BRAIN DEVELOPMENT AND PLASTICITY · Movement to final location ! Cell Differentiation: taking on...
Transcript of BRAIN DEVELOPMENT AND PLASTICITY · Movement to final location ! Cell Differentiation: taking on...
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BRAIN DEVELOPMENT AND PLASTICITY Dr. Steinmetz 1
OUTLINE
¢ Behavioral Genetics ¢ CNS development ¢ Neuron Migration ¢ Will this neuron survive? ¢ Neuroplasticity and brain damage
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OUTLINE
¢ Behavioral Genetics ¢ CNS development ¢ Neuron Migration ¢ Will this neuron survive? ¢ Neuroplasticity and brain damage
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REVIEW OF BASIC GENETICS ¢ Genes – units of
DNA ¢ Genotype - a
section of DNA that provides the code for a particular feature (phenotype)
¢ Chromosomes - strands of genes (blueprint)
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WHAT DO GENES DO?
¢ DNA in genes provides code for producing RNA
¢ RNA can be used to create proteins or enzymes � proteins may have a function � enzymes may act as a signal to
turn on / off other biological functions 5
GENES DEFINE PHYSICAL CHARACTERISTICS.
¢ Dominant gene (BB) & Recessive gene (bb) ¢ Homozygous (BB, bb) & Heterozygous (Bb)
BB Eye Color
bb
Bb Bb BB
bb
Possibilities BB
b b
Bb Bb Possibilities B
b
B b
Bb Bb Bb
Bb All Heterozygous
Both Heterozygous & Homozygous
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DIRECT EFFECT OF GENES ¢ Genes can influence the structure of our nervous
system
• This is an example of genes directly affecting behavior by permitting or eliminating a transduction mechanism.
• Dad is a nontaster & Mom is a taster, they have one child that is a nontaster, what are Mom and Dad’s genes?
Bitter Taste Ability Dominant trait (T) = Can taste PROP Recessive trait (t) = Can NOT taste PROP
TT
t t Tt
Tt Tt
Tt T t
T t Tt
Tt TT
tt
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OUTLINE
¢ Behavioral Genetics ¢ CNS development ¢ Neuron Migration ¢ Will this neuron survive? ¢ Neuroplasticity and brain damage
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THE GENESIS AND DEATH OF NEURONS
¢ Cell generation/proliferation: Mitosis
¢ Cell migration: Movement to final location
¢ Cell Differentiation: taking on the appearance and characteristics of a neuron
¢ Apoptosis: programmed cell death 9
DEVELOPMENT OF CNS SHAPE
Neural plate then Neural grove then Neural tube 10
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BRAIN DEVELOPMENT
¢ Astonishing rate of cell division � 250,000 new
neurons per minute
� Billions of neurons
� Trillions of synapses
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UNSCRAMBLE THESE STEPS
¢ Synaptogenesis ¢ Proliferation ¢ Apoptosis ¢ Myelination ¢ Migration ¢ Differentiation
Which two are the most likely to happen throughout life?
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ANSWER
1. Proliferation 2. Migration 3. Differentiation 4. Myelination 5. Synaptogenesis 6. Apoptosis All of these happen throughout
life, but mostly myelination and synaptogenesis.
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PROLIFERATION: THE GENESIS OF NEURONS
¢ Myelination ¢ Synaptogenesis
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EMBRYO IMAGES
¢ http://www.med.unc.edu/embryo_images/unit-welcome/welcome_htms/contents.htm
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OUTLINE
¢ Behavioral Genetics ¢ CNS development ¢ Neuron Migration ¢ Will this neuron survive? ¢ Neuroplasticity and brain damage
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6 STAGES OF NEURON DEVELOPMENT
1. Proliferation 2. Migration 3. Differentiation 4. Myelination 5. Synaptogenesis 6. Apoptosis
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http://www.youtube.com/watch?v=FZ3401XVYww&feature=related
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HOW ARE APPROPRIATE BRAIN CONNECTIONS MADE?
¢ Is the brain’s structure genetically determined?
¢ How do genes work?
¢ DNA found on chromosomes in nucleus Nucleic acids:
Adenine, Guanine, Cytosine, Thymine
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HOW ARE APPROPRIATE BRAIN CONNECTIONS MADE?
¢ Less than 50,000 different genes in brain
¢ But, trillions of synapses ¢ Can’t be under total genetic
control
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BRAIN REGENERATION/REPAIR STUDIES MAY REVEAL WHAT HAPPENS DURING BRAIN DEVELOPMENT
¢ R. Sperry’s studies in frogs
¢ Cut optic nerve and then inverted eye
¢ Axons grew back to original targets
¢ What was “up” looked “down”
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SPERRY’S EXPERIMENT
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BRAIN REGENERATION/REPAIR STUDIES MAY REVEAL WHAT HAPPENS DURING BRAIN DEVELOPMENT
¢ Craner et al., 1992 – rat study
¢ Fetal retinal transplant in brain projected to appropriate targets
¢ How do they “know” where to go?
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PIONEER NEURONS ¢ Targets are not there when
subcortical neurons are developing
¢ Sub-plate produces cells that migrate to border of cortex
¢ Pioneer cells set pathways for future neurons – then die leaving radial glia as guideposts
¢ But, how do pioneer neurons “know” where to go?
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GROWTH CONE GUIDANCE Filopodia
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GUIDANCE MECHANISMS ¢ Contact attraction; Chemoattraction ¢ Contact repulsion; Chemorepulsion
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6 STAGES OF NEURON DEVELOPMENT
1. Proliferation 2. Migration 3. Differentiation 4. Myelination 5. Synaptogenesis 6. Apoptosis
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DIFFERENTIATION OF NEURONS
¢ Neurotrophins provide a signal for neural differentiation once migration target is reached
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6 STAGES OF NEURON DEVELOPMENT
1. Proliferation 2. Migration 3. Differentiation 4. Myelination 5. Synaptogenesis 6. Apoptosis
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MYELINATION ¢ Oligodendrocytes
– CNS – form multiple sheaths w/ branching arms
¢ Schwann cells – PNS – form singular sheath
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6 STAGES OF NEURON DEVELOPMENT
1. Proliferation 2. Migration 3. Differentiation 4. Myelination 5. Synaptogenesis 6. Apoptosis
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SYNAPTOGENESIS OF NEURONS
¢ Similar to proliferation, during synapse formation there is an over-production of synapses
¢ Synapses continue to form through the first couple of years of life
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OUTLINE
¢ Behavioral Genetics ¢ CNS development ¢ Neuron Migration ¢ Will this neuron survive? ¢ Neuroplasticity and brain damage
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WILL THIS NEURON SURVIVE?
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NEUROTROPHINS & RECEPTORS
¢ Neurotrophins - chemicals promoting neuron survival & connectivity � Nerve Growth Factor (NGF) � Neurotrophin-3, -4, -5 � Brain-derived Neurotrophic Factor (BDNF)
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NERVE GROWTH FACTOR (NGF)
Rita Levi-Montalcini, 1954, 1956, 1972 36
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6 STAGES OF NEURON DEVELOPMENT
1. Proliferation 2. Migration 3. Differentiation 4. Myelination 5. Synaptogenesis 6. Apoptosis 37
APOPTOSIS ¢ Apoptosis - if no
appropriate target by a certain age, the neuron initiates a programmed cell death
¢ Increase of Ca2+ signals release of Diablo protein
¢ Diablo disables the IAP (Inhibitors of Apoptosis Proteins)
¢ 20-80% of neurons die 38
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NEURAL DARWINISM: PROGRAMMED CELL DEATH (APOPTOSIS)
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USE IT OR LOSE IT!
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IMPORTANCE OF NEURAL ACTIVITY
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¢ Axonal remolding (Shatz, 1992)
� neurons grow to many addresses ¢ correct address...remain
¢ incorrect address...eliminated
¢ Neurons that fire together, wire together
IN CLASS ASSIGNMENT
¢ What would happen if someone injected antibodies that block nerve growth factor into a developing nervous system?
¢ What would happen if you injected nerve growth factor into a certain area?
¢ Can you think of a way that this could be useful or harmful? 42
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¢ Nerve growth factor study: ¢ http://www.adcs.org/studies/ngf.aspx
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OUTLINE
¢ Behavioral Genetics ¢ CNS development ¢ Neuron Migration ¢ Will this neuron survive? ¢ Neuroplasticity and brain damage
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Fig. 5-12, p. 133
Brain correlates of extensive music practice
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RECENT HUMAN DATA: PARALLEL BETWEEN DEVELOPMENT AND BRAIN REPAIR
v Data suggest that the phantom is in the brain and that the brain reorganizes after damage to a limb
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THE CASE OF V.Q.
v Amputated left arm of 17-year old male
v Mapped digits on regions of face
v Water trickled on cheek also felt in phantom limb
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SOMATOSENSORY CORTEX
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PHANTOM LIMBS http://www.youtube.com/watch?v=PpEpj-JgGDI How does the brain re-organize following double hand amputation? http://sciencenow.sciencemag.org/cgi/content/full/2009/406/1
http://www.aolnews.com/2011/02/12/chase-britton-boy-without-a-cerebellum-baffles-doctors/?icid=maing|main5|dl2|sec1_lnk3|43665&a_dgi=aolshare_facebook
How does the brain re-organize following birth defects?
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COLLATERAL SPROUTING
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MARK ROSENZWEIG ENRICHED ENVIRONMENT STIMULATES BRAIN GROWTH
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DEVELOPMENT OF THE BRAIN ¢ Rats in enriched environment =
� thicker cortex � increased dendritic branching
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ENHANCED ARBORIZATION OF DENDRITES
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FOR NEXT TIME…
¢ Study for Exam 1 ¢ After that: read Chapter 8 - Movement
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