Norepinephrine and serotonin — and serotonin syndrome
Covers the two other monoamines behind most antidepressants: how they're cleared, what their receptors do, and how too much serotonin becomes dangerous.
Where this fitsConnects to 2 · Unlocks 2
- Connects to
- The synapse: release, binding and termination — SERT and NET are the reuptake step; MAO is the enzyme step.
- The course lens: biopsychosocial, and no 'chemical imbalance' — Why 'depression = low serotonin' doesn't hold up.
- Unlocks
- When enzymes change: induction, inhibition and genetics — MAO inhibition returns in first-pass metabolism (DMT, ayahuasca).
- Therapeutic window, steady state, washout — and tolerance — Washout periods matter when switching serotonergic drugs.
Orient
Norepinephrine (NE) – adrenergic receptors, all metabotropic: alpha and beta; reuptaken by NET; drives the sympathetic nervous system, “fight or flight”; produced in locus coeruleus. Serotonin; 5-HT (5-hydroxytryptamine) – tryptophan into 5-HTP is rate limiting; metabolized by MAO, reuptaken by SERT; major metabolite is 5-HIAA. Serotonin syndrome results from too much serotonin.
Course terms
Your professor's wording, word for word from the slides. Learn the term and this definition — the explanation underneath is only there to help it make sense.
- α2 receptor
“α2 inhibits sympathetic system; rest excitatory”Slides 03, p. 25
α1 and α2 are in both CNS and PNS; β1 is in the heart (beta blockers).
- NET
“reuptaken by NET (norepinephrine transporter)”Slides 03, p. 25
NE is also metabolized by MAO or COMT.
- Sympathetic nervous system
““Fight or flight””Slides 03, p. 25
Opposite effects of the parasympathetic system.
- Locus coeruleus
“Produced in locus coeruleus”Slides 03, p. 25
Where NE neurons are.
- 5-HT
“5-hydroxytryptamine”Slides 03, p. 27
Serotonin, an indoleamine; all receptors metabotropic except 5-HT3.
- SERT
“reuptaken by SERT (serotonin transporter)”Slides 03, p. 27
The target of SSRIs.
- 5-HIAA
“Major metabolite is 5-HIAA”Slides 03, p. 27
No consistent association between 5-HT or 5-HIAA levels and depression (Moncrieff et al., 2023).
- Serotonin syndrome
“Results from too much serotonin”Slides 03, p. 29
Polydrug interactions such as MAOI + MDMA or MAOI + SSRI; potentially fatal.
- Shits and SHIVERS
“Shivering Hyperreflexia (twitching) Increased temperature Vital sign instability Encephalopathy (general altered state) Restlessness Sweating”Slides 03, p. 29
Plus “shits” (diarrhea) — the serotonin syndrome mnemonic.
From your course: Course slides 03, pp. 25–31
Tip: the ← and → keys move through the lesson.
Full lesson: Norepinephrine and adrenergic receptors · Serotonin and receptor exceptions