Qualitative and quantitative freeze-fracture studies on olfactory and nasal respiratory structures of frog, ox, rat, and dog

Abstract

A comparative study using freeze-fracturing has been made of surface structures of olfactory and nasal respiratory epithelia of frog, ox, rat and dog. Special attention has been paid to cilia and microvilli present at these surfaces, although the observations include various other structures such as small intracellular vacuoles present in the olfactory receptor endings and infrequent brush cells. Within the mucus overlying the olfactory epithelium membranous vesicles, often attached to olfactory cilia, are seen. Some of these show intramembranous particle distributions similar to those of the rest of the cilia, whereas others are devoid of particles. Smooth vesicles are also found in the mucus of other types of epithelium (respiratory epithelium and Bowman's glands). The freeze-fracture morphology of intracellular secretory vacuoles present in olfactory supporting, Bowman's and respiratory glandular cells of the frog is similar in all these epithelia. Quantitative comparisons are made of the different structures of interest. When corrected for cilia which were not observed, mammalian receptor endings bear 17 cilia on average, whereas frog receptor endings have 6 cilia. The relative magnitudes of the diameters of the cilia and microvilli are, except for frog, the same for all species studied. Dimensions of other structures, e.g., axons, dendrites and dendritic endings are compared in the various species. Freeze-fracture diameters are usually larger than those seen by techniques using dehydration. Dendritic ending densities range from 4.5 X 10(6) (frog) to 8.3 X 10(6) (dog) endings per cm2. Possible sex-dependent differences are only found for these densities and dendritic ending diameters.

Fine structure of three types of olfactory organs inXenopus laevis

“…In the present study, details of the fine structure of the OE and the VNO in Xenopus laevis agreed well with those reported previously in anurans (Bloom, 1954;Burton, 1985;Franceschini et al, 1991;Kolnberger, 1971a,b;Mair et al, 1982;Menco, 1980;Reese, 1965;Scalia, 1976; et al, 1996). The olfactory cells of the OE were covered with cilia, and the sensory cells of the VNO were covered with microvilli in Xenopus laevis, similar to other species that possess both the OE and the VNO.…”

Cyclic-nucleotide–gated cation current and Ca2+-activated Cl current elicited by odorant in vertebrate olfactory receptor neurons

“…For a frog ORN with nominally 10 cilia of ∼0.2 μm in diameter and ∼40 μm in average length (60)(61)(62), the total intraciliary volume is ∼12 μm 3 . Based on this volume, and assuming for simplicity spatial homogeneity along the cilium, a 1-pC Ca 2+ influx would increase the internal Ca 2+ concentration by ∼400 μM if there were no intracellular Ca 2+ buffer.…”

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

“…Duct cells in amphibians clearly possess the ultrastructural characteristics of secretory cells (Fig. 1E;Menco, 1980a;Foster et al, 1992) with evidence for merocrine secretion (Menco, 1980a). However, conflicting reports have appeared in the literature regarding the secretory capacity of the duct cells of some mammals.…”