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Clinical Neuroscience > Developmental Disorders > Flashcards

Developmental Disorders Flashcards

1
Q

What is the process of cellular nervous system development?

A

Position cells –> mitosis –> specify cell fates –> migration –> axonal growth –> synapse

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2
Q

What causes development of the neural tube?

A
  1. Differential rates of cell division causes bulges (“telencephalon, diencephalon, etc…)
  2. The position of cells within the tube determines what kind of cell they become
  3. Cell fate is a result of transcription factors and diffusible factors
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3
Q

What is sonic hedgehog?

A

Diffusible factor in the spinal cord that determines cell fate in dorsal-ventral axis (high Shh = motor, low Shh= sensory)

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4
Q

What is Spina bifida?

A

Failure of closure of neural tube caused by lack of folic acid during pregnancy

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5
Q

What is cell migration controlled by?

A

Migration is controlled by many cell-surface, transmembrane molecules (=CAMs) & components of the extracellular matrix

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6
Q

What are some examples of cells in the CNS that migrate long distances?

A
  1. Granule cells in the cerebrum migrate from the midbrain area
  2. GABA-ergic interneurons in the cerebral cortex migrate from the striatal area to the cortex
  3. GnRH cells migrate from the olfactory epithelium to the hypothalamus
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7
Q

How many layers are formed in the cerebral cortex? Which layer is formed first?

A

Migration of cells from the ventricular wall form the 6 layers of the cerebral cortex. Layer 6 cells are born first.

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8
Q

What is Reelin? What can it cause?

A

Reelin is a cell adhesion molecule that is expressed in high levels during the development of the brain. Reelin mutations cause less white matter, enlarged ventricles and disrupted sulci and gyri.

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9
Q

How does an axon grow?

A

Diffusibile factors with specific receptors can at as chemoattractants or chemorepulsants (=tropic factors).

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10
Q

How does axonal guidance in the spinal cord work?

A

Axons are attracted to the midline, but then the attracters are silenced so the axon can go away from the midline

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11
Q

What are neurexins? Neuroligins?

A

Neurexins are presynaptic and localize synaptic vesicles and docking proteins. Neuroligins are postsynaptic and affect clustering of AMPA and NMDA receptors.

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12
Q

What is the neurotrophic hypothesis in the PNS?

A

Neurons compete for a limited supply of survival factors such as neurotrophins. This explains why we make many more synapses than we ever need.

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13
Q

How does synapse refinement at NMJ work?

A

In early development there are multiple axons of motor neurons synapse with each muscle cell, but eventually these connections are refined so only 1 motor neuron synapses on each muscle cell

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14
Q

What is Hebb’s postulate?

A

Neurons that fire together, wire together

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15
Q

How does gray matter develop in humans?

A

In human brains gray matter increases at first, then decreases during late childhood and early adolescence. Myelination = late process

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16
Q

What do Down Syndrome, Fragile X, Rett’s Disease, and Autism all have in common?

A
  1. All affect synapse development “synaptopathies”
  2. All present with intellectual impairment
  3. All have “gene dosage” effect
17
Q

Where are most excitatory synapses found?

A

Most excitatory synapses in the cortex are on dendritic spines.

18
Q

What causes DS?

A

Due to an extra chromosome 21, a problem with gene dosage not with mutated proteins

19
Q

What are symptoms of DS?

A

Dysmorphic facial features, intellectual disability, stunted growth, congenital heart defect, seizures, obesity, early onset AD, lower life expectancy

20
Q

What is the enhanced GABAergic activity theory in DS?

A
  • Excessive GABAergic inhibition leads to increased LTD and decreased LTP.
  • GIRK2 = G-protein coupled K+ channel activated by GABA receptors
  • Olig 1 & Olig 2 = transcription factors that drive overgrowth of GABAergic interneurons
21
Q

What do you see in DS transgenic mice?

A

See decreased synapse density and decreased spine numbers but abnormally large spines and wrong placement of GABAergic synapses on the dendritic shaft instead of at the base of the spine head.

22
Q

What does the wrong placement of GABAergic synapses on the dendrite cause?

A

Synapse on the shaft have a bigger effect

23
Q

What is the neurodegeneration theory in DS?

A
  • extra copy of APP gene so more amyloid plaques

- extra copy of SOD1 gene so reduced protein clearance via ubiquitin proteasome

24
Q

What are treatments for DS? What are the risks?

A
  1. Blocking GABA-R
  2. GABA-A receptor antagonist
  3. blocking GIRK2
    * risky because blocking GABA can lead to seizures
25
Q

What causes Fragile X syndrome?

A

CGG expansion on X-chromosome (not on coding region- promoter region 5’ UTR) causes silencing of FMR1 gene

26
Q

What are the symptoms of Fragile X?

A

Delayed language, biting, hand-flapping, autistic, dysmorphic facial features, enlarged ears, long faces

27
Q

What are the changes in spine morphology in FXS?

A

Increased numbers of long, thin dendritic spines

28
Q

How does enhanced mGluR5 signaling affect FXS?

A

Some mGluR5 regulated mRNAs are suppressed by fragile X mental retardation protein (FMRP) causing mGluR5 signaling to be exaggerated, leading to excessive LTD and abnormal spines

29
Q

What are the symptoms of Rett Syndrome?

A
  • Normal development initially, with regression at 6-18 months
  • Speech lost
  • Intellectual disability with transient autism
  • Replace purposeful hand movements with stereotypies
30
Q

What causes Rett Syndrome?

A

> 95% Rett syndrome is caused by de novo loss of function mutations in MeCP2 gene. MeCP2 can activate or inhibit gene expression.

31
Q

How does MeCP2 work?

A

Normal MeCP2 recruits histone deactelysas that prevent transcription. MeCP2 normally allows activity of dependent transcription and release of BDNF, but in Rett syndrome lack of functional MeCP2 impairs release of BDNF

32
Q

What dendritic spine changes do you see in Rett Syndrome?

A

Decrease in number and size

33
Q

What is the role of microglia in Rett?

A

Bone marrow stem cells give rise to macrophages and microglia, harvest cells and select for the 50% MeCP2 wild types to re-implant into patients

34
Q

What is impaired in autism, physical or intentional causality?

A

Intentional Causality

35
Q

What are the changes in synapses associated with Autism?

A

Increased synapses

36
Q

What is hypo-connectivity in Autism?

A

Despite more synapses and increased spine density, there is less network activity. This suggests less connectivity in ASD, long pathways are activated less

Clinical Neuroscience (15 decks)

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