Mapping of octopamine-immunoreactive neurons in the central nervous system of the lobster

It has been suggested that serotonin and octopamine serve important roles in behavioral regulation in lobsters. In this paper the locations of octopamine-immunoreactive neurons were mapped in wholemount preparations of the ventral nerve cord of 4th stage lobster (Homarus americanus) larvae. Approximately 86 neurons were found, distributed as follows: brain, 12; circumesophageal ganglia, 2; subesophageal ganglion, 38; thoracic ganglia, 6 each; and 4th and 5th abdominal ganglia, 2 each. All the octopamine-immunoreactive neurons are paired and located along the midline. Of the 86 neurons, 28 were identified as neurosecretory, and 26 as intersegmental ascending thoracic, ascending abdominal, or descending interneurons. The neurosecretory system is arranged segmentally and located entirely within the thoracic and subesophageal neuromeres with extensive terminal fields of endings along 2nd thoracic and subesophageal nerve roots. This set of neurons shares the features of central and peripheral endings with 2 pairs of large serotonin-containing neurosecretory neurons found in the fifth thoracic and first abdominal ganglia. The intersegmental neurons include: (1) two cells in the brain and 2 pairs of cells in the 3rd and 4th neuromeres of the subesophageal ganglion, which project to the 6th abdominal ganglion; (2) a segmentally organized group of ascending interneurons found in the subesophageal and in all thoracic ganglia; and (3) pairs of ascending interneurons found in the 4th and 5th ganglia in the abdominal nerve cord. By means of a biochemical assay, the cell bodies of octopamine-immunoreactive neurosecretory cells in the thoracic segment of the nerve cord were found to contain 40-100 fmol of octopamine, while control neurons had none.