HDS 110 Brain and Behavioral Development “Prenatal Brain Development” January 11th, 2021 Review

• Gastrulation • Process during embryonic development that changes the embryo from a blastula with a single layer of cells to a gastrula containing multiple layers of cells • Gastrulation – YouTube

• Neurulation and formation of the neural tube • Secondary Neurulation • Formation of vesicles within the neural tube th th • The front end of the neural tube organizes with (end of 4 week) (end of 7 week) a series of bulges and convolutions forming Stiles & Jernigan. 2010. The Basics of Brain Development. Prenatal Neuronal Development

• Phases in the life of a 1. Proliferation: generation of • birth of new cells that eventually become neurons 2. Migration: movement of neurons to target brain regions • New cells move from the wall of the ventricle to their final home 3. Differentiation: functional specialization • Cell takes on its adult identity, new shape and characteristics • : formation of between neurons • Begin to establish axonal and dendritic connections • Myelination • Glial cells wrap around some to insulate

Cells in your CNS • Two broad groups of cells • Neurons: primary signaling cells • Receive signals through branching and sends signals through • Some axons encased in sheath, enables faster transmission • : support neurons in various ways, also play a role in regulating signalling, and in establishing neural connections • Approximately 86 billion neurons in CNS, roughly equal number of glia

Neuron

Astrocyte

Oligodendrocyte Cells in your CNS

• Neurons have three main structures: cell body, axons, dendrites • Classified by shape and function • Multipolar, unipolar, bipolar, etc. • Sensor, motor, interneurons, etc. • Most common are pyramidal neurons Glia in Evolution

• Astrocytes • Inhibit and induce formation, activity-dependent synaptic pruning, impact excitatory communication of neurons • Larger and more complex in than non-human apes • Propagate calcium waves more quickly than those of rodents • In rodent brain, enhance and memory • Oligodendrocytes • Produce myelin in CNS, maintain neuronal health • May be important for adult neural plasticity • Upregulated gene expression in human oligodendrocytes relative to chimpanzees • Contributes to cognitive capacity in humans and susceptibility to disease • • Shape neural circuits through and synaptic pruning, promote formation of new synaptic spines • Modulate activity of interneurons • Human specific gene hSIGLEC11 expressed in microglia

Chung et al., 2015; Oberheim et al., 2006; Han et al., 2013; Hayakawa et al., 2005; Berto et al 2019, Miller et al 2012, Yeung et al., 2014; Thion & Garel, 2020 Proliferative zones

• Neurons and glia are produced in proliferative zones • From E28 until E42, cell division is symmetrical • Each round of cell division doubles the number of cells in the proliferative zone • Cells produced during this period are “progenitor” cells, capable of generating neurons and glia • After E42, asymmetric division begins • Some new cells stop dividing and migrate away from proliferative zone, these are newly born neurons • Initially, the number of progenitors producing neurons is small, proportion becomes greater over time Two types of cell division

• Symmetric • Asymmetric • Two identical daughter cells • One progenitor and one neuron • Both daughter cells can continue to • Neuron migrates away divide • Progenitor continues to divide • Begins in GW6

Progenitor Progenitor

Progenitor Progenitor Progenitor Neuron Neuronal Migration

• Migrate to different areas of the body depending on location in neural tube • Cells from neural crest migrate to peripheral nervous system and form clusters in brain • They do this by using cell-adhesion molecules • Some travel by radial glial cells • https://www.youtube.com/watch?v=ZRF-gKZHINk&safe=active • https://www.youtube.com/watch?v=SczOfOXY17U&safe=active Types of neural migration

Somal translocation Radial glial guide Tangential migration

Stiles and Jernigan. 2010. The Basics of Brain Development Migration along radial glial cells

• Radial glial cells • Strands running from proliferative zone to outside edge of brain (pia) • Form scaffolding for new neurons to climb • New neuron attaches to nearby • Propels itself along radial glia cell • Recognizes its final destination and detaches

From: Garrett: Brain & Behavior 4e Developmental Layers

• First cells to leave Ventricular Zone (VZ) form PrePlate (PP) • Next cells split PP into a Marginal Zone (MZ) and a subplate (SP) • This new layer is Cortical Plate (CP), which becomes the adult cortex. • MZ and SP are transient • Mostly disappear by end of fetal period, but serve important functions during development • Intermediate zone (IZ) eventually holds white matter

Stiles and Jernigan. 2010. The Basics of Brain Development. Cortical Layers

• After cells are born they migrate (to cortical plate or white matter) • Cortex is formed in an inside-out manner, deepest layers formed first, followed by upper layers • “stop” signal produced by layer 1 cells Myelination

• Glial cells wrap around some axons • Increase in transmission speed • Decrease crosstalk • Myelin surrounds axons and speeds signal transmission • Produced by oligodendrocytes in CNS and Schwann cells in PNS Myelination

• Production of myelin begins prenatally, but human infants have very little myelin at birth • Increased myelination results in growth of white matter

1 month 4 months 11 months Next Class

• Reading • Stiles pg. 210-235 • DWA • 5-6 sentence summary of the Stiles reading • 1 quiz question and answer