memory maintenance Flashcards
how should memories be maintained
biochemical trace needs to be maintained
how can biochemical trace be maintained (4)
- persistent protein kinases retain phosphorylation of synaptic proteins
- insertion of membrane proteins (like AMPAR) maintained
- structural changes (size of synapse) may be long-lasting
- new synapses
what process may be required for memory erasure
AMPAR endocytosis
structure of protein kinases (like PKA) in inactive state
- 2 domains: regulatory & catalytic
- binding of pseudosubstrate keeps both domains linked together -> inactive
- pseudosubstrate stops kinase from phosphorylating things
which domain makes protein kinases inactive
regulatory domain
structure of protein kinases (like PKA) in active state (3)
- 2nd messenger binds to regulatory domain -> causes conformational change
- regulatory and catalytic domains no longer linked -> active
- catalytic domain can phosphorylate things
role of anchoring proteins that bind to protein kinases
bring the protein kinase to appropriate substrate
how does PKA become persistently active
regulatory domain ubiquitinated and targeted for proteolysis
structure of PKA, how becomes active and persistent activity
- separate regulatory and catalytic subunits
- cAMP binding causes dissociation of subunits
- timing to re-bind is important
- degradation of regulatory subunit leads to persistent activity of PKA and leaves molecular memory trace
how test for induction of memory trace
inhibiting process (kinase) before or during experience tests
how test for mechanisms involved in maintaining trace
inhibiting process (kinase) after experience
effect of inhibiting PKA (during stimulation with 5HT)
- removes increase in synaptic strength (LTF) for 12 hours after stimulation
- after 12h, no more effect of inhibitor
what did experiment inhibiting PKA lead to conclude
that mechanism for memory maintenance changes bw 12 and 24 h
what is camkii and how is it activated
- kinase activated by calcium influx
- dodecamer
- calcium binds to calmodulin and both bind kinase and activate it
how does camkii become constitutively active
phosphorylation by neighboring subunit (autophosphorylation) -> cascade of phosphorylation
limits to persistent activation of camkii (2)
- critical site cannot be rephosphorylated in absence of calmodulin (calcium-camodulin acting as substrate (bound) is required)
- after end of stimulation, phosphatases remove phosphates on subunits -> inactivation
technique to measure camkii activation in-situ + explain (4)
- FRET -> measure distance bw 2 fluorophores
- add fluorophore to kinase -> activation of kinase changes distance
- inactive camkii -> fluorophores close together so red emission (FRET transfer of energy)
- active camkii -> confo change, fluorophores far from eo so no energy transfer
results of measure camkii activation with fret (4)
- camkii is transiently activated
- becomes inactie after 1 min
- however, spine got bigger (sign of LTP)
- camkii important for induction of memory, but not for maintenance of memory
what is camkii important for
induction of memory
other than autophosphorylation, what other way can camkii be persistently activated
directly binding to NMDARs that lock it into an active state
effect of losing interaction bw camkii and NMDARs (3)
- only minor learning impairments
- LTP induction inhibited
- maintenance not affected
adding camkii inhibitor (a) before inducing ltp, (b) after inducing ltp
before: blocks ltp (memory induction)
after: does nothing (memory still maintained)
what causes persistent activation of pkc
loss of regulator domain (similar to pka)
difference bw pkc and pka structure (2)
pkc: regulatory and catalytic domain on same molecule (~ camkii) + no phosphorylation site that leads to persistent activation
mechanisms of creating persistently activated pkc (2)
- translating transcript that lacks regulatory domain
- proteolysis that separates regulatory and catalytic domains
what disrupts pkc maintenance of ltp
inhibitors of pkm zeta (ZIP)
name of pkc without regulatory domain
pkm zeta
administration of zip (a) 24h after induction of ltp, (b) 1h after induction of ltp
(a) decrease of synaptic strength (loss of memory maintenance)
(b) no effect
what is pkm (zeta) important for
late maintenance of memory (not early maintenance of memory)
what molecule reverses ltp (24h)
zip (pkm zeta inhibitor)
pkm zeta inhibition and retention of spatial information (experiment of mouse on rotating arena)
- mouse learns where it is by looking + gets shock in 1 area
- after training avoids area where shock delivered
- after 24h + saline -> retains information: avoids area where shock delivered
- after 24h + zip -> no recall: goes everywhere even where received shock
is administration of zip like ablating area in hippocampus and why
no; can retrain animal so it recalls
what type of memory does zip block
blocks ltm, not stm
effect of injecting staurosporine 24h after inducing ltp on memory storage
doesn’t block memory maintenance
effect of injecting zip 30 days after induction of ltp
erases memory
ex of memory sensitive to zip and ex of memory not sensitive to zip
sensitive -> taste aversion (up to 3 months)
insensitive -> identification of novel taste
effect of zip on (a) auditory/contextual fear conditioning, (b) remembering pain, (c) drug-induced place preference
(a) both blocked by zip in LA
(b) inhibits recall of pain
(c) inhibits recall of preferred place
effect of overexpressing pkm zeta on receptors
increase in ampar number
possible mechanism of pkm zeta
blocking endocytosis of ampars
inhibition oh pkm zeta on ampars
ampars removed from pm and memory is lost
what rescues effects of zip
blocking endocytosis of ampars
what is glur23y and what does it do + effect on zip
peptide from glua2 that blocks endocytosis of glua2 by competing with endocytic adaptors -> rescues effect of zip (don’t lose memory maintenance)
effect of pkm zeta ko on (a) learning, (b) action of zip on ltp, (c) maintenance of memory
(a) normal learning
(b) zip still erases ltp and memory
(c) normal ltp maintenance
what are possibilities that explain that zip sill works in pkm zeta ko (2)
- target of zip is something else
- compensation by upregulating other memory molecule also blocked by zip
effect of pkc iota inhibitor in (a) pkm zeta ko, (b) normal; and why
(a) blocks maintenance of memory -> pkm zeta absent so pkc iota upregulated (inhibitor has impact)
(b) no decrease in maintenance of memory -> pkm zeta present so no need to upregulate pkc iota (inhibitor has no effect)
experiment of mouse on rotating arena -> injecting pkc iota inhibitor in (a) wt (b) pkm zeta ko
(a) learn where get shocked + retain info when injected with pkci inhibitor
(b) learn where get shocked + don’t remember when injected with pkci inhibitor (go where get shocked)
what supports that there are distinct molecular complexes at synapses supporting memory
zip erases memory without affecting regular synaptic functions
mechanisms of forgetting (2)
- passive loss of trace
- active removal of trace
what is passive loss of trace
normally active phosphatases remove phosphorylation when kinase becomes inactive
what is active removal of trace
circuit activates phosphates to remove trace
what is rac important for + role in memory
regulating actin cytoskeleton (and other processes); role (+) in active forgetting
effect of overexpression of dnRac
prolongs memory retention without affecting learning
effect of overexpressing rac
shortens memory without affecting learning
what is reversal learning
erasing 1st memory when later experiences show its wrong
role of rac in reversal learning
important for reversal learning because dnRac prevents reversal learning
effect of light on photoactivable rac-tagged spines + conclusion
light activates rac -> shrinking of spines + forgetting
conclusion -> part of learning is inhibiting active forgetting (rac is inhibited to remember)
ways to reduce normal forgetting (2)
- inhibit rac
- prevent ampar endocytosis
effect of inhibiting ampar endocytosis on STM
prolongs memory that would normally decay (STM)
what protein might mimic he mechanism of active forgetting
pkm (inhibition)
what process do inhibitors like zip mimic
active forgetting system (to erase memory)
how are active forgetting and erasure related
they both require endocytotic event
what processes does reconsolidation depend on
transcription and protein synthesis
recall of a memory puts a memory in which state
labile state where it needs reconsolidation (when memory can be updated, changed) -> vulnerable
what experimental manipulations can lead to loss of memory
giving a reminder trial (of shock) followed by inhibitor of protein synthesis -> no protein synthesis, no reconsolidation, memory loss
inhibitor of protein synthesis (ex)
anisomycin (aniso)
effect of injecting aniso (a) during reminder, (b) without reminder (24h later)
(a) lose memory (that animal recalled)
(b) don’t lose memory because have nothing to recall
aplysia: during sensitization, strong correlation bw … and …
new synapses and (longer-lasting) memory
if new synapses not formed (aplysia) how long does memory last
24h
effect of memory formation (rodents) on spine formation
stabilization of new spines (increase in some spines, decrease in other spines (number invariant) -> new spines maintained if learning happens)
effect of putting rodents in enriched environment on spine formation
large increase in number of synapses
why are new synapses a parallel process for generating memory
formation of new synapses and stabilization takes hours and can’t contribute to stm formation
use what to study relationship bw new synapses and erasure (2)
- sensitization behavior (withdrawal response)
- ltf in sensory-motor neuron cultures
effect of injecting aniso after reminder on (a) response to shock (b) sensitization response (withdrawal) (c) ltf (d) varicosity number
(a) decreased freezing (forgets)
(b) decreased withdrawal (forgets)
(c) decreased ltf
(d) decreased amount of (non-specific) varicosities
do varicosities = synapses?
- not all synapses are at varicosities
- not all varicosities contain synapses
effect of pkm inhibition on sensitization, ltf and varicosity number
all decrease
what are savings
even when memory not expressed, may be traces that remain -> revealed with spontaneous recovery or when relearning occurs faster than before
what kind of changes do savings experiments implicate
nuclear changes that remain after memory erasure
what does a suboptimal stimulus lead to
memory formation after reconsolidation
what is a suboptimal stimulus
stimulus that doesn’t require transcription to be activated
effect of reminder + aniso compared to reminder + aniso + suboptimal stimulus h later
reminder + aniso -> memory loss
with suboptimal stimulus -> initially forget (aniso), able to relearn because of suboptimal stimulus (recall same as control)
effect of reminder + pkm inhibition compared to reminder + pkm inhibition + suboptimal stimulus h later
reminder + pkm inhibition -> memory loss
with suboptimal stimulus -> initially forget (pkm inhibition), able to relearn because of suboptimal stimulus (recall same as control)
what is epigenetics
changes in which genes are expressed because of changes in histones (acetylation) and dna modifications (methylation)
what are hats
histone acetylases -> acetylate histones around transcription start site, freeing up dna so rna polymerase can bind and translate (increased transcription of dna)
what are hdacs
histone deacetylases -> remove acetyl groups from dna, tightening histones and making dna unavailable to rna (decreased transcription of dna)
what does a hdac inhibitor do
leads to increased histone acetylation and increasing transcription
effect of administration of pkm inhibitor and hdac inhibitor after ltp induction
normal sensitization response (like control) -> no memory loss
administration of hdac inhibitor before ltp induction after 24h
activates learning -> creation of sensitization response (same as if trained with 5HT)
hdac inhibitors are similar to which cellular process
removing creb repressor
how do hdac inhibitors affect stimulus that normally only leads to stm
turns stimulus into one that leads to ltm
how do hdac inhibitors turn stimulus that leads to stm to stimulus that leads to ltm
making transcription easier to activate (keeping chromatin more open)
action of hdac inhibitors on pkm inhibitors and what does this mean for savings/memory
block actions of pkm inhibitors -> savings can reestablish memory if transcription is ongoing
how does dna methylation change dna
adds methyl on cytosine of cpg sites
when does methylation occur and how is it retained
occurs during cell fate determination; retained after cell division by enzymes that copy methyl group as dna is replicated
role of dnmt (2)
- retain methylation on dna
- required for ltm (maybe turning off memory repressors)
what do methyl-cpg-binding (mbd) proteins do (2)
- attract repressors and hdacs
- are the effectors of dna methylation
effect of methylation on gene expression
target gene silenced (not transcribed)
proposed pkm inhibition mechanism (DNA level)
pkm inhibition (erasure) removes acetylation on dna, but leaves methylation -> savings
effect of inhibiting dna methylation before ltm induction (2)
- blocks memory formation
- blocks savings
how can memory be erased (2)
- blocking pkm
- reconsolidation
what could savings be due to
lower levels of repressors of memory formation
aspects of memory stored in nucleus (2)
- histone modifications
- dna methylation
what measures memory maintenance (2)
- forgetting
- erasure
