Important!!! 2015/5/18 本次鄭菡若及陳麗芬老師的考試部分, 開放可攜帶 1 頁 A4 的手寫筆記, 規範如下 : 1. 所有筆記只能寫在一張 A4 紙雙面 ( 兩位老師的範圍加起來 ) 2. 只能自己手寫或手繪 ; 不得影印 用電腦印 黏貼任何紙張或其他東西

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1 Important!!! 本次鄭菡若及陳麗芬老師的考試部分, 開放可攜帶 1 頁 A4 的手寫筆記, 規範如下 : 1. 所有筆記只能寫在一張 A4 紙雙面 ( 兩位老師的範圍加起來 ) 2. 只能自己手寫或手繪 ; 不得影印 用電腦印 黏貼任何紙張或其他東西 3. 請自己整理, 不可抄襲別人的 如有兩份筆記內容一模一樣, 則兩份一起沒收 4. 考試期間請放在桌面, 由淑惠代為檢查, 如有不合上述條件, 則沒收該份筆記 5. 除這張 A4 紙外, 不得攜帶任何其他東西,3C 產品考試中不得使用 Chapter 66 &67. Cellular and Mechanisms of Memory Aplysia Mouse All neurons in behavioral circuits are identified and can be recorded easily. Ideal for studying mechanisms underlying learned motor responses Similar anatomy to human Can do complex electrophysiology and behavioral tests Genetic modified technologies are available 1

2 Memory can be classified along 2 dimensions The time course of storage Short term (working) memory Long term memory The nature of the information Explicit (conscious) Implicit (subconscious) Molecular mechanism? 2 mechanisms of synaptic plasticity Implicit memory Short term: pre synaptic enhancement of transmitter release Long term: growth of new synaptic connection Explicit memory Short term: post synaptic insertion of new postsynaptic receptors Long term: growth of new synaptic connection 2

3 Why use animals to study learning and memory? Eric Kandel was originally interested in psychotherapy Wanted to locate Freud s id, ego, & superego Plato s appetitive, rational, & spirited souls Harry Grundfest told him to start one cell at a time Kandel decided that human brains are too complicated. Human brains are too complicated 3

4 The synaptic plasticity for learning and memory The number of neurons in the adult brain did not increase significantly with age, so memories were not the result of new neuron production. Short term: Changing the effectiveness of the synaptic communication (minutes) Amount of neurotransmitter released from a synapses (presynaptic) Change the sensitivity of receptors (postsynaptic) Long term: Protein synthesis and developing new synapses (hours to days) Implicit memory 4

5 Habituation Using aplysia to study learning Only 20,000 neurons Neurons are large and easy to identify. The gill withdrawal reflex can use to study both associative & nonassociative learning 5

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7 Short term habituation of the gill withdrawal reflex Habituation involves an activity dependent presynaptic depression of synaptic transmission 7

8 Sensitization Opposite of habituation Increased response with repeated stimulation. Intense and salient stimuli Examples: Earthquake Pain response Fear potentiated startle 8

9 Interneuron interneuron Regulating communication between sensory and motor neurons 9

10 Sensitization involves presynaptic facilitation of synaptic transmission Short term effect for nonassociative learning Habituation Decrease of neurotransmitters Inactivation of receptors decrease in Ca 2+ influx Sensitization Activation of interneurons with serotonin (5 HT) as transmitter. 5 HT stimulate presynaptic neurotransmitter release. normal 10

11 Short term effect for nonassociative learning Short term sensitization is mediated through serotonergic synapses of facilitating interneurons 5-HT camp PKA activity outward K + - Ca 2+ influx transmitter release 11

12 camp and diglyceride are second messengers Second messengers are small molecules that bring signals from receptors on the cell surface to target molecules inside the cell camp (Cyclic adenosine monophosphate) transmits signals from G coupled protein receptors intracellularly to effector proteins, such as protein kinase alpha (PKA). second_messenger camp.html Mechanism of presynaptic enhancement underlying behavioral sensitization 1. Serotonin (5 HT) is released by modulatory interneuron and binds to G protein coupled receptor (GPCR) 2. GPCR produces G s GTP, which binds to Adenylyl Cyclase, which produces camp 3. camp binds to and activates Protein Kinase A 4. Catalytic subunits of Protein Kinase A phosphorylates potassium channels 5. Decreased opening of K + channels prolongs the action potential, allowing more calcium influx 6. Increased Ca 2+ causes more vesicles of transmitter release onto motor neuron 12

13 Long term effect for nonassociative learning Aplysia sensory neuron usually have ~1300 terminal Aplysia experiencing sensitization had ~2800 terminals. Aplysia experiencing habituation had ~800 terminals. Classical Conditioning in Aplysia 13

14 Associative Learning in Aplysia Long Term Memory Protein synthesis Increase number of neurotransmitter receptors and active zone proteins Structural changes morphological reorganisation change in the number of synapses 14

15 Hebbiant rule for memory "Cells that fire together, wire together When an axon of cell A is near enough to excite cell B and repeatedly or persistently takes part in firing it, some growth process or metabolic change takes place in one or both cells such that A s efficacy, as one of the cells firing B, is increased. -Donald Hebb (1949) Mechanism of long term synaptic facilitation 5 HT (serotonin) is released by facilitating interneuron and binds to 5 HT receptor 5 HT receptor produces camp camp binds to and activates Protein Kinase A PKA increases transmitter release 15

16 long term sensitization involves in synaptic facilitation and the growth of new synaptic connection 1. Translocation of PKA to nucleus 2. PKA phosphorylates CREB-1 3. CREB-1 binds to CRE 4. Expression of ubiquitin hydrolase to degrade PKA regulatory subunit 5. Expression of C/EBP for the growth of new connection camp response element binding protein (CREB) CREB transcription factor: Transcription factor that binds to the camp response element (CRE) Phosphorylation is necessary for its nuclear translocation and DNA binding A D1 Cyclase Ca camp PDE kinase NMDA AMPA CRE (CREB response element): DNA sequence TGACGTCA in the promoter region of a gene CREB phosphorylation and translocation to nucleus 16

17 Long term facilitation of synaptic transmission is synapse specific Facilitation is studied in vitro with isolated preparations of neurons. Long term facilitation requires both camp dependent phsophorylation and local protein synthesis 17

18 Long term effect for nonassociative learning Habituation decrease in the # and the area of active zones of the synapse decrease in the total # of synapses per neuron and the extent of axonal branching Sensitization PKA activates transcription factor CREB to make new proteins increase in the # and the area of active zones of the synapse increase in the total # of synapses per neuron and the extent of axonal branching Anisomycin (protein synthesis inhibitor) % sensitization Explicit memory 18

19 Long term potentiation (LTP) the persistent improvement in communication between two neurons after repeat stimulating necessary for the encoding and storage of the memory LTP has a transient early and a consolidated late phase LTP happens when electrical impulses are fired successively at a high rate so that the postsynaptic neuron is depolarized A demonstration of long term potentiation In LTP, neurons continue to fire at an elevated rate, even though the stimulus has returned to normal. baseline High frequency stimulation LTP 30 min 60 min (at least) 19

20 Long term Potentiation (LTP) Synapses in LTP behave like Hebbian synapses: Tetanus drives repeated firing. Postsynaptic targets fire repeatedly due to the stimulation. Synapses are stronger than before. Long term Potentiation (LTP) occurs when one or more axons bombard a dendrite with stimulation. Leaves the synapse potentiated for a period of time and the neuron is more responsive. Main actors control LTP: Glutamate receptors AMPA receptor Na + channels NMDA receptor allows Na + and Ca 2+ ions to enter the neuron responds to glutamate ONLY when the membrane is partly depolarised by Na + glutamate excitation of NMDA receptors opens NMDA dependent Ca 2+ channels 20

21 Early LTP is protein synthesis independent Last 1 3 hours Ca 2+ entry through NMDA receptors triggers LTP Results in activation of protein kinases Insertion of new AMPA receptors into the postsynaptic Early LTP needs NMDAR APV NMDA receptor antagonist 21

22 Induction of LTP at Schaffer collateral synapses Normal Only Na + ad K + flow though AMPAR NMDAR blocked by Mg 2+ High frequency stimulation Ca 2+ enter through NMDAR and activate Ca 2+ dependent kinase: CaMKII (Ca 2+ /calmodulin kinase) PKC (Protein kinase C) Fyn (a tyrosine kinase) Early LTP More AMPAR to synapse More transmmitter Ampakines enhance AMPA receptor function 22

23 AMPA receptors and memory formation NMDA receptor dependent AMPA receptor synaptic delivery in LTP. Calcium influx through NMDA receptors initiates the delivery of AMPA receptors from the recycling endosome to the postsynaptic site. NMDA receptors are central to producing LTP but AMPA receptors maintaining it. Mechanisms of Synaptic Plasticity CaM KII (calcium calmodulin kinase type II ) Postsynaptic kinase activated by Ca 2+ Ca 2+ binds with CaM KII, linking proteins attach to NMDA receptor AMPA receptors are linked to NMDA receptor by protein. 23

24 NMDAR and AMPAR can be positively regulated by phosphorylated αcamkii Late LTP /long term memory formation Last >24 hours Involves in dopamine system Increase Ca 2+ influx activates camp-pka-mapk-creb signaling and synthesis new proteins. Produce more camp New synapse Activate kinases (CaMKII PKA, PKC) 24

25 Novel protein synthesis is required for late LTP but not early LTP Early LTP Short term memory Late LTP Long term memory Properties of LTP that suggest it as a cellular basis of learning and memory Rapid induction : LTP takes place very rapidly Cooperative: The near stimultaneous activation of several weak inputs during strong activation results LTP in all pathways. Associatively: Stimulation of strong and weak inputs together causes LTP in both pathways Synapse specificity: An unstimulated synapse does not undergo LTP in spite of strong stimulation of neighboring synapses 25

26 Evidence for an LTP/Learning Link Mice with abnormal NMDA receptors have difficulty learning Mice with more than normal NMDA receptors have super memory Drugs that block LTP block learning Drugs that facilitate LTP facilitate learning AMPA agonists: AMPA, glutamate, Ampakine antagonists: CNQX, NBQX NMDA agonists: glutamate, aspartate, NMDA antagonists: APV, AP5, MK 801, Ketamine, Phencyclidine, Mg ++ Testing learning and memory Morris water maze 26

27 The NMDA receptor and spatial learning Infusion NMDA receptor antagonist APV. Days Memory retention test in the probe trial Not impaired Impaired platform Target quadrant 27

28 The NMDA receptor and memory retention Deletion of the NR1 subunit in CA1 28

29 Deletion of the NR1 subunit in CA1 Deletion of the NR1 subunit in CA1 29

30 Overexpressing NR2B enhance learning and memory CaMKII knockout mice show impaired learning and memory 30

31 Using tta system to control the location and timing of constitutively active mutant CaMKII T286A expression Phosphorylation of CaMKII is critical for formation of memory Mutant TG on Mutant TG off Mutant TG on 31

32 Long term depression (LTD) LTD is an activity dependent reduction in the efficacy of neuronal synapses LTD induced by prolong period low frequency stimulation Phosphatases are require for LTD Protein phosphatase 1 (PP1) and protein phosphatase 2A (PP2A) remove phosphate from AMPAR 32

33 LTD contribute to behavioral flexibility 2 mechanisms of synaptic plasticity Implicit memory Short term: pre synaptic enhancement of transmitter release Long term: growth of new synaptic connection Explicit memory Short term: post synaptic insertion of new postsynaptic receptors Long term: growth of new synaptic connection 33

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