Histofluorescence and ultrastructural evidence for catecholamine‐containing sensory neurons bordering the interventricular foramen of the toad brain

Abstract

AbstractA population of catecholamine‐containing cells that borders the interventricular foramen of the toad brain has been studied by both fluorescence histochemical and electron microscopic methods. The perikaryon of these cells, which lies immediately subjacent to the ependyma, sends a fluorescent apical process between the ependymal cells to border on the ventricular surface and a basal process displaying fluorescent varicosities into the underlying neuropil. A few cells possess a broad lateral extension which runs parallel to the ventricular surface. Histochemical and pharmacological specificity tests indicate that the cells contain catecholamines, including epinephrine. The most distinctive ultrastructural feature of the subependymal cells' cytoplasm is large numbers of dense cored vesicles that vary in diameter from 500 A to 2,400 A; these are found in the perikarya, apical and basal processes, and lateral extensions. In addition, bundles of filaments ($100 A in diameter) are seen lying adjacent to the nucleus, and numerous axosomatic synapses are found along the surface of the cell bodies. The luminal surface of the apical processes is covered by microvilli and extends a short distance into the ventricular lumen. The basal processes are narrow in diameter, measuring 0.5‐1.1 $m, and contain some filaments, microtubules and dense cored vesicles, but no clusters of ribosomes and no granular endoplasmic reticulum. The characteristics of these subependymal cells, i.e., apical processes which contact the cerebrospinal fluid and basal processes which resemble axons, suggest that the cells may be sensory neurons, and as such, they may respond to the changing composition or pressure of the cerebrospinal fluid and relay this information via their axons to other neurons. The results of this study contribute further evidence that the cerebrospinal fluid provides a means of chemical communication within the brain.