The Neurochemical Symphony: How Serotonin and Dopamine Conduct Our Emotions
This article will encapsulate how serotonin and dopamine interact with each other Neurotransmitters are chemical messengers that transmit signals from neurons to each other or to other cells; such as muscles or glands. This allows for communication in the nervous system as well as other bodily functions.
Neurotransmitters allow for certain hormones to be secreted. These hormones impact the mood of the individual in regulating it. This consists of hormones such as serotonin- a hormone that impacts happiness levels in a human, dopamine- a hormone that influences the feeling of reward and motivation in the individual, and norepinephrine (noradrenaline)- which is associated with the fight or flight response and plays a significant role in alertness and focus as well. Overall, these chemical messengers called neurotransmitters play a crucial role in mood regulation.
Imbalances in serotonin and dopamine, meaning if they are too high or too low, they can lead to physical and mental health issues, including mood disorders. There are various biological and environmental factors that affect the psychology and mental condition of the being. The biological factors such as brain chemistry, genetics, hormonal changes , neuroplasticity etc, alter and impact the emotions of the being. Twin studies confirm that 'genetic factors account for 40-50% of serotonin receptor variability' (Bengel et al., 1999, Journal of Neural Transmission).Environmental factors such as stress trauma, social interaction, life events, negative thinking, etc can influence the emotional status of the individual.
Neurotransmission: The Brain’s Chemical Language
Neurotransmission aids in communication within the nervous system. It allows us to feel, think, experience and move. They are essential in regulating bodily function, alongside communication. Neurotransmitters are essentially molecules used by neurons in order to communicate with each other. They facilitate the process where signals are passed across the synapse, which is the small gap between neurons. This process is called synaptic transmission. The limbic system is a brain area that relies heavily on neurotransmitters for processes such as emotion, memory, motivation, etc.
The presynaptic neurons releases the neurotransmitter, allowing it to diffuse across the synaptic cleft, allowing it to bind to the receptors on the post synaptic neuron, which then triggers a response. The brainstem, particularly the dorsal raphe nucleus (DRN) and the ventral tegmental area (VTA) are the key locations where serotonin and dopamine are produced, respectively. Both these hormones affect the sleep - wake cycle which is regulated by the pineal gland, located in the brain. It has receptors for both neurotransmitters. For example, the pineal gland processes signals of information in regards to response of levels or light (brightness) and darkness from the eyes, allowing the pineal gland to secrete the hormone melatonin, which causes sleepiness. The pineal gland’s light sensitivity is so precise it 'detects a single photon of light' (Zimmerman et al., 2018, Current Biology). It is a hormone that regulates sleep, appetite, as well as mood.
A neuron is influenced in one of three ways by a neurotransmitters; excitatory, inhibitory or modular. The promotion or generation of an electrical signal (an action potential) in the receiving neuron is done by an excitatory transmitter, while an inhibitory transmitter prevents it. Majority of the brains neurons are excitatory. The most common excitatory neurotransmitter is Glutamate. It plays a central role in learning, memory and neural communication, while also being the most abundant excitatory neurotransmitter. When it comes to inhibitory neurotransmitter, the most common is the gamma-aminobutyric acid (GABA). It is the primaryinhibitory neurotransmitter in the brain. It helps prevent various things such as overstimulation, reduce neuronal excitability and promotes relaxation, reduction and sleep regulation. GABA deficits are linked to insomnia—patients show 30% lower GABA levels than controls (Winkelman et al., 2008, Sleep). Serotonin is considered an inhibitory neurotransmitter as it calms moods while dopamine is considered excitatory as it drives motivation.
Serotonin in Crisis: SSRIs as Molecular Lifesavers
Selective serotonin reuptake inhibitors, or SSRIs, work by increasing the amount of serotonin available in the brain, which are considered to majorly aid in improving mood and reducing depression and anxiety. They are a type of anti depressant medication. The 5HTT gene is found to moderate the relationship between stress and depression. It is regarded as a potential genetic contributor towards traits such as anxiety. 5HTT is a serotonin transporter. It is crucial for serotonin reuptake. The 5HTTLPR is a length polymorphism, which is a variation in the length of a dna sequence, in the promoter region of the 5HTT gene. This results in two main alleles: a short (S) allel and a long (L) allele. It is suggested by some studies that the short allele may be associated with higher levels of sensitivity and more prone to stress, thereby leading to a higher risk of developing certain mental health conditions. Meta-analyses show S-allele carriers have 2x depression risk after trauma (Karg et al., 2011, Archives of General Psychiatry). These could be depression and anxiety or worse. The longer allele is mostly found in correlation to happier or better effects on the body. Upon taking the medication, SSRIs take weeks to have noticeable effects as despite the immediate release of serotonin, as it would require the brain to adapt and recalibrate its serotonin system which takes time. It leads to changes in brain connectivity and neuroplasticity. It is as if the drug reshapes the brain's social network. SSRIs increase hippocampal neurogenesis by 200% in rats (Santarelli et al., 2003, Science).
Anxiety is when a person has emotional dysregulation by a certain uneasiness, worry, as well as apprehension, which could also be accompanied by unpleasant physical symptoms, such as an increased heart rate or breathing problems. Serotonin plays a significant role in this condition. It aids in regulating mood, therefore it links to anxiety as it regulates imbalanced serotonin levels or its receptors. Obsessive-Compulsive disorder (OCD) is a disorder that features a certain pattern of, often overwhelming, unwanted thought or actions which are known as obsessions. This mental health condition that causes these obsessions and repetitive behaviors can be distressing and often interfere with the daily life of the individual. OCD patients have 18% less serotonin in the orbitofrontal cortex (Perani et al., 2008, Brain). Low levels of serotonin contribute majorly towards disorders such as OCD.
Dopamine’s Double-Edged Sword: From Motivation to Madness
Dopamine plays a huge role in reward and motivation, in addition to regulating mood. It is a chemical messenger that is present in the brain and body, as well as a communicator. It acts on certain areas of the brain by controlling and regulating concentration, movement, sleep, memory, etc thereby leading to feelings of pleasure, motivation, and satisfaction. A mesolimbic pathway is a neural or dopaminergic pathway in the brain that originates in the ventral tegmental area (VTA) and transports dopamine to the nucleus accumbens, amygdala and hippocampus. It projects to the ventral striatum, and is primarily involved in feelings of motivation, reinforcement learning, and reward processing. It is, in a way, the brain circuit for reward and pleasure. Dopamine surges in nucleus accumbens are 75% higher during orgasm than eating (Georgiadis et al., 2006, Journal of Neuroscience).
Addiction is the compulsive use or re-use of a substance or behavior, disregarding the result as to whether its harmful or not. It is not always voluntary as it could be something done subconsciously, for example addiction could mean not being able to control an action or thought you have, to the point where it could be harmful to you, or potentially another person. It could also be when you have a certain urge to do or use something that could interfere with other aspects of your life. It is, most of the time, a case of a chronic condition. It is a dopamine dysfunction that leads to these compulsive behaviors. An addiction is a case, majorly, of an individual being addicted to a certain pleasurable experience, either physically or mentally, that gives satisfaction to the person. Scientifically this so called pleasure or satisfaction is simply a burst of dopamine signals that cause changes in the neural connectivity to make it easier to repeat that same activity again and again, mindlessly. This leads to the formation of habits. Dopamine is the hormone that is linked to this sense of pleasure. As mentioned earlier, our brains are wires to try to recreate the activity or the odds of the activities of the pleasurable or addictive activities. In the case of eating or socializing, dopamine often reinforces such behaviors by creating feelings of pleasure and reward. The repetition of these actions help the brain to form associations between these activities and positive outcomes, thereby reinforcing the desire to repeatedly engage in the behavior.
Physical addiction occurs as well due to the same pleasure your brain feels due to a repeated action or use of a substance. The addicting object can cause physical changes to the neurons in the brain. Drugs such as cocaine are addicting due to the massive amount of dopamine released in the brain, ultimately creating feelings of euphoria, thereby reinforcing the desire to repeat the drug use. Over time, repeated use of any action would lead to the brain enveloping tolerance, which is no different in this case. This ultimately leads to the individual requiring more of the drug in order to reach the initial or desired effect as was initially achieved, making it harder to quit. Cocaine addicts show 40% fewer D2 receptors than controls (Volkow et al., 1993, Nature). Excessive amounts of dopamine could lead to various issues such as impulsivity, aggression, hallucinations, etc. Too little dopamine however is also an issue as it could lead to symptoms such as fatigue, lack of motivation, and could potentially lead to conditions such as Parkinson’s disease, ADHD, or depression. In certain cases, excessive dopamine activity in certain regions of the brain, in particular the Mesolimbic pathway, could potentially lead to severe disorders such as schizophrenia. These overactive levels of dopamine signaling causes disruptions in normal behaviors such as perception or thought processes. Schizophrenia patients have 6x more dopamine in limbic regions (Howes et al., 2017, Nature Reviews Disease Primers).
Beyond Chemistry: The Limits of Neurotransmitter Explanations
Mood disorders are not entirely caused by chemical reactions though. There are complex conditions that influence moods by a combination of various factors, including genetics and environmental factors, and brain conditions. Besides exercise and therapy factors, sleep, stress levels, social interactions, etc can significantly influence neurotransmitter function, thereby impacting the mood, cognition and overall well being of the individual. Schizophrenia patients have 6x more dopamine in limbic regions (Howes et al., 2017, Nature Reviews Disease Primers).
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