Architecture of the nervous system in two Dactylopodola species (Gastrotricha, Macrodasyida)

Abstract

Immunohistochemical stainings have become standard tools to describe the nervous system, but usually only singular or few markers are used and consequently show only subsets of neurons within the nervous system. We investigated two species of Dactylopodola (Gastrotricha, Macrodasyida) with a broad set and combination of markers, to represent the nervous system in a more holistic approach. We suggest that markers for both neurotubuli (tubulin) and neurotransmitters (e.g. serotonin, FMRFamides, histamine) should be used. Combinations with markers for the musculature (phalloidin) and nuclei (propidiumiodide or other markers) help to reveal spatial patterns and when used with TEM can provide a more precise picture of the spatial relationships of particular nerves. Species of Dactylopodola have a brain consisting of a solid dorsal commissure and a fine ventral commissure. Cell somata of brain cells are arranged lateral to the dorsal commissure and form a dumbbell-like brain. Additionally, projections into the head region, head sensory organs, one pair of lateroventral nerve cords with three commissures and stomatogastric nerves are described. Obviously, some longitudinal transmitter-specific fibres run in parallel to the main longitudinal nerve and represent additional longitudinal fibres. In comparison with the nervous system architecture of other gastrotrich species and that of different bilaterian animals it is speculated that the gastrotrich nervous system retains several ancestral features, such as being commissural and not a compact brain.

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

“…are often cited in this context. But, for Dactylopodola baltica, Rothe and Schmidt-Rhaesa (2009) have shown the existence of only one pair of lateral longitudinal neurite bundles, an additional paired medial branching 5-HT IR fibre is restricted only to the anterior trunk region. The citation of Travis (1983) as a source for a description of multiple longitudinal nerve cords is a misinterpretation, as Travis (1983) clearly shows in Fig.…”

“…One problem in investigations of the nervous system is the absence of an ubiquitous marker to be used for the whole nervous system. Instead, one has to use a variety of neuron-specific markers for visualizing a major fraction of the nervous system, at best in combination with electron microscopy (see Rothe and Schmidt-Rhaesa 2009).…”

“…The findings of a study on two species of the marine genus Dactylopodola by Rothe and Schmidt-Rhaesa (2009) compared with data of further gastrotrich species (e.g. Hochberg 2007b) yielded a hypothesis on the construction of the common ancestor's nervous system in Gastrotricha.…”

“…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.…”

Morphology and deep metazoan phylogeny

“…We start this Special Volume with a review on the need for a standardized language for morphological descriptions (Vogt 2009), because besides the search for new characters it is equally important to develop appropriate methods to deal with such data. Contributions of Harzsch et al (2009), Rothe andSchmidtRhaesa (2009), Heuer andLoesel (2009) and Suschenko and Purschke (2009) present new data on the structure of the nervous system and photoreceptors. Scholtz and Ungerer investigate the cleavage and gastrulation in pycnogonids.…”