Ontogenesis of bombesin-like immunoreactive cells in the chicken proventriculus.

The distribution and morphological behaviour of bombesin like immunoreactive cells in the proventriculus of chick embryos, newborns and adults were investigated by indirect immunoperoxidase procedure. The first immunoreactive cells appear around the 11th day of incubation. Initially few, they increase progressively to reach a peak around the 18th day. Throughout the embryonic period almost all immunoreactive cells are column-shaped, display a typical "open" behaviour, and are situated among other superficial lining epithelial cells. Around hatching time, these "open" cells suddenly decrease in number while another immunoreactive "closed" cell type becomes more evident in a deeper location. In newborns and adults, the majority of immunoreactive cells are oval shaped and are characteristically situated near the neck of lobular glands; they seem to display a "closed" behaviour. The results demonstrate two different kinds of peptide-containing cells which probably exert different functions. During the embryonic period, in fact, they resemble a chemioreceptor, but in postnatal life they appear as a paracrine/endocrine elements.