Practice question · Multiple choice
An SSRI blocks the transporter that pulls serotonin back into the presynaptic terminal. It does not make any neuron release a single extra molecule of serotonin. Why does blocking reuptake nevertheless increase serotonin signalling at the synapse?
Hints
- Signalling depends on how much transmitter is in the cleft and for how long - not only on how much was released.
- If nothing is removing the transmitter, what happens to the amount sitting there?
Show the answer
A. Because reuptake is how serotonin is cleared from the cleft.
Why
Cleft concentration is set by what arrives and what leaves; the drug does nothing to the first and everything to the second, so the same release produces more binding for longer. Cocaine does this to dopamine, a large share of psychoactive drugs act on clearance rather than on release.
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