Making neurotransmitters: precursors and rate-limiting steps
Explains why transmitters must be made inside the brain, and how drugs like L-DOPA shortcut the process.
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- Distribution: membranes, protein binding and barriers — Transmitters are polar, so they can't cross the blood-brain barrier.
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- Dopamine: receptor families, clearance and pathways — Tyrosine → DOPA → dopamine.
- When enzymes change: induction, inhibition and genetics — Carbidopa blocks peripheral breakdown of L-DOPA — an enzyme inhibition you'll see again.
Recorrido
Transmitters stay on their side
Neurotransmitters must be made in the presynaptic neuron. They can't cross into or out of the brain through the blood-brain barrier.
Analogía y ejemplo resuelto
Analogía: A bakery whose ovens can't be moved (transmitters stay inside), so flour (precursor) is delivered and baked on site. The slowest oven sets the pace of the whole bakery. L-DOPA is delivering half-baked bread to skip the slow oven — but you have to stop it being eaten on the way.
Why can't you treat Parkinson's by giving dopamine pills?
- Dopamine is a neurotransmitter — polar and unable to cross the blood-brain barrier.
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