Cytological evidence for catecholamine-containing sensory cells bordering the ventricle of the toad hypothalamus.

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AbstractA laminar group of catecholamine‐containing cells bordering the infundibular recess of the toad hypothalamus has been studied by both fluorescence histochemical and electron microscopic methods. The perikarya of these cells form up to ten layers beneath the ependymal lining and send stout apical processes between the ependymal cells into the ventricle where they terminate as bulbous expansions. These cells fluoresce yellow‐green when studied by the method of Falck and Hillarp, indicating the presence of catecholamines. The fluorescence intensity is consistently greater in the bulbous ventricular endings than in the cell bodies and is greater in males than in females except when ovulation is induced. Electron microscopy shows that the ventricular bulb, apical process and cell body contain three distinctive cytoplasmic components: a population of dense cored vesicles (700 to 1500 Å in diameter), large aggregates of clear vesicles (440 to 600 Å in diameter) and mitochondria filled with crystalline inclusions. The nucleus is prominently lobulated. A slender process also extends from the base of the cell into the underlying neuropil; this basal process, however, contains only microtubules, a few vesicles of both types and a few mitochondria. The basal, lateral and apical surfaces of the cells form many synapses with neighboring processes. By and large these junctions are somatodendritic and are characterized by accumulations of either clear or a mixture of clear and dense cored vesiles against the perikaryal membrane. Axosomatic synapses in contrast occur only infrequently. The cytological characteristics of the cells suggest that their primary function may be to detect compounds in the cerebrospinal fluid and relay this information to neighboring neurons via the somatodendritic synapses.