Neuronal Migration Flashcards
How does migration lay down layers of cortex?
earliest to migrate lay down first layer
neurons nearest cortical surface were last to migrate
how far can neurons migrate?
up to 5-6mm
3 types of migration
neurophilic
gliophilic
biphilic
radial glial fibres
bundles of elongated radial glia span entire thickness of cortex
do neurons migrate inwards or outwards along glial track?
outwards
radial glial - transient or permanent?
transient - migration complete degenerate of form astrocytes or neurons
how does gliophilic migration ensure neighbour-neighbour relationships?
pre-formed scaffold imposes lateral restraint on neurons
attachments of radial glial fibre
ventricular zone to pial surface
neurophilic migration - where do neurons migrate to?
surface of the pons
what do purkinje cells have?
large dendritic trees
granule cell bodies origin
born in outside of cerebellum, migrates downwards with parallel fibres and neuronal projection to granule cell layer
bipolar - granule cells
horizontal process along parallel fibres of previous granule cell - neurophilic
tripolar - granule cells
vertical process to shaft of bergmann glial fibre - nucleus migrate through own nerve shaft
where is final division of granule cells?
near pial surface
golgi epithelial cell
cell body of bergmann glial fibre in purkinje layer
depth of parallel fibres and time of differentiation
deepest - first to migrate
closes to pial surface = most recent
cell adhesion molecules in biphilic migration
N-CAM = non specific NCAM-PSA = selective
where is NCAM-PSA not present?
proliferative zone
where is NCAM-PSA found?
both cell bodies and leading process of migrating neurons and on bergmann glial radial fibre
when is staining fro NCAM-PSA lost?
migration complete and synapses formed then lost
antibodies to NCAM-PSA
block granule cell migration
other CAMS also involved
NG-CAM and cytotactin
anti Ng-CAM
inhibits migration out of external granule layer - early stage of migration
not effective day 1.5-3
ab to cytotactin
inhibition effective later on in migration
what are Ng-CAM and cytotactin needed for?
Ng-CAM - binding to bergmann glia
cytotactin - migration through molecular layer
weaver mice - probelem
cerebellar granule neurons fail to migrate and die in ectopic sites
weaver mice - problem with neuron on glia?
co-culture normal and weaver tissue - normal neurons migrate on normal and weaver glia
weaver neurones do not migrate
neuronal adhesion defective
ventricular zone cell coupling
about 90 cells coupled by gap junctions
what do cells from same proliferative area use?
same radial glial guide
what do cells in same proliferative zone form?
ontogenetic columns
Lissencephaly
smooth cortex, normal thickness but reduced area
number of ontogenetic columns in lissencephaly
reduced
number of neurons in each column - lissencephaly
normal
cause of lissencephaly
early defects (first 7 weeks) when proliferating units being formed
polymicrogyria
cortex convuluted but much thinner and normal area
ontogenetic columns and number of neurons in polymicrogyria
normal columns
less neurons per column - think
week polymicrogyria occur
after week 7
cause of polymicrogyria
defective neuronal migration
radiation - appearance of brain
small, thin brain much of superficial layers missing, compromised migration
interesting finding of irradiated brains
ectopic neurons survive in wrong places
subcortical close to ventricles - proliferative area
never migrated but survived and made incorrect synpases
experimentally irradiated rats
survival of ectopic neurons - some still project down spinal cord (part of cortico-spinal projection)
accurately directed axonal growth to synapse with correct spinal targets
