Chapter 6: Neurotransmitter Systems Flashcards
3 criteria for deciding if a substance acts as a neurotransmitter
- synthesis and storage in presynaptic neuron
- released by presynaptic neuron axon terminal upon stimulation
- elicits a cell response similar to that of known NTs (when applied to a postsynaptic terminal
ways to localize transmitters and transmitter-synthesizing enzymes for study
- immunocytochemistry
- immunohistochemistry
Antibodies detect special proteins/peptides via their ()
specific binding sites
2 classes of antibodies
- monoclonal
- polyclonal
the first step of immunostaining
fixation
why is fixation important
- prevent autolysis and bacterial attack
- preserve volume and shape during tissue processing
- allow clear staining of sections
- prevent loss of small molecules during washing stages
Most fixation reagents () -> inactivates most of the enzymes and fixes the structure of proteins inside cell
cross-link proteins
3 types of tissue sectioning for fixation
- paraffin-embedded
- cryosection
- vibratome
this type of tissue sectioning is useful for live or thick tissues
vibratome
localizes synthesis of protein or peptide to a cell by detecting mRNA
in situ hybridization
a model to study CNS neurons to check for NT release upon stimulation
brain slice
summary of how brain slice is used to study NT release
Brain slice is kept alive in vitro -> stimulate synapses, collect and measure released chemicals
because using brain slice has its cons, new methods such as () have been widely used to probe specific transmitter release
optogenetics
a method to assess postsynaptic actions by ejecting (small amt) candidate molecules from micropipette; postsynaptic response is measured by microelectrode
microiontophoresis
3 ways to determine NTR subtypes
- neuropharmacological analysis of synaptic transmission
- ligand-binding methods
- molecular analysis of receptor proteins
in neuropharmacological analysis, () are used to define receptor subtypes
agonists and antagonists
2 subtypes of ACh receptors
- nicotinic
- muscarinic
antagonist of nicotinic ACh receptor
curare
antagonist of muscarinic ACh receptor
atropine
nicotinic ACh receptors are localized in the (1), while muscarinic ACh receptors are localized in the (2)
- skeletal muscle
- heart
Glutamate receptors have 3 subtypes (based on agonists):
- AMPA (alpha-amino-3-hydroxyl-5-methyl-4-isoxazolepropinate)
- NMDA (N-methyl-D-aspartate)
- Kainate
in ligand-binding methods, Identify natural receptors using ()
radioactive ligands
how were opiod receptors found
Radioactively labeled opiate compounds and applied them to neuronal membranes from brain tissues
() are involved in pain relief, euphoria, depressed breathing and constipation
Opioid receptors
types of receptor protein classes
- transmitter-gated ion channels
- G protein-coupled receptors
what is Dale’s principle
a neuron has only 1 neurotransmitter
Two or more transmitters released from one nerve terminal
co-transmitters
the usual case for co-transmitters is:
peptide + (amino acid/amine)
Only () neurons have ChAT (choline acetyltransferease)!
cholinergic
precursor for three amine neurotransmitters that contain catechol group
tyrosine
the 3 amine NTs that arise from tyrosine
- dopamine
- norepinephrine
- epinephrine
enzyme that converts tyrosine into dopamine precursor; activity of this enzyme is the rate-limiting step for catecholamine synthesis
tyrosine hydroxylase
there is no fast extracellular degenerative enzyme for catecholamines; instead, catecholamine levels are reduced by selective uptake of the neurotransmitters back into the axon terminal via ()
Na+-dependent transporters
(1) and (2) block catecholamine uptake.
- Amphetamine
- cocaine
Serotonin, aka (1) is an amine neurotransmitter derived from (2)
- 5-HT
- tryptophan
() are used as antidepressants becuase serotonin regulates mood, emotional behavior and sleep
Selective serotonin reuptake inhibitors (e.g. Prozac)
Key enzyme in GABA synthesis; Good marker for GABAergic neurons
glutamin acid decarboxylase (GAD)
GABAergic neurons are major source of () in the CNS.
synaptic inhibition
ATP excites some neurons and binds to ()
purinergic receptors
a small lipid molecule that serve as one of the retrograde messengers
endocannabinoids
endocannabinoids bind to (), which blocks presynaptic calcium channel suppressing either the inhibitory and excitatory drive onto the neurons
CB1 receptor
basic structure of transmitter-grated channels: ACh receptors
pentamer (5 protein subunits) form a pore
subunits of nicotinic ACh receptor at NMJ
2alpha, beta, gamma, delta
subunits of muscarinic ACh receptor in CNS neuron
3 alpha, 2 beta
Each subunit of a transmitter-gated ion channel has (1) alpha-helical transmembrane domains (labeled 2)
- 4
- M1-4
in contrast to pentamer ACh-gated channels, glutamate receptors are (1), and the (2) region in its subunits forms a hairpin that both enters and exits from the inside of the membrane
- tetramers
- M2
among the glutamate-gated channels, (1) and (2) coexist in most postsynaptic membranes and mediate the bulk of fast excitatory synaptic transmission;
- AMPA
- NMDA
AMPA and NMDA receptors contribute to EPSPs via presynaptic ()
glutamate release
the () subtype of glutamate receptors are present in most pre- and postsynaptic membranes, but their functions are not clearly understood
Kainate
the AMPA receptor is permeable to ()
Na and K
the NMDA receptor is permeable to ()
Na, K, and Ca
both (1) and (2) must coincide for voltage-dependent NMDA activation.
- glutamate release
- depolarization
mediates non-GABA synaptic inhibition
glycine-gated channels
GABA-gated and glycine-gated channels are mostly permeable to (1) ions, thus resulting in strong (2) to suppress neural activity
- negative ions (Cl-)
- IPSP
3 steps in transmission of activation in G protein-coupled receptors
- Binding of the neurotransmitter to the receptor protein
- Activation of G-proteins
- Activation of effector systems
Basic structure of G-protein-coupled receptors (GPCRs)
Single polypeptide with 7 membrane-spanning alpha-helices
G protein is short for ()-binding protein
guanosine triphosphate (GTP)
the shortcut pathway of G protein-coupled effector systems
From receptor to G-protein to ion channel—fast and localized (no amplification)
in (), the activation of GPCR couples neurotransmitter with downstream enzyme activation
second messenger cascades
different G-proteins stimulate or inhibit adenylyl cyclase
push-pull method
Stimulatory G proteins (Gs) bind to stimulatory () receptors
beta
Inhibitory G proteins (Gi) bind to inhibitory () receptors
alpha
GPCR activation of () is an example of where a signal cascade branches
phospholipase C (PLC)
when activated by the G_alpha subunit, phospholipase C splits into 2 effectors ()
- IP3
- DAG
() from PLC binds to Ca2+ channel on SR to release Ca2+ for activate calmodulin kinase
IP3
() from PLC can activate protein kinase C (PKC)
DAG
() activate proteins by phosphorylation
Protein kinases
() inactivate proteins by dephosphorylation
Protein phosphatases
the function of signal cascades allows for () by GPCRs
signal amplification
One transmitter activates more than one receptor subtype -> greater postsynaptic response
divergence
Different transmitters converge to affect same effector system; ensures more correct and precise signaling cascade thru multiple NTs
convergence
