glial cells

microglia (4)

• resident macrophages/immune cell of brain

• tile whole brain + spinal cord

• of myeloid origin → migrate to CNS from yoke sac at embryonic day 10

• can extend processes + phagocytose w/o moving their processes

ramified, “resting state of microglia (2)

• constantly surveying tissue for damaged cells, plaques, infectious agents

• used for sensing tissue + they do not move their somata/migrate

microglia motility ____ in response to neural activity

• increases

• can become more permanently hyper-ramified after plasticity (more active)

microglia amoeboid state

microglia retreat when need to move large distances of persistent problems in tissue (max pro-inflammatory)

microglia are activated by (5)

• glutamate

• K+

• ATP

• pro-inflammatory cytokines

• LPS → cell wall component of gram-negative bacteria

microglia secrete pro-inflammatory signals once activated like: (3)

• IL1-alpha

• IL1-beta

• TNF-alpha

synapse elimination experiment (2)

• Evidence that microglia are involved in synaptic pruning/elimination, as one can find both blue and red neural projections inside the microglia

• Blue and red are retinal ganglion cells projecting to the thalamus (LGN)

the complement cascade (2)

• series of proteins that are part of the innate immune system that attack a cell’s membrane

• helps antibodies + phagocytes eliminate damaged cells/microbes

what complement cascade do synapses express (3)

• complement 3 (C3)

• Microglia express the C3 receptor (C3R)

• knocking either out impairs synapse engulfment

oligodendrocytes (3)

• provides myelin, metabolic + trophic support (GDNF + BDNF) for neurons/axons

• processes form myelin segment that wraps around an axon

  • single cell provides myelination for multiple axons

• helps speed action potential propagation by focusing event on Nodes of Ranvier

  • 150m/s vs 0.5-10m/s unmyelinated

oligodendrocyte progenitor cells (3)

• ~4 % of the cells in the gray matter

• express the proteoglycan NG2 marker → way to differentiate

• precursor cell that can differentiate into mature, myelinating oligodendrocyte

  • don’t HAVE to differentiate

only glia to receive direct synaptic contact from neurons

• oligodendrocytes:

  • do not fire APs but receive inhibitory/excitatory synaptic transmission

what happens if an OPC develops into mature oligodendrocyte

a neighbouring OPC will divide + replace it → keeping their numbers constant

glutamatergic synapses on oligodendrocyte precursor cells in the hippocampus (OPCs)

• OPCs receive synaptic inputs to sense neural activity to determine if they need to differentiate into a mature oligodendrocyte and myelinate axons

• no AP

OPC to OL differentiation model (2)

• As an OPC (or NG2 cell) differentiates to become a mature Oligodendrocyte, they lose their synaptic contacts and lose their ionotropic glutamate receptors.

• disruption of process impairs memory consolidation