Neue morphologische Grundlagen zur Physiologie des Riechens und Schmeckens

Abstract

New results as revealed by scanning and transmission electron microscopy have given us further knowledge about the structure of the olfactory region of vertebrates. With comparative studies we are now able to discuss the functional relationship of this region. In all vertebrates the olfactory cell is a primary sensory cell. The apical segment of the olfactory cell with its olfactory vesicle is involved in the formation of the olfactory border. As a rule of the receptor possesses cilia or cilia-like processes. These are absent in the olfactory receptor of the shark, the microvillus receptor of the fish and the olfactory cell of Jabonsons organ of amphibians, reptiles and mammals. The odorous substances in the fish are brought to the receptor membrane by the water flow. In air breathing vertebrates a terminal film is present. This film is a product of secretion from the Bowmans glands. Gasous odorous substances must first be dissolved in the terminal film and penetrate it before reaching the receptor membrane. The cilia-like olfactory process of the fish in the proximal segment is not essentially different from the kinocilia of the supporting cell, except that they are shorter. In contrast the olfactory cell of air-breathing vertebrates form cilia-like processes with a short cilia-like proximal segment and a long and very thin distal end piece. In the amphibians and sauropsidians the end pieces can have a length of up to 150 mu and up to 80 mu in mammals. The olfactory vesicles with its processes undergo continuous regeneration. The olfactory epithelium of man show the same structural formation as observed in other mammals. Regressive changes in the adult can lead to a reduction in the number of sensory cells and also to a flattening of the epithelium. Morphological criteria for regenerative processes in the sensory cell structures are present. A specialized olfactory cell type has been found in some teleosts. This cell is characterized by a small pit below the olfactory border in which the cilia of the olfactory cell are redrawn. There is some evidence that this olfactory cell type may be compared with the olfactory cells in the parafollicular tubes of lamprey. The so called rod-shaped receptor in the olfactory mucosa of fishes has no axon and is therefore no olfactory cell. The same kind of cell is also present in the olfactory mucosa of air-breathing animals. We classify this cell as brush cell.(ABSTRACT TRUNCATED AT 400 WORDS)

Organization of the olfactory system in the adult zebrafish: Histological, immunohistochemical, and quantitative analysis

“…There are five cell types: (1) ciliated sensory neurons, (2) microvillar sensory neurons, (3) microvillar supporting cells, (4) goblet cells, and (5) basal cells. The two types of sensory neurons have been reported in other teleosts (Bannister, 1965;Schulte, 1972;Bertmar, 1973;Andres, 1975;Ichikawa and Ueda, 1977). In addition, a third sensory neuron type possessing a single rod-shaped appendage has been reported in some teleosts (Bannister, 1965;Wilson and Westerman, 1967;Schulte, 1972;Bertmar, 1973), but it is unclear whether or not this is a sensory neuron (Andres, 1975;Ichikawa and Ueda, 1977) or perhaps even an artifact of fixation (Eller et al, 1985).…”

Fine structural aspects of secretion and extrinsic innervation in the olfactory mucosa

“…The mucus consisted of two zones (Andres, 1969;Muller et al, 1979): an outer zone, including the terminal film, in which the distal segments of the olfactory receptor cilia were located; and an inner zone, which covered the proximal ciliary segments, the microvilli of the sustentacular cells, and the apical surfaces of the epithelial cells. The outer zone appeared to be composed of fine filaments; a marked similarity in appearance between the outer zone and the secretory material in Bowman's glands was noted in birds and mammals (Andres, 1966(Andres, , 1969(Andres, , 1975Seifert, 1971;Muller et al, 1979). The inner zone was composed of a lighter-appearing filamentous material.…”

“…Patches of respiratory mucosa were reported to occur among areas of olfactory mucosa (Andres, 1975;Nakashima et al, 1984;Nakashima et al, 1985). In light microscopic studies of human olfactory mucosa from our laboratory, using immunohistochemistry to localize olfactory marker protein for identifying olfactory mucosa unequivocally, we observed that the type of respiratory epithelium most commonly found adjacent to olfactory mucosa contained tall columnar ciliated cells; frequently, invaginations of this type of epithelium formed "glands" in the lamina propria (Getchell and Mellert, 1991).…”

Synaptic organization and development of the antennal lobe in insects

“…At least a few glomeruli in Periplaneta are innervated by both uPNs and mPNs (Kraus, 1991). Interestingly, uniglomerular PNs prevail in the mammalian olfactory bulb, where the primary dendrites of about a dozen mitral cells are found per glomerulus, but in fish, projection neurons are often pluriglomerular (Andres, 1975); however, mPNs like those found in insects have not been described in vertebrates.…”