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Chapter 8: Synaptic Plasticity
April 8, 2010
Synaptic Plasticity
Definition
• Change in strength of synapse caused
by training
• Activity dependent change in amplitud...
Outline
Major classification along two dimensions
• Time frame
Short term plasticity
Long term plasticity
• Mechanisms
...
How to Measure Synaptic Plasticity
Intracellular
• Size of evoked EPSP or EPSC
• Frequency of spontaneous EPSCs
Extracel...
Short Term Synaptic Plasticity
 Short term increase or decrease in synaptic
strength
• not thought to be involved in memo...
Short Term Synaptic Plasticity-Facilitation
Increase in PSP amplitude caused by
brief period of high-frequency stimulatio...
Short Term Synaptic Plasticity-Facilitation
This shows that
the second PSP
is larger than the
first, when the
action pote...
Short Term Synaptic Plasticity-Facilitation
This shows that
facilitation
decreases as the
interval between
action potenti...
Short Term Synaptic Plasticity-Augmentation
Steadily increasing, cumulative
enhancement of neurotransmitter release
durin...
Short Term Synaptic Plasticity-Augmentation
This shows that under low calcium, the
size of the PSP increases over several...
Short Term Synaptic Plasticity-Potentiation
Post-tetanic potentiation
• Increase in PSC that is longer lasting
than augme...
Short Term Synaptic Plasticity-Potentiation
This shows that an enhancement of the
PSP lasts for several minutes after a v...
Short Term Synaptic Plasticity-Depression
Decrease in neurotransmitter release during
sustained synaptic activity
Amount...
Short Term Synaptic Plasticity-Depression
 Under normal calcium,
stimulation for several
seconds produces
decrease in PSP...
Short Term Synaptic Plasticity
Tendency of facilitate or depress differs
between synapses
Both facilitation and depressi...
Combinations on Short-Term Plasticity at the
Neuromuscular Synapse
During train of AP,
initial PSPs (from 50-
100 ms) are...
Combinations on Short-Term Plasticity at the
Neuromuscular Synapse
During interval
• Decay of
Depression,
facilitation, a...
Learning and Memory
Learning: adaptive change in behavior
caused by experience
• Adaptive: survival value for animal
• Ch...
Types of Learning and Memory
Non-declarative or Implicit memory
• Non associative learning:
Habituation
Densitization
•...
Implicit Learning and Memory
Non associative learning:
• Habituation
Decrease in behavioral response
that occurs during ...
Implicit Learning and Memory
Associative Learning
• Classical Conditioning
Repeated presentation of a neutral
conditione...
Learning Behavior in Aplysia
What is Aplysia?
• Sea Hare
• Kingdom-Animalia
• Phylum-Mollusca
Includes squid and clams
•...
Short-term sensitization of the Aplysia gill
withdrawal reflex
Value of
Aplysia, and
other
invertebrates is
due to small
...
Learning Behavior in Aplysia
Habituation
• Light touch to siphon causes withdrawal
• Repeated light touch results in smal...
Short-term sensitization and habitulation of the
Aplysia gill withdrawal reflex
Sensitization
Habituation
Sensitization of Aplysia gill withdrawal reflex
 1 shock produces short term sensitization
 Four trains of shocks produc...
Synaptic mechanisms underlying short-term
sensitization and habituation
Critical neurons in circuit mediating
sensitizati...
Synaptic mechanisms underlying short-term
sensitization and habituation
Activation of excitatory interneuron
increases li...
Synaptic mechanisms underlying short-term
sensitization and habituation
Decrease in PSP from sensory to motor
neuron duri...
Synaptic mechanisms underlying short-term
sensitization and habituation
Critical neurons in circuit mediating
sensitizati...
Synaptic mechanisms underlying short-term
sensitization and habituation
Modulatory interneuronModulatory interneuron rele...
Synaptic mechanisms underlying short-term
sensitization and habituation
Increase in PSP from sensory to motor
neuron duri...
Synaptic mechanisms underlying short-term
sensitization
Sensitization of synapses lasts for 10s of
minutes
Mechanism of presynaptic enhancement
underlying behavioral sensitization
1. Serotonin is released by modulatory
interneuro...
Mechanism of presynaptic enhancement
underlying behavioral sensitization
2. GPCR produces GαsGTP, which binds to
Adenylyl ...
Mechanism of presynaptic enhancement
underlying behavioral sensitization
3. cAMP binds to and activates Protein Kinase A
Mechanism of presynaptic enhancement
underlying behavioral sensitization
4. Catalytic subunits of Protein Kinase A
phospho...
Mechanism of presynaptic enhancement
underlying behavioral sensitization
5. Decreased opening of potassium channels
prolon...
Mechanism of presynaptic enhancement
underlying behavioral sensitization
6. Increased calcium causes more vesicles of
tran...
Mechanism of long-term synaptic
enhancement
PKA phosphorylates CREB, which binds to
CRE, increasing transcription of genes
Mechanism of long-term synaptic
enhancement
Ubiquitin hydroxylase stimulates degradation
of regulatory subunit of PKA, al...
Mechanism of long-term synaptic
enhancement
Other genes lead to proliferation of synaptic
terminals
• Long term structura...
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Lecture - Neuroscience, 4e

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  • Transcript of "Lecture - Neuroscience, 4e"

    1. 1. Chapter 8: Synaptic Plasticity April 8, 2010
    2. 2. Synaptic Plasticity Definition • Change in strength of synapse caused by training • Activity dependent change in amplitude of PSC Importance • Thought to be mechanism underlying learning and memory • Involved in development of neural circuits
    3. 3. Outline Major classification along two dimensions • Time frame Short term plasticity Long term plasticity • Mechanisms Pre-synaptic Post-synaptic Relationship to learning and memory • Invertebrate models • Mammalian models
    4. 4. How to Measure Synaptic Plasticity Intracellular • Size of evoked EPSP or EPSC • Frequency of spontaneous EPSCs Extracellular (in Hippocampus) • Fields Potentials generated simultaneous firing of aligned neurons • Slope of population EPSP Proportional to peak synaptic conductance
    5. 5. Short Term Synaptic Plasticity  Short term increase or decrease in synaptic strength • not thought to be involved in memory storage • duration less than tens of minutes  Increase in synaptic strength • Facilitation • Augmentation • Potentiation  Decrease in synaptic strength • Depression  All are pre-synaptic
    6. 6. Short Term Synaptic Plasticity-Facilitation Increase in PSP amplitude caused by brief period of high-frequency stimulation • Two or more AP within milliseconds Rapid onset Effect decays rapidly after stimulation offset • Lasts only tens of msec Mechanism is accumulation of calcium in axon terminal • Calcium clearance is slower than interspike interval • Residual partial binding to synaptotagmin
    7. 7. Short Term Synaptic Plasticity-Facilitation This shows that the second PSP is larger than the first, when the action potentials are 10 msec apart
    8. 8. Short Term Synaptic Plasticity-Facilitation This shows that facilitation decreases as the interval between action potentials increases
    9. 9. Short Term Synaptic Plasticity-Augmentation Steadily increasing, cumulative enhancement of neurotransmitter release during a train of AP Onset and Duration – 100s of ms to seconds Mechanism is accumulation of calcium in axon terminal • Protein target of calcium is unknown
    10. 10. Short Term Synaptic Plasticity-Augmentation This shows that under low calcium, the size of the PSP increases over several seconds of stimulation
    11. 11. Short Term Synaptic Plasticity-Potentiation Post-tetanic potentiation • Increase in PSC that is longer lasting than augmentation Onset and Duration - seconds to minutes • Requires more prolonged stimulation than augmentation • Mechanism is calcium mediated release of vesicles from reserve pool Phosphorylation of synapsin (by CaMKinase)
    12. 12. Short Term Synaptic Plasticity-Potentiation This shows that an enhancement of the PSP lasts for several minutes after a very strong (tetanizing) stimulation
    13. 13. Short Term Synaptic Plasticity-Depression Decrease in neurotransmitter release during sustained synaptic activity Amount of depression depends on the amount of neurotransmitter released previously Mechanisms thought to be depletion of vesicles • Rate of release decreases till release rate balances replenishment rate • More depression when reserve pool is smaller • More depression when release probability is higher
    14. 14. Short Term Synaptic Plasticity-Depression  Under normal calcium, stimulation for several seconds produces decrease in PSP amplitude.  The amount of depression is inversely related to amount of transmitter release 0 5 10 15 20 25
    15. 15. Short Term Synaptic Plasticity Tendency of facilitate or depress differs between synapses Both facilitation and depression can occur depending on characteristics of spike trains Irregular spike trains (physiological) can produce complex pattern of depression and facilitation Generally observed that high p synapses exhibit paired pulse depression, and low p synapses exhibit paired pulse facilitation
    16. 16. Combinations on Short-Term Plasticity at the Neuromuscular Synapse During train of AP, initial PSPs (from 50- 100 ms) are increasing in size • Facililtation PSPs from 100 to 250 ms are decreasing in size • Depression
    17. 17. Combinations on Short-Term Plasticity at the Neuromuscular Synapse During interval • Decay of Depression, facilitation, and augmentation • Build up of Potentiation Larger PSP observed 30 sec later
    18. 18. Learning and Memory Learning: adaptive change in behavior caused by experience • Adaptive: survival value for animal • Change: measurable difference, selective to appropriate part of organism, independent of growth or injury • Behavior: must involve central systems Memory: storage and recall of previous experiences; necessary for learning
    19. 19. Types of Learning and Memory Non-declarative or Implicit memory • Non associative learning: Habituation Densitization • Associative learning: Classical Conditioning Operant Conditioning Declarative or Explicit Memory • Memory for events and facts • Talking about what happened before
    20. 20. Implicit Learning and Memory Non associative learning: • Habituation Decrease in behavioral response that occurs during repeated presentation of stimulus. • Sensitization Enhancement of reflex response by introduction of strong or noxious stimulus
    21. 21. Implicit Learning and Memory Associative Learning • Classical Conditioning Repeated presentation of a neutral conditioned stimulus followed (by a fixed interval) by an unconditioned stimulus (that elicits a reflex response) causes a new CS response which mimics the UR Stimuli presentation are independent of behavior
    22. 22. Learning Behavior in Aplysia What is Aplysia? • Sea Hare • Kingdom-Animalia • Phylum-Mollusca Includes squid and clams • Class-Gastropoda (snails and slugs) Stomach-foot • Order-Opistobranchia Gilled snails and slugs
    23. 23. Short-term sensitization of the Aplysia gill withdrawal reflex Value of Aplysia, and other invertebrates is due to small numbers of identifiable neurons
    24. 24. Learning Behavior in Aplysia Habituation • Light touch to siphon causes withdrawal • Repeated light touch results in smaller amplitude of withdrawal Sensitization • Electric shock to tail sensitizes animal to siphon touch • Assessed by measuring amplitude of repeated light touches with and without electric shock
    25. 25. Short-term sensitization and habitulation of the Aplysia gill withdrawal reflex Sensitization Habituation
    26. 26. Sensitization of Aplysia gill withdrawal reflex  1 shock produces short term sensitization  Four trains of shocks produces long term sensitization • Always compare to control with no shocks
    27. 27. Synaptic mechanisms underlying short-term sensitization and habituation Critical neurons in circuit mediating sensitization • Motor neuron to gill Stimulation produces withdrawal • Sensory neuron to gill Releases glutamate onto motor neuron • These two neurons constitute two neuron “reflex” circuit
    28. 28. Synaptic mechanisms underlying short-term sensitization and habituation Activation of excitatory interneuron increases likelihood of motor neuron firing
    29. 29. Synaptic mechanisms underlying short-term sensitization and habituation Decrease in PSP from sensory to motor neuron during habituation • Pre-synaptic decrease in vesicle release
    30. 30. Synaptic mechanisms underlying short-term sensitization and habituation Critical neurons in circuit mediating sensitization • Sensory neuron to tail Activated with tail shock • Modulatory interneuron Receives input from tail sensory neuron Serotonergic output onto siphon sensory neuron pre-synaptic terminal
    31. 31. Synaptic mechanisms underlying short-term sensitization and habituation Modulatory interneuronModulatory interneuron releases serotonin
    32. 32. Synaptic mechanisms underlying short-term sensitization and habituation Increase in PSP from sensory to motor neuron during sensitization
    33. 33. Synaptic mechanisms underlying short-term sensitization Sensitization of synapses lasts for 10s of minutes
    34. 34. Mechanism of presynaptic enhancement underlying behavioral sensitization 1. Serotonin is released by modulatory interneuron and binds to GPCR
    35. 35. Mechanism of presynaptic enhancement underlying behavioral sensitization 2. GPCR produces GαsGTP, which binds to Adenylyl Cyclase, which produces cAMP
    36. 36. Mechanism of presynaptic enhancement underlying behavioral sensitization 3. cAMP binds to and activates Protein Kinase A
    37. 37. Mechanism of presynaptic enhancement underlying behavioral sensitization 4. Catalytic subunits of Protein Kinase A phosphorylates potassium channels
    38. 38. Mechanism of presynaptic enhancement underlying behavioral sensitization 5. Decreased opening of potassium channels prolongs the AP, allowing more calcium influx
    39. 39. Mechanism of presynaptic enhancement underlying behavioral sensitization 6. Increased calcium causes more vesicles of transmitter release onto motor neuron
    40. 40. Mechanism of long-term synaptic enhancement PKA phosphorylates CREB, which binds to CRE, increasing transcription of genes
    41. 41. Mechanism of long-term synaptic enhancement Ubiquitin hydroxylase stimulates degradation of regulatory subunit of PKA, allowing persistence of free catalytic subunit of PKA
    42. 42. Mechanism of long-term synaptic enhancement Other genes lead to proliferation of synaptic terminals • Long term structural changes Cytoplasmic polyadenylation element binding protein (CPE) activates mRNAs enhancing local protein synthesis
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