Light and transmission electron microscopic examination of the X-organ-sinus gland complex in adult Nephrops norvegicus reveals a high density of active neurosecretory axon endings (53%) abutting onto an undulatory-release surface. At least six different categories of neurosecretory granules and related vesicles have been identified on the basis of their texture, electron density, and diameter. Computer-aided three-dimensional reconstruction of N. norvegicus sinus gland defined by its fuchsinophilia on 2.5 μm serial sections shows a multilobed organ 1.25×10−2 mm3 in volume. Immunocytochemical studies were carried out using polyclonal antibodies raised against purified Astacus leptodactylus CHH (Gorgels-Kallen and Van Herp, 1981) and Homarus americanus GIH (Meusy and Soyez, 1991). Immunocytochemical localization of CHH and GIH (VIH) at the LM and EM level specifically locate the massive presence of CHH and a more superficial and scattered distribution of GIH in the axon endings. Under TEM, specificity in type and content of granules appears to be confined to single axons. Heterologous antibodies reacting with even phylogenetically distant taxa stress a conservative homology at least of some common reactive epitopes.
