EXAM 3 REVIEW

Katherine & Tina

Developments of Neural Circuits

Lecture 19

2 Mechanisms of Development..

Activity Independent – Chemoaffinity Hypothesis (Sperry) form precedes function Experiments: eye-rotation studies; Stripe assay;

retinal ablation Mechanisms: Ephrin/Eph Receptors

Activity Dependent – Correlation-Based Change (Hebb) Experience shapes the brain Experiments: V1/A1 rewiring; eye specific stripes Mechanism: Synapse Maturation (LTP/Depolarizing

GABA); activity dependent gene expression

Activity Independent Experiments

Eye Rotation in Newt: rotate eye of ADULT newt 180º = sees world upside-down Adult v. Baby?

Retinal Ablation: Ablate ½ the retina missing connections in ½ the tectum The persisting retinal half WILL

NOT REWIRE to take up the whole tectum

Stripe Assay: temporal retinal neurons only grow on membrane stripes from anterior tectum; nasal retinal neurons project through both

Activity Independent Mxns

Ephrin/EphR Chemical Gradient Ephrin = ligand Eph = receptor

Activity Dependent Experiments

Rewiring ferret cortex: rewiring retinal projections to MGN (by deafening the ferret) A1 now has V1 features (orientation pinwheels and long horizontal connections)

Eye specific stripes: addition of APV (NMDAR inhibitor) loss of eye specific stripe segregation

Activity Dependent Mxns

Synapse Maturation: visual activity accelerates synaptic maturation Unsilence NMDAR only

synapses (LTP) increase AMPAR/NMDAR ratio

Depolarizing GABA Gene Expression:

activity drives gene expression, affecting dendritic growth and synaptic maturation Cpg15 expression of the

gene induces gene maturation

It’s not as distinct….

Layer IV ocular dominance columns (ODC) development = activity dependent and independent Independent: ODC start

to develop before eyes open

Dependent: activity required to segregate the columns Activity from spontaneous

retinal waves? Ocular dominance shift:

Monocularly deprived animals open eye’s OD stripes are much larger

In summary….

Neural development is influenced by activity independent and dependent factors Independent dictates original structure Dependent refines neural development

LTP-like mechanisms But it’s never completely distinct…

Neural Basis of BehaviorDr. Khakhalin Guest Lecture

Lecture 18

Terms to know

FIXED ACTION PATTERN: stereotypic behavior; once initiated, it is executed in its entirety Ex. Egg rolling; sneezing

RELEASING STIMULUS: triggering stimuli; object that induces certain behaviors/responses Ex. Red spot (seagull beak); egg (greylag

goose) SUPERNORMAL STIMULUS: stimulus that

works better than a “real” or “normal” stimuli Ex. Full red beak; giant eggs

Teleost Fish Escape Circuit

Major features of this circuit: Allows the fish to flee in the the correct

direction The M Cell only fires once (doesn’t swim in

circles) Has a threshold

Teleost Fish Escape Circuit

Major features of this circuit: Allows the fish to flee in the the

correct direction The M Cell only fires once (doesn’t swim in

circles) Has a threshold

Stimulus: Sound or vibrations in water

CN VIII is activated

M cell is excited sends excitatory signals down axon

Excitatory signals activate contralateral motor neuron, which then contracts the contralateral muscle

Excitatory signals also activate contralateral inhibitory interneurons, which send inhibitory signals to the ipsilateral motor neuron

Teleost Fish Escape Circuit

Major features of this circuit: Allows the fish to flee in the the correct

direction The M Cell only fires once (doesn’t

swim in circles) Has a threshold

Feedback inhibition (ipsilateral)

Stimulus: Sound or vibrations in water

CN VIII is activated

M cell is excited sends excitatory signals down axon

Excitatory signals also activate ipsilateral inhibitory interneurons, which send inhibitory signals to the ipsilateral M cell vial chemical and electrical (axon cap) means

Teleost Fish Escape Circuit

Major features of this circuit: Allows the fish to flee in the the correct

direction The M Cell only fires once (doesn’t swim in

circles) Has a threshold

Feedforward inhibition (contralateral)

Stimulus: Sound or vibrations in water

CN VIII is activated

Contralateral PHP interneuron inhibits the contralateral M cell

CN VIII activates inhibitory PHP interneurons

Ipsilateral PHP interneuron inhibits the ipsilateral M cell through the axon cap

Paper 2: Haas et al.

Hypothesis

Transient dendritic branches sample the local environment for appropriate contact sites and then stabilize to form mature synapses.

AMPAR activity is required for dendritic arbor growth

Looking to see if AMPAR are required for the stabilization/growth of dendritic synapses and branches

Figure 1

Tests the effectiveness of their gene constructs in reducing AMPAR-mediated transmission

Constructs efficiently decrease AMPAR transmission

Figure 2

Disrupting AMPAR transmission reduction in overall dendritic growth/growth rate(A and B) and dendritic branching (C and D)

Figure 3

Disrupting AMPAR transmission reduces dendrite branch stability Branches in R1/R2 neurons are more dynamic

More branches are retracted Rate of retraction is faster Branches have shorter lifespan

R1/R2 = Less Stable

Figure 4

AMPAR transmission is necessary for proper maturation of synapses R1/R2 cells have lower Ac/At ratios (similar

in value to Ac/At ratios of S39, immature neurons)

Figure 5

AMPAR transmission is required for experience dependent structural plasticity R1/R2 dendrites

decreased in arbor length and number of branch tips upon visual stimulation

Dendritic Function (Active Properties)

Lecture 13

Active Membrane Properties

VOLTAGE GATED CHANNELS Dendrites = generate spikes that

boost their signals Spikes = current entering into cell from VG

Na+, Ca+2 or K+ channels Can be activated by sub-threshold

EPSPs

Voltage Gated Channels

Different neurons = different expression patterns of VG channels Hippocampal pyramidal neuron = more dendritic

Na+ channels Perkinje neurons = few Na+ channels, lots of Ca+2 Na+ channels = proximal; Ca+2 = distal

Summation

• Active dendrites → can result in NON-LINEAR SUMMATION OF EPSPs

• Active dendrites can also affect the interaction between Excitation and Inhibitiono depends on location

of inputs (within the same branch or between branches)

Backpropogation

• Dendrites can actively “backpropogate” signals from the soma (soma → dendrite)o regulated by VG Na+

channels (addition of TTX = lose backpropogation signal)

o Somatic AP backpropogate → open channels = increase dendritic Ca+2 levels