Brain Chemicals: Global Projections of Ancient Aromatic Neurotransmitters

Brain chemicals are not unique to the brain. This article provides an evolutionary perspective on the function of aromatic neurotransmitters. Serotonin and catecholamines, such as noradrenaline and dopamine, are ancient chemicals known to have existed in unicellular organisms before flourishing in plants. Their function in primitive systems was intimately associated with photon capture and photosynthesis initiation. Many alkaloid drugs, including some of the most powerful hallucinogens known to man are derived from these aromatic chemicals and served as important antioxidants in plants. The loss of the ability in animals to synthesize both indoles and catechols when the plant plastids were lost created a crisis situation for survival. As a result, these two neurotransmitter chemicals participated in global systems in the humans with connections to every cell in the brain and spinal cord. The strategy of having global axonal projections coupled with the evolution of multiple receptors enabled human behavior to express its complex functions while maintaining a stable homeostatic environment over a human lifetime.