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Year 2 - Theme 1 > Plasticity and regeneration > Flashcards

Plasticity and regeneration Flashcards

1
Q

How do inducing factors determine gene expression in individual cells

A

Signalling molecules provided by other cells, they can be:
- Freely diffusible, exerting their action over a long range, or

  • Tethered to the cell surface, acting locally
  • They can modify gene expression, cell shape and motility. Because cells in different positions in the embryo are exposed to different inducing factors, each cell’s position in early development is critical for its fate
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2
Q

How does competence influence gene expression in individual cells

A

The ability of a cell to respond to inducing factors, which depends on:

  • Exact set of surface receptors
  • Transduction molecules
  • Transcription factors expressed by the cell
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3
Q

What is neurogenesis

A
  • The process by which neurons are generated

- 5th week - 5th month of gestation

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4
Q

number of new neurons generated per minute at the peak rate of neurogenesis

A
  • Peak rate of 250,000 new neurons/minute
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5
Q

Features of neural stem cells/neural precursor cells

A
  • Infinitely self-renewing
  • After terminal division and differentiation, they can give rise to the full range of cell classes within the relevant tissue eg. inhibitory and excitatory neurons, astrocytes, oligodendrocytes
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6
Q

Features of neural progenitor cells

A
  • Incapable of continuing self-renewal
  • Capable of giving rise to only one class of differentiated progeny, eg an oligodendroglial progenitor cell will give rise to oligodendrocytes until its mitotic capacity is exhausted
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7
Q

What are the stages of cell division for a dividing precursor cell

A
  • In G1, nucleus is near ventricular surface
  • During S stage, nucleus and surrounding cytoplasm migrate toward the pial surface and DNA replicates
  • During G2, cell grows and nucleus migrates toward lumen again
  • In mitosis, cells lose their connection to pial surface and divide. Symmetrical divisions generate two neural stem cells. Asymmetrical divisions generate a neuroblast and a progenitor cell with limited mitotic potential
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8
Q

Describe the distribution of protein in precursor cells with an example

A
  • The proteins notch-1 and numb are differentially distributed in the precursor cells of the developing neocortex
  • Vertical cleavage partitions these proteins equally in the daughters, but horizontal cleavage does not
  • Differences in the distributions proteins in the daughters causes them to have different fates
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9
Q

What is a neuroblast

A
  • Postmitotic, immature cell that will differentiate into a neuron
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10
Q

How is the fate of a precursor cell determined

A
  • Age of precursor cell
  • Position in ventricular zone
  • Environment at time of division
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11
Q

How does the layered structure of a cortex form

A
  • Inside first, outside-last order occurs
  • Differentiation of neuroblasts into a neuron will begin with the appearance of neurites sprouting off the cell body; one will become the axon, the other dendrites
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12
Q

How does the neuroblast differentiate

A
  1. Pathway selection - eg retinal ganglion cell reaching the correct thalamic location
  2. Target selection - eg selecting the appropriate thalamic nucleus, LGN.
  3. Address selection - eg which LGN layer
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13
Q

How does a growth cone work

A
  • When a tire(adhesion molecule L1) is connected to an engine(actin fibre) by a clutch molecule, the tire is pulled backward
  • Then, the tire is internalized into the inner part as a vesicle(a tiny bag made of cell membrane), which is reused after it has been returned to the front part. Thus, the growth cone advances as the tire moves in cycles
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14
Q

What are the four mechanisms of axon guidance

A
  • Chemoattractants eg netrin Axons growing toward a secreted attractive cue preferentially grow toward the source, extending up a conc gradient
  • Chemorepellents eg slit - axons preferentially turn and extend away from the source
  • Contact-mediated attraction - preferentially extend along the surface of those cells
  • Contact-mediated repulsion - retract their growth cones, resample the environment, and preferentially extend on cells expressing different cues
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15
Q

Where is netrin secreted

A
  • The protein netrin is secreted by cells in the ventral midline of the spinal cord
  • axons with the appropriate netrin receptors are attracted to the region of highest netrin conc
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16
Q

Where is protein slit secreted

A
  • Protein slit is secreted by midline cells
  • Axons that express the protein robo, the slit receptor, grow away from the region of highest slit conc. Up-regulation of robo by axons that cross the midline ensures that they keep growing away from the midline
17
Q

How is the proper match in the number of presynaptic and postsynaptic neurons produced

A
  • Neurotrophic factors(eg nerve growth factor NGF)
  • Apoptosis or programmed cell death reflects competition for trophic factors and produces the proper match in the number of presynaptic and postsynaptic neurons
18
Q

How does activity-dependent fine-tuning of neuronal connections

A
  • Initially each muscle fibre receives inputs from several alpha motor neurons.
  • Over the course of development, all inputs but one are lost.
  • Normally, postsynaptic AChR loss precedes the withdrawal of the axon branch.
  • Simply blocking a subset of receptors with α-bungarotoxin can also stimulate synapse elimination
19
Q

When does activity-mediated fine tuning occur

A
  • Is most consequential in early life, during temporal windows called critical periods
20
Q

What is the critical period concept

A
  • Variable time window for different skills/behaviours

eg. sensorimotor skills, lanuage acquisition…

21
Q

What are the two important factors for successful completion of the critical period

A
  1. Availability of appropriate influences(eg. exposure to language)
  2. Neural capacity to respond to them
22
Q

Effects of visual deprivation on ocular dominance

A
  • In normal monkeys,ocular dominance columnsseen as alternating stripes of roughly equal width are already present at birth. (B)
  • The picture is quite different after monocular deprivation.
  • A dark-field autoradiograph shows a reconstruction of several sections through layer IV of theprimary visual cortexof a monkey whose right eye was sutured shut from 2 weeks of age to 18 months, when the animal was sacrificed.
  • Two weeks before death, the normal (left) eye was injected with radiolabeled amino acids. The columns related to the nondeprived eye (white stripes) are much wider than normal, whereas as those related to the deprived eye are shrunken
23
Q

Why do critical periods end

A
  • Various hypotheses(axon growth, synaptic transmission matures, constraint cortical activation)
  • Important for understanding recovery from damage
24
Q

How does regeneration occur in the peripheral nervous system

A
  • The schwann cell is essential for this process
  • Once the macrophages have cleared the debris from the degenerating peripheral stump, the Schwann cells proliferate, express adhesion molecules on their surface, and secrete neurotrophins and other growth-promoting signalling molecules
  • In parallel, the parent neuron of the regenerating axon expresses genes that restore it to a growth state.
  • The gene products are often receptors, or signal transduction molecules, that allow the cell to respond to the factors provided by the Schwann cell
25
Q

How does regeneration occur in the central nervous system

A
  • Local cellular changes at or near an injured site include the degeneration of myelin and other cellular elements; the clearing of this debris by microglia (CNS phagocytic cells); local production of inhibitory factors by astrocytes, oligodendroglia, and microglia; and glial scar formation.
26
Q

How does adult neurogenesis occur

A
  • Sub ventricular zone to olfactory bulb
  • Hippocampus
    Primarily interneurons
    Some integrate in functional networks, but most die
27
Q

Where is the SVZ located

A
  • In the wall of the lateral ventricle
28
Q

What does the SVZ consist of

A
  • It consists of an ependymal layer, a gap region and an astrocytic ribbon, and is seperated from the caudate nucleus and the striatum by a layer of myelin
29
Q

What type of cells does the SVZ contain

A

The SVZ contains three different cell types (types A, B and C) that are organized in a specific pattern, with the type A cells closest to the ependymal layer, the type B cells forming the astrocytic ribbon and the type C cells located close to the myelin layer and the striatum. Arrows represent interconversion of cell types

30
Q

How is the SVZ different in an individual with huntington’s

A

The brain of an individual with Huntington’s disease is characterized by striatal cell loss, but increased SVZ thickness. The SVZ has more type A, B and C cells than normal and is enriched in endogenous mitogenic factors, such as neuropeptide Y (NPY), nitric oxide synthase (NOS), certain GABA receptor subunits and the cannabinoid receptor CB1

31
Q

How is the SVZ different in an individual with parkinson’s

A

In the SVZ of individuals with Parkinson’s disease (PD) there is a reduction in the dopaminergic input from the substantia nigra (depicted as a dashed inhibitory connection) that leads to the death of D2 and D3 receptor-rich type C cells (shown as red cross). The PD-affected SVZ has fewer progenitor cells

32
Q

How is the SVZ different in an individual with alzheimer’s

A

In the SVZ of individuals with Alzheimer’s disease, there is a reduction in neurogenesis because there is an imbalance in the ratio ofsecretases, leading to abnormal accumulation of-amyloid and generic cell death in the SVZ.

33
Q

What is the pial surface of the brain

A
  • A surface representing the boundary between grey matter and CSF
34
Q

Purpose of each type of cell in the SVZ

A

Four cell types are described in the SVZ:

  1. Ciliated Ependymal Cells (Type E): are positioned facing the lumen of the ventricle, and function to circulate the cerebrospinal fluid.
  2. Proliferating Neuroblasts (Type A): express PSA-NCAM (NCAM1), Tuj1 (TUBB3), and Hu, and migrate in line order to the Olfactory Bulb
  3. Slow Proliferating Cells (Type B): express Nestin and GFAP, and function to ensheathe migrating Type A Neuroblasts[8]
  4. Actively Proliferating Cells or Transit Amplifying Progenitors (Type C): express Nestin, and form clusters interspaced among chains throughout region

Year 2 - Theme 1 (30 decks)

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