Neuroendocrine glands that synthesize and secrete peptide hormones regulate the levels of these peptide messengers during development. In this article we describe a mechanism for regulating neuropeptide levels in the corpora cardiaca of the locust Schistocerca gregaria, a neuroendocrine gland structurally analogous to the vertebrate adenohypophysis. A set of five colocalized peptide hormones of the adipokinetic hormone family is synthesized in intrinsic neurosecretory cells in the corpora cardiaca. During postembryonic development there are progressive changes in the absolute and relative levels of these five peptide hormones. We show that the ability of the gland to increase peptide synthesis is due to a 100-fold increase in the number of cells which make up the gland. The gland grows by the addition of new cells derived from symmetrical division of undifferentiated precursor cells within the corpora cardiaca. We show, using double-label immunocytochemistry, that cells born in the glandular lobe mature into cells that express adipokinetic hormone peptides. The pattern of cell birth and peptide expression can account for the dramatic increase in postembryonic peptide levels.
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1993
