Neurotransmitters are endogenous chemical messengers that enable communication between neurons. Neurotransmitters play a fundamental role in brain function. Changes in neurotransmitter levels can affect normal brain function. Neurotransmitter deficiency can result from damage or dysfunction of nerve cells in brain regions, which can lead to degenerative brain diseases. Altered levels of acetylcholine are associated with degenerative brain diseases such as Alzheimer’s disease. Dysfunction of the GABA system is associated with different degenerative brain diseases such as epilepsy, schizophrenia and autism spectrum disorder.