Serotonergic signalling (finished) Flashcards
How was serotonin discovered? - describe the experiment
(more of a context card)
- Rapport & Page crystallised a compound (serotonin) in 1948 from 15L of blood serum in a 5 step process
- Experiment = exposing artery rings of rat to compound, then read contractions of this muscle = Tension of rings increased dramatically
- Named after ‘serum’ & ‘tonic’ meaning medicine = SEROTONIN
- 1949, Rapport identified the molecular structure of serotonin as 5-HT
What does 5-HT stand for?
5-hydroxytryptamine
What is the structure of 5-HT?
- Has an indole ring = 2 carbon rings
- And an amine group
= an ‘indoleamine’ due to indole ring in the centre
Where is serotonin produced?
- 90% produced in enterochromaffin cells (GI tract)
- 2% in CNS
- 8% in platelets
What molecules is serotonin similar to?
Hallucinogens/psychedelics
Specifically psilocybin
What is an example of something that contains hallucinogenic compounds?
Magic mushrooms contain psilocybin
What is another mushroom that has a similar effect but should not be confused with magic mushrooms + how is it different?
Fly agaric has muscimol as its primary psychoactive compound
Compare the effects of psilocybin with serotonin
similar psychoactive effects if concentrations high enough
When psilocybin gets into the body, what is it converted to?
Psilocin
What does psilocin act on?
serotonergic receptors
What are the functional effects of psilocybin similar to?
Lysergic acid diethylamide (LSD) = psychedelic drug
DMT , N-Dimethyltryptamine
Describe the effects of LSD
Effects typically include:
- Intensified thoughts, emotions and altered sensory perception.
- At sufficiently high dosages LSD manifests as primarily visual, auditory hallucinations.
What is DMT?
, N-Dimethyltryptamine is a substituted (5-hydroxy)-tryptamine that occurs in many plants and animals (= naturally occuring compound)- commonly used as a recreational drug & used for rituals in Southern American tribes
Name some plants that produce DMT
Phalaris, Delosperma, Acacia, Desmodium, Mimosa
What do DMT, LSD, sertonin and psilocybin all act on?
5-HT2A/C Receptor GPCR (Gq) to produce IP3 and DAG
What is this picture showing?
Label brain with radioligin which binds to seronergic receptor (shown in red)
+ psilocybin = reduction in signal- suggests psilocybin outcompetes serotonin
What are selective agonists + give one example
= molecules that bind and activate specific receptors e.g. psychedelics
What do selective agonists do?
Selective agonists stabilize a subset of receptor conformations (=different shapes) that selectively activates some but not all signaling pathways downstream
What this showing about selective agonists?
2 different drugs A and B acting on same receptor leading to activation of different pathways
Outline one hypothesis in the way in which psychedelics work
Induce different signalling routes downstream of activation of the same receptor
= biased agonism = activates receptors differentially = differing psychoactive effects between hallucinogenic and non-hallucinogenic compounds targeting the 5-HT2A receptor may be due to biased agonism.
Essentially, these compounds may activate different signaling pathways or induce different downstream effects upon binding to the receptor, leading to variations in their psychoactive effects
Where are serotonergic neurons located in the CNS and where do they project to?
2 main regions =
- Rostral raphe nuclei in the brainstem- project to forebrain, thalamus and cerebellum
- Caudal raphe nuclei- specifically raphe obscurus, pallidus and magnus – project to spinal cord and cerebellum.
What is the precursor for serotonin
tryptophan
Describe the synthesis of serotonin
- Tryptophan undergoes metabolism by tryptophan hydroxylase = 5-hydroxytryptophan
- this is further converted by L-aromatic amino acid decarboxylase into serotonin (5-HT)
What is the rate limiting step in the synthesis of serotonin?
The conversion of tryptophan to 5-hydroxytryptophan by tryptophan hydroxylase (=the rate limiting enzyme)
What does tryptophan hydroxylase require?
Enzyme requires tetrahydrobiopterin (BH4), NADPH and metal ion (iron or copper).
What does the amount of serotonin produced depend on?
The availability of tryptophan that crosses the blood brain barrier
Can tryptophan cross the blood brain barrier?
Yes- only free plasma tryptophan (unbound to albumin) crosses BBB
When crossing the blood brain barrier, what is tryptophan competing with?
Other neutral amino acids
What does increased cortisol do to tryptophan?
Plasma cortisol, which is increased in depression, decreases plasma free tryptophan concentrations: potential to trigger further depression- as reduces serotonin
What is the precursor for melatonin?
serotonin
Where is melatonin produced?
pineal gland
What enzymes are involved in the synthesis of melatonin?
5-HT N-acetyltransferase
5-hydroxyindole-O-methyltransferase
What is the main function of melatonin?
Regulate circadian activity of mammals
How is expression of enzymes that produce melatonin regulated?
Regulated in a circadian manner
What is the production of melatonin limited by?
production of melatonin is limited by the expression of enzymes
What does melatonin act on and where are they found?
Acts on melatonin receptors- predominantly MT1/2, MT3 (amphibia, birds)
- is found in the entire body including in the hypothalamus, hippocampus and other parts of the CNS
Describe the way in which metatonin works
- Melatonin binds to melatonin receptors (GPCR)
- MT1 receptors = Gi cascade- AC inhibition so reduces cAMP signalling
- MT2 receptors = Gq cascade- activates PLC and DAG signalling
What does the MT1 receptor induce downstream after activation?
Induces expression of protein called period = circadian activity protein
How does the activity of the 2 enzymes producing melatonin vary throughout the day and what effects this?
- Melatonin levels in the pineal gland show circadian variations: following changes in N-acetyl transferase activity, increasing during the night (7-150fold) and decreasing during the day.
- Light inhibits melatonin biosynthesis.
- Melatonin controls sleep patterns and hormone rhythms.
What does dysfunction of melatonin result in?
Related to disease- has effects on several cascades within brain