Wiring the Visual System Flashcards
what occurs at the optic chiasm
nasal hemiretina cross (contralateral hemisphere)
temporal RGC axons enter the ipsilateral hemisphere
midbrain projections
RGC - pretectum - pupillary reflex
RGC - superior colliculus - saccadic eye movements
central projections
LGN - primary visual cortex
(ipsilateral)
how are long range and short range cues sent
long range cues - secreted
short range cues - require physical contact
where is the retina made from
neural tissue (diencephalon)
retinal cell types
photoreceptors (1R 3C)
horizontal cells (inhibitory 2)
bipolar cells (around 11)
muller glial cells
amacrine cells
RGCs (>30)
layers of the retina
ONL
OPL
INL
IPL
GCL
optic nerve fibres
how is visual information processed
image
retina
visual input split into different information channels. Information channels defined by different circuits
what is the role of synaptic adhesion molecules
make connections
tenm3 MO
antinucci et al., 2013
cells don’t know where to interact
what are topographic maps
neuronal connections arranged such that neighbouring points in the origin are represented in adjacent locations in the CNS
regeneration experiment
Sperry 1963
remove dorsal retina = axons grow medially
remove ventral retina = axons grow laterally
remove anterior retina = axons grow posterior (bottom pair) tectum
remove posterior retina = axons grow to the anterior tectum
where does the retina project to the SC/tectum
nasal - posterior
temporal - anterior
dorsal - lateral
ventral - medial
frog with rotated eyes
temporal - anterior
nasal - posterior
dorsal - medial
ventral - lateral
if trying to catch fly, go up instead of down
what is the chemoaffinity hypothesis
specificity of wiring is based on chemical tags. Individual neurons express distinct molecular markers during development. Formation of appropriate synaptic connections depends on matching of complementary molecules on pre and post synaptic neurons.
3 principles of the chemoaffinity hypothesis
- neurons are instrincally different from eachother
- differences in position are biochemical
- differences are acquired early in development
gradients in topographic maps
source gradient (confers identity)
target gradient (where)
in vivo stripe assay
temporal retinal axons project to the anterior tectum (by attractive cues)
nasal retinal axons grow on both membranes
ephrin A2/5 expression
temporal axons only avoid high ephrin A5
eph3 is the ephrina2 receptor
removal of ephrinA
temporal: lots of receptors on the surface (high EphA conc), axons grow to posterior part
nasal: low EphA, not affected by EphrinA
types of Eph receptors
tyrosine kinase family
A and B subtypes
EphrinB1 expression in midbrain
Tectum
high medial
low lateral
EphB2 expression in the midbrain
high ventral
low dorsal
EphB-EphrinB mutant
ectopic termination zones found laterally
repressive Wnt/Ryk gradient
retina: Ryk gradient high ventrally, low dorsally
tectum: Wnt gradient high medially, low laterally
ryk mutant
no repulsion
100% medial growth
stages of development of a retinotopographic map
PD0 - projections to back of brain
PD3 - refinement
PD8 - point to point connections, axons turn towards TZs
formation of topographic map
axon extension and overshoot via EphA/EphrinA (repulsive)
topographic branching via EphA/EphrinA (repulsive)
branch guidance and aborisation via EphB/EphrinB/ryk/wnt (attractive and repulsive)
map refinement via ACh waves (dense TZ)
