PART 4: BEHAVIORAL PLASTICITY #20: LEARNING & MEMORY of a SIMPLE REFLEX in APLYSIA I F model system: sea hare ( Aplysia californica ) F behavior: the gill.

PART 4: BEHAVIORAL PLASTICITY#20: LEARNING & MEMORY of a SIMPLE

REFLEX in APLYSIA I

model system: sea hare (Aplysia californica) behavior: the gill & siphon withdrawal reflex cell biology: learning & memory summary

model system: sea hare (Aplysia californica) behavior: the gill & siphon withdrawal reflex cell biology: learning & memory summary

PART 4: BEHAVIORAL PLASTICITY#20: LEARNING & MEMORY of a SIMPLE

REFLEX in APLYSIA I

slow moving gastropod mollusk phylum: Mollusca order: tectibranchia subclass: Opisthobranchia genus: Aplysia, about 35 species A. californica: 15-30 cm, south Pacific waters

few (~ 20K) neurons, some very large & identifiable can associate neural function with behavior circuitry, cell & molecular biology of learning

SEA HARE ( Aplysia californica)

gill & siphon withdrawal reflex top view of A. californica tactile stimuli gill & siphon withdrawn under mantle & covered with parapodium reliable behavior > 30 yrs of study neural mechanisms of learning

SEA HARE ( Aplysia californica)

we will focus on 2 main ideas in this chapter non-associative vs associative learning memory phases

THE GILL & SIPHON WITHDRAWL REFLEX

in very general terms, what can animals learn?1. a single stimulus2. temporal relationships among stimuli3. influence of own behavior on #2

different types of learning: non-associative learning #1 only associative learning

Pavlovian or classical #1 & 2 operant or instrumental #1, 2 & 3


study using Aplysia restrained in aquarium tactile stimulation to siphon gill retraction

repeat at 90s interval habituation electric shock stimulation to tail (or neck)

gill retraction restored dishabituation


study using Aplysia restrained in aquarium tactile stimulation to siphon gill retraction

repeat at 90s interval habituation electric shock stimulation to tail (or neck)

gill retraction restored dishabituation electric shock stimulation to tail in naive animals

gill retraction enhanced sensitization memory fairly short for all three types (min or hrs) long-term forms can also be generated


associative learning: classical or Pavlovian US = tail shock UR = rigorous siphon withdrawal CS = siphon stimulus


associative learning: classical or Pavlovian US = tail shock UR = rigorous siphon withdrawal CS = siphon stimulus

training: US + CS test: CR = rigorous siphon withdrawal


associative learning: classical or Pavlovian test with CS alone after training with:

US only sensitization control US + CS unpaired = stimulus control US + CS paired = classical conditioned

learn siphon stimulus predicts tail shock


associative learning: differential classical US = tail shock UR = rigorous siphon withdrawal CS1+ = siphon (or mantle stimulation) paired CS2– = mantle (or siphon stimulation) unpaired


associative learning: differential classical US = tail shock UR = rigorous siphon withdrawal CS1+ = siphon (or mantle stimulation) paired CS2– = mantle (or siphon stimulation) unpaired training: US + CS1+ paired,

US + CS2– unpaired test: CR = rigorous siphon

withdrawal


associative learning: differential classical test with CS1 or CS2 alone after training with:

CS1+ = siphon (or mantle stimulation) paired CS2– = mantle (or siphon stim.) unpaired

learn that CS+ predicts tail shock


associative learning: interstimulus interval CS must precede US in training

0.5 s in A. californica no learning with backward conditioning


long-term memory short-term memory: minutes / hours long-term memory: days / weeks distributed (spaced) vs massed training is the key

TIME

MEM

ORYSPACED

MASSED


long-term memory in habituation train: 4 days (T1-4) test: 1 day (R1), 1 wk (R2), 3 wks (R3)


long-term memory in habituation train: 4 days (T1-4) test: 1 day (R1), 1 wk (R2), 3 wks (R3)


long-term memory in sensitization train: 4 days (T1-4) test: 1 day (R1), 1 wk (R2), 3 wks (R3)


long-term memory in associative learning data not shown


functional architecture of withdrawal reflexes ganglia & connectives bilaterally symmetrical prs abdominal ganglion

important for reflex: 1° sensory neurons interneurons motor neurons

CELL BIOLOGY OF LEARNING & MEMORY

functional architecture of withdrawal reflexes neural circuit of reflex

~ 20 sensory neurons motor neurons interneurons

excite inhibit


functional architecture of withdrawal reflexes neural circuit of reflex

~ 20 sensory neurons motor neurons interneurons

excite inhibit

focus onsynapses


big +s for using Aplysia: direct monitor of synaptic transmission... of identified neurons... in numerous different preparations... to measure behavior


intact preparation expose abdominal ganglion gill & siphon withdrawal triggered & measured simultaneous intracellular recordings


semi-intact preparation separate organs with neurons reliable recording


isolated abdominal gangion direct access to all neural elements mimic tactile stimulation with neural stimulation


cell culture most reduced examine properties of single synapses between

sensory and motor neurons reconstruct monosynaptic component of reflex


mechanistic analysis of sensitization – the synapse synaptic facilitation semi-intact preparation electrically stimulate tail sensory to motor EPSP presynaptic mechanism

Ca++ into neuron transmitter release

spike broadening


mechanistic analysis of sensitization – the synapse synaptic facilitation semi-intact preparation serotonin application sensory to motor EPSP

serotonin blocker prevents sensory to motor EPSP (not shown)


mechanistic analysis of sensitization – biophysics serotonin sensory to motor EPSP

whole cell current: voltage clamp single ion channel patch clamp

serotonin outward K-current by... prolonged closure of 2 S-current channels:

“serotonin-sensitive K current” (S current) delayed K current

prevents repolarization of membrane leads to spike broadening


mechanistic analysis of sensitization – molecular


mechanistic analysis of sensitization – molecular synaptic facilitation semi-intact preparation inject cAMP 2nd messenger sensory to motor EPSP


mechanistic analysis of sensitization – molecular inject PKA catalytic

subunit same result phosphorylates

(closes) K-channels

sensitization modelincomplete…


mechanistic analysis of classical conditioning presynaptic factors

similarities with sensitization reflex facilitation of siphon withdrawal induced by tail shock

facilitation amplified by temporal CS-US pairing

same (amplified)mechanism or not?



similarities with sensitization reflex facilitation of siphon withdrawal induced by tail shock

facilitation amplified by temporal CS-US pairing same (amplified)

mechanism or not? test with differential

conditioning paradigm



semi-intact preparation CS1 = siphon (SN) CS2 = mantle (SN) US = tail shock



enhanced facilitation inpaired training = paired vs unpaired = paired vs US alone

temporal pairing effect activity-dependent presynaptic facilitation



differential synaptic facilitation results similar to behavioral experiments


BREAK

PART 4: BEHAVIORAL PLASTICITY #20: LEARNING & MEMORY of a SIMPLE REFLEX in APLYSIA I F model system: sea hare ( Aplysia californica ) F behavior: the gill.

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