Exam 2: Chapter 6 Flashcards
Steps of target selection
1) Defasiculation
2) Branch, get trapped
3) Topographic location
4) Cell layer
5) Connect to targets
In sympathetic NS: needs ___ to innervate
Neurotrophin (NT-3)
KO NT-3 in mice
No SCG external ear innervation.
Blood vessels make NT3 in external ear
What reduces NT3 dependence?
NGF –> TrkA receptor –> P75 –> increase NGF dependence, decrease NT3
Tumors can come from
Pancrease FGF uptake
Non-sympathetic: INNER ear
Semicircular = BDNF (Trk B) Cochlea = NT3 (Trk C)
Inner ear:
1) KO both TrkB and Trk C
2) Swap NT3 for BDNF
1) no innervation
2) NT3 same spot, but off, can sub in, both not all equal
FGF in tectum, we talked about this
1) Axon FGF insensitive
2) Fill tectum with FGF
FGF lower in tectum to say we made it
1) Never gets to tectum
2) keeps going
Why make visual connections to somatosensory that we pull out later?
Backup system.
Experiment:
A) Destroy LGN
AND
B) Destroy auditory axons
Visual axons –> MGN –> AC
Experiment: cut auditory axons, but late in the game
stays on the right side, thanks to EphrinA2/A5 expression barrier
Experiment on LGN/MGN: KO Ephrin As and cut auditory
Visual connections to both LGN and MGN
Ligand and Receptors:
1) NT3
2) NGF
3) BDNF
4) Lots of neurotrophin
1) NT3 TrkC
2) NGF Trk A
3) BDNF Trk B
4) Neurotrophins to p75
Retina/Tectum craziness of Roger Sperry’s Frog Eyes
Retina/Tectum
1) Dorsal –> Ventral/Lateral
2) Ventral –> Dorsal Medial
3) Nasal –> Posterior/Caudal
4) Temporal –> Anterior/Rostral
1) Retina: EphA3
2) Tectum: Engrailed/Ephrin A
1) Temporal side
2) Caudal/Rostral side
1) Retina: Ephrin B
2) Retina: Eph B
1) Dorsal
2) Ventral
Bonhoeffers Chemical Cues: AP mapping
Experiment: Treat cells with PI-PLC
Nasal goes to A or P
But Temporal Anterior only
Experiment: Destroys Ephrin A, temporal axons lose preference.
Significance: Force is repulsion
Temporal injection in Retina:
1) Wild Type
2) KO Ephrin As
3) Eph3A under control of Brn3c
1) Anterior
2) axons go crazy
3) different levels, split into two stop groups
Nasal injection in Retina:
1) Wild Type
2) KO Ephrin As
3) Eph3A under control of Brn3c
1) Posterior
2) axons go crazy
3) different levels, split into two stop groups
Engrailed in Tectum
At posterior/caudal, attracts nasal
Ephrin-B in Xenopus
axons carry Ephrin B LIGAND to the receptor
(Eph B –> Ephrin B)
Reverse
Eph-B in Mouse
dorsal axons also attracted to Wnt
carry EphB
(Ephrin B –> Eph B)
Ephrins in the cortex
thalamus layer 4 attracted by Eprhin A5 ad NT3.
IF you don’t need to stop in layer 4, repelled by Ephrin A
Ephrin mediates branching in ____
dendrite
Ephrin inhibits branching in___
axons
Somatographic maps
spatial representation of physical features in nervous system
Netrin + what happens when its gone?
some MNs target muscles expressing increased netrin levels.
Abolish netrin/netrin receptor = target defects
Connectin + what happens when its gone?
CAM type, in subset of muscles and neurons
pairs axons and target site
KO- does little if KO, but mis-expressed, leads to targeting errors
Fas 2/3
Cell adhesion
No major issues if KO, but misexpress = targeting error
Semaphorin 2
wrong thing has it = targeting problem
Conclusion for all these KO with no big effects?
Relative concentration matters more than presence/absence in target selection
Normal muscle 6 and 7 innervation from TN and RP3
6 and 7 both get RP3,
TN doesn’t innervate either
Muscle 6 and 7 innervation from TN and RP3:
Increase Fas2 on 6
More green (attractive factors) So TN and RP3 innerate, and RP3 fails to get 7
Muscle 6 and 7 innervation from TN and RP3:
Increase netrin OR Fas 2 OR decrease Sema 2
TN now innervates 6 and 7
Muscle 6 and 7 innervation from TN and RP3:
Incrase netrin OR fas 2 and increase Sema 2 (raise/lower together)
TN no innervation, RP3 normal
Shows ratio is what is important here
Muscle 6 and 7 innervation from TN and RP3:
Decrease netrin OR increase Sema2
RP3 no innervation
Neuronal defasiculation:
1) Ko beta-1a
2) KO beta-1a and KO fas2-/-
1) can’t defasiculate
2) KO both defasiculation and fasiculation, so it keeps going and can defasiculate again
How does axonal branching occur?
Pause looks like microtubules all over, but then builds stably off growth cones.
Goldfish visual system
1) 1/2 tectum
2) 1/2 Retina
Takes on new axons.
Reprobes environment
1) as it grows, middle becomes middle again
2) if cut nasal, middle will take it, no wasted space
Wilder Penfield Mapping cortical function
homunculi is creepy
Parts of body next to each other tend to have locations next to each other
Cortex vs. Thalamus: What do we do with free space
Cortex: use it
Thalamus: no way, sensory neurons good, phantom limb sensation. Only remap when the neurons die
Experiment:
1) Peripheral Damage (remove middle cortex)
2) Central amputation (remove middle cortex and Sensory neurons)
1) DRG neurons survive, A innervates in FT areas
2) DRG axon degenerate F –> F, T –> T
Rodent Barrel Cortex Somatotopic Map:
1) Extra whisker
2) Damage/missing whisker
3) Tie 2 whiskers together
Rodent Barrel Cortex Somatotopic Map:
1) Extra whisker- Extra Barrel
2) Damage/missing whisker- other barrels bigger
3) Tie 2 whiskers together - barrels fuse
Significance? Flexibility early on
Olfactory mapping
Messy looking, relies on odorant
Epithelium –> Glomeruli
Odorant receptor protein is on
Axons/dendrites of olfactory neurons
Experiment:
1) Normal olfactory mapping
2) P2 receptor deleted
3) Give M71 receptor
4) P2 –> P3
1) Get to p2 glomerulus in olfactory bulb
2) Go to blub, but can’t find P2
3) Go to middle between M71/P2
4) Get a little closer since P3 is near P2
