Golgi impregnation study of a new catecholamine-containing cell type in the toad hypothalamus

Tanycytes in the sunfish brain: NADPH-diaphorase histochemistry and regional distribution

NADPH-diaphorase histochemistry has been shown to be a useful method for identifying cells that synthesize and release nitric oxide, which is implicated in the modulation of a variety of neural functions, including synaptic transmission, cerebral blood flow, and excitotoxicity. In the sunfish brain, NADPH-diaphorase histochemistry stains tanycytes specifically and almost exclusively, allowing for a thorough examination of the morphology and distribution of this type of cell. Tanycytes are nonciliated, process-bearing ependymal and extraependymal cells that contact the ventricular surface via apical processes, and the pial surface via basal processes. Ependymal tanycytes are located at the ventricular surface, and project basal processes into the parenchyma of the brain. Extraependymal tanycytes are found away from the ventricular matrix. Some extraependymal tanycytes are small, bipolar, and tend to be associated with bundles of basal processes. Isolated extraependymal tanycytes are larger, darkly stained, and multipolar. Their basal processes terminate in specialized endfeet on blood vessels, neuronal somata, or the pial surface. Specialized types of tanycytes are found in the optic tectum, the epineurial septum between axonal bundles along the midline in the medulla, and in restricted regions on the pial surface in the medulla. The only NADPH-diaphorase-positive neurons are found in the commissural nucleus of area ventralis telencephali. Injection of horseradish peroxidase into the ventricles shows that tanycytes lining the third and fourth ventricles are capable of taking up the tracer and transporting it into their basal processes. Tanycytes are unevenly distributed in the brain. There is a rough rostrocaudal gradient of cell density: tanycytes are sparse in the telencephalon and dense in the isthmus and medulla, although cell density is low in the spinal cord. Not all ventricular linings contain tanycytes: cell density is low in the medial ventricle of the telencephalon and in the infundibular recess, and high along the fourth ventricle. The function of tanycytes in the sunfish is not known. The association of tanycytes with both the ventricles and blood vessels raises the possibility that they play some role in sampling the biochemical constituents of both compartments and communicating the information to neural elements. It is proposed that tanycytes react to the biochemical composition in the ventricle and plasma by increasing or decreasing nitric oxide synthesis and release, which in turn influence neuronal activity or cerebral blood flow.

Spinal tanycytes in the adult rat: a correlative Golgi gold-toning study

In Golgi impregnated transverse sections through the cervical spinal cord of the 7-12-week-old adult rat, numerous tanycytes were observed radiating from the ependyma into the gray matter that surrounds the central canal. The tail processes of these tanycytes terminated as foot processes in association with blood vessels. Spinal tanycytes were classified into ependymal (E) and subependymal (S) types on the basis of the shape and position of the soma. The soma of the E tanycyte was shaped as a column and was entirely located within the ependyma. In contrast, the soma of the S tanycyte was flask shaped, with the widest portion of the flask located subependymally and the elongated portion extending through the ependyma ultimately reaching the luminal surface. Selected Golgi impregnated sections were gold toned and deimpregnated for direct correlative analysis at the ultrastructural level. Gold-toned tanycytes contained the fine clusters of gold particles underlying the plasma membrane of the cell body and coarse clusters of gold particles throughout the tail and foot processes. The apical surface of tanycytes was characterized by numerous microvilli and large cytoplasmic protrusions that evaginated from the apical surface into the lumen of the central canal. At the luminal surface, adjacent tanycytes were joined laterally by junctional complexes with punctate tight junctions and zonulae adhaerentes associated with fibrils and microtubules. In contrast, gap junctions, hemidesmosomes, and puncta adhaerentia were found between adjacent tail processes of tanycytes. The foot processes interdigitated with one another and abutted the basal lamina around the perivascular space of blood vessels. The basal lamina was continuous around the lateral walls of foot processes and filled the spaces between membranous infoldings of the lateral walls. These basal membrane labyrinths were continuous with the basal lamina of the blood vessel and may provide an extensive surface relation between the perivascular space and the neighboring extracellular compartment. The findings of the present study support the contention that tanycytes may modify the composition of substances moving between the perivascular and extracellular spaces.

Morphological relations between the receptor neurons, sustentacular cells and Schwann cells in the olfactory mucosa of the salamander

The morphological characteristics of olfactory receptor neurons and their relations to the sustentacular cells and to the sheath cells of Schwann in the olfactory mucosa of the salamander (Ambystoma maculatum et tigrinum) were studied using a modification of the rapid Golgi technique. The bipolar receptor neurons had a fusiform-shaped cell body whose apical pole gave rise to a surface-reaching dendrite and a basal pole which gave rise to an axon. The length and width of the dendrite, although variable, were positively correlated with the relative depth at which the cell body was located in the sensory epithelium. Beyond the initial segment, the axon had a sinuous course prior to its entrance into the lamina propria. Within the lamina propria, the axons were associated with the sheath cells of Schwann to form the olfactory nerve fascicles. The processes of adjacent sheath cells formed an elaborate network of continuous cavities through which the axons coursed. Two morphologically distinct varieties of sustentacular cells, designated types I and II, were found in the sensory epithelium. Both types had a columnar profile consisting of an elongated cell body, a central stalk, and a basilar expansion of the stalk found at the junction of the epithelium with the lamina propria. The central stalk of type I sustentacular cells was unbranched, whereas that of type II cells gave rise to riblike processes from which cytoplasmic veils extended to envelop the cell bodies of receptor neurons. The basilar expansions were found in close apposition to the wall of capillaries or to acinar cells of Bowman's glands located in the most superficial region of the lamina propria. The morphological relationships and possible interdependencies among receptor neurons, the types of sustentacular cells, and the sheath cells are discussed.

Immunohistochemical demonstration of the serotonin-containing subependymal cells in the frog hypothalamus

The localization of serotonin(5HT)-containing subependymal cells was demonstrated by immunochemistry. The 5HT-containing subependymal cells were predominantly located in the paraventricular organ, while a small number of them were situated in the nucleus infundibularis dorsalis. The basal processes of these 5HT cells of the paraventricular organs appeared to have contact with the wall of blood vessels. The result was discussed in comparison with that obtained by the formaldehyde induced fluorescence (FIF) method.