An enzyme may produce a (brain chemical messenger serotonin).
A serotonin may be contained in neurons of a central nervous system.
A role can be for some modulation of (serotonin receptor levels).
A (serotonin receptor subtype) may regulate neurotransmission.
Responses to drugs may be affected by an activity of a (brain chemical serotonin).
Brains can be vulnerable to effects of a (serotonin neurotoxin).
Clusters can be constituted-of-or-filled-with (serotonin neurons).