Do Glial Cells Exist in the Nervous System of Parasitic and Free-Living Flatworms? An Ultrastructural and Immunocytochemical Investigation

Abstract

It is still unclear whether flatworms have specialized glial cells. At present there are no special methods available for the identification of glial cells in flatworms. The aim of this research was to carry out detailed investigations of the CNS in two species of cestodes, and to get an idea whether these cells may fit into the concept of glia. Three types of glial cells have been found in Grillotia erinaceus: (1) fibroblast- like cells in the cerebral ganglion (CG); (2) glial cells in bulbar nerves with filaments and laminar cytoplasm; (3) a 3rd type of cells forms multilayer envelopes in the main cords (MC); also they make contacts with the excretory epithelium. To demonstrate the existence of glial cells, an immunocytochemical and ultrastructural investigation of Ligula intestinalis was undertaken. Intensive S100b-like immunoreaction (IR) was found in the GG and in the MC. IR-varicosities were mostly located asymmetrically on the MC, and no IR was found in neuropiles. Small glial cells were found on the surface of the MC; they have oval nuclei and dense cytoplasm with slim processes going around the neuropile and enclosing neurons. Long junctions are seen between cell processes but with neurons they usually possess juxtaposition contacts. Glial cells lack vesicles or synapse-like structures. Intensive S100b-like-IR has been shown in the CNS of cestodes for the first time. Results from ultrastructural research support the immunocytochemical date.

Abbreviations

A:

axon

CG:

cerebral ganglion

GAx:

giant axon

EX:

excretory vessel and cells

F:

fibrillar matrix

GC:

glial cell

GP:

glial processes

InM:

invaginations of the neuron membrane

M:

muscle cells and processes

MC:

main nerve cord

Mh:

mitochondria

N:

neuron

NP:

nervous processes

npl:

neuropile

Nu:

nucleus

L:

lipid drop

sy:

synapse

T:

tegument and subtegument

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Correspondence to Natalia M. Biserova.

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Biserova, N.M. Do Glial Cells Exist in the Nervous System of Parasitic and Free-Living Flatworms? An Ultrastructural and Immunocytochemical Investigation. BIOLOGIA FUTURA 59, 209–219 (2008). https://doi.org/10.1556/ABiol.59.2008.Suppl.30

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Keywords

  • Glia
  • flatworms
  • S100b
  • ultrastructure
  • immunocytochemistry