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Taste buds occur in the epithelium of the catfish barbel along its entire length. Two major cell types, light and dark cells, occupy the upper two-thirds of the taste bud. A third cell type, the basal cell, lies on the basal lamina and is essentially separated from the light and dark cells by a plexus of unmyelinated nerve fibers. The dark cells have branching processes, both apically and basally whereas the light cells have a single apical process and many basal processes. The apical processes of dark cells contain secretory granules, while the apical processes of light cells contain an abundant agranular endoplasmic reticulum. Light cell nuclei contain bundles of 10 nm filaments, often arranged in the shape of a cup or ring, but nucleoli are rarely seen. It is suggested that this morphology indicates a low degree of RNA synthesis by light cells. The basal cells contain large numbers of vesicles, about 60 nm in diameter, which are sometimes seen in clumps in relation to an adjacent nerve fiber in a configuration resembling a synapse. Curiously, although basal cells present a large surface to the basal lamina, there are no hemidesmosomes. This suggests that the basal cell does not originate from the epidermis.

Deficient vascular innervation in familial dysautonomia, an explanation for vasomotor instability An ultrastructural study of peripheral blood vessels in familial dysautonomia demonstrates the absence of autonomic nerve terminals. In control subjects both sympathetic terminals containing dense‐cored vesicles and presumptive cholinergic terminals containing agranular vesicles are readily shown. Lack of autonomic innervation of blood vessels in familial dysautonomia accounts for postural hypotension and other abnormalities of vasomotor reflexes. It also explains exaggerated responses to sympathomimetic and parasympathomimetic agents in terms of denervation hypersensitivity. Ultrastructural analysis of vascular nerve terminals may be of general value in the study of many diseases which show vasomotor instability.

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