There are many physical effects of our mental health. Neurotransmitters play a huge role in mental and cognitive functions. A lot of people separate mental and physical health issues, and mental health still carries a lot of stigma.
“It’s all in your head!”
Except, that doesn’t make it any less real. Mental health problems are real, important and worthy of the same consideration. Neurotransmitters affect nearly all parts of the body in some fashion, which means that mental health issues do have physical effects.
The full relationship is unclear, whether changes in brain chemistry cause the symptoms and behavioural changes. Or the symptoms and behavioural changes cause the changes in brain chemistry.
Neurotransmitters are chemical messengers that cross the synapses and bind to receptors to send messages between the neurons and end organs. They either stimulate or inhibit depending on the receptor type. This subject is complex, so we’re going to fous on the important neurotransmitters that matter the most in mental health disorders.
Serotonin
A very important neurotransmitter, serotonin is known as 5-hydroxytryptamine or 5-HT. It is a monoamine neurotransmitter produced by the gastrointestinal tract. Enterochromaffin cells release serotonin, which is synthesised from tryptophan in dietary proteins.
Serotonin regulates mood, cognition, reward, learning, memory and sleep. It also regulates the digestive system, including appetite, vomiting and other digestive processes. It also acts on the blood vessels to manage blood pressure.
Excessive levels of serotonin result in serotonin syndrome, a serious and potentially life-threatening condition. Overdose or certain combinations of drugs put a patient at risk of serotonin syndrome. For example, combining an SSRI (Selective serotonin reuptake inhibitor) and an MAOI (Monoamine oxidase inhibitor) together. However, serotonin receptors make up important targets for all kinds of pharmaceuticals, including but not limited to mood disorders, anti-emetics (stop vomiting/nausea) and migraine treatments.
Dopamine
Known as the ‘pleasure chemical’, dopamine plays many roles in the body. It is a catecholamine neurotransmitter produced in the brain. There are many dopamine pathways, the most important and well known being the ‘reward-motivated behaviour’.
Anticipation of a reward increases dopamine levels, as do pleasurable experiences. Dopamine plays a role in motor control and managing the release of a number of hormones. Addictive drugs affect dopamine levels and reinforce the cravings and addiction.
Parkinson’s disease involves the loss of dopamine producing cells in the brain, causing the symptoms of the disease. Dopamine plays important roles in schizophrenia and ADHD as well.
Dopamine acts as a stimulant to treat low blood pressure, slow heart rates and cardiac arrest, especially useful in newborns. Amphetamines increase dopamine levels in the brain, hence their use in treatment of ADHD, which improves quality of life for lots of people.
Norepinephrine
You may know this one as ‘noradrenaline’, both terms are correct but norepinephrine is the general international standard. It is a catecholamine with endocrine (hormone) functions as well. It plays a role in the ‘fight or flight’ response by increasing alertness, vigilance, enchancing memory functions and focusing attention.
Adrenergic receptors respond to norepinephrine and are a common target for medications. Stimulants increase the amount of norepinephrine. Serotonin-norepinephrine reuptake inhibitors (SNRIs) and amphetamines fit into this category. Antagonistic drugs include beta-blockers which are prescribed to manage anxiety by reducing the heart-rate.
Stress and anxiety, both acute and chronic, increase the levels of norepinephrine alongside other signalling molecules like epinephrine (adrenaline) and cortisol. Norepinephrine function may also play a role in ADHD. Lack of REM sleep increases norepinephrine secretion and leads to degeneration of the nervous system.
GABA
Gamma-aminobutyric acid, the chief inhibitory neurotransmitter in adult mammalian central nervous systems. Growing animals require it for brain development. The pancreatic beta-islet cells produce GABA to inhibit glucagon secretion.
Many drugs target GABA receptors, including most commonly used anaesthetic drugs like propofol and barbiturates. GABA analogues like pregabalin and gabapentin have anti-convulsant effects and pain management functions.
Glutamate
Glutamic acid, an amino acid that humans can produce in the body. This means it’s not an essential amino acid. GABA synthesis uses glutamate as a precursor. It plays a role in learning and memory functions.
Ketamine modulates glutamate and has proven beneficial in treating depression, especially treatment-resistant depression.
Glutamate and its salts are a flavour enhancing compound, found in many foods. It gives an umami, or savoury, flavour in foods. A well-known example, monosodium glutamate (MSG) was unfairly maligned in the past.
MSG naturally occurs in fermented or aged foods like soy sauce, fermented bean paste such as miso, and cheese. MSG is also an additive used in food production. The controversy around it is based in racism against East Asian people. You can eat it, it’s safe.
Acetylcholine
An important neurotransmitter, acetylcholine is an ester of acetic acid and choline, the body parts that it affects are called cholinergic. Acetylcholine activates the muscles via the motor neurons, as well as a vital role in the autonomic nervous system. Especially the parasympathetic nervous system.
In the brain, it is involved in arousal, attention, memory and motivation. Toxins from plants, animals and bacteria act on cholinergic receptors to deactivate or hyperactivate them, causing paralysis.
Atropine acts on muscarinic cholinergic receptors to treat heart and eye conditions, but excessive doses are toxic. Nicotine acts on nicotinic cholinergic receptors in the brain, which is why nicotine is so powerfully addictive.
Myasthenia gravis is an autoimmune disorder where antibodies against the acetylcholine receptors cause muscle weakness and fatigue, which is often progressive. In addition, acetylcholine is involved in cognitive decline, Alzheimer’s disease and may also play a role in mood disorders, schizophrenia and ADHD.
Conclusion
This summary of neurotransmitters will help as we discuss common mental health disorders and the impact they have on the body. All of these chemical messengers facilitate physical and physiological effects on us.
We need to discuss mental health more often, reduce the stigma around it and educate people. It’s important, yet often subject to misunderstanding and willful ignorance. Come back next week when we will discuss depression. Thanks for reading! Here’s a short summary of these neurotransmitters and their effects.
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