Correlation of axon frojections anct peptide immunoreactivity in mesocerebral neurons of the snail helix aspersa

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Abstract
The purpose of this investigation was to elucidate the organization of efferent neurons in the mesocerebrum of a terrestrial snail. The mesocerebrum is one of three regions, or lobes, that can be identified by gross inspection. Previous studies have indicated a possible function for the mesocerebrum in the control of mating behavior. We used both anterograde and retrograde tracing methods to determine the axon projections of mesocerebral neurons. Virtually all the neurons (96%) send an axon into the cerebropedal connective nerve, and about 25% of these fibers continue into the nervus cutaneus pedalis primus dexter, which innervates the dart sac. Many neurons have additional axon branches in other perves, especially the penial nerve, which receives projections from about 25% of mesocerebral cells. Neurons that are backfilled from the nervus cutaneus pedalis primus dexter are predominately immunoreactive for FMRFamide, whereas neurons that are backfilled from the penial nerve are predominately immunoreactive for APGWamide. These results suggest a functional association between FMRFamide and dart shooting on the one hand, and between APGWamide and penial eversion on the other. Some cells contain both APGWamide and FMRFamide; these cells, may have dual projections in both the penial nerve and the nervus cutaneus pedalis primus dexter.

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