Nature’s Mood Boosters: The Role of Happy Hormones in Animals and Humans

Fig no 1. The Emotional Support Animals Provide to Humans

Pathways of the brain that involved in the localization of happiness

The human brain weighs more than one kilogram, almost 2.2 pounds, and has an estimated 86 billion neurons.Signals are conveyed along each nerve through electrical gradients of charged ions, with each neuron forming many connections to its neighboring neurons.  This extensive chemical and electrical network facilitates the intricate processes that allow us to experience emotions, ranging from the overwhelming addiction of love to the profound anguish of bereavement. [2] Neuroscientific research lacks definitive conclusions regarding the placement of happiness; however, certain brain regions are identified as emotion regulation centers: the prefrontal cortex, amygdala, hippocampus, anterior cingulate cortex, and insular cortex.  Neurotransmitters lack a definitive explanation; however, the primary neurotransmitters associated with happiness are endorphin, dopamine, serotonin, norepinephrine, and melatonin.  The limbic system participates in memory processing and decision-making.  The nucleus accumbens is recognized for its role in emotional processing.  The basal ganglia are recognized for their role in the planning and coordination of movement; however, specific regions also activate in response to pleasant emotional inputs and are believed to participate in reward and reinforcement mechanisms.  The orbitofrontal cortex, situated slightly above the eyes, is believed to be involved in assessing reward vs punishment.  The hypothalamus connects the neurological system to the endocrine system, which generates hormones that are crucial mediators of mood and emotion.  The brain contains multiple 'reward pathways,' with the mesolimbic route being the most extensively researched. [2] The pathway conveys dopamine signals from neurons in the central brain to the limbic system and the prefrontal cortex, both of which participate in emotional processing.  Under typical circumstances, this pathway acts as a catalyst for constructive behaviors*, eliciting pleasure sensations that promote evolutionarily advantageous actions like as consuming high-calorie foods, engaging in social interactions, and reproduction.  The sympathetic nervous system of the autonomic nervous system employs the neurotransmitters adrenaline and noradrenaline to prime the body for "fight or flight," increasing heart rate and mobilizing resources to energize the muscles.  The parasympathetic nervous system of the autonomic nervous system utilizes acetylcholine to facilitate relaxation and digestion, decelerating heart rate and respiration while redirecting blood flow to the gastrointestinal tract. [2]

Combination

Neurotransmitters facilitate the transfer of messages between neurons across a synapse. Researchers have identified that some diets affect the brain's synthesis of certain neurotransmitters. Complex carbs enhance serotonin levels, while protein-rich diets stimulate the synthesis of dopamine and norepinephrine. Neurotransmitters are prone to oxidation; therefore, it is advisable to consume sufficient antioxidants.

Dopamine

"The Reward Molecule," is responsible for reward-driven behavior and the pursuit of pleasure.  A dopamine molecule comprises a catechol structure, characterized by a benzene ring with two hydroxyl side groups, and an amine group linked through an ethyl chain.  Dopamine is the most basic catecholamine. All forms of reward-seeking behavior examined elevate dopamine transmission in the brain.  It is an inhibitory neurotransmitter that obstructs the transmission of impulses across a receptor.  Optimal dopamine levels enhance pleasure and reward-seeking behaviors essential for happiness.  L-Phenylalanine and L-Tyrosine are prevalent amino acids vital for dopamine production in the body.  Dopamine is produced in a limited array of cell types, mostly neurons and cells within the adrenal medulla. [3] Two primary regions of the brain synthesize dopamine.  One is referred to as the substantia nigra, a small strip of tissue situated on either side of the brain's base, located in the midbrain region.  Adjacent to here is the ventral tegmental region, which additionally produces dopamine.  The principal and secondary metabolic pathways are as follows:

Primary: L-Phenylalanine → L-Tyrosine → L-DOPA → Dopamine [4, 5]

Minor : L-Phenylalanine → L-Tyrosine → p-Tyramine → Dopamine [6]

Minor : L-Phenylalanine → m-Tyrosine → m-Tyramine → Dopamine [6]

Cocaine inhibits the reuptake of dopamine, prolonging the presence of these neurotransmitters in the synaptic cleft.  Substances such as cocaine, opium, heroin, alcohol, and nicotine elevate dopamine levels.  Evidence suggests that individuals with extroverted personality types exhibit elevated amounts of dopamine compared to those with introverted personalities. Dopamine is mostly released in the nigrostriatal tract, where it plays a role in mood regulation.  Dopamine facilitates reinforcement, motivating an organism to repeatedly engage in a behavior.  Dopamine is the neurotransmitter that compels a laboratory animal to incessantly activate a lever to obtain palatable food pellets.  Rewards and reinforcement assist our learning regarding the locations of essential resources, such as food and water, enabling us to return for additional supplies.  Reducing dopamine levels can cause animals to experience a diminished sense of pleasure in behaviors such as eating and drinking.  This state devoid of pleasure is termed anhedonia.  Dopamine facilitates concentration in animals due to its functions in reward and reinforcement. [7]

serotonin

"The Happiness Hormone" or 5-hydroxytryptamine, is made up of amino acids.  Serotonin is made in animals, including humans, from the amino acid L-tryptophan through a short metabolic route made up of tryptophan hydroxylase (TPH), aromatic amino acid decarboxylase, and pyridoxal phosphate.  There are many behaviors that serotonin controls, such as sleep, hunger, excitement, and anger. Serotonin keeps people from getting depressed and makes them happy.  It comes out when you go outside in the sun, eat foods that are high in sugars, or work out.  This type of cell body is mostly found in the upper pons and the midbrain. There are links between these neurons and the basal ganglia, the limbic system, and the brain cortex.  Serotonin is made at the end of an axon from the amino acid tryptophan, which is a precursor.  Not getting enough tryptophan in your food makes you irritable and hungry. Taking it as a vitamin has been shown to help people sleep, calm down, and feel better overall.  Monoamine oxidase is the main enzyme that breaks down serotonin, and 5-hydroxyindoleacetic acid is the end result of this process.  When it comes to mental illnesses, sadness is the main one that serotonin is linked to.  That too little serotonin is linked to sadness and that too much serotonin is linked to mania is the idea behind mood disorders.  The hormone serotonin is best known for making people happy, but researchers at the University of Wisconsin–Madison have found that it also helps dairy cows make milk. Low calcium levels are a big problem for cows' health because they can lead to immune and digestive problems, fewer births, and longer breaks between pregnancies.  All of these things are bad for dairy farmers, International Journal of Veterinary Sciences and Animal Husbandry, because their income rests on having healthy cows that give them a lot of calcium-rich milk.  A happy cow makes milk that is better for you.  While cows are sick with milk fever, the amount of calcium in their blood drops, and they get cold and start shaking.  There is a new study in the Journal of Endocrinology that shows that higher amounts of serotonin cause higher levels of calcium.  In the study, both Jersey and Holstein cows were given shots of a chemical that is broken down into serotonin.  Serotonin raised the calcium level in the milk of Jersey cows but raised the calcium level in the blood of Holstein cows.  Calcium levels are controlled in two different kinds in different ways. These differences happen at the molecular level and can be used to find new ways to treat milk fever.  Higher levels of serotonin would raise the amount of calcium in the blood, which normally strengthens bones.  On the other hand, this helps treat milk fever in cows [8].

Oxytocin

Oxytocin is a peptide hormone and neuropeptide. It is also known as "The Bonding Molecule," "The Trust Hormone," or "The Love Hormone."  Most of the time, the paraventricular region of the hypothalamus makes oxytocin, and the posterior lobe of the pituitary gland releases it.  The oxytocin peptide is made from a precursor protein that is not active.  Neurophysin I, an oxytocin transport protein, is also part of this precursor protein.  Oxytocin is a hormone that helps people bond with each other and trust and love grow. Some studies have found a link between high amounts of oxytocin and romantic attachment.  People sometimes call this hormone the "love hormone" or the "cuddle hormone" because it is released when people bond and feel recognized.  A 2009 study in the journal Hormones and Behavior found that even playing with a dog can make your oxytocin level rise.  Researchers have found that the levels go down after people experience bad things like being insulted or having negative thoughts.  It is suggested that you eat foods that are high in proteins, oils with HDL, and veggies like avocados and bananas.  Mothers care for their young by licking, cleaning, and nursing them. This is an important part of keeping the young alive.  It is clear that research on oxytocin and how it affects the behavior of mothers in farm animals is necessary to make the babies healthier and more likely to survive.  The higher levels of oxytocin that are released after good social interactions may help people who are sick get better.  Oxytocin levels went up in both the dog and the owner after "cuddling" in a 2003 study. Oxytocin may be a scientific reason for the strong emotional bond between people and dogs. Oxytocin is known to be very important for the milk let down response. When it comes to good social behavior like maternal and affiliative behavior, oxytocin may make a big difference in the health and happiness of farm animals [9]. It was thought that oxytocin worked with the HPA system to reduce stress.  Researchers found that giving oxytocin through the nose lowered the adreno-cortico-tropic hormone response in monkeys and decreased the release of cortisol in Holstein steers [10].  When cows were grazing, their serum oxytocin levels were usually higher than when they were housed.  It seems likely that the grazing system makes cows more comfortable and encourages them to eat and chew more than the house system. This is because cows release more oxytocin when they are comfortable [11]. A rise in blood oxytocin levels would make farm animals happier and healthier if they were raised in a natural way [12]. The natural suckling systems, in which calves are nursed by dams and have social contact with other calves and cows, are better for calf wellbeing. For example, the calf's daily gain and vitality are better in these systems than in the artificial ones.

Endorphins

Endorphin is the name of a chemical that literally means "self-produced morphine." The chemical makeup of endorphins is similar to that of opiates, and they can relieve pain. Endorphins are opioid neuropeptides and peptide hormones that are naturally found in people and other animals. In times of intense physical effort, the pituitary gland and the central nerve system make them. Getting a lot of exercise, eating hot peppers, eating chocolate, or laughing and making love are just a few of the things that can create endorphins. They play a role in controlling pain, stress, and mood. Endogenous opioid-containing neurons can be found in the middle hypothalamus, the diencephalon, the pons, the hippocampus, and the midbrain, among other places. Endorphins are linked to the "no pain" part of aerobic exercise. More endorphins are made during high energy "anaerobic" cardio and strength training. A study done by the late Dr. Johannes Odendaal, research professor at the Life Sciences Research Institute in Pretoria, South Africa, with dogs and people in 2003 showed that petting a dog or cat released endorphins and other "feel good" chemicals in the brain, such as dopamine, oxytocin, prolactin, and norepinephrine. Dr. Adnan Qureshi of the Zeenat Qureshi Stroke Research Center found in his research in 2009 that people who owned cats had a much lower chance of getting heart disease. In his study, he even said that having a cat might be a good way for people who are at risk of heart disease to stay healthy [13]. Patients in Animal-Assisted Therapy (AAT) associate with companion animals to help them feel better. This can help with depression, anxiety, and giving people who are suffering a sense of well-being and purpose. Animal Assisted Therapy is used to help people in many ways, from improving the happiness of people in nursing homes to helping kids with developmental disabilities think and learn better. This is because interacting with animals can release endorphins.

cortisol

Hydrocortisone is a well-known steroid in the body that is released when there is inflammation. It comes from the adrenal glands.  This hormone is controlled by CRH, which is released from the brain and makes ACTH levels rise.  Taking care of stress is what this hormone does for the mind. Several studies looked at the link between cortisol and sadness as something opposite to happiness.  It has been proven that cortisol is a reliable sign of sadness.  Depression and neuroticism have been linked to having a lot of cortisol in the morning.  Different patterns of cortisol release have also been linked to worry, depression, and stress.  Researchers have found that lower levels of cortisol in saliva are a good indicator of happiness.  Still, more research needs to be done on the link between happiness and this hormone.  Animal welfare has often been judged by checking the amounts of cortisol in the blood, which is the main physiological sign of stress in dogs [14, 15], and looking at how they act when they are stressed.  A lot of different mental and physical stimuli can cause cortisol to be released, such as intense emotions, situations, and actions [16].  Even though cortisol is normally released in response to bad things happening, it can also be released in response to things that aren't normally seen as bad, like flirting, mating, and hunting [17, 18].  People who felt more "personal growth" and "purpose in life" had lower and more stable amounts of cortisol in their saliva.

Adrenaline

The adrenal glands produce epinephrine, which is both a hormone and a neurotransmitter.  Adrenaline is an important part of the fight-or-flight reaction of the sympathetic nervous system. It is released when the body is stressed, working out, or scared.  Most of the time, an animal can either fight back or run away as fast as it can when it feels threatened.  When someone is scared, their brain sends messages to their kidneys, which then release a lot of adrenalin into the bloodstream.  This speeds up the heartbeat and breathing to get ready for what's coming next. Urine adrenaline levels are a good indicator of how happy someone is, according to research.  People who felt more "personal growth" and "purpose in life" had lower and more stable amounts of adrenaline in their urine.  Epinephrine is used to treat serious allergic reactions (anaphylactic), asthma attacks, and to raise a dog or cat's blood pressure.

CONCLUSION

Happiness hormones are a key sign of well-being because they make us feel good, reduce stress, and make more of them.  These hormones are released when you do something good and normal, and when you enjoy something, like brushing your teeth, it can speed up their release even more.  So, research on the health of farm animals should focus more on ways to improve management so that these hormones are released, which makes the animals feel better and better able to handle stress. Happiness is deeply rooted in the brain's neurochemical processes, where neurotransmitters such as dopamine, serotonin, oxytocin, endorphins, cortisol, and adrenaline play a crucial role in regulating emotions, social interactions, and stress responses. The release of these "happy hormones" not only influences human well-being but also serves as an essential marker for assessing animal welfare. Positive social behaviors and affiliative interactions have emerged as reliable indicators of good welfare, highlighting the importance of environmental and management factors in maintaining a healthy neurochemical balance. By understanding and implementing strategies that enhance the natural release of these neurotransmitters, we can promote a higher quality of life for both humans and animals. Future research should continue to explore the intricate connections between neurobiology, behavior, and welfare to develop effective interventions for improving overall well-being.

CONFLICT OF INTEREST:

Regarding this investigation, the authors have no conflicts of interest.

ACKNOWLEDGMENTS:

For the literature review, the authors are grateful to the Rajarshi Shahu College of Pharmacy Library in Buldana.

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