In Vivo and In Vitro Studies on Peptide Release

The discovery that many peptide hormones previously identified in endocrine glands and/or in the endocrine brain (H�kfelt et al., 1980 ) are also present in central and peripheral neurons has unexpectedly increased the list of potential messengers participating in neuronal communication. To this list we must add other newly discovered peptides first detected as endogenous ligands of brain receptors (Hughes et al., 1975 ) and peptides whose existence was initially deduced from nucleotide or amino acid sequences in genes or protein precursors studied with the powerful techniques of modern molecular biology (Nakanishi et al., 1979 ; Lenoir et al., 1985 ). In order to understand the role of this growing list of peptides in neurohumoral coding of brain function, we must not only study the ways in which they interact with classical transmitter systems and modify the behavior of their target nerve cells, but also the ways in which they are produced, stored, and released.