Neurotransmitters

Question 1

what do postsynaptic receptors do?

Answer 1

elicit EPSPs, IPSPs, or a signaling cascade

Question 2

what do intracellular receptors do?

Answer 2

alter gene transcription and protein synthesis

Question 3

what do autoreceptors do?

Answer 3

provide negative feedback, always metabotropic
on terminal: reduce NT synthesis and NT/NP release
on cell body: reduce AP firing, NT synthesis, NT/NP release

Question 4

what are the four ways that cause termination of action in synapse?

Answer 4

1. enzyme degradation of NT/NP in the synaptic cleft or NT in the terminal
2. reuptake by reuptake protein (symporter) of NT followed by recycling or degradation
3. reuptake by astrocytes of NT in tripartite synapse
4. passive diffusion into extracellular space

Question 5

what are the requirements for a neurochemical to be classified as a neurotransmitter or neuropeptide?

Answer 5

1. synthesized in the neuron
2. released from the presynaptic terminal in a Ca2+ -dependent manner
3. specific postsynaptic receptors are present on the postsynaptic neuron; its action on the receptor can be duplicated experimentally
4. termination mechanism exists

Question 6

what are the techniques to record in vivo?

Answer 6

in vivo microdialysis, fast scan cyclic voltammetry (FSCV), in vivo fiber photometry, positron emission tomography (PET), and photoactivated receptor visualization

Question 7

how does in vivo microdialysis work?

Answer 7

a probe with an artificial membrane is inserted into the brain, NT diffuses across the membrane into the probe where is is flushed into a vial, NT are then separated and quantified based on oxidation potential

Question 8

what are the advantages and disadvantages of in vivo microdialysis?

Answer 8

advantages: animal is alive, can measure multiple NT at once, can predict therapeutic effects of newly discovered drugs
disadvantages: low time resolution (2 min+ /sample)

Question 9

how does fast scan cyclic voltammetry (FSCV) work?

Answer 9

uses a carbon fiber microelectrode to record reactions taking place on its surface, voltage is changed to the level at which target NT is oxidized, NTs are quantified by measuring current generated during oxidation

Question 10

what are the advantages and disadvantages of fast scan cyclic voltammetry (FSCV)?

Answer 10

advantages: used in awake and alive animals, small electrode, high spatial and time resolution (10ms/sample)
disadvantages: limited ability to discriminate between NT, can only detect amount of oxidation so probe must be in a specialized area that only releases one type of NT

Question 11

how does in vivo photometry work?

Answer 11

uses a virally introduced fluorescent protein-based biosensor to detect fluorescence caused by target NT

Question 12

what are the advantages and disadvantages of in vivo fiber photometry?

Answer 12

advantages: high resolution, can detect multiple NTs using different fluorophores
disadvantages: can only measure one or two NT at once since only a few colors can be used as fluorophores

Question 13

how does positron emission tomography (PET) work?

Answer 13

radioisotope-labeled tracers are injected that bind to receptors or reuptake proteins, receptors/reuptake proteins are then quantified based on emitted radiation

Question 14

what are the advantages and disadvantages of positron emission tomography (PET)?

Answer 14

advantages: used in awake subjects, live imaging with anatomical resolution
disadvantages: radioactivity, low-resolution images, must extrapolate NT levels from image

Question 15

how does photoactivated receptor visualization work?

Answer 15

fluorescently labeled receptors are visualized using a 2-photon confocal microscope through a skull window

Question 16

what are the advantages and disadvantages of photoactivated receptor visualization?

Answer 16

advantages: mouse is awake and moving, can be trained to position under microscope
disadvantages: requires a skull window, field of vision is limited to area within skill window

Question 17

what are the techniques to record ex vivo?

Answer 17

receptor binding assays, in situ hybridization/RNA scope, immunohistochemistry, and western immuniblot

Question 18

how do receptor binding assays work?

Answer 18

labels nonspecific and total binding before finding the specific binding (total - nonspecific binding)

Question 19

how does nonspecific binding take place in receptor binding assays?

Answer 19

a mixture of labeled and mostly unlabeled ligand is used, the unlabeled ligands outcompete the labeled ligand to bind to the receptor first while the labeled ligands bind to the remaining off target sites

Question 20

how does total binding take place in receptor binding assays?

Answer 20

a labeled ligand is used to bind to the receptor of interest as well as to off-target sites with a lower binding affinity

Question 21

what do titration and scatchard plots show in receptor binding data?

Answer 21

titration plots show the amount of labeled ligand bound as a function of labeled ligand concentration with a line for total, specific and nonspecific binding
scatchard plots show the number of bound receptors over the total as a function of the number of receptors specifically bound

Question 22

what do Bmax and Kd represent in regards to receptor binding data?

Answer 22

Bmax shows the total receptor number (Bmax is the x-intercept of scatchard plots and the specific binding y-intercept on the titration plot)
Kd shows the receptor affinity (Kd is the negative inverse of the slope on the scatchard plot and the concentration of ligand that results in 50% of max specific binding on the titration plot)

Question 23

what are the advantages and disadvantages of receptor binding assays?

Answer 23

advantages: can study neuropathy and effects of drug exposure on all known receptor reuptake proteins, can have anatomical resolution if its combined with autoradiography/fluorescence microscopy and image analysis
disadvantages: only detects single time point data, results depend on selectivity of ligand, and gives no information about receptor function

Question 24

what are the advantages and disadvantages of in situ hybridization/RNA scope?

Answer 24

advantages: identify location of cells with receptor mRNA
disadvantages: mRNA may not be translated into the receptor

Question 25

what are the advantages and disadvantages of immunohistochemistry?

Answer 25

advantages: can detect receptor anatomical location
disadvantages: receptor may not be inserted into the synapse

Question 26

how does western immunoblot work?

Answer 26

uses antibodies generated against the receptor or phosphorylation site on the receptor to label specific proteins on the gel after electrophoresis, by detecting the phosphorylation that occurs at a specific protein we can detect what change that protein made in the cell

Question 27

what are the advantages of western immuniblot?

Answer 27

can measure total and phosphorylated receptors to predict synaptic location and receptor functionality

Question 28

what is receptor pharmacology?

Answer 28

when you manipulate receptors with drugs and measure the resulting changes in physiology or behavior

Question 29

agonist vs antagonist?

Answer 29

agonists facilitate NT action while antagonists block or counteract NT action

Question 30

how do direct agonists work?

Answer 30

they bind at the active site mimicking the neurotrasmitter, can be full or partial (nicotine for nAchR)

Question 31

how do indirect agonists work?

Answer 31

they bind to another site other than the active site and increase the NT affinity for the active site, the synthesis/release of the NT, receptor efficacy, or inhibits degradation/reuptake of the NT (lDOPA for dopamine and norepinephrine)

Question 32

how do direct/competitive antagonists work?

Answer 32

physically block the active site (curare binds to ACh receptors and blocks ACh from binding, paralyzing the subject)

Question 33

how do indirect/non-competitive antagonists work?

Answer 33

bind at another site other than active site and interfere with receptor stimulation by reducing NT synthesis, release or receptor efficacy, or by increasing degradation (reserpine for dopamine or negative allosteric modulators)

Question 34

how do inverse agonists work?

Answer 34

bind at active site and have opposite action on signaling compared to the NT, acts only on GPCRs (AM251 for CB1R)

Question 35

what are the four drug characteristics that impact their effects?

Answer 35

selectivity, efficacy, potency, and safety

Question 36

what is drug selectivity?

Answer 36

when the drug either non-selectively binds to all receptor types or binds to only specific types

Question 37

what is drug efficacy?

Answer 37

the maximum effect at saturating concentration when all the receptors are bound by the drug (measured based on Emax, higher Emax = higher efficacy)

Question 38

what is drug potency?

Answer 38

the inverse concentration that elicits 50% of the maximum effect, when 50% of the receptors are bound, measured based on 1/EC50, lower EC50 = more potent since less drug is required to bind 50% of receptors

Question 39

what is drug safety?

Answer 39

how close the therapeutic dose is to a lethal/toxic dose, measured by therapeutic index (TI), TI = TD50/ED50 or TI = LD50/ED50

Question 40

ED50/EC50 vs TD50 vs LD50?

Answer 40

ED50/EC50: the concentration or dose that achieves 50% receptor binding
TD50: dose of the drug that elicits 50% of the maximum toxic effect
LD50: dose that elicits death in 50% of subjects