1. Exam 2 3/30/16
Range:
Average: 79.8
Exam 1 2/17/16
Range: 49-98
Average: 77

2. Per student performance comparison exam 1 vs. 2

3. The four basic stages of neurotransmission

4. The generation & release of a synaptic vesicle

5. Synaptic vesicles are recycled following exocytosis

6. From action potential to postsynaptic depolarization

7. Action potential via Na+ channels depolarizes the presynaptic cell to open PSM Ca2+ channels & promote vesicle fusion

8. AMPA-R: Na+/K+ channel; NMDA-R: Ca2+ channel
NMDA-R required for postsynaptic depolarization

9. Remember: the NMJ synapse requires ACh - AChR

10. # docked vesicles (pre) + active Rs (post)
Both presynaptic and postsynaptic factors influence release probability
**Kandel 3rd ed Chap 65 p1009 this lecture
See pg Fig 65-3 for sensitiz’n, facilit’n
# docked vesicles (pre) + active Rs (post)
# release sites (pre) + active Rs (post)
# active Rs & # spines (post) contacting AZ (pre)

11. Habituation vs. sensitization to repeated stimulus
mild stimulus
Habituation: repeated stimulus gives progressively reduced response (eg. EPSP)= neuronal output
Sensitization: repeated stimulus gives heightened response after time; this mechanism is how an organism learns to respond to a noxious stimulus (= learned avoidance or adaptation)
noxious
stimulus
Sensitization:

12. Aplysia as a model for learning and memory
Aplysia californica: marine snail
Eric Kandel utilized this organism because it has a simple gill withdrawal reflex defensive behavior that he could modulate and study in the laboratory
Eric Kandel

13. Aplysia protects itself from potential harm by withdrawing its gill when the siphon is touched

14. 40 sensory neurons (siphon skin) synapse w/ 6 gill MNs & excitatory and inhibitory INs

15. Electrophysiology in Aplysia using the abdominal ganglia

16. Habituation was observed in Aplysia by EPSP recordings after repeated siphon stimulation
Decrease in the open probability of Ca++ channels----decreased NT release as a result

17. Possible mechanisms for short-term habituation

18. Habituation leads to decreased neurotransmitter release and reduced gill withdrawal

19. Long-term habituation after 4 days of training synaptic depression & fewer sensorimotor synapses
See Kandel Fig 65-2 p.1011
Long term habitutation 10 X 4 days

20. A strong aversive stimulus leads to enhanced neurotransmission via facilitatory INs  amplified signal to MNs = sensitization
See Kandel Fig.65-3 p.1013

21. Sensitization/short-term memory involves 5-HT, cAMP, & PKA
All 3 increase
Glu release

22. Increased MN response (EPSPs) after injecting 5-HT, cAMP, or PKA

23. 5-min incubation with 5-HT causes cAMP increase (pre) + EPSP (post) = cAMP facilitates sensitization

24. Ionotropic Rs (eg. AMPA): ion channel; GABAB-R, 5HTR: metabotropic R

25. Decreased K+ via PKA phosphorylation prolongs action potential
1) 5-HT binds R;
AdCyc ON
2) cAMP turns PKA ON
3) PKA phos. K+
channel– closed
4) action potential
keeps Ca2+
channels open
normal
action
potential
*see Kandel p Fig. 65-3
1) 5-HT binds 5-HTR to activate AdCyc; 2) cAMP increases activates cAMP-dep protK (PKA); 3) PKA phos. K+ channel to close it; 4) action potential continues to open Ca2+ channels
after
sensitization

26. PKA also acts directly on neurotransmitter release machinery

27. Presynaptic facilitation targets K+ channels, NT vesicles, & Ca2+ channels
L-type Ca2+ channel: long-lasting voltage-gated channels

28. Repetitive shocks for 4 days induces shock memory for 2-3 weeks = LTM
In left panel, control is touched w/ brush every 30 min; “one shock” animals receive a shock after 3rd brush touch [remember for 1h]
In right panel, “4 single shocks” received 4 shocks/day & remembers for 2-3d; animals receiving 4 per day x 4d remember for 2-3 weeks= LTM!

29. Catalytic subunits of PKA translocate from the cytoplasm to the nucleus

30. RNA polymerase needs direct contact w/ enhancer binding proteins to activate transcription
DNA in promoter & regulatory regions is thought to loop around to bring activating proteins in contact w/ polymerase

31. CREB-2 represses transcription; CREB-1 displaces it to activate
CREB: cAMP response element binding protein; becomes phosphorylated by PKA then binds CRE; CBP then binds CREB to co-activate txn (CREB-CBP can also repress)
CREB: basic Leu zipper protein complexing Mg2+

32. Sensitizing stimulus in tail results in heightened responses at the synapse & in behavior
stimulating the tail then
the siphon increased
response in gill with
drawal
requires interneuron
release of 5HT 
increased cAMP 
increased PKA 
enhanced NT release
Sensitization causes increased synaptic potentials & heightened behavioral responses to stimulus

33. Long-term LTP: MAPK, CREB transcription/short-term LTP: 5HT,
cAMP increases, activating PKA, closing K+ chan & incr NT release
see Kandel p.1015 Fig. 65-5: short-term response to tail stimulation: 5HT interneuron activated AdCyc  increase cAMP  PKA activity  shut off K+ channel, more Ca2+ for vesicle/NT release
long-term response to tail stimulation: CREB binds to CREs & upreg transcription for synaptic stabilization, growth

34. Learning to pair stimulus with reward: classical conditioning

35. US/CS: unconditional/conditional stimulus
Classical conditioning in Aplysia: pairing tail shock with water jet on the siphon; output= gill withdrawal reflex US CS
US/CS: unconditional/conditional stimulus
Mechanism: activation of interneurons via CS increases Ca2+ to
enhance response to stimulus (activation of Ca2+-dep AdCyc)

36. Training and neuronal circuits in learning in Aplysia
5HT neuron (tail)
siphon
Conditioned stimulus: learned response (water on siphon)
US: shock
The animal learns to withdraw siphon for an interval

37. Conditioning: APCa2+ influx calmodulin  cAMP  PKA increased NT release

38. Presynaptic depolarization by INs increases Glu release to amplify
PSP response

39. Figure Intracellular signaling pathways during sensitization and classical conditioning in the Aplysia gill-withdrawal reflex arc. Sensitization occurs when the facilitator neuron is triggered by the unconditioned stimulus (US) in the absence of the conditioned stimulus (CS) to the siphon sensory neuron (see Figure 21-52). Classical conditioning occurs when the CS is applied 1 – 2 seconds before the US, and involves coincidence detectors in both the presynaptic siphon sensory neuron and the motor neuron. In the sensory neuron, the detector is an adenylate cyclase that is activated by both Ca2+-calmodulin and by Gsα· GTP (see Figure 21-42). In the motor neuron, the detectors are NMDA glutamate receptors (see Figure 21-40). Partial depolarization of the motor neuron induced by an unconditioned stimulus (via an unknown transmitter) from interneurons activated by the tail sensory neuron enhances the response to glutamate released by the siphon sensory neuron.

40. Learning & memory w/ odor + shock in Drosophila melanogaster

41. Genetic mutants in Drosophila that identified memory pathways
amnesiac: enhances AdCyc; dPACAP=
pituitary AdCyc activating peptide
Ddc: Dopamine
decarboxylase
rutabaga: defective
Ca2+-calmod dep.
AdCyc
dunce: PDE mutation