Neural Communication Part 2 (Neurotransmitters) Flashcards
Ionotropic Receptors
AKA Ligand-gated ion channels
Ionotropic receptors are channels that open to allow ions to pass through a membrane in response to the binding of a neurotransmitter (a neurotransmitter binds at the ionotropic receptor’s binding site). They have a fast, transient effect.
Metabotropic Receptors
AKA G-protein coupled receptors/GPCRs. A protein in the cell membrane that binds to neurotransmitters and transmits signals from the neurotransmitters to a intermediate protein, the G protein. They can influence the opening of ion channels and can also affect enzymes and activate molecules that cause signalling cascades that trigger neuronal messages. They modulate cells, upregulate the expression of genes and have slower, longer lasting effects than ionotropic receptors.
What does a G-protein snapping off a GPCR cause?
A signal cascade that triggers neuronal messages.
Ligands/Drugs
Agonist
A chemical that binds to and activates receptors in the brain (by chemically mimicking neurotransmitters/hormones).
Ligands/Drugs
Partial agonist
Binds to a receptor & activates it, but less potent & has intermediate efficacy relative to a full agonist.
Ligands/Drugs
Inverse agonist
Binds to the same receptor as an agonist, but initiates a biological action opposite to that produced by the agonist.
Ligands/Drugs
Competitive antagonist
An antagonist that binds at the same active site as an endogenous ligand or agonist, but does not activate the receptor. Once bound, this antagonist will block binding.
Ligands/Drugs
Noncompetitive Antagonist
Doesn’t bind at the same site as an agonist (and does not activate the receptor), but will change a receptor’s shape, which interferes with cell processes and agonist binding.
Allosteric Modulators (Regulators)
A substance that binds to a site on a receptor other than an active site, modifiying a receptor’s response to an agonist.
Positive Allosteric Modulator
Allosteric modulators that upregulate a receptor. They increase agonist affinity/efficacy.
Negative Allosteric Modulators
Allosteric modulators that downregulate a receptor. They decrease agonist affinity/efficacy.
Downregulation: The process by which a cell decreases the production and quantities of its cellular components, such as RNA and proteins, in response to an external stimulus.
Glutamate
A primary excitatory neurotransmitter used throughtout the brain that acts on both ionotropic and metabotropic receptors..
Glutamate-affecting drugs given to humans are antagonists, as a glutamate agonist could cause anxiety and even seizures.
GABA (gamma amino butyric acid)
A primary inhibitory neurotransmitter that acts on both ionotropic and metabotropic receptors.
GABA-affecting drugs given to humans are agonists, as a GABA antagonist could cause anxiety and even seizures.
Amines (neurotransmitters)
ALL metabotropic. Play a modulatory role in the brain.
Dopamine
Location: The brainstem (the ventral tegmental area and the substantia nigra) and the hypothalamus contain the majority of the brain’s dopamine neuron cell bodies.
Function: Regulates motivation, mood, sleep, memory, concentration and movement. Has some effect on pleasure and satisfaction, stimulates the brain. Dopamine can motivate individuals to complete more challenging tasks, and increases activity in the reward centre of the brain. Dopamine also plays a major role in addiction (discussed later in the course), as addictive drugs disregulate the brain’s dopamine.
Effects:
Extremely high levels: Can cause delusions and hallucinations. High dopamine levels are found in individuals with schizophrenia.
High levels: Impulsive behaviour, euphoria, aggression, high energy levels.
Normal levels: Alertness, motivation, increased heart rate (happens at normal levels and above), happiness (sometimes), ability to concentrate.
Low levels: Fatigue, lack of motivation, low mood.
Epinephrine
Location: Produced in adrenal glands
Function: Activates the sympathetic nervous system (increases focus, released in high amounts during excitement, stress or panic).
Effects: Fast heartbeat, increased blood pressure, faster breathing, pupil dialation
Epinephrine is also known as adrenaline.
Norepinephrine
Location: Norepinephrine originates in the brain stem region called the locus coeruleus.
Function: Norepinephrine causes heterosynaptic facilitation (binding to heteroreceptors to turn up or down the intensity of signals).
Effects: Norepinephrine enhances memory via inducing stress/emotion, which is evolutionarily useful.
Norepinephrine is also known as noradrenaline.
Serotonin
Location: Raphe nuclei (brainstem)
Precursor: Tryptophan (serotonin is synthesized by tryptophan)
Function:
Effects: Involved (a little) in regulation of mood, hence SSRIs can be used to treat depression. Serotonin depletion causes aggression and impulsivity and decreases cognitive flexibility.
Hallucinogens act on serotonin receptors. So serotonin is likely involved in sensory perception as well.
Propranolol
Drug Type: Propanolol is a norepinephrine receptor antagonist.
Effect: A potential PTSD treatment via reconsolidation (restabilization/’alteration’ of memories that have been destabilized through memory retrieval).
Effects, efficiacy
SSRIs (Selective Serotonin Reuptake Inhibitors)
Effect: Treat depression by blocking serotonin from being removed from the synapse. Effects are quick but mood improvements are slow.
Efficacy (meta-analysis): No better than placebo for mild to moderate depression. Can help with severe/major depression. However this could be due to regression to the mean (if one’s depresion is severe, it might just get better anyways).
They are indirect agonists.
Location, effects
Acetylcholine
Location: The neuromuscular junction and basal forebrain.
Effects: Plays a role in wakefulness, attention, muscle contractions, blood pressure etc.
Transmission, function,
Endocannabinoids
Transmission: Retrograde transmission. (Travels from dendrite to axon.)
Function: Weakens the connection between two cells at a synapse.
Endocannabinoids are naturally occuring neurotransmitters within the body.
Adenosine
Adenosine is an ATP (adenosine triphosphate) byproduct.
Effect: Causes tiredness/fatigue/sleepiness.
Caffeine
Adenosine receptor antagonist.
Theophylline
Adenosine receptor antagonist.
Found in tea.
