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 acids
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
NEN
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
Reboxetine
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
Describe beta 2 reeptors for noradrenaline
High affinity for epinephrine
Which noradrenaline receptor has high affinity for adrenaline?
Beta 2
Disorders in which low levels of noradrenaline is seen?
Depressin
Disorders in which abnormal levels of noradrenaline is seen?
Panic and anxiety disorders
Source of seretonin?
Tryptophan -> 5 hydroxy 1-trytophan -> seretonin
Rate limiting step of seretonin
Availability of tryptophan
Synthetic enzyme for seretonin
Tryptophan hydroxylase
Breakdown enzyme of seretonin
MAO-A
Break-down product of seretonin
5-hydroxyindoleaetic acid (5-HIAA)
What allows reuptake of seretonin?
Seretonin reuptake channel
What inhibits seretonin reuptake?
Tricycles
SSRIs
Function of seretonin
Mood Perception of pain Feeding Sleep-wake cycle Motor activity Sexual behaviour Temperature regulation
Receptors for seretonin
14 known subtypes
Which seretonin receptors are C-protein coupled?
All except 5 HT-3
Which seretonin receptor is in the gut?
5HT3
Describe 5HT1a receptors
Gi coupled postsynaptic.
Antidepressant response.
Sexual behaviour.
Describe 5HT1B receptors
Gi coupled presynaptic.
Describe 5HT1D receptors.
Gi coupled, both pre and postsynaptic.
Describe 5HT2 receptors
Phospholipase C coupled.
Postsynaptic.
Antagonism can lead to antipsychotic response (atypicals) and sedation.
Which seretonin receptor can be stimulated by LSD?
5HT2
Which seretonin receptor is downregulated after antidepressant or ECT treatment?
5HT2
Which seretonin receptor can lead to a response from atypical antipsychotics if antagonised?
5HT2
Which seretonin receptor is involved with regulation of circadian rhythym?
5HT7
Describe disorders related to low seretonin levels
Depression
Aggression
Suicide
Impulsivity
How do seretonin levels have a role in psychosis?
Regulate dopamine system
Which medication is an agonist on 5HT1a?
Antidepressant
Which medication is a partial agonist on 5HT1a?
Anxiolytics
What action can 5HT1B receptor lead to?
Aggression
Which medication is an antagonist for 5HT1D?
Antimigraine
Which medication is an antagonist for 5HT2A?
Antipsychotic
Which medication is an agonist for 5HT2A?
Hallucinogens
Which seretonin receptor is involved in working memory, platelets and smooth muscle
5HT2A
Which receptor stimulation (seretonin) may result in cardiac valvular fibrosis
5HT2B - dexfenfluramine
What effect can stimulation of 5HT2C have?
Axiogenic and anorexic effect
What medication has an antagonistic effect on 5HT3?
Antiemetic
Which medication has an antagonistic effect on 5HT6?
Antipsychotic
Antidepressant
Which receptor helps as an antiemetic?
Anatogonist of 5HT3
Which seretonin receptor can act as antimigraine?
Antagonist to 5HT1D
What is DOPA decarboxylase involved in?
Synthesis of dopamine and seretonin.
How does DOPA decarboxylase form dopamine?
Tyrosine -> hydroxylation -> L-dopa -> catalyses by tyrosine hydroxylase -> DOPA decarboxylase decarboxylates L-DOPA to form dopamine.
Where is dopamine produced by the DOPA decarboxylase enzyme?
Basal ganglia
Sympathetic nervous system
What is dopamine the precursor of?
Catecholaminergic hormones, noradrenaline and adrenaline in adrenal medulla.
How does DOPA decarboxylase produce seretonin?
Tryptophan hydroxylase produces 5-PH tryptophan, which is decarboxylated by DOPA decarboxylase, forming seretonin.
Which type of enzyme is DOPA decarboxylase?
Homodimeric
Pyridoxal
Phosphate-dependent
Source of acetylcholine?
Choline and acetyl-coenzyme A
Rate limiting step of formation of acetylcholine?
Availability of choline
Synthetic enzyme for acetylcholine?
Choline acetyltransferase
Breakdown ezymes for acetylcholine?
Acetylcholinesterase - rapid
Breakdown product of acetylcholine?
Choline
Reuptake of acetylcholine?
None.
Function of acetylcholine?
Modulate arousal Learning Memory Rapid eye movement sleep Pain perception Thirst Parasympathetic mediation
acetylcholine receptors?
Muscarinic (M1 - M5) - G-protein coupled.
Nicotinic - ion channels.
Where are nicotinic, acetylcholine receptors more common?
Peripheral parasympathetic system
What do muscarinic acetylcholine receptors do?
Mediate attention
Disorders where there is reduced acetylcholine?
Alzheimers
How is acetylcholine involved in Parkinsons?
Involved in dopamine balance
Source of GABA
Glutamic acid
Rate limiting step for formation of GABA
Glutamic acid decarboxylase
Synthetic enzymes involved in formation of GABA?
Glutamic acid decarboxylase
Breakdown enzyme for GABA
GABA transaminase
Breakdown product of GABA?
Glutamate, then succinic acid
Reuptake of GABA?
Presynaptic nerve terminals
Glial cells
Uptake is bidirectional and temperature and ion-dependent.
What inhibits GABA reuptake?
Tiagabine
Function of GABA?
Mediates anxiety
Seizure cessation
In which medications is GABA involved in?
Benzo
Barbituates
EtOH
Receptors for GABA
GABAa and GABAb
Function of GABAa
Opens chloride channel, leading to hyperpolarization (inhibitory).
Structure of GABAa receptor?
5 subunits, at least 14 subunits.
Structure of GABAb receptor
G-protein coupled.
Selective agonist of GABAb receptor?
Baclofen
Disorders of GABA?
Anxiety disorders
Alcoholism
Epilepsy
Huntington’s
Source of glutamate?
- 2-oxoglutarate and aspartate by aspartate aminotransferase or
- glutamine by glutaminse or
- 2-oxoglutarate by ornithine aminotransferase.
Regulation of gluamate?
Accummulation of precursors or end-product inhibition
Synthetic enzyme for gluamate?
Glutaminase
Breakdown enzymes for gluamate?
Glutamate dehydrogenase
Glutamine synthetase
Breakdown product of gluamate?
Glutamine or alpha-ketoglutarate
Reuptake of glutamate?
Glial with conversion to glutamine
Function of glutamate?
Metabolic: Intermediary in oxidation, ammonia cycle. Precursor of all GABA in CNS. NMDA - memory acquisition. Developmental plasticity. Epilepsy. Ischaemic brain injury.
Receptors of glutamate
Metabotropic - 8 in total, 3 groups.
Ionotropic - NMDA and non-NMDA.
Structure of metabotropic receptors for gluamate
Group I - mGluR1&mGluR5 are linked to phospholipase C.
Structure of NMDA glutamate receptor
Subunits with distinct binding sites for glutamate, glycine, phencyclidine, magnesium, zinc.
Structure of non-NMDA receptor for glutamate?
Kainate binding or AMPA type.
Which glutamate receptor mediates long term potentiation?
NMDA
Which disorders are linked to glutamate toxicity?
Stroke
Schizophrenia
Seizures
What can NMDA antagonists cause?
Hallucinations - PCP, ketamine
What is the primary inhibitory neurotransmitter in the spinal cord?
Glycine
How is glycine synthesized?
From serine by serine trans-hydroxymethylase and glycerate dehydrogenase
What are the rate-limiting steps of glycine production?
Serine trans-hydroxymethylase
Glycerate dehydrogenase
Function of glycine
Mandatory adjunctive neurotransmitter for glutamate receptors
What is the name of the excitatory glycine site on NMDA receptors?
Non-strychnine sensitive glycine receptor.
What is the Non-strychnine sensitive glycine receptor?
Inhibitory receptor.
Where is the Non-strychnine sensitive glycine receptor found?
Spinal cord
How are glycine and schizophrenia linked?
Facilitating glycine transmission can reduce negative symptoms.
What is the name of an experimental glycine reuptake inhibitor which is being trialled to reduce negative symptoms?
Bitopertin
Name two endogenous cannabinoid substances
Anandamide - a weak ligand
Arachnidonylglycerl - strong ligand
How are anandamide and Arachnidonylglycerl formed?
Arachidonic acid and ethanolamine
What are the cannabinoid receptors?
Central - CB1
Peripheral - CB2
What do both cannabinoid receptors bind?
Tetrahydrocannabinol - active ingredient of maraijuana.
Functino of anadamide?
Lowers intraocular pressure
Decreases activity level
Relieves pain
What are neurotrophins?
Substances that act as polypeptide growth factors influencing proliferation and differentiation of neurons and glial cells.
Well-known neurotrophins?
Nerve growth factor
Brain derived neurotrophic factor
Neutotrophin 3 and 4
What is the neurotrophin hypothesis?
Neurons compete during development for limited resource of growth factors.
Those neurons that are responsive (high affinity binding site) survive.
Incorrect targeting of axons may lead to apoptosis.
Which neurotrophin is involved in long-term potentiation of memory?
Brain derived neurotrophic factor
Which medications affect brain derived neurotrophic factor?
SSRI and ECT upregulate it.
Which mutation causes reduced brain derived neurotrophic factor activity?
Single nucleotide polymorphism in BDNF gene on chromosone 11p13 results in aa substitune of valine with methionine at codon 66.
What do humans with the 11p13 BDNF mutation have?
Impaired hippocampal activation and performance
What is reduced to a greater extent in patients with hallucinations in Lewy body compared to those without?
Corticol choline acetyl transferase
What can chronic antidepressant use lead to?
Induces a reduction in beta adrenoreceptor density around 2 weeks after treatment.
What is Kapur’s aberrant salience theory?
In a normal person, role of mesolimbic dopamine is to attach significance to external stimulus or internal thought. This converts neutral info to attention grabbing.
Implications for psychosis in aberrant salience theory?
In psychosis where this is high dopamine in mesolimbic system, insignificant events and perceptions receive inappropriate significance, resulting in delusions.
What are the clinical implications of the aberrant salience theory?
Antipsychotics dampen the significance of abnormal experiences, but do not erase symptoms - they provide the platform for psychological resolution.
Where is an increase in 5HT2A receptors most prominent in those with depression?
Dorsolateral prefrontal cortex
Platelets
Effect of longterm antidepressant use on seretonin receptors
Reduce 5HT2 receptors
Increase 5HT1A function