HOCHBERG, R; Univ. of Massachusetts, Lowell: Immunohistochemistry and 3-D reconstruction of the cerebral ganglion in the rotifer Asplanchna brightwelli

The basic organization of the rotifer nervous system has been known for over a century, while recent ultrastructural and behavioral observations have provided valuable insights into its fine structure and function. The freshwater carnivorous rotifer, Asplanchna brightwelli, is a well-known model for the study of cyclomorphosis and cyclical parthenogenesis, but as of yet, few details exist on its neurobiology. To gain insight into the structure of its nervous system, and provide a foundation for future research, the cerebral ganglion was studied with immunohistochemistry, CLSM, and computer modeling. Immunoreactivity to serotonin, FMRFamide, SCPb, and alpha- and beta-tubulin revealed numerous connections within the brain and between the brain and other organ systems. Anti-5HT was especially useful in delineating intracerebral connections and connections to presumed sensory structures in the apical field and trunk region. Approximately 20 pairs of serotoninergic perikarya and their axonal extensions were all symmetrically arranged within the cerebral ganglion � a distinct fibrous neuropil was absent. Decussations, or the crossing of axons at the body midline, were prevalent within the cerebral ganglion and formed pathways to regions in the corona and trunk. Early stage juveniles, still retained within the adult pseudocoelom, also showed significant immunoreactivity in the cerebral ganglion and displayed a similar pattern of connections within the brain as the adults. The utility of neuroanatomical characters derived by CLSM and immunohistochemistry is discussed in reference to the future of rotifer research.