Snapshot A 26-year-old female patient presents to her physician due to chronic fatigue. Upon further questioning, the patient reports that she no longer enjoys seeing her younger cousins, something that has brought her great happiness in the past. She has lost 10 pounds over the past month, which she attributes to her decreased appetite. She says that it has been very difficult for her to concentrate lately, is unable to sleep, and finds it difficult to get out of bed due to feeling "drained." (Major depressive disorder) Overview Neurotransmitters Neurotransmitter Site of Synthesis ↑ in Disease ↓ in Disease Comments Acetylcholine (ACh) Basal nucleus of Meynert Parkinson's disease Alzheimer's disease Huntington's disease Involved in learning and memory in the central nervous system (CNS) All motor neurons to skeletal muscles use ACh All preganglionic neurons use ACh at the ganglion of the parasympathetic and sympathetic system Postganglionic parasympathetic fibers use ACh Presynaptic neurons of the adrenal medulla use ACh Dopamine Ventral tegmentum Substantia Nigra pars compacta Arcuate nucleus (tubuloinfundibular pathway) Huntington's disease Schizophrenia Parkinson's disease Depression Also known as prolactin-inhibiting factor antipsychotics (dopamine antagonists) can lead to increased prolactin secretion → galactorrhea and amenorrhea Involved in movement and working memory Involved in addiction γ-Aminobutyric acid (GABA) Nucleus accumbens - Huntington's disease Anxiety Major inhibitory neurotransmitter of the brain glycine is the major inhibitory neurotransmitter in the spinal cord Benzodiazepines act on GABA receptors to enhance GABA activity Baclofen is a GABA B receptor agonist that relieves spasticity Norepinephrine (NE) Locus ceruleus Anxiety Depression Involved in mood control and sleep-wake cycle Postganglionic sympathetic fibers release NE important for maintaining blood pressure Serotonin (5-HT) Raphe nucleus - Depression Anxiety Serotonin re-uptake inhibitors (SSRIs) are effective in treating depression, anxiety disorders, obsessive compulsive disorder Serotonin syndrome secondary to high levels of sertonin (e.g., MAO inhibitor + SSRI)