Dopamine in the lobster Homarus gammarus : II. Dopamine‐immunoreactive neurons and development of the nervous system

Dopamine‐immunoreactive neurons were revealed in lobster embryos, larvae, and postlarvae, and staining patterns were compared to neuronal labeling in the juvenile lobster nervous system (Cournil et al. [1994] J. Comp. Neurol. 344 :455–469). Dopamine immunoreactivity is first detected by midembryonic life in 35–40 neuroi somata located anteriorly in brain and subesophageal ganglion. When the lobsters assume a benthic life during the first postlarval stage, an average of 58 cell bodies are labeled. The acquisition of dopamine in lobster neurons is a protracted event spanning embryonic, larval, and postlarval life and finally reaching the full complement of roughly 100 neurons in juvenile stages. Some of the dopaminergic neurons previously identified in the mature nervous system, such as the paired Br cells, L cells, and mandibular cells, are labeled in embryos and persist throughout development. In contrast, other neurons stain transiently for dopamine during the developmental period, but, by the adult stage, these neurons are no longer immunoreactive. Such transiently labeled neurons project to the foregut, the thoracic dorsal muscles, the neurohormonal pericardial plexus, and the pericardial pouches. It is proposed that these neurons are alive and functioning in adult lobster but that dopamine levels have been abolished, proving that neurotransmitter status is a dynamic, changing process. © Wiley‐Liss, Inc.