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
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
SEA HARE ( Aplysia californica)
 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 tactile stimuli  gill & siphon withdrawn under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
THE GILL & SIPHON WITHDRAWL REFLEX
 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 stimulus
2. temporal relationships among stimuli
3. 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
THE GILL & SIPHON WITHDRAWL REFLEX
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
THE GILL & SIPHON WITHDRAWL REFLEX
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
THE GILL & SIPHON WITHDRAWL REFLEX
associative learning: classical or Pavlovian
US = tail shock
UR = rigorous siphon withdrawal
CS = siphon stimulus
THE GILL & SIPHON WITHDRAWL REFLEX
associative learning: classical or Pavlovian
US = tail shock
UR = rigorous siphon withdrawal
CS = siphon stimulus
training: US + CS
test: CR = rigorous siphon withdrawal
THE GILL & SIPHON WITHDRAWL REFLEX
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
THE GILL & SIPHON WITHDRAWL REFLEX
associative learning: differential classical
US = tail shock
UR = rigorous siphon withdrawal
CS1+ = siphon (or mantle stimulation) paired
CS2– = mantle (or siphon stimulation) unpaired
THE GILL & SIPHON WITHDRAWL REFLEX
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
THE GILL & SIPHON WITHDRAWL REFLEX
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
THE GILL & SIPHON WITHDRAWL REFLEX
associative learning: interstimulus interval
CS must precede US in training
0.5 s in A. californica
no learning with backward conditioning
THE GILL & SIPHON WITHDRAWL REFLEX
long-term memory
short-term memory:  minutes / hours
long-term memory:  days / weeks
distributed (spaced) vs massed training is the
SPACED
MASSED
MEMORY
key
TIME
THE GILL & SIPHON WITHDRAWL REFLEX
long-term memory in habituation
train: 4 days (T1-4)
test: 1 day (R1), 1 wk (R2), 3 wks (R3)
THE GILL & SIPHON WITHDRAWL REFLEX
long-term memory in habituation
train: 4 days (T1-4)
test: 1 day (R1), 1 wk (R2), 3 wks (R3)
THE GILL & SIPHON WITHDRAWL REFLEX
long-term memory in sensitization
train: 4 days (T1-4)
test: 1 day (R1), 1 wk (R2), 3 wks (R3)
THE GILL & SIPHON WITHDRAWL REFLEX
long-term memory in associative learning
data not shown
CELL BIOLOGY OF LEARNING & MEMORY
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
CELL BIOLOGY OF LEARNING & MEMORY
functional architecture of withdrawal reflexes
neural circuit of reflex
~ 20 sensory neurons  motor neurons
interneurons
excite
inhibit
focus on
synapses
CELL BIOLOGY OF LEARNING & MEMORY
big +s for using Aplysia:
direct monitor of synaptic transmission...
of identified neurons...
in numerous different preparations...
to measure behavior
CELL BIOLOGY OF LEARNING & MEMORY
intact preparation
expose abdominal ganglion
gill & siphon withdrawal triggered & measured
simultaneous intracellular recordings
CELL BIOLOGY OF LEARNING & MEMORY
semi-intact preparation
separate organs with neurons
reliable recording
CELL BIOLOGY OF LEARNING & MEMORY
isolated abdominal gangion
direct access to all neural elements
mimic tactile stimulation with neural stimulation
CELL BIOLOGY OF LEARNING & MEMORY
cell culture
most reduced
examine properties of single synapses between
sensory and motor neurons
reconstruct monosynaptic component of reflex
CELL BIOLOGY OF LEARNING & MEMORY
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
CELL BIOLOGY OF LEARNING & MEMORY
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)
CELL BIOLOGY OF LEARNING & MEMORY
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
CELL BIOLOGY OF LEARNING & MEMORY
mechanistic analysis of sensitization – molecular
CELL BIOLOGY OF LEARNING & MEMORY
mechanistic analysis of sensitization – molecular
synaptic facilitation
semi-intact preparation
inject cAMP 2nd messenger
 sensory to motor EPSP
CELL BIOLOGY OF LEARNING & MEMORY
mechanistic analysis of sensitization – molecular
inject PKA catalytic
subunit same result
phosphorylates
(closes) K-channels
sensitization model
incomplete…
CELL BIOLOGY OF LEARNING & MEMORY
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?
CELL BIOLOGY OF LEARNING & MEMORY
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?
test with differential
conditioning paradigm
CELL BIOLOGY OF LEARNING & MEMORY
mechanistic analysis of classical conditioning
presynaptic factors
semi-intact preparation
CS1 = siphon (SN)
CS2 = mantle (SN)
US = tail shock
CELL BIOLOGY OF LEARNING & MEMORY
mechanistic analysis of classical conditioning
presynaptic factors
enhanced facilitation in
paired training
 = paired vs unpaired
 = paired vs US alone
temporal pairing effect
activity-dependent presynaptic facilitation
CELL BIOLOGY OF LEARNING & MEMORY
mechanistic analysis of classical conditioning
presynaptic factors
differential synaptic facilitation results similar to
behavioral experiments
BREAK