Gangliogenesis in the prosobranch gastropod Ilyanassa obsoleta

Abstract

We determined that the larval nervous system of Ilyanassa obsoleta contains paired cerebral, pleural, pedal, buccal and intestinal ganglia and unpaired apical, osphradial, and visceral ganglia. We used a modified form of NADPH diaphorase histochemistry to compare the neuroanatomy of precompetent (including specimens 6, 8, and 12 days after hatching), competent, and metamorphosing larvae with postmetamorphic juveniles. This method highlighted ganglionic neuropils and allowed us to identify individual ganglia at various stages of development, thereby laying a foundation for concurrent histochemical studies. The first ganglia to form were the unpaired apical and osphradial ganglia and the paired cerebral and pedal ganglia. In larvae 6 days after hatching, the neuropil had already appeared in the apical and osphradial ganglia. Neuropil began to be apparent in the cerebral and pedal ganglia 2 days later. At that time, the pleural and buccal ganglia were identifiable and adjacent to the posterior edge of the cerebral ganglia. The ganglia of the visceral loop were concurrently recognizable, although the supraintestinal ganglion developed slightly earlier than the subintestinal and visceral ganglia. By 12 days after hatching all of the major adult ganglia were discernible. The apical ganglion was retained by newly metamorphosed juveniles, but not by juveniles 2 days later. After metamorphosis was complete, the central nervous system (CNS) was consolidated into its juvenile form with ipsilateral cerebral and pleural ganglia being partially fused. The metamorphic translocation of ganglia, which included a caudal relocation of the cerebrals and the migration of the buccals from above the esophagus to a position below it, correlated with the movement of the proboscis to the dorsal part of the head.

Neural control of the velum in larvae of the gastropod,Ilyanassa obsoleta

“…Furthermore, the larval nervous system of I. obsoleta probably contains other transmitters, [as suggested by Dickinson and Croll (Dickinson and Croll, 2003)], which potentially mediate additional controls over velar effectors than those examined in this initial survey. Nonetheless, the present paper, together with previous detailed studies of larval neuroanatomy (Dickinson and Croll, 2003;Lin and Leise, 1996) demonstrate that I. obsoleta may prove to be a valuable system for basic understanding of how neurons regulate behaviours in such planktotropic larvae. [But see for preliminary results (Pires and Penniman, 2003) using another model species, Crepidula fornicata].…”

NADPH-Diaphorase activity changes during gangliogenesis and metamorphosis in the gastropod molluscIlyanassa obsoleta

“…NADPHd staining was significantly reduced in most ganglia of metamorphosing larvae and in the apical ganglion of young juveniles. This ganglion is lost in advanced juveniles (Lin and Leise, 1996). Whether this occurs by apoptotic or necrotic cell death related to NO release or by the translocation of these cells into other ganglia is unknown.…”

“…Larval culture methods and specimen preparation were described in the preceding paper (Lin and Leise, 1996). NADPHd histochemistry was performed as follows: anesthetized, whole larval or juvenile Ilyanassa obsoleta were fixed at 4°C for 1.5 hours in chilled 4% paraformaldehyde in 0.1 M phosphate buffer solution (PBS) at pH 7.6 and then rinsed once with 0.5 M PBS (Eloffson et al, 1993 and K. Lukowiak, personal communication).…”

“…No antemedium such as acetone was used to dissolve the plastic resin. Embedding, sectioning, and photographic procedures were as previously described (Lin and Leise, 1996).…”

Serotonin Injections Induce Metamorphosis in Larvae of the Gastropod Mollusc Ilyanassa obsoleta

“…This site was just lateral to the brain and avoided direct injection into ganglionic neuropils (Fig. 1) (Lin, 1995). Glass micropipettes were pulled on a Flaming/Brown Model P-87 automatic puller (Sutter Instruments).…”