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Biology 467 > Circuit formation > Flashcards

Circuit formation Flashcards

1
Q

The ten-a homolog in mammals (mice) is called

A

Ten-3

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2
Q

Where is ten-3 expressed in the hippocampus? (3)

A

proximal ca1
distal subiculum
medial entorhinal cortex

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3
Q

Ten-3 is expressed in neurons of the Ca1 hippocampal region which project to…

A

the distal subiculum

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4
Q

What is happening in this image?

A

When ten-3 is knocked out only in ca1 neurons, the ca1 neurons form random connections outside the distal subiculum – find incorrect targets

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5
Q

What happens when (right column) ten-3 is knocked out of the distal subiculum?

A

Ca1 ten-3+ neurons still find their correct targets: required in ca1 but not in subiculum

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6
Q

What are the 2 functions for ten3 in the hippocampus? Both via…

A
  1. targeting
  2. synaptic specificity

Both via homophilic interactions

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7
Q

What is a “lazy eye” called? What is it?

A

Amblyopia

One eye fails to achieve proper visual acuity even with correction

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8
Q

Amblyopia usually begins…

A

In infancy or early childhood

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9
Q

Amblyopia has 2 primary causes which are…

A
  1. congenital cataract
  2. strabismus – not having correct motor control for that eye, sporadic eye mvmt
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10
Q

What do the retinas look like for someone with amblyopia?

A

Completely normal - defect is downstream

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11
Q

The phenomenon which is affected in amblyopia is called…

A

Ocular dominance

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12
Q

More cells in the V1 cortex receive input from (one eye/both eyes)

A

Both eyes – but some receive from just one eye!

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13
Q

Define ocular dominance

A

Preference for the use of one eye

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14
Q

The (ipsilateral/contralateral) eye typically has more input on a given side

A

Contralateral

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15
Q

If one eye is “silenced” (or covered), synapses from that eye…

A

Are retracted from the V1 cortex

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16
Q

What happens to the synapses from one or both eyes when an individual experiences binocular deprivation?

A

Synapses form pretty normally, no obvious ocular dominance

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17
Q

The fact that binocular deprivation has little effect on synapse formation, but monocular deprivation tends to cause retraction of synapses coming from the deprived eye suggests a (1) mechanism for synapse formation

A

Competitive

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18
Q

Hubel and Wiesel got the nobel prize for demonstrating that (1) is required for proper visual system development

A

Visual experience

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19
Q

Given that amblyopia results in ocular dominance from competitive synapse formation, how could it be treated?

A

By depriving the good eye during development

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20
Q

Monocular deprivation in adulthood results in…

A

Nothing

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21
Q

The fact that monocular deprivation has little effect on vision suggests that…

A

There must be a critical stage for visual synapse formation

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22
Q

Based on this image, when is the critical period for visual input in establishing synaptic circuits in the visual cortex?

A
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23
Q

In visual system development, there are at least 2 stages when neuronal activity is crucial for development, they are:

A

Spontaneous activity before eye opening
Critical period of visual experience

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24
Q

What are the very general steps of the geniculate pathway

A

Eye > LGN > V1 cortex, layer IV

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25
Q

What is the premise of this experiment?

A

Inject radio isotope into ONE EYE and see where it labels in the LGN and V1 cortex: see segregation of ipsilateral/contralateral eye input

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26
Q

Describe the segregation of the V1 cortex and LGN

A

There are distinct regions in these projection areas which receive input from a single eye

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27
Q

What is happening in this image?

A

ocular inputs from one eye are being labelled: as you can see during development these areas start off more mixed and gradually become increasingly segregated

28
Q

Most of the ocular dominance and visual cortex experiments were performed on…

29
Q

Define an ocular dominance column

A

Stripes of neurons in the visual cortex of certain mammals that respond preferentially to input from one eye or the other

30
Q

Ocular input segregation arises from…

A

Refinement of synaptic connectivity

31
Q

Spontaneous firing of these cells prior to eye opening is thought to play a mechanistic role in early ocular input segregation

32
Q

Retinal ganglion cells are physically connected to each other by…

A

Gap junctions

33
Q

Describe the role of gap junctions in ocular segregation prior to eye opening

A

Spontaneous, synchronized activity of RGCs i provides the mechanism to distinguish left and right eye inputs in the LGN, allowing segregation

34
Q

Explain what is happening in this image

A

Epibatidine applied to ferret RGCs, blocks sEPSP

When sEPSP blocked, get no segregation of inputs: confirms the hypothesis that spontaneous activity is required for segregation

When sEPSP blocked in only one eye, the blocked eye loses input on the opposite eye which means that the nature of these synapses forming is COMPETITIVE

35
Q

Define the 2 “regressive” events associated with neural circuit refinement

A

Synapse elimination
Axon and dendrite pruning

36
Q

Most neural circuit refinement occurs during…

A

the critical period

37
Q

What is the rodent barrel cortex?

A

A somatosensory cortical area associated with sensory input from whiskers

38
Q

Describe the input pathway from whiskers to barrel cortex

A

Whisker > brainstem > thalamus > M1 motor cortex > S1 somatosensory barrel cortex

39
Q

The cortical map for whiskers is maintained in…

A

Both the M1 and S1 cortices

40
Q

The barrel cortical map is primarily in this layer of the somatosensory cortex

A

2/3 (pyramidal neurons)

41
Q

Describe the takeaways from this image

A

If you deprive (trim all the whiskers) of a mouse early on (P9) the barrel map is completely disrupted, but if you deprive later (P15) this is not observed. This shows the critical window for the development of this somatosensory map is around P9

42
Q

(1) in the postnatal period guides the formation of whisker receptive fields

A

Sensory experience

43
Q

Why is it beneficial to have critical windows of development?

A

You can optimize functioning behaviours without the need for maintenance or renewal

44
Q

What is happening in this image?

A

Immature neural connections are established with many muscle fibers, but as the individual matures it will eliminate its connections with some neurons and strengthen its connections with others

45
Q

Developing neurons will eliminate its connections with some neurons and strengthen its connections with others: What is the advantage of this?

A

You can focus increasing the capacity of transmitter on a decreasing number of targets: more succinct signaling

Also ensures that all fibers get innervated to start, then prunes – like an assurance mechanism

46
Q

What is the working hypothesis for how a cell determines which synaptic connections will be pruned?

A

When the activity of an input decreases, that axon is likely to withdraw

47
Q

TrkB is the receptor for..

48
Q

Describe how male mammary gland development is halted

A

Androgens induce the transcription of TrkB.T1 which is a truncated version of the TrkB receptor, this prevents binding of BDNF to TrkB (by sequestering it) and axons withdraw from the region

49
Q

Semaphorin is a (attractive/repulsive) axon guidance cue

50
Q

Visual corticospinal tract axons in mice undergo pruning during this stage (1) and this pruning is mediated by…

A

Late embryogenesis, Sema3F, neuropilin-2, plexin A3/plexin A4

51
Q

When plexinA3/plexinA4 are knocked out, what happens to axons in the mouse visual corticospinal tract?

A

They are not pruned - retain connectivity

52
Q

Refinement of topographic maps in the retina is provided by (2)

A

Spontaneous waves of neural activity and Ephrin A signaling

53
Q

Microglia are derived from…

A

Yolk-sac macrophages beginning at embryonic day 7.5

54
Q

The cell type that microglia are derived from before macrophages is…

A

Hematopoeitic stem cells

55
Q

How do primitive macrophages become microglia?

A

Migrate to the brain and just stay there for life, sustained by local progenitors

56
Q

What is the role of microglia?

A

Survey the environment and engulf shit

57
Q

Describe the connectivity of microglia to synapses

A

They make frequent and transient connections to synapses

58
Q

Migration of microglia is mediated through this signaling pathway

A

Fractalkine

59
Q

What receptor is required for microglia migration?

60
Q

The CA of the hippocampus is shorthand for…

A

Cornu Ammonis

61
Q

Ca1 neurons of the hippocampus project to… (2)

A

The entorhinal cortex, the striatum

62
Q

Ca3 neurons of the hippocampus receive input from…

A

The dentate gyrus

63
Q

The hippocampus is considered to be part of the (1) system

64
Q

Axons from Ca3 neurons projecting to Ca1 region are called…

A

Schaffer collaterals

65
Q

What is PSD95?

A

A scaffold protein that is on the post-synaptic side of Ca3 > ca1 synapses

Biology 467 (20 decks)

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