Cell Types

Question 1

Features of Astrocytes

Answer 1

• Non-neuronal (neural precursor but not a neuron)
• Heterogeneous
• Can proliferate
• Come from radial glial cells (RGCs) from neuroepithelium lining neural tube
• Biomarkers = GFAP (not on all; when under stress) and Aquaporin 4
• Lots of connections and gap junctions w/ ea other

Question 2

Functions of Astrocytes (6)

Answer 2

• Signal epithelial cells to maintain BBB (otherwise leaky)
• Neurovascular coupling (more blood to more active neurons - prostaglandins, NO, AA)
• Aquaporin4, VEGF, NO for fluid balance (inc AQP4 leads to inc cytoplasm fluid; dec AQP4 leads to extracellular edema)
• Synaptic pruning in development (C1q - marks for destruction)
• Clear K+ and neuroT (special Kir4.1 channel)
• Tissue repair (mild or moderate); glial scars of ECM

Question 3

Astrocytosis (or gliosis)

Answer 3

Mild

- Non-penetrating, non-contusive injury, viral infection, systemic bacterial infection
- Variable up-regulation of GFAP, hypertrophy of cell bodies and processes w/o loss of individual domains, little/no astrocyte proliferation, no reorganization

Moderate

- Severe focal lesions, acute inflammation and infections, chronic neurodegenerative disorders (like MS), abscess, penetrating trauma
- Pronounced up-regulation of GFAP and hypertrophy, proliferation so overlap in domains,  greater chance of persistent reorganization/change in architecture of tissue

Can cause pathology …inflammation, can inhibit axon growth and cell migration, edema, chronic pain, dec seizure threshold

Question 4

Features of Oligodendrocytes

Answer 4

• Non-neuronal
• From OPCs of ventricular lining; not until 2nd trimester
• Migrate uniformly then some exit cell cycle and become mature myelinating oligodendrocytes whiles others remain quiescent immature OPCs (stem cells)
• Biomarkers = Myelin components (ex - myelin basic protein)

Question 5

Function of Oligodendrocytes

Answer 5

• Myelinate axons (wrap axons in their plasma membrane)
  
  • **Unlike in PNS, they can myeline multiple axons

Re-myelinate if injury; REPAIR (important b/c w/o myelin there is damage and CNS cannot regenerate axons)
**Immature OPCs called out of quiescence and differentiate to make new sheath (rate-limiting step)

Question 6

Features of Microglia

Answer 6

• Non-neural (migrate into CNS)
• From yolk sac monocytes
• Mobile ameboid form in early development b/c debris from pruning THEN become resting/ramified microglia (rod nucleus and multiple processes; resident macrophages)
• Biomarker = CX3CR1 (receptor)

Question 7

Function of Microglia (how are they activated? what happens once activated?)

Answer 7

• Detect foreign agents and local physiological changes (resident macrophages)
• Activated by virus, bacteria, dead cells, debris from necrosis, toxins, damage, active astrocytes, etc
• Once active, become APCs (uptake MHC class I and II) and recruit pro-inflammatory agents
• Once active, some retract and thicken processes while others go back to ameboid shape and phagocytose

Question 8

How can microglia cause damage?

Answer 8

• If chronic —> inflammatory cascades —> damage and cell death
• Activate microglia may also secrete specific toxic molecules (HIV —> activate microglia —> NO/cytokines that cause damage —> dementia)