BMS11004 - WEEK 3 THURSDAY Flashcards
Glutamate, GABA, types of NT, receptors, glycine, dendritic integration
how can we determine if an NT is present
immunostaining
how can experimentally determine if molecules are NT
- presence
- do cells express enzymes synthesising it or transporter proteins storing it
- is it released
- does it affect postsynaptic cell
- can we block NT
how can we test if cell express enzyme to synthesis or transporter proteins to store NTs
immunostaining
in-situ hybridisation to detect if RNA is expressing in cells
how can we test if NT has been released
collect fluid around neurons after stimulating them and then carry out chemical analysis
how can we test if NT is present and affects postsynaptic cell
test if molecule mimics effect of stimulating presynaptic cell
how can we block NT to test if molecules are NT
apply drugs, delete genes encoding enzymes/transporters/receptors. if you can block neurotransmission, NT present
give 2 broad categories of NT
small molecules (amino acids and amines)
large molecules (peptides)
what are amino acids and amine NTs
small molecules stored in synaptic vesicles, binding to ligand-gated ion channels, or G-protein coupled receptors
what are peptides
chains of aa made in RER and processed through protein secretion pathway, stored in secretory granules, and only bind to G-protein coupled receptors
what do peptide-releasing neurons also release when releasing peptides
co-transmitters
name 2 type of NT receptor
ligand-gated ion channels (ionotropic receptor, directly depolarise/hyperpolarise postsynaptic cell
G-protein coupled receptor (metabotropic receptor, indirectly initiates more complex effects)
give structure of G-protein coupled receptor
single polypeptides with 7 membrane-spanning alpha helix
2 extracellular loop to form transmiter binding site (variations determine what NT, agonist, antagonist can bind)
2 intracellular loops to bind/activate G-proteins
give examples for G-protein coupled receptors
GABA, glutamate, Ach, serotonin, dopamine, noreinephrine, opioids, cannabinoid, ATP, adenosine
give an example for G-protein
GTP
explain G-protein subunit cycle
each G-protein has 3 subunit (a, b, y)
1. resting state = GCP molecule bound to Ga
2. if GDP-bound G-protein bump into specific receptors, if receptor has transmitter bound, G-protein release GDP, exchanged for GTP in cytosol
3. activated GTP-bound G-protein split into Ga+GTP and Gby complex
4. Ga is enzyme and break down GTP into GDP so eventually terminate own activity
5. Ga and Gb join, allow cycle to begin again
define convergence
multiple NT acting on multiple receptors, which can then sum-up and act on one effector system
define divergence
single NT acting on multiple receptors, each receptor activate different effector system
allows one single molecule to have diverse effects on/in cells
explain prevalence of glutamate
CNS most common excitatory NT
aa, so is found in all neuron (cannot use enzymes that make glutamate as marker for gluatminergic neuron, as all neurons contain it)
what are the 3 ionotropic glutamate receptor subtypes (based on drugs acting as selective agonist)
AMPAreceptors, kinase, NMDA
action terminated by selective uptake into presynaptic terminal, glia
name structure of ionotropic and metabotropic glutamate receptor and mechanisms of working
ionotropic glutamate receptor = 4 subunits forming gated-ion channel eg: AMPAR, NMDAR. mechasism- open ion channel
metabotropic glutamate receptor = G-protein coupled receptor eg: mGluR1, mGluR2. mechanism- activate g-protein and trigger downstream signal casc.
what type of transmission do AMPA (ionotropic, glutamate) receptors mediate
fast excitatory transmission
how does AMPA receptors (ionotropic glutamate) work
when glutamate bind opens AMPA receptors (permeable for Na, K)
both Na in and K out, depolarising cell and causing EPSP
how do NMDA receptors (ionotropic glutamate) work
coexisting with AMPA receptors
at rest = Mg2+ blocking pore so nothing etner
1. when depolarised lessens electrical force so Mg2+ leave
2. NMDA receptor also permeable to Ca so allow in, downstream signalling
what makes GABA
synthesised from GAD enzyme
how does GABA work as NT
usually inhibitory NT, however depend on exact circumstances (membrane potential, current actual potentials of chloride in/out of cell)
opens channel and cause hyperpolarisation
why is having right amount of inhibition via GABA important
too much= coma as silences all neurons in brain
too little= seizures, as not enough inhibition to dampen down brain activity so uncontrolled excitation
what other chemicals can bind to GABA receptors
but has no effect without GABA binding
ethanol - alcoholics brain adapts and reduce GABA receptor. cold turkey causes seizures as lacking enough GABA for inhibitions
benzodiazapine
barbituates (sedative)- overdose stop breathing
neurosteroid (metabolise steroid hormone)
how can GABA act through metabotropic receptors
mGluRs, GABAb receptors are examples of GPCRs
can:
1. open K+ channels
2. close Ca2+ channels
3. trigger other second messengers like cAMP
4. often presynaptic or autoinhibitory
what is glycine
regular amino acid NT, inhibitory through binding to glycine gated Cl- channels but also can bind to NMDA receptor
explain dendritic integration
each EPSP not enough to trigger AP so need several EPSPS to depolarise cells to threshold
what molecule is glutamate and glycine synthesised from
glucose
what are GABA synthesised from
not an aa
synthesis in large quantities by neurons using it as NT
glutamate precursor, and GAD enzyme
where can you find glutamate, glycine and GABA
glutamate and glycine made from aa so in all body cells
GABA only present in neurons that make it
if AMPA receptors are permeable to both Na+ and K+, why does activating them cause depolarisation
more Na+ enters cell due to electric pull which makes membrane less negative, and so results in depolarisation
what would happen if GABA opens GABAa receptor and membrane potential is below Cl Nernst potential
net inflow of Cl- ions
