Abstract
Ontogeny of various kinds of neuropeptides such as cholecystokinin-8-like (CCKI), leucine-enkephalin-like (ENKI), neurotensin-like (NTI), substance P-like (SPI) and somatostatin-like immunoreactive (SOMI) structures was examined in the rat brain using immunocytochemistry. The prenatal early appearance of immunoreactive structures in the brain is a common feature in the development of the peptidergic system. However, the developing patterns of peptides vary according to the peptides themselves, among individual peptides depending on the regions. The early appearance of peptides in the fetus brain suggests the role of peptides in the development of the brain in addition to their neuromodulator role.