Concept:

• Neurotransmitters refer to the chemical messengers in the brain. Neurotransmitters help to communicate between nerve cells. There are three types of neurotransmitters that play a vital role in depression.

1. Dopamine: It is responsible for motivation. Low levels of dopamine result in not being able to enjoy or have pleasure in activities.
2. Norepinephrine: Norepinephrine is responsible for fight and flight response. The deficiency results in depression and an excessive amount results in mania.
3. Serotonin: It also plays an important role in the body. It affects emotional processing.

Explanation:

• The deficiency of acetylcholine is associated with Alzheimer's and Parkinson's disease. Alzheimer's is characterized by dementia. Parkinson's disease is characterized by involuntary movements.
• GABA is a non-protein amino acid. It has a calming effect on the brain. The deficiency of GABA results in anxiety disorder.
• 5-HT, 5-hydroxytryptamine receptors are also known as serotonin receptors.