Histochemical and ultrastructural analyses of the lubrication systems in the olfactory organs of soft-shelled turtle

Morphological Analysis of the Olfactory System of the Pig-Nosed Turtle, Carettochelys insculpta

The turtle olfactory organ consists of the upper (UCE) and lower (LCE) chamber epithelium, projecting to the ventral and dorsal parts of the olfactory bulbs, respectively. The UCE is associated with glands, contains ciliated olfactory receptor neurons, and is assumed to detect odorants primarily in air, while the LCE is devoid of glands, contains microvillous olfactory receptor neurons, and is assumed to detect odorants primarily in water. Examining the olfactory system of the pig-nosed turtle, Carettochelys insculpta, this study found that both the upper and lower chambers of the nasal cavity were lined with sensory epithelium devoid of associated glands and contained ciliated olfactory receptor neurons. Moreover, the olfactory bulbs were not divided into dorsal and ventral parts. These results suggest that the olfactory system of the pig-nosed turtle is a single system specialized for detecting odorants in water.

Histological features and Gαolf expression patterns in the nasal cavity of sea turtles

Sea turtles use olfaction to detect volatile and water-soluble substances. The nasal cavity of green turtles (Chelonia mydas) comprises morphologically defined the anterodorsal, anteroventral, and posterodorsal diverticula, as well as a single posteroventral fossa. Here, we detailed the histological features of the nasal cavity of a mature female green turtle. The posterodorsal diverticulum contained spongy-like venous sinuses and a wave-shaped sensory epithelium that favored ventilation. Secretory structures that were significant in sensory and non-sensory epithelia were probably involved in protection against seawater. These findings suggested that green turtles efficiently intake airborne substances and dissolve water-soluble substances in mucous, while suppressing the effects of salts. In addition, positive staining of Gαs/olf that couples with olfactory, but not vomeronasal, receptors was predominant in all three types of sensory epithelium in the nasal cavity. Both of airborne and water-soluble odorants seemed to be detected in cells expressing Gαolf and olfactory receptors.

Gross morphology, histology, and ultrastructure of the olfactory rosette of a critically endangered indicator species, the Delta Smelt, Hypomesus transpacificus

The Delta Smelt (Hypomesus transpacificus) is a small, semi-anadromous fish native to the San Francisco Bay-Delta Estuary and has been declared as critically endangered. Their olfactory biology, in particular, is poorly understood and a basic description of their sensory anatomy is needed to advance our understanding of the sensory ecology of species to inform conservation efforts to manage and protect them. We provide a description of the gross morphology, histological, immunohistochemical, and ultrastructural features of the olfactory rosette in this fish and discuss some of the functional implications in relation to olfactory ability. We show that Delta Smelt have a multilamellar olfactory rosette with allometric growth. Calretinin immunohistochemistry revealed a diffuse distribution of olfactory receptor neurons within the epithelium. Ciliated, microvillous and crypt neurons were clearly identified using morphological and immunohistochemical features. The olfactory neurons were supported by robust ciliated and secretory sustentacular cells. Although the sense of smell has been overlooked in Delta Smelt, we conclude that the olfactory epithelium has many characteristics of macrosmatic fish. With this study, we provide a foundation for future research into the sensory ecology of this imperiled fish.

Comparative histochemical analysis of glycoconjugates in the nasal vestibule of camel and sheep

While Corriedale sheep survive in a wide range of climates, which prevents them to specialize for one climatic condition only, dromedary camels strictly adapted to desert areas. This demands more adaptive mechanisms to hot, dry conditions in camels than in sheep. Being the entrance of the nasal cavity, nasal vestibule is subjected to various environmental stressors. A protective way is the lining epithelium which is cornified in camel, but not in sheep. Mucus nasal secretions also play a key role in the protection of underlyings. Additionally, arterio-venous anastomosis is present in the lamina propria of the nasal vestibule of camel. In the present paper, sugar residues in the nasal vestibule of camel were analyzed and compared with those of sheep using 14 types of lectins to explore the distribution of glycoconjugates that may help the function of camel nasal vestibule in desert environment. In camel, none of the lectins could label the basal cells of the vestibular epithelium, although the basal cells reacted with six lectins in sheep. In camel, LEL and RCA-120 markedly labeled the luminal surface. WGA, DBA, SBA, and VVA produced marked intensities on the luminal surface in sheep. The mucous glands reacted with six lectins: WGA, s-WGA, VVA, PNA, PHA-E, and PHA-L in camel, while all lectins used except s-WGA and PHA-E reacted in the sheep. In summary, great differences are observed in the glycoconjugate expression between camel and sheep. This suggests that these glycoconjugate are related to camel's tolerance for environmental stressors.

Number of olfactory receptor neurons in the Chinese soft-shelled turtle

The olfactory organ of turtle consists of the upper chamber epithelium (UCE) and the lower chamber epithelium (LCE), detecting air-borne odorants and water-borne odorants, respectively. In this study, we investigated the number of olfactory receptor neurons (ORNs) in the UCE and LCE of soft-shelled turtle in order to find their possible differences among terrestrial, semi-aquatic and highly-aquatic turtles. The number of ORNs in the soft-shelled turtle was higher in the LCE than in the UCE, suggesting its close relationship to the environment the turtle lives. In addition, relative abundance of the ORNs in the LCE to the UCE varied in accordance with the size of individuals, although its functional significance remains elusive.