Sequential developmental acquisition of neuromodulatory inputs to a central pattern-generating network

The activity of the adult stomatogastric ganglion (STG) depends on a large number of aminergic and peptidergic modulatory inputs. Our aim is to unders tand the role of these modulatory inputs in the development of the central pattern-generating networks of the STG. Therefore, we analyze the developme ntal and adult expressions of three neuropeptides in the stomatogastric ner vous system of the lobsters Homarus americanus and Homarus gammarus by usin g wholemount immunocytochemistry and confocal microscopy. In adults, red pi gment concentrating hormone (RPCH)-like, proctolin-like, and a tachykinin-l ike immunoreactivity are present in axonal projections to the STG. At 50% o f embryonic development (E50), all three peptides stain the commissural gan glia and brain, but only RPCH- and proctolin-like immunoreactivities stain axonal arbors in the STG. Tachykinin-like immunoreactivity is not apparent in the STG until larval stage II (LII). The RPCH-immunoreactive projection to the STG consists of two pairs of fibers. One pair stains for RPCH immuno reactivity at E50; the second RPCH-immunoreactive pair does not stain until about LII. One pair of the RPCH fibers double labels for tachykinin-like i mmunoreactivity. The adult complement of neuromodulatory inputs is not full y expressed until close to the developmental time at which major changes in the STG motor patterns occur, suggesting that neuromodulators play a role in the tuning of the central pattern generators during development. (C) 199 9 Wiley-Liss, Inc.