List of Serotonin Receptors and their Function

So many of you have seen my work in regards to other neurotransmitter discussions, and the neuroendocrine role of neuromodulator's such as histamine. However many questions that I've addressed in personal conversations, have now ignited my motivation to compile an easy list of what all the serotonin receptor subtypes do. 

What do the serotonin receptors do?

Are they all INHIBITORY? Can serotonin be stimulating ? Is it so linear that one simply needs to raise serotonin to alleviate a whole host of neurological conditions? Is serotonin some god-almighty chemical that everyone should aim to raise?

The answer to these questions are not to be found very easily, but I will tell you this - before even getting to the compilation I want to stress how ridiculous it is for someone to generalize the effects of a given neurotransmitter, and that is even more baffling (and depressing) that some people stay firm with a tunnel-vision that leads to many negative outcomes. 

Serotonin has more negatives than positives, especially in moderate to high amounts, and while some people derive benefit from tryptophan supplements and SSRI drugs - that vast amount of serotonin receptors have very negative neuroendocrine roles, which some not only causing an exaggerated stress response, but also initiating it.

The absurdity of one to believe that serotonin should be increased to a certain level, or that drugs that target serotonin receptors are the one "holy grail" to improving quality of life - is outrageous. 

It's stupid and it's narrow.

Serotonin does have some benefits, and deficient levels may lead to anxiety and certain forms of depression, however, high levels of serotonin produce a much more apparent and persistent depression; marked by extreme anhedonia and lack of interest in everything. Taste buds disappear, sense of smell and all motivation and zest is exiled into oblivion. (1) (2) (3)

This is going to be a long list, so bear with me.
Use the search function or Control + F if you want to find the effects of one particular subtype. Colors in text will indicate the element or attribute associated with that receptor, with darker colors indicating receptors with more transient and inhibitory effects. Brighter Colors indicate a primarily stimulating effect. 


I will try to simplify things in the end notes with as accurate a summary I can give to those with limited understanding of neuroscience terms.

 5-HT1A Receptors

::::EFFECTS ON BEHAVIOR::::

____________________________________________

-Decrease aggression. (4) (5)

-Pro-Social (6)

-Euphoric complimentary effects when dopamine is also raised.(7)

-Inhibition / Decreased Impulsivity (8)
-Inhibition of drug seeking behavior (both alcohol and stimulant cravings) (9) (10) (11)
***Facilitation of sex drive and arousal (?)(!)(12)(13)
Decreases Appetite, Diminishes Food Intake (14)
***Questionable, it may facilitate libido by means of serotonin reduction (as they are autoreceptors and would reduce serotonin by activating them, however the postsynpatic neuroendocrine effects inhibit penile erection induced by dopamine agonists (!)(!) - indicating a primary inhibiting role, at least in males)***
Though it seems plausible that it would increase bonding and play a strong role (positive) in the feelings of love and trust. 5-HT1A activation can increase oxytocin release. (!)


::EFFECTS ON HORMONES::

• -Increases Beta-Endorphin Release
• -Increases Prolactin
• -Increases Cortisol, and ACTH
• -Increases Oxytocin
• Decrease Sex Hormones (due to above mechanisms)

EFFECT ON OTHER NEUROTRANSMITTERS

• Inhibits GABA activity in the PVN (ParaVentricalNucleus) and Spinal Cord (!)

::General Physiological Functions::

• Decreases Blood Pressure and Heart Rate (!)
• Decreases body temperature (!) (!)
• Vasodilation of blood vessels in Skin. (^)(^)

|*NOTATIONS*|

• 5-HT(1)A Activation causes blood vessel dilation in the hands/feet and thus, improves peripheral resistance to Cold Weather, this is due to anti-sympathetic effects; the reduction of Serotonin-induced  nervous system stimulation and reduction of noradrenergic-activity .
• 5-HT(1) Activation is a primary activator of the euphoric-responses in Cocaine-sensitized individuals, in fact, many stimulant drugs rely on the Serotonin 5-HT1A dependent activation of opioidergic-pathways to Exert their addictive properties (euphoria, endorphin rush, hypomania).
• When you RUN or work out for a long period of time, or even a moderate amount of time, or heck, even 20-30 mins, the endorphin rush and 'runner's high' comes from, partly, the 5-HT1A Receptor/s. <see here>

5-HT1B Receptors (!) (!)



::EFFECTS ON BEHAVIOR::
__________________________________________


-Decrease Aggression (!)
-Decrease Exploratory Behavior (!)
-Decrease Excitation (!)
-Decrease need for Alcohol (!)


PHYSIOLOGICAL

-Effect on Growth Hormone, Bone Formation and Osteoclasts
-Brain Vasoconstriction
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