Ultrastructural analysis of peptide-hormone release by exocytosis

The release of neuropeptides and other proteinaceous hormones by exocytosis was studied in some detail by means of tannic acid in combination with glutaraldehyde (TAGO-method). This method strongly enhances the electron density of extracellular proteins including exocytosed secretory products, and therefore facilitates visualization of the release process in qualitative and quantitative respects. This study included a variety of neurosecretory cell types in the CNS of the freshwater snail L. stagnalis, the storage and glandular lobes of the corpora cardiaca of the locust L. migratoria, and the posterior pituitary of the rat. In addition, peptide secreting cells in the anterior pituitary were examined. The cytochemical specificity of the TAGO-method as well as the significance of "frozen" contents of exocytosing secretory granules in mammotrophs and somatotrophs of the rat is discussed.