Immunohistochemical Localization of a Gastrin-like Peptide in the Brain of an Amphibian, Xenopus Laevis Daud

The indirect immunofluorescence technique was used to demonstrate a substance reacting with gastrin antisera in the brain of Xenopus laevis. Immunoreactive material was found in two sites: (1) In the caudal hypothalamus more precisely in the nucleus infundibularis ventralis, (NIV) of the pars ventralis of the tuber cinereum, (PVTC). The fluorescent axons of the reactive parikarya of the NIV give rise to two symmetrical tracts which run rostro-ventrally and join, in the infundibular floor, the preoptico-hypophysial tract, where they form an uneven median tract coursing caudally and running along the medio-tuberal area before entering the external zone of the median eminence. (2) In the anterior preoptic area (APOA), where numerous nerve fibers and endings form a dense network near the preoptic recess. The exact origin of these terminals has not yet been determined. Control of immunohistochemical specificity shows that the labeling by gastrin antisera is suppressed by gastrin (2--17), but also by cholecystokinin (CCK) and pentagastrin (Peptavlon). These results indicate that the immunoreactive substance revealed belongs to the gastrin group and has an antigenic determinant composed of the amino acid sequence or a protion thereof common to gastrin, CCK and Peptavlon (Trp-Met-Asp-Phe). It should be emphasized that, in the brain of Xenopus laevis, both gastrin-immunoreactive sites correspond to the sites of uptake of steroid hormones (Kelley et al., 1975; Morrell et al., 1975).