Neurochemistry Flashcards
What are the roles of the presynaptic neuron?
Synthesis, transports and stores neurotransmitter.
Where does synthesis of neurotransmitter take place?
Cell body/soma
What happens to the neurotransmitter once it is synthesized?
Axonal transport to synaptic terminal and storage in synaptic vesicle.
By which processes are neurotransmitters released?
Membrane fusion
Ecxocytosis
What happens once a neurotransmitter is released?
Occupies receptors on the surface of the postsynaptic neuronal membrane.
What is autoreceptor activity?
When neurotransmitter molecules are also receptors on the presynaptic neuronal membrane.
Why is autoreceptor activity important?
For feedback inhibition of neurotransmitter release and synthesis.
What is saturation?
More neurotransmitters than receptors
Which neurotransmitters are more likely to bind to receptors?
The ones of which there is a high er concentration.
What is an irreversible neurotransmitter?
One that once bound to a receptor, produces irreversible structural alterations in the protein of the receptor complexes.
How does cessation of neurotransmitter action take place?
Reuptake back to presynaptic neuron
Enzymatic breakdown at the cleft
Removal by glia or plasma circulation
GIve an example of transporters that reuptake neurotransmitters
Monoamine transporters
Give an example of enzyme that breaks down neurotransmitters at the cleft
COMT/MAO-A enzyme
Name the monoamines
Dopamine Norepinephrine Epinephrine Serotonin Acetylcholine Histamine
Name the amino acid neurotransmitters
GABA
Glycine
Glutamate
Name the peptides
Endorphins Cholecystokinin Neurotensin Neuropeptide Y Leptin Ghrelin
What type of neurotransmitter is Acetylcholine?
Monoamine
What type of neurotransmitter is GABA?
Amino acid
What type of neurotransmitter is endorphin?
Peptide
How are receptors classified?
Ligand-gated (ionotropic)
Metabotropic
Ligand-dependent regulars of nuclear transcription
How do ionotropic receptors work?
Binding of chemical messenger alters probability of opening of transmembrane pores or channels
How do metabotropic receptors work?
Receptor proteins are coupled to intracellular G proteins as transduscing elements
Which type of receptor leads to a fast response?
Ionotropic
Gave examples of medications that lead to ionotropic response?
GABAa benzo
Give e.g. of medications that lead to metabotropic response
Most antipsychotics
Antidepressants
What is the structure of ion channel receptors?
4-5 protein subunits make up a pore like structure.
Each protein subunit is a string of amino acids which passes in and out of the cell membrane four times.
At the extracellular end of this string is a N-terminal, which mediates GABA-channel interactions.
In the middle of the string is a large intracellular loop of amino acids with four sites where phosphorylation occurs.
Where is the N terminal in an ion channel receptor?
Extracellular end of the amino acid string
What ion do inhibitory neurotransmitter action lead to?
Chloride
What ion do excitatory neurotransmitter lead to?
Calcium
What are some ionotropic receptors?
GABAa
NMDA
5HT3
Structure of G-protein-coupled metabotropic receptors
Proteins that span cell membrane seven times.
How do G0protein-coupled metabotropic receptors act?
Via cyclase mediated second messenger activation - GTP, ATP etc.
Which proteins are stimulatory in metabotropic receptors?
Gs-proteins
Which proteins are inhibitory in metabotropic receptors?
Gi-protein
What is a third way that G-protein receptors can act?
Via phospholipase C
How do metabotropic receptors cause longer lasting effects?
Influence protein synthesis.
Give e.g. of metabotropic receptors
Dopamine receptors
Most 5HT receptors except 5HT3
Adrenergic receptors
Opioid receptors
Structure of nuclear receptors
Cysteine-rich DNA-binding domain, ligand-binding domain and variable amino terminal region.
How do nuclear receptors work?
Upon appropriate ligand binding, a nuclear receptor becomes a transcription factor and binds to DNA via zinc fingers.
What is a transcription factor?
A nuclear receptor once ligand binding has occurred.
How does a transcription factor bind to DNA?
Via zinc fingers
Give e.g. of nuclear receptors
Receptors for: Glucocorticoid Progesterone Androgen Vitamin D
Source of dopamine
Tyrosine -> L-Dopa -> Dopamine
Rate limiting step of formation of dopamine
Tyrosine hydroxylase
Breakdown enzymes of dopamine
MAO
COMT
MAO-A - selective for norepinephrine and seretonin
MAO-B - selective for dopamine
Breakdown product of dopamine
Homovanillic acid
How is dopamine re-uptaked?
Dopamine transporter
What drug inhibits re-uptake of dopamine?
Cocaine
Function of dopamine
Motivation Novelty seeking Reward - addictions Arousal Motor - basal ganglia
Receptors of dopamine
D1 to D5
All G-protein coupled.
D1 exclusively postynaptic - resistant to antagonism
D5 more limbic in distribution and 10x higher dopamine affinity.
D4 mainly in frontal cortex, high affinity for clozapine.
D4 selective antagonists do not have antipsychotic efficacy.
Which dopamine receptors are inhibitory?
D2 to D5
How to D2 to D5 cause inhibition?
Decrease adenylate cyclase
Which dopamine receptor has high affinity with clozapine?
D4
What disorder can low dopamine cause?
Parkinsons
What disorder can high dopamine cause?
Psychosis - particularly if in mesolimbic area.
If in mesocortical area - negative symptoms
Where does high dopamine levels suggest psychosis?
Mesolimbic area
Where does high dopamine levels suggest negative symptoms of schizophrenia?
Mesocortical
Source of noradrenaline?
Tyrosine -> L-dopa -> dopamine -> norepinephrine -> epinephrine
Rate limiting step of noradrenaline?
Tyrosine hydroxylase
Synthetic enzymes for noradrenaline
Dopamine-b-hydroxylase modulates production.
Phenylethanolamine-N-methyltransferase modulates conversine of norepinephrine to epinpherine.
Which enzyme changes norepinephrine to epinephrine?
Phenylethanolamine-N-methyltransferase
Breakdown enzyme of noradrenaline?
MAO-A
COMT
Breakdown product of noradrenaline?
3-methoxy-4-hydroxyphenylglycol (MHPG)
Vanillyl mandelic acid (VMA)
What is the major metabolite of noradrenaline in the CNS?
MHPG
What is the major metabolite if noradrenaline in the endocrine/peripheral nervous system?
VMA
How is noradrenaline re-uptaked?
Noradrenaline reuptake channel
What drugs inhibit reuptake of noradrenaline?
Tricyclics
SNRIs
Reboxetine
Bupoprion (noradrenaline-dopamine reuptake inhibitor)
Function of noradrenaline?
Arousal
Anxiety
Mood regulation
Autonomic mediatino
Receptors for noradrenaline
Alpha 1, Alpha 2, Beta 1, Beta 2
Describe alpha 1 receptors for noradrenaline
Phospholipase C coupled
Mostly postsynaptic
Describe alpha2 receptors for noradrenaline
Gi-coupled
Mostly presynaptic autoreceptors
Describe beta receptors for noradrenaline
GS-coupled
Predominate in locus cereulus
Regulate arousal
Describe beta 1 receptors for noradrenaline
High affinity to noradrenaline
Mostly peripheral Gs protein coupled
Describe beta 2 reeptors for noradrenaline
High affinity for epinephrine
peripheral