DEVELOPMENTAL EXPRESSION OF NEURONAL AND ENDOCRINE MARKERS IN THE PARATHYROID-GLANDS OF THE RAT

The parathyroid glands of the adult rat harbor a number of neuroendocr ine markers, biologically active peptides and ''classical'' neuromesse ngers in addition to parathyroid hormone (PTH). Their appearance durin g parathyroid development is, however, not known. In the present study we have examined several neuroendocrine markers and neuromessengers i n the parathyroid glands of the developing rat [embryonic stage 21(E21 ), newborn, 1, 2, 3, 4 week old, and adult rats] using immuno-cytochem istry. Chromogranin A- and PTH-mRNA were also examined by in situ hybr idization and the mRNA levels were quantitated by computerized image a nalysis. Protein gene product 9.5- and synaptophysin-containing nerve fibers appeared already before birth and then gradually increased in n umber postnatally, and at the age of 4 weeks the nerve fibers were mod erate in number to numerous. Nerve fibers containing calcitonin gene-r elated peptide, neuropeptide Y and vasoactive intestinal polypeptide a lso increased gradually in number, while galanin- , substance P- and t yrosine hydroxylase-containing fibers remained few throughout developm ent. The glandular cells expressed chromogranin A, pancreastatin and P TH already before birth. The levels of chromogranin A-and PTH-mRNA wer e low at E21 and increased markedly at birth; chromogranin A mRNA leve ls had increased even more at 1 week postnatally. Three to 4 weeks aft er birth the levels of PTH- and chromogranin A mRNA again increased, t hen stabilized at a slightly lower level in the adult rat. Our finding s demonstrate that the parathyroid glands of rat are already innervate d and express PTH and chromogranin A before birth and that the density of peptide-containing nerve fibers changes during development. The st epwise increases of PTH- and chromogranin A mRNAs during development i ndicate marked changes in parathyroid activity occurring at birth and at weaning.