Electron Microscopic Observations on the Taste Buds of the Rabbit

Abstract

An examination of the fine structure of the taste buds in the rabbit was undertaken. Gustatory epithelium was fixed in OsO4 or 1 per cent KMnO~ solution, containing polyvinylpyrrolidone (PVP). Thick sections were examined in the phase microscope and contiguous sections prepared for the dectron microscope.The bud contains two types of cells, gustatory receptors and sustentacular cells. The receptors are characterized by a dark nucleus and densely granular cytoplasm. The apical processes bear numerous microvilli which extend into the taste pore. Imbedded between the microvilli there is a dense substance, which is also present in the apical cytoplasm of the receptors. The sustentacular cells contain a large pale nucleus and less dense cytoplasm. Their basal surfaces rest upon a basement membrane.The subepithelial nerve plexuses comprise the fibers which innervate the gustatory receptors. The nerve fibers vary in diameter from 500 A to 0.3 g, and are ensheathed by Schwaun cells. The intragemmal fibers enter the taste bud between adjacent cells, and are ensheathed by the plasma membranes of the supporting cell until they synapse upon the gustatory cell. The synaptic terminaLs contain synaptic vesicles, which at this junction reside in the postsynaptic element. This observation is discussed with reference to synapses described elsewhere in the nervous system.The problem of the relation of structure to function in the nervous system is one that has occupied neurologists for many years. In recent decades, morphological investigations have failed to keep pace with physiological and chemical advances, primarily because of the limited reliability of silver impregnation and methylene blue staining methods and the limited resolving power of the light microscope. This has been especially true in the general area of sensory receptors, where, morphologically, the neural basis of sensory discrimination is not much better understood today than it was fifty years ago. However, it is now possible with the electron microscope to examine more intimately the relation between structure and function and some progress has been made (22). * This investigation has been aided in part by Grants B-425 and RG 3784 from the United States Public Health Service, Nationai Institutes of Health.A number of primary receptors, e.g., the retina (7, 29-31), the inner ear (10, 32, 34), the Pacinian corpuscle (23), and the olfactory mucosa (6) have already been studied with the electron microscope. The taste buds offer an additional region for study, since the mechanism of taste bud excitation (chemoreception) remains obscure, despite the fact that a good amount of physiological (3,4, 24) and histochemical data (2) is available. Of special interest to the morphologist is the fact that the taste buds undergo degeneration following interruption of their nerve supplies (17, 19, 33). Thus they offer a particularly useful region for correlating structure and function and for observing degeneration.Since the early descriptions of Loven (15), Schwalbe (...

Ultrastructural and histochemical studies on the taste buds in some reptiles.

“…Some investigators (FAHRMANN, 1967;MURRAY and MURRAY, 1967;FARBMAN and YONKERS, 1971;GROVER-JOHNSON and FARBMAN, 1976;TAKEDA and HOSHINO, 1975) thought that these cells containing secretory granules correspond to supporting and/ or secretory cells, while others (DE LORENZO, 1958;IRIKI, 1960) thought that they are gustatory cells, although they did not demonstrate a synaptic contact. Synaptic contacts in this type of cells have been reported only in fishes (WELSCH and STORCH, 1969;STORCH and WELSCH, 1970;REUTTER, 1971), but HIRATA (1966 and GROVER-JOHNSON and FARBMAN (1976) failed to find synapses in this type of cell.…”

Histochemical Observation on the Phosphatases of the Tongue, with Special Reference to Taste Buds

“…15) (TORREY 1934, 1940, GUTH 1957, 1958. The activity is localized in the cytoplasm of the acinar cells.…”

“…Although the receptor potential of a single taste cell in the rat has been recorded by KIMURA and BEIDLER (1961), the kind of change or changes occurring in the taste cell initiating this receptor potential is still unknown. Recent electron microscopic observations (TRUJILLO-CENOZ 1957, DE LORENZO 1958, MURRAY and MURRAY 1960, NEMETSCHEK-GANSLER and FERNER 1963, FARBMAN 1965, GRAY and WATKINS 1965, HIRATA 1966 have greatly advanced and enlarged the knowledge concerning the structural details of the taste organ, but have afforded no specific clues that might serve to resolve this problem. What role enzymes play in the mechanism of taste is still uncertain, since electro-physiological experiments heretofore conducted have not resulted in equivalent or even similar conclusions (BEIDLER 1955, YUR'EVA 1957, 1961, KOSHTOIANTS and KATALIN 1958.…”

Taste Buds in the Vallate Papillae of the Rat Studied with Freeze-Fracture Preparation

“…Previous papers on the fine structure of taste buds demonstrated the occurrence of tight junctions and desmosomes in them (DE LORENZO, 1958;SCALZI, 1966;MURRAY andMURRAY, 1967, 1970;MILLER and CHAUDHRY, 1976). But the existence and distribution of gap junctions in the buds have not been clarified yet.…”