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Understanding Neural Circuit Development: Key Stages of Cellular Activity

This lecture explores the six distinct stages of cellular activity in neural circuit development: neurogenesis, cell migration, differentiation, synaptogenesis, neuronal cell death, and synaptic rearrangement. It delves into the processes of neurogenesis, including precursor cell dynamics, neuronal migration mechanisms guided by cell adhesion molecules, and the formation of specialized neuron and glia types. Additionally, it examines the intricate processes of axon guidance, synapse formation, and the critical balance between neuronal survival and death.

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Understanding Neural Circuit Development: Key Stages of Cellular Activity

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  1. Development of Neural Circuits Lecture 4

  2. Stages of Cellular Activity • 6 distinct stages 1. Neurogenesis 2. Cell migration 3. Differentiation 4. Synaptogenesis 5. Neuronal cell death 6. Synaptic rearrangement ~

  3. Neurogenesis • Precursors (stem) cells • Neural tube’s ventricular zone • Induction signals • Asymmetrical mitosis •  another stem cell • Can divide again •  neuroblast • Cannot divide • Neuroblasts  neurons & glia ~

  4. Neuronal Migration • Neural crest  PNS • Guided by cell adhesion molecules (CAMs) • Neural tube  CNS • along radial glia • later: along other neurons ~

  5. Cell Migration • Long-distance migration • Along radial glia • Tangentially to other brain areas • Cerebellar neuroblasts • Mesoencephalon  • Rhombencephalon ~

  6. Differentiation • Into specific neuron & glia types • Cell-autonomous • Genetic instructions • Cell-to-cell interactions • Induction signals • Critical periods ~

  7. Construction of Circuits • Linkage of neurons in different regions • Growth of axon from origin to target • Formation of appropriate synapses • Cell-to-cell signaling • Tropic factors • Trophic factors ~

  8. Axon Guidance • Axonal growth cone • Filopodia • Decision points • Decussate or not • Chemical cues • Ligands/receptors ~ • Non-diffusable cues • CAMs • Tropic & trophic • Diffusable chemical signals • Attraction • netrins • Repulsion • Semaphorins ~

  9. Synaptogenesis • Superior cervical ganglion (PNS) •  eyes •  ear blood vessels • After axons reach target • Establish synapse • Retract & regrow • Do not form synapse ~

  10. Synaptogenesis • Neurotropic factors • Ephrins & cadherins • Specificity  ligand/receptor types • Neurotrophic factors (neurotrophins) • After synapse formation • Cell-to-cell signals • Nerve growth factor (NGF) •  neurite growth ~

  11. Apoptosis • Neuronal cell death • programmed cell death • 20-80% of neurons in a region • lack of neurotrophic factors • Wrong or no connection • neurons wither & die ~

  12. Synaptic Rearrangement • Competition • elimination of synapses • formation of new synapses • Activity-dependent • Neurotransmitter release • Losing axon retracts • May strengthen synapse at other targets • Winner  synapses at target ~

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