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Neurosciences > cours 3: Brain development > Flashcards

cours 3: Brain development Flashcards

1
Q

Blastula

A

100aine de cellules, vide au milieu.

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2
Q

Gastrula

A

Suit la phase de Blastula, la paroi s’enfonce en blastomères en 3 couches.

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3
Q

Quels sont les 3 tissus de la Gastrula?

A
  • Ectoderm: nervous system and sensory organs
  • Mesoderm: skeletal system and voluntary muscle (striés)
  • Endoderm: guts and digestive system
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4
Q

Qu’est-ce qui est formé dans la gastrula dans l’axe dorsale/ventral?

A

La plaque neurale (neural plate)

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5
Q

Qu’est-ce qui est formé dans l’axe antérieure / postérieurs de la gastrula?

A

Le tube neural (neural tube).

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6
Q

Comment s’appelle la maladie la plus connue concernant le tube neural?

A

Spina Bifida:

  • tube neural est défectueux, il ne se ferme pas (supposé de se fermer jour 28 de la grossesse
  • concerne 0.04% bébé nés aux US
  • Arrive plus souvent si la mère a un déficit de la vitamine B (acide folique B9)
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7
Q

Schéma de l’embryo en formation

A
  • Myélencéphale (Bulbe rachidien - medulla)
  • Métencéphale (pont et cervellet)
  • Mésencéphale (cerveau moyen)
  • Diencéphale (thalamus et hypothalamus)
  • Télencéphale (cortex)
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8
Q

Quels sont les stades de développement Neural?

A
  1. Proliferation neuronale (Neuronal Proliferation – Neurogenesis)
  2. Migration neuronale (Neuronal Migration)
  3. Determination et differenciation neuronale (Neuronal Determination and Differentiation)
  4. Synaptogenese et elimination (Synaptogenesis and Pruning)
  5. Connectivite et determination fonctionelle (Connectivity and Functional Determination)
  6. Matière blanche – Myelination (White Matter - Myelination)
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9
Q

Quelle méthode utilise-t-on pour déterminer la neurogenèse?

A

Autoradiographic method: cell labeling: radioactively labeled thymidine -> integrate in DNA of dividing cells

Marks neuronal genesis (corticogenesis)

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10
Q

Neurogenèse chez les humains

A
  • Begins during first quarter of gestation
  • Continue for several months
  • Specificity depending on brain area: Neurogenesis in area V1 lasts longer….

In primate, all (99.999%…) neurons present at birth have been produced during middle third of gestation;

Neurogenesis after birth is rare (only in specialized structures; not true of all species - bird who learns a new song to impress female every spring, then nerves liquify in autumn and are constructed again the next spring)

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11
Q

Comment se produit la migration neuronal lors de la formation des colonnes corticales?

A

De l’intérieur vers l’extérieur

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12
Q

Combien de couches cellulaires contien le cortex cérébral?

A

6 couches.

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13
Q

Depuis où est-ce que les cellules du cortex cérébral migrent?

A

Depuis les régions sous-ventriculaires.

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14
Q

Dans quelle zone du cerveau est-ce que la neurogénèse à lieu?

A

Dans l’hippocampe et le bulbe olfactif

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15
Q

A quoi servent les cellules gliales radiales lors de la migration neuronale?

A

Elles servent “d’autoroute” et aident les neurones à migrer au bon endroit.

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16
Q

Résumé migration neuronale

A
  • Inside-out pattern
  • Time line varies by area, but in primate complete well before birth (happens during 2nd trimester)
  • Determines the exact cortical lamination
  • Disruption of neuronal migration leads to ill constructed cortex
    • – Fetal alcohol syndrom
17
Q

Qu’est-ce qui est la Heterotopia?

A

Collection of gray matter in abnormal location due to arrest of radial migration (double cortex)

18
Q

Qu’est-ce que dit l’hypotèse d’unité radiale?

A

Pour avoir un cerveau plus grand, p.ex. l’éléphant fait plus de cycles de division depuis le même domaine de division dans la zone ventriculaire.

=> exponential growth

=> small changes in cell division leads to large changes in cortex size

19
Q

Neurogenèse et migration durant la vie

A
  • Long thought impossible
  • Now well established in the hippocampus (dentate gyrus) and the olfactory bulb
  • New neurons make connections in network and become functional
  • Neurogenesis is greater in animals that are active (physical exercise, exploration behavior, enriched cages) rather than deprived
20
Q

Quelle est la méthode pour vérifier la neurogenèse en cours de vie?

A
  • Need a marker of cell division: BrdU - form of Thymidine
  • Need to check that newly formed cell is a NEURON (not a glial cell): Neuronal marker – NeuN
  • New neurons only when the two markers co-localize…
  • On peut faire cette méthode que sur des personnes en phase terminale de cancer.
21
Q

Determination and Differentiation

A
  • Cells in VZ (ventricular zone) are homogeneous, yet differentiate into different brain structures….
  • Neuron type (structure!) determined at point of cell division, not by its surrounding:
  • Prevent neuron to migrate (chemically) - still display the connectivity corresponding to its time of genesis
  • Transplant Studies
22
Q

Comment sait-on que fonction/migration d’un neurone est déterminé par le moment de sa naissance et non de son environnement?

A

On a transplanté un neurone produit d’un donneur jeune dans un organisme un peu plus âgé, (on le marque) et on voit que ce neurone va là où il serait allé dans le donneur - donc il ne migre pas aussi loin que ses neurones voisins.

23
Q

Synaptogenèse

A
  • Time when new synapses are formed
  • Different time line for different tissue
  • Followed by synaptic pruning
  • Important because defines overall connectivity (sculpting of the brain…)
24
Q

Synaptogenèse - qu’est-ce qui veut dire que son time line is area specific?

A
  • les synapses dans le cortex sensoriel se forment avant celles du cortex frontal
25
Q

Comment peut-on mesurer la densité des synapses - synaptogenèse?

A

PET - positron emission tomography:

PET at rest at different ages (steady state glucose utilization) - the more synapses the greater the glucose consumption

26
Q

Procédure PET

A
  • PET at rest at different ages (steady state glucose utilization)
  • Quantify synaptogenesis by increased glucose utilization

Peak of synaptogenesis at different times for different regions

– Primary and Motor cortices
– Hippocampal and Cingulate cortices – Association cortices
– Prefrontal cortex

27
Q

Quelles sont les avantages et les désavantages de la PET?

A
  • Functional link not well established: between synaptic count and plasticity of function
  • Measure is too global: Creation and pruning of synapses does not happen at the same time in different cortical layers
  • PLUSES: Can show synaptogenesis down-regulated in adult cortex (synaptic over-expression ONLY early during development)

Neurosciences (22 decks)

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