events->cell death in a given brain region

Question 5

Evaluate various neuroprotective strategies to treat ischemia reperfusion injury

Answer 5

• THROMBOLYTICS
• NMDA receptor antagonists
• GABA agonists
• protein synthesis inhibitors
• cascade inhibitors
• -*OMEGA 3 FA (DHA)-anti-inflammatory effects, protective in ischemia/Spinal Cord injury-docosanoid-neuroprotectin(NPD1). DHA leads to NPD1
• Heat shock response
• antioxidants-free radical scavengers (spin traps)
• Growth factors-basic fibroblast growth factor
• neurotrophins

Question 6

Apply various techniques to study ischemia reperfusion

Answer 6

• Primary neuronal cultures: excitatory/inhibitory (GABA)
• Cell lines: those that undergo cell division
• brain-isolated organelles (mito., cytosol, synaptosomes), brain slice cultures.
• surgical methods performed on live animals middle cerebral artery occlusion-focal ischemia. Carotid artery occlusion-global occulsion
• in vivo imaging techniques (PET,MRS)

Question 7

What is the mediator of damage in the brain by means of eicosanoids?

Answer 7

Ca++

Question 8

NMDA and AMPA/kainate overactivation lead to:

Answer 8

Excitotoxicity

Explained: loss of ion gradients leads to elevated intracellular [Ca++]. Then, Neurotransmitter levels rise, glutamate receptor activation causes influx of Ca++ and Zn++. This activates intracellular pathways

Question 9

Activation of death receptor (Fas)->formation of DISC->DISC site activation for procaspase-8->cascade 8 directly activates cascade-3, an effector caspase.

Answer 9

Extrinsic pathway.

Question 10

Excessive influx of Ca++ into cytoplasm disrupts normal homeostasis. This AFFECTS THE FUNCTION OF MITO. AND ER.
->release of cytochrome c from mitochondrial intermembrane space results in cascade-3 activation via apoptosome complex.

->ER stress induces activation of caspase12,caspase9, and caspase3.

Answer 10

Intrinsic activation