Chapter 4A: The Chemistry of Behavior: Neurotransmitters and Neuropharmacology Flashcards
Neurochemistry
Focuses on the basic chemical composition and processes of the nervous system
Neuropharmacology
The study of compounds that selectively affect the nervous system
Co-localization (co-release)
Some neurons contain more than one type of neurotransmitter
Receptor subtypes
Different receptor subtypes may trigger different responses in target cells
Varied outcomes because of these subtypes
Subtypes differ based on what cells they’re on
Criteria for neurotransmitters
Substance exists in presynaptic axon terminals
Synthesized in presynaptic cells
Released when action potentials reach axon terminals
Receptors for the substance exist on the postsynaptic membrane
When experimentally applied, substance produces changes in postsynaptic cells
Blocking substance release prevents changes in postsynaptic cell
Types of neurotransmitters
Amino acid
Amine
Peptide
Gas
Amino acid neurotransmitters
GABA, glutamate
Amine neurotransmitters
Acetylcholine, dopamine, serotonin
Peptide neurotransmitters
Short-chain amino acids
Gas neurotransmitters
Soluble gases, nitric oxide, carbon dioxide
Most prevalent excitatory neurotransmitter in the brain
Glutamate
Most prevalent inhibitory neurotransmitter in the brain
GABA
GABAa
Ionotropic, producing fast, inhibitory effects
GABAb
Metabotropic, slow, inhibitory effects
GABAc
Ionotropic
GABA agonists
Potent tranquilizers
Ex: Valium
First neurotransmitter identified
Acetylcholine (ACh)
Two types: nicotinic, muscarinic
Cholinergic cells
Release ACh
These cells project to amygdala, hippocampus, and throughout cortex
Important for learning and memory, lost with Alzheimer’s disease
Nicotinic ACh receptors
Ionotropic, excitatory, fast
Muscarinic ACh receptors
G protein-coupled, slower, and excitatory or inhibitory
2 main classes of monoamine neurotransmitters
Catecholamines: dopamine, epinephrine, norepinephrine
Indoleamines: melatonin, serotonin
2 main pathways for dopamine
Mesostriatal pathway: motor control
Mesolimbocortical pathway: reward and reinforcement
Norepinephrine
Metabotropic
Alertness, mood, sexual behavior
Serotonin
Mainly found in raphe nuclei
Sleep, mood, sexual behavior, anxiety
Peptides
Act as neurotransmitters or as hormones
Some are opioid peptides, which are endogenous substances that resemble opiate drugs
Gas
Nitric oxide is a soluble gas neurotransmitter
Made in dendrites, diffuses out immediately into cells to stimulate second-messenger systems
Retrograde transmitter
Agonist
Drug that binds to and activates a specific receptor
Antagonist
Binds to the receptor but does not activate it
Noncompetitive ligand
Can either activate receptor or block it from being activated
How do drugs know where to go?
They find the receptor where they have their action
Affinity
The binding affinity is the degree of attraction between a ligand and a receptor
A drug with high affinity will be effective at low doses and stay bound for a long time
Low-affinity ligands
Neurotransmitters are low-affinity ligands, allowing them to rapidly dissociate from receptors
Efficacy
The ability of the bound ligand to activate that receptor
Agonists: high efficacy
Antagonists: low efficacy
Partial agonists: produce a medium response regardless of dose
Dose-response curve
Graph of the relationship between drug doses and the effects
At some point it levels out and you can’t get more of a response no matter how much more you add
Potency
Can be determined by comparing ED50 values (dose at which the drug has 50% of its maximum effect)
A drug that has comparable effects at lower doses is more potent
You don’t have to give as high of a dose to get that 50% response
Therapeutic index
Separation between ED50 and LD50 (dose at which 50% of subjects start to show signs of toxicity)
We very rarely approve drugs with narrow therapeutic index because if you forget you take a medication and accidentally take it again then you could die
Pharmacokinetics
Factors that affect the movement of a drug into, through, and out of the body
Blood-brain barrier
Tight junctions within the CNS that prevent the movement of large molecules
Lined with glial cells (astrocytes)
Route of administration can affect…
Amount of drug that reaches the brain
Speed with which it starts acting
Bioavailability: amount of drug free to act on the target tissue
Repeated treatments may reduce the effectiveness of a drug
Changes in receptor number on the postsynaptic membrane
Increasing: upregulation
Decreasing: downregulation
Both of these change the way the postsynaptic cell is firing
Presynaptic events can be modified by drugs that affect…
Transmitter production
Neurotransmitter release
Transmitter clearance
Drugs can act postsynaptically
Block specific receptors
Or change upward or downward regulation
