IMMUNOCYTOCHEMICAL LOCALIZATION AND DEVELOPMENT OF MULTIPLE KINDS OF NEUROPEPTIDES AND NEUROENDOCRINE PROTEINS IN THE CHICK ULTIMOBRANCHIAL GLAND

The ultimobranchial gland is an endocrine organ consisting of C cell groups. In chickens, the glands are richly supplied by nerve fibers immunoreactive for neurofilaments. It was found by immunocytochemical staining that C cells of chick ultimobranchial glands showed immunoreactivities for multiple kinds of neuropeptides and neuroendocrine proteins in addition to calcitonin, i.e., calcitonin gene-related peptide (CGRP), somatostatin, neurotensin, chromogranin A, and tyrosine hydroxylase. Furthermore, enkephalin-immunoreactive cells that showed long cytoplasmic processes and large cell bodies, being distinct from the C cell feature, were detected. The densities of these cells per unit area of ultimobranchial gland were assessed using computer-assisted image analysis system; calcitonin cells were 42.9 +/- 10.0%; CGRP cells 26.9 +/- 5.6%; neurotensin cells 8.6 +/- 6.9%; somatostatin cells 3.1 +/- 1.4%; chromogranin A cells 11.8 +/- 1.8%; tyrosine hydroxylase cells 10.0 +/- 5.2%; enkephalin cells 2.9 +/- 1.3%. Dense distributions of peptidergic nerve fibers were also detected in chick ultimobranchial glands. Numerous varicose fibers immunoreactive for substance P were distributed in the close vicinity to C cell clusters and blood vessels. Enkephalin-immunoreactive fibers were also prominent around C cell clusters. Galanin-, vasoactive intestinal peptide (VIP)-, and tyrosine hydroxylase-immunoreactive fibers were distributed around blood vessels only. Subsequently, the ontogeny of these neuropeptides, neuroendocrine proteins, and peptidergic innervations was examined in chickens at various developmental stages. In 10-day-old embryos, weak to moderately intense immunoreactivity for calcitonin was already present in almost all C cells. Immunoreactivities for somatostatin, CGRP, and tyrosine hydroxylase began to appear at this age. At 12 days of incubation, substance P-immunoreactive fibers were first detected in the parenchyma of ultimobranchial glands. Considerable numbers of enkephalin-immunoreactive fibers and cells were also observed. At 14 days of incubation, the largest populations of somatostatin- and enkephalin-immunoreactive cells were attained; the densities of somatostatin- and enkephalin-immunoreactive cells per unit area were 21.2 +/- 3.2% and 12.9 +/- 3.1%, respectively. Substance P-immunoreactive fibers became numerous throughout the gland at this age. Thereafter, calcitonin-, CGRP-, tyrosine hydroxylase-immunoreactive cells progressively increased in number with embryonic age, whereas somatostatin- and enkephalin-immunoreactive cells started to decrease. Chromogranin A- and neurotensin-immunoreactive cells began to appear at 16 days and 18 days of incubation, respectively. Galanin-, VIP-, and tyrosine hydroxylase-immunoreactive fibers were inconspicuous during embryonic life.