Dopamine in the lobster Homarus gammarus. I. Comparative analysis of dopamine and tyrosine hydroxylase immunoreactivities in the nervous system of the juvenile.

As a catecholamine, dopamine belongs to a class of molecules that have multiple transmitter and hormonal functions in vertebrate and invertebrate nervous systems. However, in the lobster, where many central neurons have been identified and the peripheral innervation pattern is well known, the distribution of dopamine-containing neurons has not been examined in detail. Therefore, immunocytochemical methods were used to identify neurons likely to contain dopamine and tyrosine hydroxylase in the central nervous system of the juvenile lobster Homarus gammarus. Approximately 100 neuronal somata stain for the catecholamine and/or its synthetic enzyme in the brain and ventral nerve cord. The systems of neurons labeled with dopamine and tyrosine hydroxylase antibodies have the following characteristics: 1) the two systems are nearly identical; 2) every segmental ganglion contains at least one pair of labeled neurons; 3) the positions and numbers of cell bodies labeled with each antiserum are similar in the various segmental ganglia; 4) six labeled neurons are anatomically identified; two interneurons from the brain project within the ventral cord to reach the last abdominal ganglion, two neurons from the commissural ganglia are presumably neurosecretory neurons, and two anterior unpaired medial abdominal neurons project to the hindgut muscles; and 5) no cell bodies are labeled in the stomatogastric ganglion, but fibers and terminals in the neuropil are stained. The remarkably small numbers of labeled neurons and the presence of very large labeled somata with far-reaching projections are distinctive features consistent with other modulatory aminergic systems in both vertebrates and invertebrates.