Summary
The paraventricular organ (PVO) and the posterior recess organ (PRO) of two elasmobranch species, the spiny dogfish,Squalus acanthias, and the skate,Raja radiata, were investigated by use of scanning and transmission electron microscopy and immunocytochemistry employing a series of primary antisera. The PVO and PRO contained four types of cerebrospinal fluid (CSF)-contacting neurons. One type was free of secretory granules and projected a dendrite-like process into the ventricle. The other three types were distinguished according to the size of their secretory granules. The ventricular extensions of these cells were filled with secretory granules. By means of immunocytochemistry three types of CSF-contacting neurons were observed in the PVO and PRO. Type I contained only serotonin; type 2 displayed only somatostatin; type 3 was endowed with both serotonin and somatostatin. Type I dominated in the PRO, whereas type 3 was the most frequent in the PVO. The latter cells appear to be the site of origin of a loose tract formed by serotonin- and somatostatinimmunoreactive fibers projecting from the PVO into the neuropil of the PRO. Compact bundles formed exclusively by serotonin fibers were also shown to extend between the PVO and PRO. The basal processes of the CSF-contacting neurons of the PRO penetrated into the underlying neuropil. This neuropil is rich in synapses and can be regarded as an integrative area to which the basal processes of the local CSF-contacting neurons, serotonin and somatostatin fibers from the PVO, and fibers containing immunoreactive thyrotropin-releasing hormone of unknown origin, support a conspicuous input. The present findings indicate that the PVO and PRO of elasmobranchs are functionally integrated structures.
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Dedicated to Professor Erik Dahl on the occasion of his 75th birthday.
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Meurling, P., Rodríguez, E.M. The paraventricular and posterior recess organs of elasmobranchs: A system of cerebrospinal fluid-contacting neurons containing immunoreactive serotonin and somatostatin. Cell Tissue Res. 259, 463–473 (1990). https://doi.org/10.1007/BF01740772
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DOI: https://doi.org/10.1007/BF01740772