Liman Lecture 6 for BISC 421 construction of neural circuits 1 &2post

Liman Lecture 6 for BISC 421 construction of neural circuits 1 &2post

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How do axons find their targets?
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_ Do neurons “know” who their synaptic partner is.
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Roger Sperry (1940s) Frog can regenerate axons Rotate the eye Result: Behavior is as though cells grew back to their original location in the brain
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Rotated retina Regenerated axons Normal frog: Fly in field of view of nasal retina -> activity in posterior tectum -> stick out tongue Rotate eye: Fly in field of view of temporal retina-> acting in ???.-> stick out tongue If we assume activity in posterior tectum -> stick out tongue, then temporal retina in rotated eye is now projecting to posterior tectum. That is, it projects to it’s original target. This implies sensory axons can recognize their target. How??
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Three main hypotheses: 1. Mechanical guidance (steriotropism)- growing axons follow a track 2. Resonance -that growing and connecting axons induce the identity of the postsynaptic cell 3. Chemoaffinity – pre and post synpatic cells have ligand/receptor pair How do axons find their targets?
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Axon guidance cues
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Axons are guided along complex paths There are many decision points and many types of cues Attraction: short range or long range Repulsion: short range or long range
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molecules of growth cone guidance
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Short range interactions in the retinal tectal system Retinal explant grown on tectal membrane from anterior or posterior tectum (in stripes) Temporal retinal axons grow only on anterior membranes Nasal (anterior) axons do not discriminate. Tells us that: 1. There is a short range interaction between axons from the temporal retina and a component of the tectal membrane 1. This interaction could be attraction of temporal retina for anterior tectum OR repulsion between temporal retina and posterior tectum A = anterior tectum P = posterior tectum nasal
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Is temporal retina attracted to anterior tectum or repulsed by posterior tectum? Boil either A or P tectal
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This note was uploaded on 04/18/2010 for the course BISC 421 taught by Professor Hirsch,liman,quick during the Fall '08 term at USC.

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Liman Lecture 6 for BISC 421 construction of neural circuits 1 &2post

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