PBL 7 - Anxiety Flashcards
What determines whether an input leads to an action potential?
AP depends on the summation of synaptic inputs on the postsynaptic neuron
What is the main excitatory neurotransmitter?
What receptors does it work on?
How does it work?
Glutamate
• causes influx of Na or Ca leading to depolarisation
• More than half of all brain synapses release glutamate
• Starts AP and also keeps them going
• NMDA or AMPA
What is the main inhibitory neurotransmitter?
What receptors does it work on?
How does it work?
GABA • Causes Cl influx and K efflux • Leads to hyperpolaration • 30-40% of all synapses release GABA • Stops or prevents AP • GABA receptors
What are the two main neurotransmitter receptor types?
How do they differ?
What kind of NT act on each?
Ionotropic receptor • Ligand gated ion channel • Not a transporter • Has a direct action • Action is rapid and brief
Metabotropic receptor • GPCR • Indirect action • Takes longer to work • Catecholamine and peptide NT work on these only
NOTE:
Most NT can act on both
What are some examples of Ionotropic receptors?
• Excitatory ○ Ach gated cation channels ○ Glutamate gated ca channels ○ Serotonin cation • Inhibitory ○ Gaba-a gated CL channels ○ Glycine gated CL channels
What type of receptors are GABA-A?
What are the characteristics?
How do they work?
What stimulates and inhibits them?
- Ionotropic
- Causes CL influx
- Inhibitory effect on the AP
Structure:
• 5 sub-units
• Has a benzo and a barbitruate binding site
• Potentiated by neurosteroids, benzos, barbitruates and alcohol
Inhibited by toxins - picrotoxin and convulsants
How do Barbitruates work on the GABA receptor?
- Does not need GABA present to work
* Increases channel opening DURATION
How do Benzodiazepines work on the GABA receptor?
- It is a modulator
- Has no intrinsic activity
- Needs GABA to work
- Increase channel opening FREQUENCY
- Increases affinity of GABA for receptor by slowing GABA unbinding from receptor
- Number of receptor occupancy determines effects
What type of receptor is a Neuronal ACH R
What is the structure?
What effect does it have
- Ligand gated ion channel- ionotropic
- Many different combinations of a pentamer
- Allows calcium to come in
- Excitatory effect
- Alterations are found in many diseases for example alzheimers disease
What kind of receptor is a Glutamate ?
What are they implicated in?
What works on them?
- It is an excitatory ionotroic receptor
- There are 3 functional classes○ NMDA
§ Has binding sites for glutamate, mg, glycine and others
§ At resting membrane state the channel is blocked by magnesium
§ When the cell is depolarised the Mg is removed to allow Na and Ca can flow in, often K efflux○ AMPA
§ Glutamate opens AMPA channel allowing Na influx
§ This depolarises the membrane and removes the Mg from the NMDA channel which must have glutamate bound aswell○ Kainate
• They are modulated by many substances
○ Alcohol
○ PCP: NMDA antagonists - There are 3 functional classes○ NMDA
What causes Glutamate toxicity?
What are the consequences?
Glutamate toxicity
• Due to excess glutamate ○ Either through excessive release and or decreased reuptake by neuronal or glial cells • Causes sustained stimulation of postsynaptic glutamate receptors- mainly NMDA • Causes increased Ca influx leading to intracellular Ca overload • Increased oxidative and metabolic stress • Cell death
How fast are effects of GCPR mediated signalling?
- Can induce both slow initial synaptic potentials and long term effects
- Can open ion channels
- Also enzymes, structural proteins and gene transcription
How to metabotropic receptors work?
- There is an indirect action of the NT on the ion channel
- Binding activates a G protein which causes activation of a second messenger that creates a cascade to eventually open the ion channels
- Sometimes the Channel has a g-protein that directly opens the ion channel
Do NT only work on one type of receptor?
What is an example?
- Not usually
- It is possible for one NT to activate different classes of receptors
- Ie there is an iGLUr and a mGLUR that glutamate can act on
What will determine the effect of the NT on the receptor?
What is an example?
- One class of receptor can have many subtypes which will effect the response
- Each subtype can have broad or restricted tissue/cell distribution
- Example the type of GCPR and the G protein will determine the effect of the NT
Is the action of the NT signalling pathway linear? Why?
- NO the same NT can activate a variety of effectors through activation of signalling pathways
- There is signal amplification and signal DIVERGENCE
- Signals from unrelated receptors may converge to activate a comon target ex- memory formation- stress pathway assists with memory by activating the same pathway
- There is cross talk between different distinct NT activated pathways