Serotonin - The Chemical Gush of Joy and Resilience

Happiness, joy, bliss, contentment- everything we do in life is often tied to our drive to feel these emotions. But what does it mean to ‘feel good’? 

In the brain, our emotions are a result of neurochemical reactions. Among the neurotransmitters (chemicals that carry messages between neurons), serotonin is known as the natural feel-good hormone. It plays a crucial role in regulating mood, memory, sleep, fear and stress response.

It is also known to be important for digestion. In fact, contrary to popular belief, 90% of the body's serotonin is found in the gastrointestinal tract. 

When serotonin levels are low, a person may experience anxiety, depression, sleep problems, and digestive issues.

All the central serotonin pathways originate from a cluster of nuclei in the brain-stem. As the nuclei are present at the midline of the brain-stem, they are denoted by the Greek word for seam, ‘Raphe’. These Raphe nuclei modulate signalling in the ascending (projecting upwards) and descending (projecting downwards) serotonergic pathways. 

The ascending pathways regulate mood, cognition, and decision-making through the cortex, emotions and memory through the limbic system, movement and reward through the basal ganglia, and appetite and sleep through the hypothalamus.

The descending pathways project into the spinal cord for motor control and autonomic centers to regulate heart rate. 

Apart from these two, there are also peripheral serotonergic pathways which describe serotonin signalling and production by enterochromaffin cells (which are basically endocrine cells in the gut that stain with chromium). 

More serotonin does not mean more happiness, though it would have been convenient if it were so. We could all just take doses of the drug and stop worrying about everything else in life.

In reality, serotonin drugs do not directly create happiness but modulate emotional responses, reduce negative bias, and increase our ability to tolerate distress.

Selective Serotonin Reuptake Inhibitors (SSRI) are a common type of antidepressants that block the re-uptake of released serotonin, helping it remain in the synapse for longer. Zoloft (Sertraline), Prozac (Fluoxetine), and Lexapro (Escitalopram) are some examples of serotonin drugs that help manage symptoms of depression through this mechanism.

Serotonin receptors like 5-HT1A (a fancy code name for type A of serotonin receptors from the first family) are associated with pain relief. A novel drug ST171 was discovered recently which helps in treating both acute and chronic pain by acting on this receptor. Its unique binding with 5-HT1A enables precise and selective action as compared to standard drugs. It only switches ON the primary pain blocking pathway, avoiding unwanted effects like heightened pain sensitivity (called hyperalgesia) and sedation, linked to the secondary pathway. Fascinating, right? This approach is a promising new strategy that is helping make medications safer and more effective.

Now that we know all this about serotonin, can we utilise this science to feel happier? Serotonin is no magic drug, and what I am about to suggest next might sound like a sophisticated way of saying the same things our moms have been telling us to do all along. 

A natural way to increase serotonin is actually through exercise. Working out releases the amino acid tryptophan, which is used by the body to make serotonin. Sunlight exposure or ‘light therapy’ is another way to improve serotonin levels. 

Diet is also a crucial aspect that helps release the happiness hormone through tryptophan-rich foods and a healthy gut microbiome. 

Serotonin works together with other neurotransmitters like dopamine (we've talked about it in the October issue!) to activate brain circuits to uplift our mood. While Dopamine tells us to seek rewards, Serotonin is the calm voice that signals contentment. Serotonin gives us the strength to get through a hard day and brings a lasting sense of satisfaction. 

Imagine, how this tiny molecule made up of a bunch of Carbons, Hydrogen, Nitrogen, and Oxygen atoms, is capable of adding so much to our lives! It's not surprising then, that neuroscientists refer to the brain as an ‘enchanted loom’- weaving patterns that make our world meaningful.