Mammalian Neuropeptide Families

Mammalian genomes contain approximately 90 genes that encode precursors of neuropeptides. Neuropeptides are small proteineous substances that are expressed and released by neurons in a regulated fashion and that mediate or modulate neuronal communication as signaling molecules. Neuropeptides can be clustered in at least 10 subfamilies according to structural features, which often related to activity for shared or related receptors. (A complete overview can be found in the online bioinformatic databases of genome and transcripts, protein structure, and brain expression.) Other proteineous signaling molecules in the nervous system which originally were discovered in other biological systems, particularly chemokines, growth factors, and peptide hormones, share the hallmarks of classical neuropeptides and may be considered to belong to the neuropeptide family as well. Chemical signaling is the fundament of communication between neural cells. Among chemical signals, neuropeptides are one particular class with distinct characteristics. Neuropeptides mediate relatively slow responses in a long-term manner and thus exert a long-lasting modulation on neural communication. These underlie adaptive processes and are evident in physiological and endocrine set points and in behavioral and cognitive responses. Neuropeptides form the most diverse class of chemical messengers. They share a common architecture that reflect their biosynthetic and secretory pathways and mode of action. The particular nature of neuropeptides also raises the question: When is a chemical messenger a neuropeptide, or what precisely is a neuropeptide? This article defines neuropeptides and enlightens the dim borders of other proteineous messengers, such as peptide hormones, growth factors, similarities and chemokines, that were originally discovered in other biological systems. Second, it overviews neuropeptide families according to shared structural and functional properties.