test 2 (neurotransmitters) Flashcards
What are the three criteria that make something a neurotransmitter (NT)?
- Present in the presynaptic neuron
- Must be released during synaptic activity
- Must bind receptors on the postsynaptic neuron
What are co-transmitters?
A neuron can synthesize and release more than one type of neurotransmitter
What are the categories of neurotransmitters (NTs)?
- Small Molecules (e.g. acetylcholine, amino acids, biogenic amines, purines)
- Neuropeptides or peptides (e.g. enkephalins, gastrin)
What is acetylcholine (ACh)?
1st neurotransmitter discovered
Used in NMJ and ganglionic synapses
How is acetylcholine synthesized?
From acetyl-CoA and choline by choline acetyltransferase
How is acetylcholine metabolized?
To acetate and choline by acetylcholinesterase
How is acetylcholine loaded into synaptic vesicles?
Via a vesicular transporter (VAChT)
What are the two types of acetylcholine receptors?
- Ionotropic (nAChRs)
- Metabotropic (mAChRs)
What activates ionotropic ACh receptors?
Nicotine (agonist); inhibited by curare
Where are ionotropic ACh receptors located?
- Neuromuscular junction
- Autonomic ganglia
- Adrenal medulla
What type of response do ionotropic ACh receptors mediate?
Excitatory
What activates metabotropic ACh receptors?
Muscarine; inhibited by atropine
What are the targets of metabotropic ACh receptors?
- Smooth muscle
- Glands
What channels do some metabotropic ACh receptors activate?
- GIRK channels (inhibitory)
- Ca2+-regulated K+ channels (excitatory)
What is glutamate (Glu)?
Main excitatory neurotransmitter in the brain
How is glutamate synthesized?
From glutamine by glutaminase
How is glutamate loaded into synaptic vesicles?
Via vesicular glutamate transporters (VGLUTs)
How is glutamate taken up by neighboring glial cells?
Via excitatory amino acid transporter (EAAT)
What are the types of ionotropic glutamate receptors?
- AMPA (fast response)
- Kainate (fast to start, slower near end)
- NMDA (slow response)
What is the role of NMDA receptors?
Channel pore admits Ca2+, Na+, and K+; voltage dependent
What blocks the NMDA channel?
Mg2+ blocks the channel; depolarization pushes Mg2+ out
What is gamma-aminobutyric acid (GABA)?
Main inhibitory neurotransmitter in the brain
What is the synthesis pathway for GABA?
Glucose -> glu -> GABA
How is GABA taken up from the synaptic cleft?
Via Na+-dependent co-transporters (GAT)
How is GABA loaded into synaptic vesicles?
Via the vesicular inhibitory amino acid transporter (VIAAT)
What are the types of GABA receptors?
- Ionotropic (GABA-A R)
- Metabotropic (GABA-B)
What type of channel does the GABA-A receptor form?
GABA-gated ion channel for Cl-
What is the effect of GABA-A receptor activation in young individuals?
Excitatory (Cl- outflux)
What is the effect of GABA-A receptor activation in mature individuals?
Inhibitory (Cl- influx)
What does GABA-B receptor activation do?
- Activates K+ channels
- Inhibits Ca2+ channels
How is glycine (Gly) synthesized?
From serine by serine hydroxymethyltransferase
How is glycine packaged into vesicles?
By VIAAT (same as GABA)
How is glycine removed from the synaptic cleft?
By glycine transporters
What type of receptor does glycine have?
Ionotropic (ligand-gated Cl- channels)
What inhibits glycine receptors?
Strychnine
