Role of Dopamine, Serotonin, Oxytocin and Endorphins on the Brain
I would first like to point out that although Dopamine, Serotonin and Endorphins are neurotransmitters, Oxytocin is better known as a hormone. Nevertheless, they all play important roles in regulating brain function and behavior. Listed below is a summary of how each chemical influences human lifestyle and health.
Dopamine: Although primarily known as responsible for ‘reward and pleasure’[1], dopamine is responsible for several functions — including ensuring normal locomotive ability[2], enhancing one’s learning by increasing motivation[3], maintaining memory[4], regulating attention and cognitive ability[5], and emotion.[6] Dopamine imbalances have therefore contributed to pathologies such as Parkinson’s Disease[7], schizophrenia[8], and amphetamine and cocaine addiction.[9]
The multitudinous effects of dopamine on humans can likely be explained by the fact that dopamine is a slow-acting neurotransmitter — i.e, it can produce longer-term changes in the brain by indirectly modulating the activity of other neurons.[10] It’s specific effects on pleasure occurs by acting upon specific brain regions responsible for reward, pleasure, and decision-making, such as the Ventral Tegmental Area[11], the Nucleus Accumbens, and the frontal lobe[12].
Serotonin: Similar to dopamine, serotonin is also a slow-acting neurotransmitter, and also known for its role in sensations of pleasure.[14]However, it’s other roles include modulating the pathophysiology of mood disorders, emesis (vomiting), migraine, irritable bowel syndrome (IBS), and hypertension, by modulating gastrointestinal motility, degree of blood vessel constriction, and platelet function.[15] It also contributes to regulating circadian rhythms[16]. Lower serotonin has been linked to depression[17] and schizophrenia[18].
These multitudinous effects can generally be suggested to occur due to the omnipresence of serotonergic neurons across the brain, particularly concentrated at the brain stem (the region responsible for involuntary, basic body functions e.g. breathing, heart rate).[19]
Oxytocin: Oxytocin is a hormone and not a neurotransmitter by itself, but does affect neuromodulation in the brain and thus in this context, perhaps, can be considered a neurotransmitter.
Nevertheless, Oxytocin, titled the “love hormone”, has consistently found to play an important role in social function — such as sensitivity to facial emotions[21], trust[22], reducing anxiety[23], pair bonding[24], and even orgasm[25] and ejaculation[26]. It also promotes uterine contraction during childbirth[27], and milk ejection from mammary glands for breastfeeding[28]. It has also shown to have an antidiuretic effect (i.e reduces amount of urine produced), by increasing levels of aquaporins (that facilitate water reabsorption) in the kidneys.[29]
Oxytocin stimulates uterine contraction by increasing intraneuronal Calcium, which strongly depolarizes neurons, making them more likely to fire. Thus, the uterine muscles contract more frequently and with greater strength.[30]Oxytocin’s effects on love are suggested to arise due to interactions with vasopressin (another hormone), which modulate specific neural receptors that produce corresponding emotions[31].
Endorphins: Endorphins are essentially the body’s “natural painkillers”. Produced during exercise or stress, endorphins work by binding to opioid receptors in the brain, which are responsible for producing feelings of pleasure[32]. Specifically, the binding inhibits the release of substance P that contributes to the transmission of pain[33]. Due to its painkilling effects, several painkillers (e.g. icodin, Morphine, Fentanyl) mimic endorphins in order to produce their effects. It is endorphins that are associated with the “runner’s high”, and is useful in designing painkilling drugs for surgery[34].
