CAIN, Shaun D.*; CHRISTIE, Andrew E.; Univ. of Washington, FHL; Univ. of Washington, FHL: Distribution of NOS-like immunoreactivity within the Nudibranchia

Within the invertebrates, the gaseous neurotransmitter nitric oxide (NO) has been shown to mediate a variety of behavioral pathways. Although there is evidence that NO functions in some sensory systems, the majority of studies have linked NO signaling to motor patterns governing feeding or locomotion. Indeed, most of the pathways in which NO has been implicated, including non-motor pathways, involve rhythmically active neurons or neuronal circuits. The primary effect of NO within these cells and circuits is to modulate the output of the system, thereby changing the duration or frequency of the rhythm or the phase relationship of the neural components underlying the rhythm or oscillations. Previously, attempts were made to identify the distribution patterns of NO producing neurons in a number of molluscan species (Moroz and Gillette, 1995). This and subsequent work has shown variability in the number and location of NO producing cells throughout the nervous system that correlated with habitat and/or feeding characteristics. In this study we investigated the distribution of putative NO producing cells in 13 species of nudibranchs representing all 4 suborders (Arminacea, Doridacea, Dendronotacea, and Aeolidacea) of this molluscan group. Using a universal NOS antibody, we found that the number and locations of immunopositive cells varied greatly across this monophyletic group. Interestingly, one set of apparently homologous neurons consistently labeled within the pleural ganglia in all 13 species investigated. Our results suggest that, with the exception of this one group of neurons (whose location suggest that they function in either feeding or locomotion), the use of NO as a neurotransmitter/neuromodulator can change rapidly within a closely related group of species.