mod 3 Flashcards
steps of memory storage in brain
- release of neurotransmitter
- activation of postsynaptic receptors
- trafficking of receptors to PSD
- local translation of new proteins
- altered gene expression
sodium potassium pump pumps
3 Na out and 2 K in
calcium homeostasis
pumping Ca out of cell, and intracellular calcium-binding proteins and organelles: mitochondria and endoplasmic reticulum
influx of +ve ions
depolarised, excites the neurons EPSP
influx of -ve ions
hyperpolarized, inhibits the neurons IPSP
membrane potential changes during an action potential
- stimulus moves membrane potential to threshold
- opens voltage-gated Na channel, Na flows in
- Na channels close and voltage-gated K channels open
- K flows out until K equilibrium potential reached
- Na/K pumps return membrane to resting potential
spatial summation
multiple input neurons (EPSP) generate simultaneously at many different synapses on a dendrite
temporal summation
one input neuron strongly activated
chemical synapse
transmission via the release of a neurotransmitter
electrical synapse
transmission via electrical currents flowing from one neuron to the next at gap junctions
presynaptic events
- action potential reaches axon terminal and depolarises membrane
- voltage-gated Ca channels open and Ca flows in
- Ca influx triggers synaptic vesicles to release neurotransmitters
- neurotransmitter binds to receptors on target cell
visualising communication between neurons
through micro-periscope, in vivo. view calcium activity in subfield CA1 in excitatory neurons
small synaptic vesicles
50nm diameter, clear, membrane bound, most abundant within CNS, contain glutamate, GABA and glycine
small synaptic vesicles at readily releasable pool
docked at the active zone
small synaptic vesicles at reserve pool
distal to active zone, associated with cytoskeleton
small synaptic vesicles at recycling pool
diffusing
vesicle cycle
formed in golgi apparatus —– transport along microtubules to axons —> filled with neurotransmitter at never terminal —> release transmitter then ercycle via endocytosis to endosomes or reserve pool and refilled with transporters
large dense core vesicles structure
100nm diameter, electron dense/dark, membrane bound, contain catecholamine neuropeptides, neurotrophines, nor/adrenaline
large dense core vesicles function
local diffusion to active synaptic partners, act on g-protein-couple receptors, may contribute to presynaptic modulation in addition to postsynaptic effects, comprise of 1-2% of vesicles
synthesis pathway
- synthesis and modification of neuropeptides (RER and golgi apparatus)
- packaging pro-peptide and modifying enzymes
- axonal transport
- cleavage of pro-peptide (will dock on membrane to release contents)
- release
why prolonged stimulation of LDCV
not pre-docked, requires more widespread increase in Ca including activation of CaMKII via calcium - induced calcium release from ER.
primary locations of LDCV
neurosecretory and neuroendocrine cells as well as sympathetic neurons of PNS, neurohypophysis, hypothalamus
neurosecretory cells (location of LDCV)
neurons that secrete their products into pituitary portal vessels at the median eminence
neuroendocrine cells (location of LDCV)
cells which receive neuronal input and release hormones into the blood stream - chromaffin cells
chromaffin cells
neurendocrine cells: medulla of adrenal glands, enriched with LDCVs
chromaffin cells role
contain and release many substances into circulatory system: catecholamines, peptides, proteins, microRNa, neuromodulations, stress transducers
what are the snares involved with
exocytosis
v-snare
synaptopbrevin (from synaptic vesicle)
t-snare from cytosol
SNAP25
t-snare from embedded in plasma membrane
syntaxin
binding of snares
synaptobrevin binds to alpha primed end of SNAP25 while syntaxin binds to alpha helix terminal at end of SNAP25
what drives the dissociation of the SNARE complex
ATPase N-ethylmaleimide-sensitive fusion (NSF)
Rab proteins
small GTP binding proteins
rab protein function
involved in vesicle guiding and docking at membrane. GTP is hydrolysed which results in fusion of vesicle and release of neurotransmitter
what results in the fusion of vesicles and release of neurotransmitter
GTP hydrolysis
exocytosis
synaptic vesicle protein, calcium sensor, docking, vesicle fusion+release, ca influx
clathrin-mediated endocytosis
the process by which vesicular membrane is retrieved back into the cytoplasm
clathrin
assists in the formation of a coated pit on the inner surface of the plasma membrane of the cell which buds into cell to form a coated vesicle
clathrin structure
subunits comprise 3 large and 3 small polypeptide chains that form a triskelion and assemble into basket-like frameworks.
dynamin
a GTPase, binding to form a bud on membrane. forms a helical collar around the neck of the bud
what do dynamin spirals undergo
a length-wise extension which pinches or pops the vesicle from the parent membrane
synaptic vesicle cycle exocytosis
Rabs, v-SNARE, t-SNARE, synaptotagmin
synaptic vesicle cycle endocytosis
clathrin, dynamin
botulinum toxin
blocks release of acetylcholine at the NMJ resulting in muscle paralysis lasting 3 months
one of the most poisonous biological substances
botulinum toxin (produced by clostridium botulinum)
heavy chain toxin binds to what
binds selectively and irreversibly to presynaptic receptors on cholinergic neurons
behaviour of heavy chain - preventing muscle contraction
binded with cholinergic neurons, it is endocytosed during which the light chain is cleaved and released from heavy chain to bind to SNAP25. this prevents exocytosis.fusion of vesicles so no acetylcholine is release and muscles cannot contract
tetanus toxin
cleaves synaptic vesicles associated proteins synaptabrevin in cytosol. meaning glycine or gaba cannot be secreted nor acetylcholine so no muscle contraction will be halted resulting in spastic paralysis
what does botulinum toxin cause
muscle paralysis
what does tetanus toxin cause
spastic paralysis
tetanus toxin pathway
binds to presynaptic membrane of NMJ, then transports back to CNS by axon to bind to inhibitory neurons by endocytosis, then leaves vesicle and goes into cytosol to cleave
alpha latrotoxin
derived from widow spiders - causes release of small synaptic vesicles, via forming a calcium channel - causes spasms?
synapsin
a phosphoprotein controlling synaptic vesicle mobility and post-docking steps of exocytosis
- maintain the SSV reserve pool and contribute to synaptic plasticity
most abundant isoform of synapsin
SYN1
ca activation of CaMKii / protein kinase results in what
phosphorylation of synapsin
what does the phosphorylation of synapsin result in
reduction of synapsin binding to the actin cytoskeleton. this makes vesicles now available for exocytosis
what happens in the absence of synapsin
binding disperses the distal cluster of SV’s, while docked SV’s remain intact. synaptic depression is hastened following peptide injection
cellular changes from excitatory synapses
synapsin deletion reduces size of reserve pool of synaptic vesicles. this impairs the glutamate release and delayed recovery from synaptic transmission with relatively normal basal transmission
cellular changes from inhibitory synapses
knockout of synapsins inhibitory neurons result in a loss of synaptic vesicles from both the readily releasable and the reserve pool (excitatory is just reserve pool only)
knockout phenotype
deletion of SYN gene produces epileptic phenotype
synapsin in terms of autism
those autistic have many mutations in genes which encode synaptic proteins
knockout mouse results of synapsin 2 deletion mouse
displayed deficits in short-term social recognition and increased repetitive self-grooming behaviour
knockout mouse results of synapsin 1 and 3 deletion
displayed an impaired social transmission of food preference
knockout mouse results of synapsin 1 and 2 deletion
displayed a decreased environmental interest
four classes of neurotransmitters
- amino acids (glutamate excit, GABA inhib)
- amines and purines (actyl, nor/adren, serotonin)
- neuropeptides (opioids, substance P, neuropeptide Y)
- gases (NO, CO)
where amines and purines found
small synaptic vesicles
where neuropeptides found
large dense core vesicles
dopamine
a catecholamine - involved in regulation of movement, attention, mood, cognition, addiction, reward
parkinsons prevalence
age of onset 55 to 65 years
1 in 100 people >60 years of age
arvid carlsson
discovered that circuits that control movements dont work properly when dopamine levels are decreased
parkinsons is a loss of what
dopamine and substantia nigra
tyrosine to epinephrine process
tyrosine -> L-Dopa -> dopamine -> norepinephrine -> epinephrine
synaptosomes
are a synaptic terminal isolated from a neuron, involved in reuptake
bromocriptine
an agonist approved to treat parkinson’s disease, hyperprolactinemia and related conditions
haloperidol
an antagonist that is used in treating schizophrenia, bipolar disorder and stimulant-induced psychosis
L-Dopa treatment for Parkinson’s disease
L-dopa treatment does not stop neurodegeneration but might enhance the activity of the neurons remaining
what side effects does prolonged L-DOPa treatment result in
L-DOPA-induced dyskinesia and psychosis
NO - what its not
not stored in lipid vesicles, not released by exocytosis, not bind to receptors, not metabolized by hydrolytic enzymes
NO
a gas derived from arginine, synthesized on demand, an important retrograde messenger involved in the long-term potentiation model for memory
fast acting receptors
ligand-gated ion channels (glutamate receptors)
milliseconds
excitatory or inhibitory, depending on ion involved and its direction of movement
slow acting receptors
- g-protein coupled receptors
- D1 - like receptors (D1 and D5)
- D2 - like receptors (D2, D2, and D4)
g-protein coupled receptors
metabotropic receptors
7-transmembrane domains
directly regulates ion channels
generate second messengers
D1 like receptors
stimulation of adenylate cyclase, coupled to Gs, mediate excitatory neurotransmission
D1 like receptors
stimulation of adenylate cyclase, coupled to Gs, mediate excitatory neurotransmission
D2 like receptors
inhibition of adenylate cyclase, couple to Gi/Go, mediate inhibitory neurotransmission
dopamine sites of actions
substantia nigra to striatum circuit
ventral tegemental area to cortex
limbic system
dopamine can be in SSV and LDCV
ventral tegemental area dopamine system
projects to the nucleus accumbens
is a reward system which reinforces desirable behaviours - opiates and nicotine stimulate VTA neurons
what do opiates and nicotine stimulate
VTA neurons
cocaine and amphetamines do what
block reuptake which increases dopamine at synapses
what does prolonged activity of VTA result in
down-regulation, drug tolerance, and with any removal - withdrawal
ATP a neurotransmitter
acts on purinergic receptors it is co-stored and co-released with classical neurotransmitters, are both ion channel and G-protein coupled
brain derived neurotropic factor
high levels found in hippocampus, has a role in neuronal plasticity
proBDNF
BDNF is synthesized as the precursor proBDNF but proBDNF is not an inactive precursor, it is a signalling protein in its own right
proBDNF
BDNF is synthesized as the precursor proBDNF but proBDNF is not an inactive precursor, it is a signalling protein in its own right
BDNF action
undergoes Ca influx-dependent release from pre and post synaptic sites, act on ligand-gated ion channels, voltage-gated ion channels, second-messenger pathways
what activates CB1 receptors which are coupled to G-protein
endocannabinoids
how many transmembrane domains does each unit of an enzyme-linked receptor usually have?
one
GABA-A receptors
ionotropic
GABA-A receptors
ionotropic
GABA-B receptors
metabotropic
what is GABA
an amino acid, not found in proteins, is synthesized in GABA’ergic neurons by glutamatic acid decarboxylases
GABA-A distribution
widespread CNS, PNS, limbic system, eye, amygdala, nuerons, oligodendrocytes, NMJ
activation of GABA gated ion channels cause a
IPSP via opening chloride ion channels and resulting influx of Cl.
substances that enhance the natural effect of GABA
benzodiazepines and ethanol enahnce the natural effect of GABA
phasic inhibition
GABA is released from presynaptic terminals and binds to postsynaptic GABA-A R’s
tonic inhibition
ambient extracellular GABA binds to extrasynaptic GABA-A r’s and modulates resting membrane potentials and cell excitability
drugs that enhance GABA action are what
anxiolytic - they reduce anxiety or panic
GABA - B distribution
both pre and post synaptically
GABA-B receptor associated with
epilepsy, spasticity, schizophrenia, anxiety, depression, cognitive deficits, and addiction
acetylcholine receptor distribution
transmitter at NMJ, autonomic ganglia, postganglionic parasympathetic synapses
acetylcholine synthesization
AcH is synthesized by choline acetyltransferase and transported into vesicles. following synaptic release, AcH degraded by acetylcholinesterase
muscarinic AchR
metabotropic - sensitive to muscarine, G-protein couples, found in: glia, heart muscle, salivary glands
nicotinic AchR
ion channels - sensitive to nicotine, ligand-gated channel, mediate fast synaptic transmission, occur in high density at neuromuscular junction, sensitive to alpha-bungarotoxin
ligand-gated ion channels
results in depolarisation of muscle cell, opening of voltage-gated sodium channels; action potential and muscle contraction
in vitro
molecular and cellular events: cells in culture, acute brain slices, organotypic brain slices
in vivo
simple invertebrate models, vertebrate rodent models
in vivo
simple invertebrate models, vertebrate rodent models
in vivo
simple invertebrate models, vertebrate rodent models
in vivo
simple invertebrate models, vertebrate rodent models
in vivo
simple invertebrate models, vertebrate rodent models
in vivo
simple invertebrate models, vertebrate rodent models
nonassociative learning: behavioural responses
habituation and sensitization
aplysia california models learning and memory with example of what reflex
siphon-gill-withdrawal refex, undergoes either habituation or sensitization when a stimulus is applied
presynaptic facilitation (gill-withdrawal response)
stimuli activate interneuron L29. this enhances neurotransmitter release from the sensory neuron presynaptic terminal and alters gene expression
single tailed shock
L29 releases serotonin activates its receptors on presynaptic nerve terminals as well as stimulates formation of cAMP, which activates protein kinase A and the release of neurotransmitter
PKA increases what
phosphorylation of Ca and K+ channels
multiple tailed shock
same as single except PKA moves to nucleus, alters gene expression and new proteins stimulate synapse growth
drosophila melanogaster
small genome and nervous system, rapid life cycle, easy to identify circuits
aplysia california
small nervous system, large neurons, easy to identify individual neurons and circuits
AMPA receptors
ligand-gated, mediate fast depolarisation, na channel
NMDA receptor subtypes
ligand and ion-gated, slightly slower response, ca and na channel
long term potentiation summary
ca influx into dendritic spine activates protein kinases such as Ca calmodulin-dependent protein kinase II. it phosphorylates the AMPA receptor to increase conduction.
AMPA receptors get trafficked to the membrane, and long term changes are made to gene expression
long term depression summary
repetitive low frequency stimulation results in a low level Ca influx through NMDARs
low levels of Ca activate protein phosphatases, removing phosphates from AMPA receptor and other targets, results in long-term changes to gene expression
AMPAR subunit GluA1-GluA4
assemble as dimers-of-dimers to form hetero-tetrameric or homomeric receptors (GluA1)
GluaA2 permeability
impermeable when containing AMPAR, permeable without
what would create more long term significant change
homomeric receptors (AMPA)
what would create more short lasting changes
properties of phosphorylation
polyribosomes
found in spines, translocate from dendritic shafts to spines in response to activity
mRNA
found in dendrites, translated in response to activity
immediate early genes
are fast responding genes that are altered in response to activity. they are transcription factors and will also mediate target genes. these target genes will mediate significant changes
secondary response genes
receptors and many others, new and larger synapses, re-structured synapses
amyloid beta causing an initial hyperexcitability of neurons leads to what
excessive levels of glutamate in the extra-synaptic space, leading to overstimulation of NMDA receptors and subsequently synaptic loss and cell death
what does AB-induced endocytosis of the AMPA-type glutamate receptors lead to?
long-term depression
what does disruption to actin dynamics from AB cause
impairments in the trafficking of AMPA, NMDA
memantine
antagonist of the NMDA receptor subtype of glutamate receptor. it is used to slow neurotoxicity
what did researchers at Genetech find?
a small molecule that enhances GluN2A function to boost synaptic NMDAR signalling. found that abnormal low-frequency oscillations and epileptiform bursts were reduced and morris water maze performance impoved
sAPPalpha
enhances plasticity, protein synthesis, GluA1 synthesis
hypothalamus
a hypophysis that secretes many hormones and regulates the function of other hormone-secreting glands
lateral and medial zones of the hypothalamus
project to brain stem and telencephalon
periventricular zone of the hypothalamus
multiple functions including regulation of the pituitary
magnocellular
release neurohormones, oxytocin and antiduretic hormone into the capillary bed
oxytocin involved in
uterine contraction and milk ejection
antidiuretic hormone
regulates extracellular fluid volume and acts on kidney to increase water retention and constricts blood vessels
magnocellular neurons project to where
posterior lobe of pituitary
what neurons regulate the anterior lobe of the pituitary
parvocellular neurons
parvocellular neurons
secrete hypophysiotropic hormones into the hypothalamic pituitary portal circulation
follicle stimulating hormone (FSH)
stimulates estrogen secretion, egg production, sperm production
luteinizing hormones (LH)
triggers ovulation, progestin production (females), androgen production (males).
LH and FSH collectively known as
gonadotrophins
thyroid stimulating hormone (TSH)
triggers thyroid hormone release called thyroxine
adrenocorticotropic hormone (ACTH)
stimulates glucocorticoid release from the adrenal gland
growth hormone (GH)
stimulates growth via somatomedins released from liver
prolactin
stimulates mammary gland development and milk secretoin
gonadotropin-releasing hormone (GnRH)
is released by hypothalamus and travels to anterior pituitary where it causes the release of LH/FDH and travels to target tissues testes/ovaries to produce estrogen/androgen
absence of gonadotrophins in females
means ovaries are inactive (e.g. childhood)
estrogen distribution
distributed in CNS, concentrated in pituitary and hypothalamus and also in cortex, midbrain and cerebellum
estrogen
alters the intrinsic excitability of neurons via modulating the flow of potassium ions, depolarisation and more potentials. fast action
estrogen role
development and regulation of female reproductive system as well as physiological roles in males
estrogen receptors
intracellular
reverse transcription-polymerase chain reaction (4)
- isolate (purify) RNA
- convert RNA to DNA by process of reverse transcription
- amplify target DNA (PCR)
- analyse products
