Comparative immunohistochemistry of the cerebral ganglion in Gastrotricha: an analysis of FMRFamide-like immunoreactivity in Neodasys cirritus (Chaetonotida), Xenodasys riedli and Turbanella cf. hyalina (Macrodasyida)

Abstract

The neuropeptide FMRFamide (Phe-Met-ArgPhe-NH 2 ) is part of a large and diverse family of peptidergic neurotransmitters present throughout the animal kingdom. To date, no such neuropeptides have been demonstrated in gastrotrichs despite their presence in closely related invertebrates such as nematodes. Here, the FMRFamidergic nervous system of three marine gastrotrichs is investigated with immunoXuorescence, CLSM, and 3D computer imaging to gain insight into structure of the cerebral ganglion and test various phylogenetic hypotheses on its organization. Results reveal that FMRFamide-like immunoreactivity (IR) is present throughout the nervous systems of three species: Neodasys cirritus (Chaetonotida), Xenodasys riedli and Turbanella cf. hyalina (Macrodasyida). Both macrodasyidans possess FMRFamide-like IR in the central, peripheral-and stomatogastric-nervous systems, while FMRFamide-like IR is restricted to the CNS in N. cirritus. In all three species, the cerebral ganglion is dumbbell-shaped and bordered bilaterally by cerebral perikarya: numerous perikarya are present in X. riedli and N. cirritus, while few perikarya are present in T. cf. hyalina. Cerebral perikarya Xank the nerve ring neuropil, which contains IR Wbers in the supra-and subpharyngeal commissures of both macrodasyidans, but in N. cirritus, only contains IR Wbers in the suprapharyngeal commissure. Together, these results conWrm the peripharyngeal nature of the gastrotrich cerebral ganglion, but are equivocal on hypotheses of its tripartite structure. Still, the neural organization of gastrotrichs, in particular, the architecture of the cerebral ganglion, is expected to hold valuable information for future assessments of gastrotrich phylogeny, and may yet provide key insights into the evolution of this enigmatic taxon.

The nervous system of Neodasys chaetonotoideus (Gastrotricha: Neodasys) revealed by combining confocal laserscanning and transmission electron microscopy: evolutionary comparison of neuroanatomy within the Gastrotricha and basal Protostomia

“…The only published data based on the IHC of the nervous system of a species of Neodasys are from N. cirritus on RFamide-like IR (Hochberg 2007b). Our results confirm these previous findings in general.…”

“…In addition, some (weak) IR soma-like structures could be found associated with the posterior longitudinal fibres (Fig. 7b), as shown by Hochberg (2007b) in Neodasys cirritus. Comparable structures could be found only in freshly prepared material (storage under 1 week) from samples of sediment enriched with detritus.…”

“…Hochberg 2007b) yielded a hypothesis on the construction of the common ancestor's nervous system in Gastrotricha. According to Rothe and Schmidt-Rhaesa (2009), the gastrotrich stem species might have possessed a bilateralsymmetric brain with somata of neurons arranged laterally on both sides of the strong dorsal commissure.…”

“…There is an additional, but fine, ventral commissure and a pair of ventral longitudinal neurite bundles that span the whole trunk and fuse posteriorly. Although there already exists a reconstruction of the RFamide-like immunoreactive components in the central nervous system of one species of the marine gastrotrich taxon Neodasys cirritus Evans, 1992 (Hochberg 2007b), we here describe the neuroanatomy of a second species of that taxon, Neodasys chaetonotoideus Remane, 1927. The taxon Neodasys is of important phylogenetic value (see e.g.…”

“…As demonstrated in a recent study dealing with the reproductive system of Gastrotricha, the newly obtained data on N. chaetonotoideus had been obligatory for the evolutionary inferences drawn by a parsimonious character optimization (Kieneke et al 2009). Since the only data of the nervous system of Neodasys by means of immunohistochemistry comprises the RFamide-like components in the brain of N. cirritus (Hochberg 2007b), we here try to gather a maximum of signals by using a variety of techniques (i.e. immunolabelling with antibodies against 5-HT, acetylated a-tubulin and b-tubulin and FMRFamides, in addition musculaturelabelling with phalloidin, DNA staining with DAPI).…”