A Golgi study on the cerebrospinal fluid (CSF)-contacting neurons in the paraventricular nucleus of the Pekin duck.

The present investigation based on classical neurohistological techniques (Nissl-staining, Golgi-impregnation) was focussed on the cytoarchitecture of the periventricular layer of the paraventricular nucleus in the Pekin duck. This region is endowed with intraependymal neurons, the perikarya of which are mostly covered by a thin ependymal lamella. Several of the intraependymal neurons were shown to give rise to dendrites extending into the third ventricle. An additional population of nerve cells located in the deeper layers of the periventricular region also gained direct access to the cerebrospinal fluid by means of long dendrites terminating with a bulbous-like swelling in the third ventricle. This cerebrospinal fluid (CSF)-contacting dendrite branched off several times in a rectangular fashion to give rise to collaterals running in the subependymal or periventricular layers. The axons of these CSF-contacting neurons were followed into the magnocellular portion of the paraventricular nucleus. Small bipolar nerve cells with processes parallel to the surface of the third ventricle occupied a subependymal position. The isodendritic magnocellular neurons of the paraventricular nucleus emitted dendritic processes that reached the basal pole of the ependymal cells. The complex arrangement of the periventricular layer of the paraventricular nucleus might provide the structural basis for the mechanisms of cerebral osmoreception defined by means of physiological parameters.