Lecture 10 Flashcards
Criteria for neurotransmitters:
- present in presynaptic terminals
- released in response to stimulation
- able to interact with postsynaptic receptors
- rapidly removed from the synapse
Neurotransmitters need mechanisms for:
- synthesis and/or storage
- release
- transmitter action i.e. specific receptors
- transmitter removal
It does not count as neurotransmitters if:
has continuous stimulation
cannot be removed from the synapse
What are the three main types of transmitters/modulators?
ACh
Amino acids
Biogenic amines
Name four amino acid neurotransmitters
Glutamate (excitatory)
GABA (inhibitory)
glycine (inhibitory)
aspartic acid
Name biogenic amine neurotransmitters
Catecholamines (adrenaline, noradrenaline, dopamine; go through different steps to synthesize specific amine)
Serotonin (also called 5-HT)
Histamine
Name four neuropeptides
Enkephalin (natural opiate)
Substance P
Cholecytokinin
beta - endorphin (hugely different in size but works in same system)
Amino acid and amine neurotransmitters are:
small molecules
stored and released from synaptic vesicles
capable of many binding to and activating (ligand-gated channel receptors, G-protein coupled receptors)
Can do short-term and long-term signalling
The peptide neurotransmitters are:
large molecules
stored in secretory granules
only activate G-protein coupled receptors
made in soma
Glutamate is:
Most common, excitatory transmitter in CNS
Amino acid, found in all neurons
3 glutamate receptor subtypes based on the drugs which act as selective agonists
Action is terminated by selective uptake into presynaptic terminals and glia
Glutamate cannoe be used as a what? and why?
Marker
- Found everywhere but in neurons which use glutamate as a neurotransmitter, the concentration is much higher
How much more glutamate do glutamatergic neurons have compared to neurons that use glutamate for protein synthesis?
2-3 times
Name the three receptor subtypes::
- AMPA receptor
- NMDA receptor
- Kainate receptor
Where is AMPA receptor found and how is it activated?
Most widely distributed
Only activated by AMPA drug
How is NMDA receptor activated?
Only activated by NMDA drug
What are glia?
Supporting cells (2 neuron + 1 glia hypothesis formed now)
What do AMPA receptors do?
Mediate fast excitatory transmission
Glutamate binding to AMPA receptors trigger Na and K currents resulting in an EPSP
AMPA is not very permeable to Ca
What are NMDA receptors?
NMDA receptors often co-exist with AMPA receptors
- AMPA receptors can be on their own but hard to find
NMDA receptors on their own
NMDA receptors have a voltage-dependent Mg block
- Mg pops out during depolarization
- NMDA receptors become more permeable to Ca
- NMDA receptors need to be indirectly activated by
another transmitter
NMDA receptors are permeable to Ca as well as Na and K
- Their activation can have more widespread, lasting changes in the postsynaptic cell
- Involved in strengthening of synapses
What is an enzyme that converts glutamate to gamma-amino butyric acid (GABA)?
Glutamic acid decarboxylase (GAD)
GAD 65 and 67 are markers for GABAergic neurons
How does the conversion from glutamate to GABA terminate?
There is a transporter protein that finds GABA and selective uptake into presynaptic terminals and glia
What is GABA?
Most common inhibitory transmitter in CNS
In what cases can GABA become an excitatory transmitter?
During development when other Cl transporters make sure there is more Cl inside at rest, Cl moves out of cell through GABA-gated Cl channels
- causes depolarization
Where in the CNS are GABA especially found?
Cortex and striatum
What happens when there is too much or too little inhibition via GABA?
Too much: Coma or loss of consciousness
Too little: Seizures
