Immunocytochemical evidence for melanotropin- and vasopressin-like material in a cephalopod neurohemal organ

Antibodies against the peptide hormone α-melanotropin (α-MSH) and antibodies against arginine-vasopressin (AVP) recognized material in two different sorts of nerve endings of the “neurosecretory system of the vena cava” in the octopus. AVP-like immunoreactivity occurred together with neurophysin-like immunostaining in the same terminals. Among the tested antibodies against different portions of the proopiocortin molecule, including β-endorphin, corticotropin (ACTH), and the 16,000 MW fragment, only anti-α-MSH serum produced immunostaining. These observations may indicate that some of the smallest bioactive peptides of the vertebrate pituitary have persisted for long periods in evolution.