ONTOGENIC ALTERATION IN PEPTIDERGIC EXPRESSION WITHIN A STABLE NEURONAL POPULATION IN LOBSTER STOMATOGASTRIC NERVOUS-SYSTEM

In the adult lobster, Homarus gammarus, the stomatogastric ganglion (S TG) contains two well-defined motor pattern generating networks that r eceive numerous modulatory peptidergic inputs from anterior ganglia. W e are studying the appearance of extrinsic peptidergic inputs to these networks during ontogenesis. Neuron counts indicate that as early as 20% of development (E20) the STG neuronal population is quantitatively established. By using immunocytochemical detection of 5-bromo-2'-deox yuridine incorporation, we found no immunopositive cells in the STG by E70. We concluded that the STG neuronal population remains quantitati vely stable from mid-embryonic life until adulthood. We then investiga ted the ontogeny of FLRFamide- and proctolin-like peptides in the stom atogastric nervous system, from their first appearance until adulthood by using whole mount immunocytochemistry. Numerous FLRFamide-like-imm unoreactive STG neuropilar ramifications were observable as early as E 45 and remain thereafter. From E50 to the first larval stage, one to t hree STG somata stained, while somatic staining was not observed in la rval stage II and subsequent stages. From E50 and thereafter, the STG neuropilar area was immunopositive for proctolin. One to two proctolin ergic somata were detected in the STG of the three larval stages but w ere not seen in embryos, the post-larval stage or in adults. Thus, pep tidergic inputs to the STG are present from mid-embryonic life. Moreov er, whereas in the adult, STG neurons only contain glutamate or acetyl choline, some neurons transiently express peptidergic phenotypes durin g development. Although this system expresses an ontogenetic peptiderg ic plasticity, the STG neurons produce a single stable embryonic-larva l motor output (Casasnovas and Meyrand [1995] J. Neurosci. 15:5703-571 8). (C) 1998 Wiley-Liss, Inc.