Just a quick observation re: the actions of SSRI drugs and serotonin. The time course of response to SSRIs is variable but usually several weeks must pass before the desired effects are manifest. This delay could be due to "recruitment" of other transmitters but it is more typically viewed as a manifestation of up- or -down-regulation of serotonin receptor(s). Modifying receptor numbers or affinity can lead to a cascade of possible effects. So the punchline is: don't forget that receptors "adapt" to changes in their environment, too.