Synaptic clefts are made to be crossed: Neurotransmitter signaling in the central nervous system

The primary means of communication between neurons in the mammalian central nervous system (CNS) is via release of chemical transmitters. Although the first transmitters to be discovered were the biogenic amines, such as acet ylcholine and norepinephrine, involved in transmission in the autonomic ner vous system, the contribution of other types of transmitters, such as amino acids and peptides, to CNS transmission has been the subject of recent stu dy. Part of this interest stems from the relatively large percentage of neu ronal connections that make use of amino acid transmitters such as gamma-am inobutyric acid and glutamate and also from the tremendous diversity possib le when peptides are used as transmitters. Several disorders of CNS transmi ssion are related to the degeneration of neuronal pathways in the brain. Tw o of the most prevalent neurologic disorders that result from degeneration are Alzheimer's and Parkinson's diseases. Aspects of these disorders relate d to chemical neurotransmission are discussed, along with implications with regard to therapeutic strategies. Functions of and possible abnormalities in amino acid transmission that may be associated with CNS disorders are ex amined. Several peptides are postulated to play a role in neurotransmission and concepts regarding the significance of the coexistence and release of biogenic amines and peptides at the same neuronal terminals are presented.