Glial Cells and Neurogenesis Quiz

Glial Cells & Neurogenesis

• Oligodendrocytes are found in the central nervous system (CNS)
• Oligodendrocytes wrap axons with myelin sheaths, increasing action potential conduction velocity.
• Schwann cells are in the peripheral nervous system (PNS)
• Schwann cells myelinate peripheral nerves (motor and sensory neurons), similar to oligodendrocytes.
• Not all neurons are myelinated.
• Microglia function like macrophages, proliferating via mitosis.
• Microglia are crucial for the immune response in the brain.
• Unlike neurons, microglia do not require stem cells to proliferate.
• They originate from blood cell lineage, not neural stem cells.
• Exercise increases microglial proliferation in the hippocampus.
• Neurons do not divide like other cells (skin, liver, blood).
• Stem cells are needed to generate new neurons.
• Astrocytes and oligodendrocytes can divide from stem cells.
• Microglia do not originate from stem cells.

Neurogenesis Locations

• Olfactory Bulb: New neurons are created in the lateral ventricles and migrate to the olfactory bulb.
• Hippocampus (Dentate Gyrus): Stem cells are in the granule cell layer.
  • Stem cells divide asymmetrically, creating one stem cell and one new neuron (granule cell).
  • New neurons stay within the hippocampus.
  • Neurogenesis slows with age.

Experimental Evidence of Neurogenesis

• BrdU Labeling: BrdU is used, like thymidine, to indicate cell division.
  • It's incorporated into DNA during cell division
  • Immunohistochemistry visualizes the new cells.
  • If BrdU-labeled cells also display neuronal markers, neurogenesis is confirmed.
• Early studies (1960s) hinted at neurogenesis, but lacked evidence of neuronal differentiation.
• Advanced double-labeling techniques (1980s) confirmed new neurons in the hippocampus.
• Exercise boosts neurogenesis (studies in running mice).

Synaptic Transmission & Receptors

• Chemical Synapses: Presynaptic neurons release neurotransmitters into synapses; postsynaptic neurons' receptors determine the effect (excitation or inhibition).
• Calcium influx triggers neurotransmitter release.
• Electrical Synapses (Gap Junctions): Direct ion flow between adjacent neurons; faster than chemical synapses; crucial for synchronous firing (e.g., gonadotropin-releasing hormone neurons).

Types of Receptors

• Ionotropic Receptors (Fast-acting): Neurotransmitter binding directly opens ion channels.
  • Example: AMPA receptors allow sodium influx.
• Metabotropic Receptors (Slow-acting): Neurotransmitter binding triggers intracellular signaling cascades.
  • Example: Dopamine, serotonin, beta-endorphin receptors.
  • Utilize G-protein coupled receptors (GPCRs).

G-Protein Coupled Receptors (GPCRs)

• Mechanism:
  • Neurotransmitter binds GPCR.
  • GPCR changes shape, activating G-protein (GTP replaces GDP).
  • G-protein subunits detach, initiating an intracellular signal.
  • This can lead to ion channel opening or second messenger cascades.
  • Example GPCRs: Beta-adrenergic receptors, dopamine receptors, serotonin receptors

Neurotransmitter Receptors & Synaptic Plasticity

• AMPA Receptors: Ligand-gated; glutamate binding causes sodium influx and depolarization; fast, simple.
• NMDA Receptors: Ionotropic; require glutamate binding and significant depolarization to remove magnesium block.
  • Allow calcium influx, essential for learning and memory.

Long-Term Potentiation (LTP)

• LTP strengthens synaptic connections.
• Mechanism:
  • Initial weak stimulation opens only AMPA receptors, resulting in weak depolarization.
  • Repeated strong stimulation maintains AMPA receptor opening, increasing depolarization.
  • NMDA receptors open (Mg²⁺ removed).
  • Calcium influx triggers intracellular signals.
  • More AMPA receptors are inserted into the membrane.
  • Future weak stimuli trigger stronger responses.
• NMDA receptors act as "coincidence detectors," registering strong and repeated activity.
• Blocking NMDA receptors prevents LTP.
• LTP is crucial for learning and memory (cellular level example: from no action potential to triggering one, with the same weak signal after LTP.)
• Drugs affecting NMDA receptors can affect memory.

Key Takeaways (for Exam prep)

• Glial cell functions (oligodendrocytes, Schwann cells, astrocytes, microglia)
• Neurogenesis (locations, BrdU labeling)
• Synaptic transmission (chemical vs. electrical)
• Receptor types (ionotropic, metabotropic)
• NMDA and AMPA receptor roles in plasticity/learning
• LTP as the cellular basis of learning/memory.
• Experimental techniques (BrdU labeling, immunohistochemistry).

Recommended Study Actions

• Review figures (ionotropic vs. metabotropic).
• Understand NMDA receptor function (depolarization, Mg²⁺ block).
• Reinforce LTP concept (connecting NMDA to learning).
• Read the electrical membrane primer.
• Prepare for potential exam questions (comparisons, neurogenesis study, LTP, receptor differences, NMDA importance for plasticity).