Excerpt:
Most antidepressants don't show an immediate effect - instead, they
take about three weeks to kick in. For the longest time, scientists
couldn't actually explain this delay. They knew the antidepressants had
to somehow "adapt" themselves to the neural pathways, but what that
actually meant was anyone's guess. Now a team of French researchers have
figured it out: antidepressants need three weeks to shut down a
particular chemical regulator of microRNA.
This particular microRNA, designated miR-16, is in charge of making
the serotonin transporter, and is generally found in the serotonergic
neurons that produce serotonin. However, miR-16 is also found in neurons
responsible for making the neurotransmitter noradrenaline. Here, miR-16
has precisely the opposite purpose - it completely blocks the
production of serotonin in these neurons.
When drugs like Prozac go to work, they cause the serotonergic
neurons to release signals. These signals cause the miR-16 to die off,
which frees up the noradrenaline neurons to start making the serotonin
transporter as well. Thus, Prozac both directly boosts the production of
serotonin in the serotonergic neurons and indirectly causes the
noradrenaline neurons to start making it as well.
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