model system: sea hare (Aplysia californica)

1
PART 4 BEHAVIORAL PLASTICITY 21 LEARNING
MEMORY of a SIMPLE REFLEX in APLYSIA II

• model system sea hare (Aplysia californica)
• behavior the gill siphon withdrawal reflex
• even more cell biology learning memory
• summary

2
PART 4 BEHAVIORAL PLASTICITY 21 LEARNING
MEMORY of a SIMPLE REFLEX in APLYSIA II

• model system sea hare (Aplysia californica)
• behavior the gill siphon withdrawal reflex
• even more cell biology learning memory
• summary

3
CELL BIOLOGY OF LEARNING MEMORY

• mechanistic analysis of classical conditioning
• convergence of CS US in sensory neuron
• adenylyl cyclase (AC) coincidence detector?
• sensitization
• Ca channels closed
• Ca not bound to calmodulin
• calmodulin not bound to AC
• some cAMP ...

4
CELL BIOLOGY OF LEARNING MEMORY

• mechanistic analysis of classical conditioning
• convergence of CS US in sensory neuron
• adenylyl cyclase (AC) coincidence detector?
• associative learning
• Ca channels open
• Ca bound to calmodulin
• calmodulin bound to AC
• lots of cAMP ...

5
CELL BIOLOGY OF LEARNING MEMORY

• mechanistic analysis of classical conditioning
• postsynaptic factors
• glutamate, excitatory transmitter
• activates N-methyl-D-aspartate (NMDA) receptor

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CELL BIOLOGY OF LEARNING MEMORY

• mechanistic analysis of classical conditioning
• postsynaptic factors
• glutamate, excitatory transmitter
• activates N-methyl-D-aspartate (NMDA) receptor
• no signal...
• NMDA channel closed
• no Ca enters cell

7
CELL BIOLOGY OF LEARNING MEMORY

• mechanistic analysis of classical conditioning
• postsynaptic factors
• glutamate, excitatory transmitter
• activates N-methyl-D-aspartate (NMDA) receptor
• signal...
• glutamate binds to receptor
• postsynaptic membrane
• depolarizes
• postsynaptic neuron fires
• test this model?

8
CELL BIOLOGY OF LEARNING MEMORY

• mechanistic analysis of classical conditioning
• postsynaptic factors
• differential conditioning

9
CELL BIOLOGY OF LEARNING MEMORY

• mechanistic analysis of classical conditioning
• postsynaptic factors
• differential conditioning
• aminophosphonovalerate
• (APV) block of NMDA receptor

10
CELL BIOLOGY OF LEARNING MEMORY

• mechanistic analysis of classical conditioning
• postsynaptic factors
• differential conditioning
• block NMDA receptor with APV during training

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CELL BIOLOGY OF LEARNING MEMORY

• mechanistic analysis of classical conditioning
• postsynaptic factors
• differential conditioning
• block NMDA receptor with APV during training
• associative synaptic facilitation ?

12
CELL BIOLOGY OF LEARNING MEMORY

• mechanistic analysis of classical conditioning
• postsynaptic factors
• differential conditioning
• block NMDA receptor with APV during training
• associative synaptic facilitation ?
• NMDA receptor necessary

13
CELL BIOLOGY OF LEARNING MEMORY

• mechanistic analysis of classical conditioning
• postsynaptic factors
• differential conditioning
• same result during training if
• postsynaptic neuron
• hyperpolarized
• Ca blocked
• presynaptic neuron
• PKA blocked
• Ca ?

14
CELL BIOLOGY OF LEARNING MEMORY

• mechanistic analysis of classical conditioning
• postsynaptic factors
• implication that the postsynaptic neuron
  communicates with the presynaptic neuron
• retrograde (backward) signaling
• evidence (not shown) associative facilitation
  mechanism in postsynaptic neuron changes
  signaling properties in the presynaptic neuron
• neurons communicate in both directions
• but... what is the signal?

15
CELL BIOLOGY OF LEARNING MEMORY

• mechanistic analysis of classical conditioning
• revised model
• 2 sites of CS-US coincidence
• presynaptic AC

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CELL BIOLOGY OF LEARNING MEMORY

• mechanistic analysis of classical conditioning
• revised model
• 2 sites of CS-US coincidence
• presynaptic AC
• postsynaptic
• NMDA receptor
• gated channels

17
CELL BIOLOGY OF LEARNING MEMORY

• mechanistic analysis of classical conditioning
• revised model
• 2 sites of CS-US coincidence
• presynaptic AC
• postsynaptic
• NMDA receptor
• gated channels
• retrograde signal
• (hypothetical)

18
CELL BIOLOGY OF LEARNING MEMORY

• mechanistic analysis of long-term memory
• long-term synaptic facilitation in sensory
  neurons
• terminology
• long-term memory (LTM) behavioral measure
• long-term facilitation (LTF) physiological measure

19
CELL BIOLOGY OF LEARNING MEMORY

• mechanistic analysis of long-term memory
• long-term synaptic facilitation in sensory
  neurons
• distributed sensitization training

20
CELL BIOLOGY OF LEARNING MEMORY

• mechanistic analysis of long-term memory
• long-term synaptic facilitation in sensory
  neurons
• distributed sensitization training
• siphon withdrawal ?

21
CELL BIOLOGY OF LEARNING MEMORY

• mechanistic analysis of long-term memory
• long-term synaptic facilitation in sensory
  neurons
• distributed sensitization training
• siphon withdrawal ?
• sensory EPSPs ?

22
CELL BIOLOGY OF LEARNING MEMORY

• mechanistic analysis of long-term memory
• long-term synaptic facilitation in sensory
  neurons
• distributed sensitization training
• siphon withdrawal ?
• sensory EPSPs ?
• S-current ?
• (data not given)

23
CELL BIOLOGY OF LEARNING MEMORY

• mechanistic analysis of long-term memory
• long-term synaptic facilitation in sensory
  neurons
• distributed sensitization training
• siphon withdrawal ?
• sensory EPSPs ?
• S-current ?
• serotonin-induced
• presynaptic transmitter release ?
• (data not given)

24
CELL BIOLOGY OF LEARNING MEMORY

• mechanistic analysis of long-term memory
• long-term synaptic facilitation in sensory
  neurons
• distributed sensitization training
• siphon withdrawal ?
• sensory EPSPs ?
• S-current ?
• serotonin-induced
• presynaptic transmitter release ?
• (data not given)
• presynaptic neuronal plasticity

25
CELL BIOLOGY OF LEARNING MEMORY

• mechanistic analysis of long-term memory
• long-term synaptic facilitation in sensory
  neurons
• distributed sensitization training
• serotonin substitutes for tail shock _at_ sensory
• cell body ? LTF
• terminal ? STF

26
CELL BIOLOGY OF LEARNING MEMORY

• mechanistic analysis of long-term memory
• long-term synaptic facilitation in sensory
  neurons
• distributed sensitization training
• serotonin substitutes for tail shock _at_ sensory
• cell body ? LTF
• terminal ? STF

27
CELL BIOLOGY OF LEARNING MEMORY

• mechanistic analysis of long-term memory
• long-term synaptic facilitation in sensory
  neurons
• serotonin induces
• LTF
• intracellular signal
• protein synthesis (?)
• neural plasticity (?)
• STF
• locally _at_ synapse

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CELL BIOLOGY OF LEARNING MEMORY

• mechanistic analysis of long-term memory
• long-term synaptic facilitation in sensory
  neurons
• protein synthesis (?)
• transcription
• translation
• transport ? synapses

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CELL BIOLOGY OF LEARNING MEMORY

• mechanistic analysis of long-term memory
• long-term synaptic facilitation in sensory
  neurons
• protein synthesis inhibited by blockers
• also block LTF
• during serotonin application only
• not before or after...
• narrow temporal window

30
CELL BIOLOGY OF LEARNING MEMORY

• mechanistic analysis of long-term memory
• long-term synaptic facilitation in sensory
  neurons
• protein synthesis inhibited by blockers
• also block LTF
• during serotonin application only
• not before or after...
• narrow temporal window
• no block of STF

31
CELL BIOLOGY OF LEARNING MEMORY

• mechanistic analysis of long-term memory
• long-term synaptic facilitation in sensory
  neurons
• protein synthesis inhibited by blockers
• also block LTF
• during serotonin application only
• not before or after...
• narrow temporal window
• no block of STF
• ... and does block LTM (behavior)
• ?protein synthesis necessary for LTM

32
CELL BIOLOGY OF LEARNING MEMORY

• mechanistic analysis of long-term memory
• long-term sensitization / serotonin treatments ?
  molecular changes in sensory neurons
• persistent phosphorylation of existing proteins
• synthesis of new proteins
• growth of sensory neurons... neural plasticity

33
CELL BIOLOGY OF LEARNING MEMORY

• mechanistic analysis of long-term memory
• long-term sensitization / serotonin treatments ?
  molecular changes in sensory neurons
• growth of sensory neurons... neural plasticity
• visual examination
• ? axonal processes,
• branching, varicosities

34
CELL BIOLOGY OF LEARNING MEMORY

• mechanistic analysis of long-term memory
• long-term sensitization / serotonin treatments ?
  molecular changes in sensory neurons
• growth of sensory neurons... neural plasticity
• visual examination
• ? axonal processes,
• branching, varicosities

35
CELL BIOLOGY OF LEARNING MEMORY

• mechanistic analysis of long-term memory
• long-term sensitization / serotonin treatments ?
  molecular changes in sensory neurons
• growth of sensory neurons... neural plasticity
• model for synaptic restructuring / plasticity
• ? varicosities
• ? terminal active zones
• opposite for habituation

36
CELL BIOLOGY OF LEARNING MEMORY

• mechanistic analysis of long-term memory
• long-term sensitization / serotonin treatments ?
  molecular changes in sensory neurons
• growth of sensory neurons... neural plasticity
• model for synaptic restructuring / plasticity
• ? varicosities
• ? terminal active zones
• ? long-term increase in synaptic transmission
• what are the molecular mechanisms?

37
CELL BIOLOGY OF LEARNING MEMORY

• mechanistic analysis of long-term memory
• molecular induction of LTF in sensory neurons
• cAMP pathway implicated
• cAMP injection ... S-current ?
• PKA inhibitors ... block serotonin-induced LTF
• serotonin application ... PKA catalytic subunit
  cytoplasmic ? nuclear
• activity of genes
• immediate early (IEG), transcription factors
• late-responsive, leave nucleus

38
CELL BIOLOGY OF LEARNING MEMORY

• mechanistic analysis of long-term memory
• molecular induction of LTF in sensory neurons
• cAMP pathway implicated
• cAMP response elements (CREs) on DNA
• CRE binding protein (CREB)
• phosphorylated by PKA...
• CREBs ? IEGs
• IEGs ? late-responsive genes

39
CELL BIOLOGY OF LEARNING MEMORY

• mechanistic analysis of long-term memory
• molecular induction of LTF in sensory neurons
• single training event ? some PKA, STF
• distributed training ? more PKA... nucleus, LTF

40
CELL BIOLOGY OF LEARNING MEMORY

• mechanistic analysis of long-term memory
• molecular induction of LTF in sensory neurons
• competition studies using injected CRE sequences
  ? block CREB binding LTF ?

41
CELL BIOLOGY OF LEARNING MEMORY

• mechanistic analysis of long-term memory
• molecular induction of LTF in sensory neurons
• competition studies using injected CRE sequences
  ? block CREB binding LTF ?

42
CELL BIOLOGY OF LEARNING MEMORY

• mechanistic analysis of long-term memory
• molecular induction of LTF in sensory neurons
• competition studies using injected CRE sequences
  ? block CREB binding LTF ?
• enhanced CREB 1 serotonin application ?
• LTF
• structural enhancement
• CREB essential for LTF LTM
• similar findings in Drosophila (next chapter)

43
CELL BIOLOGY OF LEARNING MEMORY

• mechanistic analysis of long-term memory
• LTF molecular model
• what proteins?
• how do they work?
• other 2nd messenger
• cascades?
• homology (flies, mice)

44
CELL BIOLOGY OF LEARNING MEMORY

• middle-term memory... read the section on your own

45
SUMMARY

• defensive withdrawal reflex after stimulation
  (CS) of
• siphon, mantle, gill
• shows non-associative learning properties
• habituation, dishabituation, sensitization
• sensitization reflex with preceding tail shock
• associative learning
• reflex (CS) paired shock (US)
• differential conditioning CS1 US, CS2
• distributed training ? long-term memory

46
SUMMARY

• tail shock sensitization
• interneuron serotonin release ? sensory neuron
• ? K current flow (out of cell)
• spike broadening
• synaptic facilitation
• cAMP cascade mediated
• sensory neuron transmitter release

47
SUMMARY

• classical conditioning
• interneuron serotonin release ? sensory neuron
• tail shock US responses augmented by concurrent
  CS signal...
• activity-dependent presynaptic facilitation
• postsynaptic process, NMDA receptor in motor
  neuron

48
SUMMARY

• long-term memory
• dispersed training
• protein synthesis-dependent
• cAMP CREB ? IEGs
• IEGs ? late-response genes
• proteins ? neuron terminals
• neuronal plasticity