Dopamine

Dopamine is a chemical compound that functions as a neurotransmitter in humans.  It is also a key factor in the development of Parkinson's Disease.

Degeneration of dopamine receptors in the brain can lead to muscle tremors associated with Parkinson's Disease.
Several other diseases of the nervous system are associated with dysfunctions this neurotransmitter for example schizophrenia and attention deficit hyperactivity disorder.

Dopamine itself can be used as a medication in smaller doses to treat ADHD and heart failure/shock in newborn babies.

Dopamine is mainly synthesised in neurones and cells in the medulla of the adrenal glands.