Molecular Biology of Memory Storage: The Persistence of Memory

Transcription

1 Molecular Biology of Memory Storage: The Persistence of Memory

2 The Study of Memory Has Two Parts: (1) The Systems Problem of Memory: Where in the brain is memory stored? (2) The Molecular Problem of Memory: How is memory stored at each site?

3 There are Two Major Forms of Long-Term Memory Explicit (Declarative) Implicit (Procedural) Facts and Events People, Objects and Places Skills and Habits Nonassociative and Associative Learning Medial Temporal Lobe Hippocampus Requires Conscious Attention Amygdala, Striatum, Cerebellum, Reflex Pathways Does Not Require Conscious Attention

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5 There are Two Major Forms of Long-Term Memory Explicit (Declarative) Implicit (Procedural) Place: Spatial Memory Medial Temporal Lobe Hippocampus Requires Conscious Attention Nonassociative Learning: Learned Fear (Sensitization) Reflex Pathways Does Not Require Conscious Attention

6 Parietal Frontal Occipital Temporal

7 Abdominal Ganglion of Aplysia

8 Identified Cells and Clusters of the Abdominal Ganglion

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10 The Gill Withdrawal Reflex has a Simple Stereotypical Neural Circuit. Repetition of Sensitization Training Leads to Altered Gene Expression and the Growth of New Synaptic Connections.

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12 Sensitization Produces Both Pre- and Postsynaptic Structural Changes in the Intact Animal (HRP) Control Sensitized

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15 There are Two Major Forms of Long-Term Memory Explicit (Declarative) Implicit (Procedural) Place: Spatial Memory Medial Temporal Lobe Hippocampus Requires Conscious Attention Nonassociative Learning: Learned Fear Reflex Pathways Does Not Require Conscious Attention

16 Hippocampus of Humans Encodes Space (Mental Time Travel) Primrose Hill Route from Hyde Park to Primrose Hill Hyde Park

17 Hippocampus of Mice Also Encodes Space

18 Multi-Sensory Information About Spatial Memory is Brought Together in the CA1 Region of the Hippocampus

19 Relating Molecular Signaling to the Cognitive Map for Space: The Hippocampal Pyramidal Cells in the CA1 Region Encode Space

20 Is Synaptic Plasticity in the Hippocampal Ca1 Region Importand for Learning a Spatial Representation and for Storing a Spatial Memory? LTP

21 The Long-Term Stability of Hippocampal Synaptic Plasticity( Long Term Potentiation) Requires PKA x

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23 Both the Long-Term Memory for Space and the Long- Term Stability of the Place Cell Map Require PKA Long-Term Stability of the Place Cell Map x Similarity Score WT R(AB) 1 h 24 h Long-Term Memory of Spatial Context % Freezing (5 min) 1 h 24 h

24 How Does Attention Affect the Internal Representation of Space?

25 Is Attention Important to Form the Spatial Map or to Stabilize and Perpetuate it? Four Degrees of Attention

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27 Short Term Stability of Place Cells Does Not Require Selective Attention Short vs. Long Term Instability min longterm

28 Long Term Place Cell Stability Requires Selective Attention

29 Dopamine as a Candidate Mediator of Attention

30 Both Explicit and Implicit Memory Storage Use Modulatory Transmitters as a Salience Signal and a CREB-Mediated Transcriptional Switch for Converting Short-term to Long-term Memory Aplysia (bottom up modulation) Hippocampus (top down modulation) What- Prefrontal Cortex Where- Posterior Parietal Cortex How is synapse specificity achieved? How is it maintained for the long term?

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34 What is the Molecular Nature of the Synaptic Mark?

35 There are Two Molecular Components to the Synaptic Mark 50 camp 0 +rp-camp

36 Rapamycin, a Selective Inhibitor of Protein Synthesis also Blocks the Growth-Dependent Late Phase of LTF Initiation Capture Initiation 5 x 5-HT 1 x 5-HT 5 x 5-HT + or Rapamycin + or Rapamycin Synaptic Capture + Rapamycin Synaptic-Specific LTF + Rapamycin

37 Rapamycin Blocks the Maintenance of 72 Hrs

38 What is the Function of Local Protein Synthesis? How are the mrnas that are Transported to the Synapse Activated Locally?

39 The Cytoplasmic Polyadenylation Element Binding Protein Can Activate Dormant mrna ORF 3UTR CPEB Maskin Symplektin GEF CPSF PAP AAAAAAAAAAAAAAA Protein Richter And Colleagues

40 Branch-specific transduction of tat-ss-cpebas1 in L15 Local inhibition of CPEB blocks maintenance of LTF

41 CPEB: A Switch for Activating Local Protein Synthesis CRE 5 x 5HT mrna: (e.g. N-Actin, Tubulin) CPEB (Synaptic Mark) 1x 5HT PKA PI3 Kinase AA AA AA CPEB mrna Translational Machinery AA Proteins: N-Actin Tubulin

42 How does CPEB remain active for the long term in the absence of any further synaptic stimulation?

43 A Prion-Like Domain at the N-terminal End of Aplysia CPEB 20 Random Aplysia Proteins

44 Properties of a Prion 1) Two distinct conformational states:one of which forms aggregate. 2) The conformational states are metastable and functionally distinct Inactive Active 3) The aggregated state is self-perpetuating

45 The Full-Length CPEB Protein Can Exist in Two Functional Conformational States

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48 Blue White X W303a Kar1-15pO Kar1-15pO

49 CPEB as a Candidate for the Self-Perpetuating Switch of Local Protein Synthesis CRE 5 x 5HT 1 x 5HT Conformation B AA Conformation A AA Growth and proteins

50 3) Is the Aggregated Form The Active Form of CPEB? Only Aggregated Aplysia Neuronal CPEB Protein Binds Selectively to CPE-Containing RNA 1) Aplysia CPEB 2) mcpeb1 3) GEF 4) meif6 Purified proteins RNA Protein Control Proteins Free RNA

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52 The Prion-Like Properties of Aplysia CPEB Are Different from Known Prions The conversion from one state to the other is regulated by a physiological signal. The dominant self-perpetuating state is the active state. Aplysia CPEB might be representative of a new class of proteins with prion-like properties, which has normal physiological function.

53 A Prion-Like Domain at the N-terminal End of Mouse CPEB-3: Comparison with Aplysia CPEB Aplysia CPEB (1-160) mcpeb-3 (1-232) MQAMAVASQSPQTVDQAISVKTDYEDNQQEHIPSNFEIFRRINALLDNSL EANNVSCSQSQSQQQQQQTQQQQQQQQQQQQQQHLQQVQQQRLLK QQQQQAQRQQIQQQLLQQQQQKQQLQQQQQQEQLQQQQLQLQQQL QQQLQHIQKEPSSHTYTPGP MQDDLLMDKSKTQPQSQQQQRQQQQQQQQLQPEPGAAEAPSTPLSSEIP KPEDSSAVPALSPASAPPAPNGPDKMQMESPLLPGLSFHQPPQQPPPPQEPT APGASLSPSFGSTWSTGTTNAVEDSFFQGITPVNGTMLFQNFPHHVNPVFGG TFSPQIGLAQTQHHQQPPPPAPQPPQPAQPPQAQPSQQRRSPASPSQAPYAQ RSAAAYGHQPIMTSKPSSSSAVAAAAA ~48% Q/N ~18% Q/N Average Q/N content in mammalian proteins mcpeb-2 mcpeb-1 mcpeb-4 mcpeb-3

54 Modulatory Transmitters Serve as Salience Signals to Stabilize Synaptic Plasticity and Behavior for Both Implicit and Explicit Memory Is the mechanism for maintenance also general? Implicit Memory: Sensitization in Aplysia Explicit Memory: Spatial Memory in the Mouse

55 Naveen Agnihortri Cliff Kentros Joung-Hun Kim Kelsey Martin Maurizio Giustetto Amit Etkin Martin Theis Angel Barco Juan Marcos Alarcon Isabel Muzzio Kausik Si Robert Muller Craig Bailey Susan Lindquist