how are dopamine serotonin and endorphins different?

Question

From a layman’s perspective they are all described as happy brain chemicals. What’s the role that they play that makes them different from each other?

In: 29

Answer 1

I’ll keep this brief. There are a lot of ways these different neurotransmitters differ. Dopamine and serotonin are monoamines while endorphins are peptides. All of these neurotransmitters have different receptors. Serotonin targets 5HT1-5HT7 receptors, dopamine targets D1-D5 receptors, and endogenous opioids target the delta and mu opioid receptors. *None* of these neurotransmitters are necessarily “happy chemicals.” Dopamine is released in aversive conditions too and in addition it regulates movement. It is also not responsible for euphoria or “feeling good”, but rather it reinforces certain behaviors, compelling an animal to repeat those behaviors. It is a “craving” or “motivation” neurotransmitter, not really a “pleasure” neurotransmitter, and only in the ventral striatum.

Serotonin does play a role in mood (5HT2A receptors are enriched in the cortex while 5HT1A receptors are located in the cortex and subcortically). The 5HT1A receptor is probably responsible for the “calming” effects of serotonin (i.e. when you take MDMA) and is thought to dampen chronic stress (see https://pubmed.ncbi.nlm.nih.gov/28858536/). However serotonin can mediate a lot of other processes like gut motility (5HT4 receptor), vomiting (5HT3 receptor), and satiety (5HT2C receptor). I like to think of serotonin as a monoamine that regulates homeostasis or alters homeostasis in adverse conditions. Serotonin functionally opposes dopamine signaling, even though neurons that produce it seem to be involved in reward.

Endorphins are tricky because they can release dopamine and serotonin (by binding to mu opioid receptors on inhibitory interneurons). This is also how they block pain signals — by inhibiting inhibitory neurons. The difference between monoamines and endorphins is that endorphins are degraded very rapidly.

Most dopamine receptors are Gi/o coupled (inhibitory G-protein), while all opioid receptors are Gi/o coupled. Serotonin receptors are a mix of Gi/o, Gq, and Gs coupled proteins. Ultimately the behavioral effects of these neurotransmitters depends on three factors:

1) The anatomical location of receptors and expression of the appropriate G-proteins

2) The identity of the neuron (or glial cell) the receptor is expressed on

3) The connectivity of the neuron expressing these receptor