-No recitations this week -Exams will be graded by Monday 4/8

1. -No recitations this week -Exams will be graded by Monday 4/8 -Start working on your final presentations -Today: molecular mechanisms of learning/memory

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 potentials depolarize the presynaptic cell to open Ca2+ channels & promote synaptic vesicle fusion

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

9. Both presynaptic and postsynaptic factors influence release probability # docked vesicles (pre) + active Rs (post) # release sites (pre) + active Rs (post) # active Rs & # spines (post) contacting AZ (pre)

10. Synaptic function at the organismal level: behavior Associative learning Non-associative learning • Operant conditioning: • stimulus/response/con- • sequence relationships • Classical conditioning: • associating stimulus w/ • reward • Habituation: • tuning down response • to repetitive stimulus • Sensitization: • heightened response • to subsequent stimulus

11. Habituation vs. sensitization to repeated stimuli Habituation: mild stimulus noxious stimulus Sensitization:

12. Aplysia as a model for learning and memory Eric Kandel

13. Gill withdrawal reflex using Aplysia californica sea slug: -A mantle-covered gill is used for breathing -A siphon is used for expelling seawater and waste -Gill withdrawal occurs when the siphon is touched -Defensive mechanism used by Aplysia

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

15. 40 sensory neurons (siphon skin) synapse w/ 6 gill MNs & excitatory and inhibitory INs

16. Electrophysiology in Aplysia using the abdominal ganglia

17. Habituation was observed in Aplysia by EPSP recordings after repeated siphon stimulation

18. Possible mechanisms for short-term habituation

19. Habituation leads to decreased neurotransmitter release and reduced gill withdrawal • decreased • release • from: • SNIN • SNMN

20. Long-term habituation after 4 days of training synaptic depression & fewer sensorimotor synapses

21. A strong aversive stimulus leads to enhanced neurotransmission via facilitatory INs  amplified signal to MNs = sensitization

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

23. Increased MN response (EPSPs) after injecting 5-HT, cAMP, or PKA *each can mimic sensitization

24. 5-min incubation with 5-HT causes cAMP increase (pre) + EPSP (post) = cAMP facilitates sensitization SN MN

25. Ionotropic Rs (eg. AMPA): ion channel; 5HTR: metabotropic R PKA

26. Metabotropic receptors can be directly or indirectly coupled to ion channels

27. 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 SN after sensitization

28. Habituation: leads to homosynaptic depression [strong stimulation of one synapse  heterosynaptic depression of weaker neighbor synapse] Sensitization: leads to heterosynaptic facilitation by the interneurons that synapse on sensory neurons to enhance their NT release to the motor neuron

29. PKA also acts directly on neurotransmitter release machinery

30. Presynaptic facilitation targets K+ channels, NT vesicles, & Ca2+ channels

31. Repetitive shocks for 4 days induces shock memory for 2-3 weeks = LTM

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

33. RNA polymerase needs direct contact w/ enhancer binding proteins to activate transcription

34. CREB-2 represses transcription; CREB-1 displaces it to activate PKA

35. 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 Ub hydrolasePKA C/EBP  morphology

36. Long-term LTP: MAPK, CREB transcription/short-term LTP: 5HT, cAMP increases, activating PKA, closing K+ chan & incr NT release

37. Learning to pair stimulus with reward: classical conditioning

38. 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 cAMP

39. Training and neuronal circuits in learning in Aplysia 5HT neuron (tail) siphon water jet

40. Conditioning: APCa2+ influx calmodulin  cAMP  PKA increased NT release sensory neuron

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

42. Figure 21-53. 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.

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

44. Genetic mutants in Drosophila identified 5HT, cAMP in memory pathway amnesiac: enhances AdCyc; dPACAP= pituitary AdCyc activating peptide Ddc: Dopamine decarboxylase rutabaga: defective Ca2+-calmod dep. AdCyc dunce: PDE mutation