Summary
Small nerve cells are scattered among the ependymal cells of the central canal of the filum terminale in Cyprinus carpio. The dendrites of these neurons form bulb-like endings in the cerebrospinal fluid (CSF). These endings are similar to the CSF contacting dendritic terminals of the medulla oblongata and spinal cord. Therefore, we consider these nerve cells to belong to the CSF contacting neuronal system.
The axons of these neurons enter the hypendymal fibrous zone where nerve processes of various calibres and axon terminals on dendrite-like profiles and sometimes on ependymal processes were found. In addition to cytoplasmic elements ordinarily present in nerve cells there are granulated vesicles of about 800 to 900 Å in diameter in the perikarya of the CSF contacting neurons. Axons containing synaptic and dense-core vesicles (diameter about 400 Å and 800 Å, respectively) build up synapses on the basal part of these neurons. The CSF contacting neurons described are dissimilar to the Dahlgren cells present in the urophysis and in the rostral part of the filum.
In addition, we found axon terminals forming synaptic semidesmosomes on the basal lamina of the external surface of the filum. At some places these terminals are numerous, building up primitive median eminence-like areas on the surface of the filum. In addition to synaptic vesicles these terminals contain numerous granulated vesicles of 800 Å. The axons forming these terminals are supposed to originate from the CSF contacting neurons. The presence of special nerve terminals on the external surface furnishes morphological evidence for the passage of substances from the nervous tissue into the external CSF space at the level of the filum terminale.
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Vigh, B., Vigh-Teichmann, I. & Aros, B. Intraependymal cerebrospinal fluid contacting neurons and axon terminals on the external surface in the filum terminale of the carp (Cyprinus carpio). Cell Tissue Res. 148, 359–370 (1974). https://doi.org/10.1007/BF00224263
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DOI: https://doi.org/10.1007/BF00224263