HOCHBERG, R; Univ. of Massachusetts, Lowell: Immunohistochemisty and 3-D cerebral architecture in species of Asplanchna (Rotifera)

The structure of the rotifer nervous system has been historically depicted as a simple network of neurons that innervate equally simplistic sensory and motor organ systems. Until recently, very little was known about the nature of these connections or the neurotransmitters involved, especially within the cerebral ganglion. Species of Asplanchna are especially amenable to neurobiological investigation because of their large size and ease of culture. They also display a simple behavioral repertoire that can be manipulated by pharmacology and mechanical stimulation, allowing for the identification of neurons that elicit specific responses. The purpose of the current investigation was to map out the structure of the cerebral ganglion in two closely related species of Asplanchna, thereby providing a foundation for future studies that wish to investigate the physiology of rotifer nervous systems. Comparisons were made between saccate female forms of Asplanchna brightwelli and A. priodonta, two polymorphic freshwater species, using antibodies to three neurotransmitters: Serotonin, FMRFamide, and SCPb. Confocal microscopy and computer modeling permitted unprecedented views of the three-dimensional structure of each rotifer�s brain, revealing differences in the number of immunoreactive perikarya and their connections. Anti-serotonin staining provided the best insight into brain architecture, revealing 20 bilateral pairs of 5HT perikarya in A. brightwelli compared to only 3 bilateral pairs in A. priodonta. Moreover, cerebral decussations were only present in the former species, though their pathways were not easily traced. Additional differences were also present. Details of the rotifer nervous system are discussed in reference to future research on cyclomorphosis, polymorphic induction, and phylogeny.