Morphometric Analysis of Serotoninergic Structures in the Nervous System of Planarian Schmidtea mediterranea

Abstract

The nervous system of planarians includes cerebral ganglia situated in the anterior part of the body and a pair of well-defined ventral nerve cords that extend throughout the whole animal. Serotoninergic components of the nervous system were determined by indirect method of immunocytochemical staining of whole mount tissue preparations of planarians Schmidtea mediterranea, followed by analysis using a fluorescence microscope. The results obtained show the presence of serotoninergic components in the central and peripheral parts of the nervous system of planarians S. mediterranea. The morphological parameters of serotonin-immunopositive structures were estimated, as well as neuron counts in the cerebral ganglion were done. The measurements were carried out on micrographs taken through a digital camera from stained whole mount preparations. The size of serotonin neurons in three areas of the body, the thickness of the nerve trunks and cerebral ganglion, and the distance between the nerve cords and transversal commissures were taken into consideration. For the first time, the new quantitative data were obtained characterizing the morphological properties of the nervous system of planarian S. mediterranea. Also, the observation of the eyes regeneration in planarians in response to decapitation and exposure to serotonin was performed. It was found that exogenous serotonin at concentrations of 0.01–1 μm accelerated eye differentiation during the regeneration of the head end of S. mediterranea planarian.