Whats the difference between an SSRI and a seretonin receptor agonist?
An agonist is a molecule that functions as a mimic to the original neurotransmitter, like serotonin. An SSRI actually increases the levels of the native molecule by blocking its clearance from the synapse. Both have their effects and side-effects by over-stimulation of serotonin receptors, along with cross-reactivity with other pathways.
You ask very good questions, and let me put it this way. In theory, both an agonist and an uptake blocker will produce the same effect, i.e. stimulation of the receptor. In fact, many consider uptake blockers to be “indirect agonists”. However, when you inhibit uptake, you still have the endogenous transmitter which can be metabolized by endogenous enzymes, many of which are specific for that transmitter. In the case of serotonin, you have MAO as the main enzyme. With the man-made agonists, like Buspiron, these are generally not metabolized in the brain. They are metabolized by liver enzymes, but many times it is the metabolite that is the active agonist. Also, SSRI’s are not really that selective, as most of them also inhibit the uptake of norepinephrine. Side effects will have a bearing as well.
