Immunocytochemical demonstration of peptidergic cells in the pond snail Lymnaea stagnalis with an antiserum to the molluscan cardioactive tetrapeptide FMRF-amide.

With an antiserum to the molluscan cardioactive tetrapeptide FMRF-amide immunoreactive perikarya and nerve fibers were identified in the central and peripheral nervous system of the pond snail Lymnaea stagnalis. Their localization is described. The same antiserum yielded reactive product in particular cells of the epithelium of the alimentary tract. The use of two different fixatives, glutaraldehyde, and a mixture of glutaraldehyde, picric acid, and acetic acid (GPA) showed that certain nerve cells can be identified only in material fixed with either the one or the other of these two fixatives, a result which indicates that in Lymnaea more than one FMRF-amide-like substances may occur. "Positive" axon endings were found in the periphery of various nerves, i.e., in places where neurohormones are released into the blood. Other fibers were found to end, probably synaptically, on other neurons, on epithelial cells in the stomach, and between muscle cells in various parts of the body, e.g., in the heart. In these cases the FMRF-amide-like substance may function as a neurotransmitter or a neuromodulator.