Immunohistochemical evidence for a neurosecretory and neurotransmitter function of CDD/ANP-immunoreactive neurons in molluscs

Abstract

Recently, our group showed (5,6,7) that cardiac hormones of the atrial natriuretic polypeptide (ANP)/cardiodilatin (CDD)-family (for review see 2) occur in myoendocrine cells of the hearts from representatives of all vertebrate classes. In the snail Helix pomatia (Gastropoda, Pulmonata), however, CDD/ANP-immunoreactivity was found exclusivly in neuroendocrine endings of the cardiac atrium while no CDD/ANP- immunoreactivity was present in cardiac myocytes (4,5). In correlation, no “specific” granules which characterize the cardiac myoendocrine system of all vertebrates (1,5,6,7) could be observed in heart muscle cells of the snail. Since furthermore, CDD/ANP-immunoreactivity was present in perikarya of the subesophageal ganglion and in nerve fibers of the intestinal nerve which supplies the heart, the cardiac hormone-like substances seem to constitute a neuroendocrine-cardiac axis in the snail Helix pomatia (4,5). In order to investigate this peculiar phylogenetic pattern in more detail we expanded our studies 1) by analyzing the exact distribution patterns of CDD/ANP-immunoreactive (-IR) neurons in the central ganglia of Helix pomatia and 2) by investigating the hearts and the central ganglia of other molluscan species, i.e., Aplysia depilans (Gastropoda, Opisthobranchia) and Sepia officinalis (Cephalopoda, Decabrachia) for the occurance of cardiac hormones. The study was carried out with Bouin-fixed paraffin-embedded tissue by means of immunohistochemistry applying several region-specific antisera against alpha-ANP (=CDD-28) and the peroxidase-antiperoxidase (PAP) technique.