2A, what? No heck, what is Serotonin first?
Okay, let's get slowly there.
Ever felt happy after receiving an Amazon package waiting for a week? Serotonin. Ever ate your favourite chocolate and felt a rush of joy? Serotonin. Ever had your heart skip a beat when your crush asked you out for coffee? Serotonin. Ever felt...you get the idea.
If Dopamine if your reward molecule, Serotonin is your "happy" molecule.
(Ofcourse, it is much more complex than that, but to first degree of approximation, it'll work for us today.)
1A Serotonin Receptor
There is a 1A now? What happened to 2A?
We are getting there, piece by piece.
Image you wake up, go to whereever you go to, and your supervisor is a prick. He insults you, doesn't like you, basically makes your life miserable. After a month, you get depressed. Your physician refers you to a psychiatrist, your newly formed psychiatrist talk to you and after few weeks she diagnose you as depressed. You are prescribed anti-depressents, basically SSRIs.
What is this acronym SSRI you ask?
Let's think for a second based on what we know. You are depressed, which means you are unhappy, meaning a low level of serotonin in your system. Now, if I shower you with Serotonin, you'll be "not-depressed"?
SSRIs, or Selective serotonin reuptake inhibitors, essentially inhibts the low amount of serotonin from being absorbed by the nerve cells, meaning you'll have more serotonin lying around, meaning a happier you.
So my depression is cured, right?
Unfortunately, nothing up there in our brains works this easily.
It turns out there are two common serotonin receptors, 1A and 2A. And these SSRIs are 1A agonist, a fancy term for saying "it stimulates the 1A".
What's happens when 1A is stimulated?
You go back to work, you boss is still a prick, but you have changed somehow. You, you are more accepting of the situation. You accept the fact that it's the way of life and it's how it is and no point being depressed and being hard on yourself. And you live life, as it is.
With your 1A stimulated, you become a stoic. Sure you become less depressed, not by means of actions, but my means of accepting the way life is to you.