Cognition part 2 (lec 11/12) Flashcards
what are the 3 main classes of NT?
amino acids
amines
peptides
name the 3 amino acid NT
GABA
glutamate
glycine
list 6 amine NT
ACh
DA
epinephrine
histamine
NE
5-HT
list some (9) of the peptide NT
CCK dynorphin Enk NAAG neuropeptide Y somatostatin substance P thyrotropin-releasing hormone VIP
the CA1 region has how many kinds of glutamate receptors? name them
2
NMDA
AMPA
describe the state or AMPA and NMDA receptors in normal synaptic transmission
AMPA: when activated it depolarizes cell, glutamate and Na bind
NMDA: inactive because block by Mg (glutamates tries to enter)
what occurs at the NMDA/AMPA rec in order to induce LTP?
with repeated activation of AMPA rec, the change in postsynaptic membrane potential drives Mg out of NMDA channel
- inc in Ca (pos charge) =depolarization
describe how Na and Ca enter into cell
Na= through AMPA rec
Ca= through NMDA rec
what is the 1st mechanism of inc Ca?
- Ca dependent signalling is important for activation of CaMKII = chaparoning of more glutamate rec to membrane surface
- 3 kinds of receptors
- goal: guide these AMPA rec that havent been embedded yet, and embed them to membrane, changing sensitivity of membrane to further glutamate exposure
what is 2nd mechanism of inc Ca
- inc Ca= activate Ca-dependent pathways= inc in CREB
- CREB is like transcription factor, can bind to promoter regions and inc amount of glutamate receptors
- CREB important for activating more promoters to express more of the AMPA rec
*** gene expression is crucial for stability of LTP
what is the response/mechanism of inc Ca?
- inc Ca through NMDA rec through retrograde signalling
- NO and arachidonic acid and other retrograde messengers that can be sent through extracellular matrix to the cell that is stimulating the presynaptic cell, to stimulate more NT release
- can be facilitated by NO and arachidonic acid
- CREB is important mediator
stimulate more glutamate release results in…?
more representation of a receptor (like feedback loop)
more rec= have same effect whether have little or a lot of glutamate released
what occurs of 1+ AMPA rec have been repeatedly stimulated?
enough Na ions enter to largely depolarize the dendrites membrane
- this displaces the Mg ions, enables glutamate to open the NMDA rec
- Na and Ca enter
feedback= further release of glutamate, due to Mg that facilitates it
the large Ca influx activates certain ____ _____, which are ..?
protein kinases
enzymes that add P groups to protein molecules
what is an example of a protein kinase that is activated by Ca influx?
CaMKII (calcium-calmodulin kinase II)
- important because involved in regions of brain that are involved with learning/memory
name 3 ways in which CaMKII affects AMPA rec
1) cause more AMPA rec to be produced and inserted in postsynaptic membrane
2) moves existing nearby AMPA rec into active synapse
3) inc conductance of Na and K ions in membrane-bound AMPA receptors
describe what happens to dendritic branches in response to LTP
more AMPA rec are built and dendritic branching is increased
in response to LTP get inc in structure of dendrite= more platforms for insertion of more AMPA
strong stimulation of a postsynaptic cell releases a ____ ____
retrograde messenger
what is a retrograde messenger?
often a diffusible gas like carbon monoxide or nitric oxide that travels across the synapse
a retrograde messenger alters the function of pre/postsynaptic neuron????
PRESYNAPTIC
how does retrograde messengers alter function of presynaptic neuron?
1) dec in AP threshold= inc release of NT
2) expansion of axons= transmitter release from additional sites
how do the changes of the retrograde messengers affect glutamate?
- inc the synaptic sensitivity to glutamate and the synapse is strengthened (bc inc in rec)
- inc later responsiveness of the dendrite to incoming glutamate
what is an enhanced synapse?
after induction of LTP
- changes from LTP make synapse more responsive
- synapse now ready to give more rapid and stronger response, because more transmitter is released and there are more AMPA receptors in the postsynaptic membrane
what are the 5 main steps in the neurochemical cascade during induction of LTP?
1) activated protein kinases trigger protein synthesis
2) kinases activated CREB (cAMP responsive element-binding protein)
3) CREB binds to cAMP responsive elements in DNA promoter regions
4) CREB changes the transcription RATE of genes
5) regulated genes then produce proteins that affect synaptic function and contribute to LTP (e.g. AMPA and NMDA rec)
- CREB recruits and binds to histone acetylase transferase and targets it for further gene activation
gene expression is crucial for ….
LTP stability
what is role of actinomycin D in LTP?
- inhibits transcription by binding DNA at the transcription initiation complex
- prevent elongation of RNA chain by RNA polymerase
- inhibited the maintenance of LTP in rat hippocampal neurons ex vivo and in vivo
–> study concluded that gene transcription was required for maintenance of LTP
3 experiments that show evidence that LTP may be a part of learning and memory formation
correlational observations
somatic intervention experiments
behavioural intervention experiments
what are correlational observations for LTP?
time course of LTP is similar to that of memory formation
what are somatic intervention experiments?
pharmacological treatments that block LTP impair learning
- if lack function of NMDA rec= learn slowly
- extra expression of NMDA rec= faster learning
—> NMDA rec must be important in learning
behavioural intervention experiments
training an animal in a memory task can induce LTP
- e.g. water maze
explain the model for role of histone acetylation in long term memory formation
- glutamate acting at AMPA and NMDA rec
- results in Ca-dependent activation
- series of phosphorylations (PKC) which result in huge cascade
- MEK-ERK pathway is general signalling cascade results in activation of CREB and CRB binding= histone acetylation and transcription iniation
name 3 drugs that are HDAC inhibitors
sodium butyrate
valporate
TSA
what is the suggestion of role of histone acetylation in long term memory formation???
if we can regulate amount of histone acetylation MAYBE we can regulate LTP and MAYBE improve the memory formation in animals
HDAC inhibitors (enhnace/inhibit) LTP????
ENHANCE
- they do not create LTP
- promote acetylation, enhance induction of LTP
describe the contextual fear conditioning behavioural paradigm
- animal placed in training chamber (novel context)
- exposed to foot shocks, then removed from box
- flash a light
- frequency of freezing behaviour measured during 1-24hr after trial
- condition these animals to freezing behaviour if in box and shock them and flash a light while giving shock
- if place in box and shine light (no shock), look at frequency of freezing behaviour
contextual fear memories are stored where??? for how long???
- amygdala
- area CA1 of hippocampus
- at least 24 hr after contextual fear conditioning
explain how HDAC inhibitor activity enhances formation of long term memory in vivo
- animals injected with HDACI or vehicle 1hr prior to one-shock contextual fear conditioning
- HDACI did not effect animals ability to perceive and respond to foot shock
- HDACI increased histone H3-acetylation, enhanced the formation of long-term contextual fear memory
what is the effect of a DNMT inhibitor on long term memory?
inhibitor of DNMT activity in hippocampus blocks formation of LTM in vivo
explain the experiment of using DNMT inhibitor to block LTM formation
- inject with DNMT inhibitor (Zebularine/RG108) or vehicle 1h prior to one-shock contextual fear conditioning
- DNMT inhibitor did not effect animals ability to perceive and respond to foot shock
- DNMT inhibitor specifically blocked formation of long-term contextual fear memory
what occurred if animals injected with HDACI and then inject with DNMT inhibitor
why??
DO NOT show memory impairment
bc methylation pattern is already laid down, changes have occurred
enhance or block LT contextual fear memory??
- HDAC inhibitor
- DNMT inhibitor
HDAC= enhance formation
DNMT= block formation
is DNA methylation involved in LT memory formation??
observations suggest that DNMT activity is not only necessary for memory and plasticity but
DNA methylation works in concert with histone modifications to regulate plasticity and memory formation in the hippocampus
with age, we tend to show some memory impairment int asks of conscious recollection that … (2)
1) require effort
2) rely primarily on internal generation of the memory rather than on external cues
as we age, experience decreases in ____ memory and ______ skills
spatial memory
navigational skills