What Are Serotonin, Dopamine and Norepinephrine? A Brief Introduction to Neurotransmitters
Brain neurotransmitters are chemical substances that transmit signals between nerve cells. They not only influence our thinking, emotions and behaviour, but are also closely linked to many psychiatric disorders. In this article, I will briefly introduce several major brain neurotransmitters, including their functions, mechanisms of action, and associations with mental health. Understanding these substances helps us gain deeper insight into how the brain works and provides a scientific foundation for treatment.
What Are Neurotransmitters?
Neurotransmitters are chemical molecules released by brain neurons to transmit signals across the synapse. When a neuron is stimulated, it releases neurotransmitters into the synaptic cleft; these substances then bind to receptors on the neighbouring neuron, triggering the continuation of the electrical signal. This process is like the brain’s “communication system,” sustaining our cognition, emotional regulation and physiological functions. If the levels of these substances are too high, too low, or if their function is abnormal, it may lead to mood disorders, anxiety, depression or other mental health problems. Common neurotransmitters include dopamine, serotonin, norepinephrine, acetylcholine, GABA and glutamate. These will be introduced one by one below.
Dopamine: The Engine of Motivation, Reward and FocusDopamine is the core substance in the brain’s “reward system” circuits. It regulates motivation and the experience of pleasure, while also modulating motor coordination, attention and executive function. For example, when we achieve a goal or complete a task, the release of dopamine produces a sense of satisfaction, making us feel happy and motivated.
Imbalances in dopamine are commonly seen in various conditions:
Excessively high: May contribute to schizophrenia, in which patients experience hallucinations or delusions because excessive dopamine over-stimulates the brain’s “filtering system.”
Excessively low: Linked to the motor symptoms of Parkinson’s disease. In addition, lack of motivation in depression and attentional difficulties in ADHD are also associated with insufficient activity in the dopamine system.
Serotonin: The Stabiliser of MoodSerotonin, also known as 5-hydroxytryptamine (5-HT), primarily regulates mood, appetite, sleep and cognitive function. It brings a sense of calm, contentment and stability, and helps modulate anxiety and stress responses. Serotonin is also involved in the gut-brain axis; approximately 90% of the body’s serotonin is actually produced in the gut, which helps explain why gut health can affect mood.Low serotonin function is considered one of the core pathophysiological features of depression, anxiety disorders (especially generalised anxiety disorder and obsessive-compulsive disorder), and post-traumatic stress disorder. Many antidepressant medications (such as SSRIs / selective serotonin reuptake inhibitors) work by increasing the concentration of serotonin in the synaptic cleft.
Norepinephrine: The Mediator of Alertness, Focus and StressNorepinephrine is mainly responsible for alertness, concentration of attention and the stress response. It forms part of the “fight-or-flight” reaction, helping us respond rapidly in dangerous situations.
AcetylcholineAcetylcholine is primarily released in the basal forebrain and is involved in learning, memory and muscle control. In the hippocampus it helps form new memories, and in the peripheral nervous system it controls heart rate and digestion.Deficiency of acetylcholine is commonly seen in Alzheimer’s disease, where patients experience progressive memory decline due to degeneration of cholinergic neurons. Medications used in dementia mainly inhibit the enzyme that breaks down acetylcholine, thereby prolonging its action.
GABA (Gamma-Aminobutyric Acid)GABA is the brain’s main inhibitory neurotransmitter. It helps slow down neural activity, promoting relaxation and sleep. It functions like the brain’s “brake system,” preventing over-excitation. Insufficient GABA function or reduced receptor sensitivity is associated with generalised anxiety disorder, panic disorder and related conditions. Common sedative-hypnotic medications and alcohol produce their effects by enhancing the action of GABA.
GlutamateGlutamate is an important “excitatory” neurotransmitter in the brain, involved in learning, memory and neuroplasticity. Excessive glutamate can lead to neurotoxicity and neuronal damage, and may be linked to schizophrenia. Insufficient levels may impair cognitive function.
Other Related SubstancesIn addition to the major neurotransmitters above, there are substances such as endorphins (the body’s natural “feel-good” hormones) and oxytocin (which promotes social bonding and trust). Although these are not strictly classified as neurotransmitters in all contexts, they are closely related to emotion.
Conclusion: The Key Is Maintaining Balance
Understanding these chemical messengers of the brain helps us view mental distress through a more scientific and less judgmental lens. It demonstrates that symptoms have a real biological basis and are not simply the result of “weak willpower” or a “fragile personality.” This understanding is the first step towards reducing stigma and opening the door to effective treatment.
If you or someone close to you is going through an emotional storm, please remember that it may reflect a temporary loss of harmony in the brain’s chemical dialogue. With appropriate intervention, it is possible to help the brain regain its chemical balance and rhythm.
Written by: Specialist in Psychiatry, Dr. Dennis Cheung
