Neuro exam 2
What evidence supports a role for CaMKII in memory formation?
Prevent autophosphorylation through GM= LTP couldn't be induced in CA1 by stim Schaffer , can be induced in dentate gyrus via stim perforant path and Showed deficient inhibitory avoidance learning and in contextual fear conditioning • Fear conditioning increased presendce of autophosphorylating CaMKII in dendritic spines =experience activated the kinase show drug that inhibits CaMKII blocks acquisition of context and autidory fear conditioning CaMKII KO-cannot learn location of hidden platform, can do visible platform (=time in all quadrants)
Describe the essential experimental steps and results in the AMPA receptor trafficking experiments by Malinow's group (i.e., the Rumpel et al. experiments).
Put in faulty GluA1 receptors Non functional GluA1 rats displayed reduced fear memory (measured in freezing) depends on functional GluA1 AMPA trafficking to the membrane
Discuss the pitfalls associated with using protein synthesis inhibitors like anisomycin to test the de novo protein synthesis hypothesis.
-Protein synthesis inhibitors are toxic -even with localized injections, drug caused increases NT levels when injected in the BLA, causes super conductance and No electrical activity when drug injected for over 2 hours
Discuss some of the problems associated with pharmacological approaches to blocking NMDA receptors.
-drugs/genetic manipulations can modify bx with out affecting learning and memory -pharm/genetic can have multiple effects ( target might be involved I'm multiple processes) -memory formation can take place without NMDA receptor
Several sources of evidence indicate that the basolateral amygdala modulates memory storage. What are they?
-if you take the amygdala out, you can still form the memory -injecting no rep into BLA post trianing enhances memory -injecting propranolol into the BLA prevents memory enhancement from arousing experience -injecting lidocaine into the BLA =impaired memory
What are glucocorticoids? Are they effective memory modulators? Are they different from epinephrine?
-thought to ,modulate via the BLA -if dexamethasone is administered systemically after inhibitory avoidance training, memory enhanced -if BLA lesioned, dexamethasone has no effect -if glucocorisone agonist is injected into BLA, performance enhanced -if proprolol also injected in addition to dexamethasone, no effect =need coordinated effect
What is the evidence for the neuro-hormonal circuit?
-when epinephrine is administered to anetetized rats, it stimulates the vagus nerve , this stimulation is prevented by a beta-adrenergic-receptor antagonist sotalol. (=epinephrine stims vagus nerve) -epinephrine injected in to the periphery increases firing in the LC -inactivation of neurons in the NTS reduces memory enhancement normally seen by perish injection of epinephrine (= epic in the perish activates the LC via NTS) -electrical stim of vagal nerves increases glutamate int the NTS, antagonizing NMDA receptors in the NTS prevents enhancement normally seen from epinephrine -stmi the vagus= firing in the LC -stim the vagus post inhibitory avoidance training can enhance memory -can see increases in norep in the BLA after avoidance training
What are the three waves of consolidation? What is accomplished in each one?
1 hour local translation of new protein regulated by BDNF-mTOR pathway genomic signaling cascades activated to phosphorylate CREB to make more BDNF/Arc for new wave on consolidation 3-9 hours also dependent on BDNF-mTOR pathway active for 24 hour phase depends on activity of transcription factor C/EBPbeta and one target IGF-2
Describe the experiments with PKMζ by Yadin Dudai. What did he find?
2 ways he tested PKMζ for maintenance of memory 1. blocked it with ZIP in the insular cortex to taste aversion injected at 3,7,25 days, still erased memory 2. used LV to make faulty PKMζ injected 5 days post training, tested at 6 days, blocked memory maintencane also able to make weak memory stronger and prevent normal forgetting (LVwith PKMζ) injected 5 days before training of weak memory made strong injected 6 days after training, tested day 9 f weak truing, prevented normal forgetting
What is the composition of NMDA receptors? What subunit is always present in functional NMDA receptors?
4 subunits consisting of GluN1 and GluN2 types GluN1
Given what you know about mechanisms of synaptic plasticity how would you explain short-term memory?
??? short-term memory possibly related to autophosphorylation of CaMKII after cell has been depolarized to cause post-translational changes
Describe how the subunit composition of AMPA receptors affects working and reference memory.
AMPA short-lasting early phase LTP requires insertion of AMPA GLuA1 receptors AMPA-o GluA1 KO mice make many errors in the radial arms task • Suggest that working memory requires rapid addition of GluA1 receptors int ot he PSD • Supported by fact that LTP/radial task can be made normal by adding GluA1 expression system back into the mice -able to learn reference portion of task =probably enduring form of LTP reference memory might depend on processes that regulate trafficking of GluA2 AMPA
What are the three immediate early genes targeted by CREB?
BDNF ARC C/EBPbeta
The study of which three proteins has provided evidence that consolidation takes place in multiple rounds of protein synthesis? Provide experimental examples.
BDNF • Interference with BDNF 30 min before training reduced 1 day test and 7 day tests o Intereference with 9 hours after training reduced only 7 day test Arc • see other card IGF-2 o Antisense w/I 8 hours of training impaired performance for 24 hour retention o Antisense infused 36 hours after training impaired performance fro 48 hour retention test
How have genetic engineering approaches supported the hypothesis that NMDA receptors are critical to memory formation?
CA1KO mice developed by Tonegawa have dysfunctional NMDA receptors (by not having any N1 subunits) KO mice unable to perform place or visual place task = can't form memories or LTP but can swim
examples of how APV might affect sensory/motor requirements
Cain taught rats to learn swimming in pool before APV and when tested they did not have decreased performance on the task, Morris had APV during training Wiltgen-mice can do fear task with APV if conditioned in another context conclusion-experience can modify dependency of learning on NMDA receptors and enhance ability of calcium from other sources to compensate
Describe how the subunit composition of NMDA receptors affects working and reference memory.
GluN1 and GluN2 required for working memory, GluN2B not needed for reference or enduring LTP
What is the significance of the PKMζ KO mouse?
KO mice can still maintain and form memories, and KO mice with ZIP ave impainred maintenance = ZIP does other things in body besides blocking PKMζ all this indicates PKMζ is essential for memory maintenance, but brain probe has redundancies
What are the effects of ZIP in the PKMζ KO mouse?
KO mice with ZIP ave impainred maintenance = ZIP does other things in body besides blocking PKMζ
What pharmacological evidence supports the idea that NMDA receptors are important in memory formation?
Morris bathed brain in APV (NMDA antagonist) and found rats unable to learn place-learning task APV prevented LTP and possibly memory formation
Briefly describe three strategies that have been used to determine if NMDA receptors are involved in memory formation.
Morris-blocked NMDA:no memory formation Tonegawa-deleted important subunit for NMDA (N1)= no memory formation Tsien-overexpressed important NMDA subunit (N2B) = enhanced memory formation
What is the difference between NMDA receptors composed of GluN1-GluN2A versus GluN1-GluN2B subtypes?
N2B allows longer time to be open, more influx of Ca2+, easier to induce LTP, better memory formation
What is the role of NMDA and AMPA receptors in the acquisition and retrieval of memory? Describe evidence to support your answer.
NMDA important for acquisition not retrial, APMA important for both acquisition and retrial Morris flavor quest o APV had effect when injected before acquisition , but not when injected befre retrieval (testing retirval wit no effect taight APV has no effect on senses or motor control) o CNQX impaired memory when injected before acquisition and before retrieval
Systemic injections of anisomycin following training impair long-term memory but have no effect on short-term memory. What conclusions you can draw from this outcome?
STM trace doesn't need protein synthesis LTM trace does need protein synthesis that comes from the behavioral experience
problems with morris task
The morris task (pharm approach using APV) reduced performance but didn't completely wipe out memory formation APV also thought to affect sensory and motor requirments of water task
Describe the memory modulation framework. What is the role of the amygdala, the hippocampus, and the adrenal gland?
a theory that assumes the experience activates both the neurons that store the memory and other modulating neural-hormonal events that can influence the neurons that store memory hippo-site of memory storage and consolidation amygdala-thought to be meidatry of the hormonal near connection adrenal gland-stimulated by the learning experience and releases epinephrine
How are amphetamine and lidocaine used to study the amygdala?
amphetamine is a stimulant, lidocane temporarily numbs neurons, can use both to study effect of overactive and nonactive amydala
What is a behaviorally induced genomic cascade?
an experience that triggers creation of new mRNA and protein needed for consolidation ???pg 209
What role does the vagus nerve play in memory modulation?
attaches to the NTS, which synapse onto LC, which release norepinephrine onto the BLA which is big memory modulator. It allows epinephrine to have an influence on the brain the it can't otherwise have bc it can't cross the BBB, instead, the vagus nerve is stim by epinephrine, and then signals the LC to release norepinephrine in the brain
memory formation process
begins with bx experience that activates set of weakly connected neurons activated process strengthen synaptic connections and create a neural representation of bx experience ==MEMORY TRACE
What is propranolol?
beta-adrenergic-receptor antagonist
How was propranolol used to study the role of norepinephrine? Why was it paired with a strong electrical shock?
beta-adrenergic-receptor antagonist , competes with norepinephrine to cause a decreased response. this allows study of the effects of the shock or experience to see if that has an effect on memory modulation. there is a linear relationship with strength of shock and amount of modulation, if trying to decrease modulation (by preventing effectiveness of norep) need to use strong shock to avoid floor effects
What, in general, does the antisense methodology accomplish?
by preventing CREB from functioning, can't transcribe mRNA
what is superconductance -
causes over production of mRNA
What is the locus coeruleus? How is it involved in memory modulation?
collection of neurons in the brain stem projects to many far brain regions, forebrain, hippo, and amygdala activation of the LC= release Norep onto target neurons (place of interest is BLA)
Describe the composition of NMDA receptors.
contains 4 subunits, of which 2 types GluN1 and GluN2 need N1 for proper fx
Summarize the techniques used to test that CREB contributes to long-term memory.
delete CREB CREB antisense overexpression o CREB selections of neurons that participate in the memory trace
ampakines
developed by lynch can crossBBB, slows deactivation of channel causing prolonged current flow enhances memory!!
intial conclusions from LTP about 2 rounds of protein synthesis
early round that occurs locally in the dendritic spine late round that occurs after new mRNA have been transcribed and trafficked out of the nucleus
Given that the hormone epinephrine does not cross the blood-brain barrier, how can it influence amygdala function?
epinephrine activate adrenergic receptors on the vagus nerve, this synapses on to the solitary tract nucleus , axons from the NTS synapse onto the locus coeruleus. the LC releases norepinephrine and projects yo forebrain hippo and amygdala. BLA is the important target no rep can cross the BBB
what waves is retention at day one post training dependent on?
first and second wave
How is glucose connected to epinephrine and to memory modulation?
glucose is the primary source of energy for the brain.
What are memory modulators?
hormonal and other neural systems that are not part of the storage system but can nonetheless influence the synapses that store the memory
Discuss the rationale for the AMPA receptor trafficking experiments by Malinow's group (i.e., the Rumpel et al. experiments).
if GluA1 were seen to enter the dendritic spine after a learning experience, blocking entry should prevent memory formation
What is the function of epinephrine in the body? Where is it secreted? How is it different from norepinephrine
in the body, epinephrine energizes and mobilizes secreted by the adrenal gland norepinephrine can cross the BBB and act in the brain
How does glucose-release change with age? Does it have effects on memory?
increase epinephrine but not glucose form stimulating experience. o Old animals can aquire memories but forget more rapidly than younger animals (weeks vs days) o Gold hypothesized rapid forgetting in old animals is related to failure of liver to respond to epinephrine by secreating glucose • Rapid forgetting can by prevented by systemic injection of glucose
What changes in NMDA receptor composition are observed during neural development? What are the differences in the properties of the different subunits?
increased prevalence of GluN2A subunit replacing Glun2B N2B hold channel open longer, possibly related to easier formation of memories
HOW IS CAMKII IMPORTANT FOR LTP
increases channel conductance at PKA site, AMPA kept near to allow reinsertion
Describe an experiment that supports the hypothesis that the hormone epinephrine modulates memory storage processes.
inhibitory avoidance training and injection of epinephrine
What is reference memory?
memory of radial arms consistently baited with food
What is the evidence that BDNF is important for memory consolidation?
memory site relavent increase in levels BDNF levels increase in the hippo by contextual fear and place learning , increased in BLA for fear conditioning tx that interfere with BDNF fx impair LTM
How was microdialysis used to study the role of epinephrine?
micro dialysis allows extracellular fluid to be collected from deep within the brain allowed conclusion that after rats were shocked, there was an increase in norepinephrine in the BLA
What is the radial arm maze methodology?
multiple arms of maze with food, if eaten food not replaced, must remember where it has been=working memory can also be used to test both working and reference memory if same arms consistently baited
Describe the role of AMPA receptors in memory formation and retrieval.
necessary for both, suggested by Morris - CNQX impaired memory when injected before acquisition and before retrieval
Why is propranolol used in memory modulation experiments?
norepinephrin and epinephrine are bite adrenergic molecules, and they are both suspected to be involved in memory modulation
Describe Morris's experiment to study the effects of NMDA and AMPA receptors on memory acquisition and retrieval. What did he find?
o Acquisition phase, exposed twice, needed to use landmark to know where food is and what flavor, learned eat certain flavor, find food in certain spot injected APV and or CNQX during acquisition phase and retrieval phase of the experiment found:o APV had effect when injected before acquisition , but not when injected befre retrieval (testing retirval wit no effect taight APV has no effect on senses or motor control) o CNQX impaired memory when injected before acquisition and before retrieval o Made clean analogy for LTP vs memory induction/expression and acquisition/retrieval
Describe the de novo protein synthesis hypothesis.
o Consolidation of memeory trace requires that the target experience initiate synthesis of new protein
What is working memory?
o Maintains and manipulates info to solve a particular problem
What is the connection between aging, CREB, and memory modulation?
o Old rats display impaired CREB activation in response to memory-inducing behavorial training o Long lasting memory depend on genes targeted by CREB • Injection of either epinephrine or glucose after trining increases phosphorylated CREB in the DG in young rats • In old rats, only glucose increases phosphorylated CREB Also cfound in CA1
Describe the basic research design used to provide evidence that a drug or genetic manipulation influences the consolidation of a long-term memory.
o Train with fear conditioning or inhibitory avoidance learning o Two variables Drug/genetic manipulation to influence target molecule Retention interval o Assumptions:test performance at 4 or less hours for short term, after that requires consolidation/ LTM
Defend the following assertion: Some forgetting is the result of active molecular processes.
o continuo sp0Antagonist NMDA receptors= prevent decay of LTP and memory • =ca enterin synapses says might be a signal to internalize AMPA
Describe the conceptual basis of Joe Tsien's experiments featuring Doogie mice.
over expressed N2B subunit which allows longer NMDA opening for influx of CA2+. overexpression caused increase in LTP and memory formation
Which memory tasks can be learned and remembered even with the amygdala removed? Why is that important?
place-learning and visible-platform =amygdala not critical for storage site for these memories
What is the consolidation window?
possibly over 30 hours but ~24 hours
implications of the de novo hypothesis
protein synthesis critical for LTM but not induction of STM and that protein synthesis has to be above basal levels (from expereince and not regular syntesis
what is anisomycin
protein synthesis inhibitor
dual role of PKMzeta
release pools of GluA2 inhibit GluA2 endocytosis cycle
PKMzeta uniquness
self perpetuates had no inhibitory unit,
disruption of memory maintenance processes
should erase the memory but not limit the neuron's ability to relearn
Describe the results from experiments that used strychnine, a lethal poison, to study memory modulation.
strychnine is a stimulant at low doses, administration post learning increased performance, no effect when injected prior to performance **period of time where memory can be modified
How might AMPA receptor trafficking be involved in memory modulation?
study found that norepinephrine in the hippocampus contributes to LTP and memory of an explored context by facilitating trafficking of GluA1 AMPA receptors increased number of AMPA receptors=increased activation of the synapse, facilitating LTP and possibly memory
dexamethasone
synthetic glucocorisone
What is the evidence that new protein synthesis for consolidation happens in waves?
the supply of new proteins needed to consolidate memories is not continuous, different proteins come in discrete waves
Why is the fact that PKMζ KO mice can maintain memories not conclusive evidence against the hypothesis that PKMζ is a memory maintenance molecule?
there are probably redundancies in the brain for memory consolidation, redundancies making up for lack of PKMζ (still can be useful in maintenance )
What is the role of transcription in establishing LTM?
they modify synapses for long term changes by mRNA being translated into protein ex: CREB is protein that makes RNA, necessary for LTM
What is the retention interval?
time between training experience that establishes the memeory and the test used to retrieve the memeory
How was the lentivirus approach used to study PKMζ? What two questions did it answer?
used lent virus to block normal PKMζ function and to deliver gene for PKMζ 1. can it make weak memory strong 2. can it prevent normal forgetting
effect of CREB selections of neurons that participate in the memory trace
• Amount of CREB expressed in a neuron determines if it will be part of the neuronal ensamble that supports memory • Used Herpers vector virus to infect neurons in the LA with CREB and a neurotoxin to kill some • Found: Overexpression CREB neurons preferentially chosen for part of fear memory in LA Established fear memory erased when neurotoxin killend neurons
What is the evidence that Arc is important for LTM?
• Antisense ODNs prevent Arc o Injected in hippo, rats abel to leanr location of the hidden platform and remember following 30 min retention interval , but not after 2 days o Injcted into the LA reduce Arc and impair memory for fear conditioned response for a 24 hour retention interval, but not a 3 hour interval
What is the evidence that insulin growth factor-II (IGF-2) is involved in memory consolidation?
• Important for consolidating inhibitory avoidance training o Antisense w/I 8 hours of training impaired performance for 24 hour retention o Antisense infused 36 hours after training impaired performance fro 48 hour retention test o No effect when administered 104 hours and test at 120 hours o Impairment could be rescued bu co-infusion of IGF into hippo
effect of CREB antisense
• Inserted into the dorsal hippocampus • Trined water maze \ escape • Rats normal after 30 min but impaired after 3 days
effect of deletion of CREB
• KO mice had normal fear conditioning when retention interval short but impaired over a long interval • Hard time learning place-learning versin of Morris water escape
What evidence suggests that the amygdala modulates memory strength by regulating the translation of Arc
• McIntyre Reported increase amount of Arc in the hippo post inhibitory avoidance training • When lidocane is injected into the BLA prior to training, level of Arc in the hippo is reduced and memory is impaired • When clenbuterol (adrenergic receptor agonist ) injected into the BLA, the level of Arc is increased and memory strengthened
Describe Tonegawa's experiment with the CA1KO mouse. What is its significance?
• Tonegawa deleted GluN1 in psyramidal cells of CA1 of hippocampus LTP could not be induced in CA1 bc lack of N1 subunits • ****NMDA receptors in CA1 critical for memory
Describe the evidence that CREB can rescue long-term memory impairment.
• With inter-trial interval , normal rats show a short term memory but not long term conditioned experience when there is a short time between trials • Overexpressed CREB in lateral amygdala • Rats able to acquire LTM of the light-shock experience
effect of overexpression of CREB
• With inter-trial interval , normal rats show a short term memory but not long term conditioned experience when there is a short time between trials • Overexpressed CREB in lateral amygdala • Rats able to acquire LTM of the light-shock experience
