Neurotransmitters in the brain By Joon Kim

Neurotransmitters  A neurotransmitter is a specialized messenger chemical that transfers or sends information from one type of cell to another.  Scientists have managed to identify over 100 neurotransmitters in the human brain alone  Major neurotransmitters: GABA - (gamma-aminobutyric acid) is an inhibitory neurotransmitter, contributes to motor control, vision, and many other cortical functions. It also regulates anxiety.  Serotonin – contributes to various functions, such as regulating body temperature, sleep, mood, appetite and pain.  Acetylcholine - is an excitatory neurotransmitter that triggers muscle contraction and stimulates the excretion of certain hormones. In the CNS, involved in wakefulness, attentiveness, anger, aggression, sexuality, and thirst, among other things.  Norepinephrine - important for attentiveness, emotions, sleeping, dreaming, and learning. Also released as hormone into the blood, causes blood vessels to contract and heart rate to increase.  Glutamate - associated with learning and memory.

Sympathetic and Parasympathetic Nervous System  The sympathetic nervous system (SNS) controls the body's responses to a perceived threat and is responsible for the "fight or flight" response. Function is to control the body’s response during perceived threat. Body response is to speed and tense up, become more alert.  The parasympathetic nervous system (PNS) controls homeostasis and the body at rest and is responsible for the body's "rest and digest" function. Function is to control the body’s response while at rest. Body response is to counterbalance the sympathetic nervous system; it restores the body to a state of calm.

Parkinson’s Disease  Parkinson’s disease is a condition in which a part of the brain becomes progressively damaged over many years.  The disease affects how the person moves, including how they speak and write.  Main Symptoms:  1) tremor  2) slowness of movement (bradykinesia)  3) muscles stiffness (rigidity)  Other symptoms include loss of balance and smell, nerve pain, erectile dysfunction, depression, anxiety, insomnia and dementia.

Causes of Parkinson’s Disease  Caused by low and falling dopamine levels.  Nerve cells in the substantia nigra produce a chemical called dopamine.  Dopamine acts as a messenger between the parts of the brain and nervous system that help control and co-ordinate body movements.  Damaged nerve cells = less dopamine.  So the part of the brain controlling movement cannot work as well as normal, causing movements to become slow and abnormal.

What causes the loss of nerve cells?  Still unknown, but believed to be a combination of genetic changes and environmental factors that may be responsible for the condition.  Genetics: mutations have been identified as increasing a person's risk of developing Parkinson's disease. Parkinson's disease can run in families as a result of faulty genes being passed to a child by their parents, however, inheriting the disease in this way is rare.  Environmental factors: Exposure to certain toxins or environmental factors may increase the risk of later Parkinson's disease, but the risk is relatively small.

Treatments  No cure  Treatment for Parkinson’s disease is aimed at restoring the levels of dopamine in your brain and controlling your symptoms.  Medicines: Three main types of medication are commonly used. These are levodopa, dopamine agonists and monoamine oxidase-B inhibitors.  Dopamine agonists act as a substitute for dopamine in the brain and have a similar but milder effect compared to levodopa. They are used to treat early Parkinson’s disease.  Monoamine oxidase-B (MAO-B) inhibitors, including selegiline and rasagiline, are another alternative to levodopa for treating early Parkinson's disease. They block the effects of a brain chemical that destroys dopamine (monoamine oxidase-B).  Surgery: Deep brain stimulation involves surgically implanting a pulse generator (similar to a heart pacemaker) into your chest wall. This is connected to one or two fine wires placed under the skin and inserted precisely into specific areas in your brain. A tiny electric current is produced from the pulse generator, which runs through the wire and stimulates the part of your brain affected by Parkinson's disease.  Other therapies: Other therapies that are important for managing and living with Parkinson’s disease include physiotherapy, speech therapy and occupational therapy.

Depression  Depression is a common mental disorder that causes people to experience depressed mood, loss of interest or pleasure, feelings of guilt or low self- worth, disturbed sleep or appetite, low energy, and poor concentration.  Causes: Depression can happen suddenly as a result of physical illness, abuse, certain medications (Accutane), unemployment, bereavement, family problems or other life-changing events.

How is depression caused?  Hippocampus (storing memories) is smaller in some people with depression than in those who've never been depressed.  Smaller hippocampus has fewer serotonin receptors.  Serotonin is a neurotransmitter which is believed to influence a variety of psychological functions such as mood.  In depression, it is likely that the transmission of serotonin is reduced or disrupted.  Unknown why the hippocampus may be smaller in some people with depression.  Some researchers say the stress hormone cortisol is produced in excess in depressed people. Believed that cortisol has a toxic or "shrinking" effect on the development of hippocampus.  Some experts say that depressed people are born with a smaller hippocampus thus inclined to suffer from depression.

Treatments for depression  Depends on severity, mild depression can be treated through exercise, help groups, talking therapy or may even improve over time.  Whereas severe depression can be treated in various ways:  Antidepressants (tablets to treat symptoms of depression)  Combination therapy (a course of antidepressants plus talking therapy)  Mental Health teams