The glucose transporter GLUT1 and the tight junction protein occludin in nasal olfactory mucosa.

The nervous cells in the brain and the peripheral nerves are isolated from the external environment by the blood-brain, blood-cerebrospinal fluid and blood-nerve barriers. The glucose transporter GLUT1 mediates the specific transfer of glucose across these barriers. The olfactory system is unique in that its sensory cells, olfactory receptor neurons, are embedded in the nasal olfactory epithelium and send their axons directly to the olfactory bulb of the brain. Only the apical parts of the olfactory receptor neurons are exposed to the lumen, and these serve as sensors for smell. Immunohistochemical examination showed that the tight junction protein occludin was present in the junctions of the olfactory epithelium. Endothelial cells in the blood vessels in the lamina propria of the olfactory mucosa were also positive for occludin. These observations suggest that the olfactory system is guarded from both the external environment and the blood. GLUT1 was abundant in these occludin-positive endothelial cells, suggesting that GLUT1 may serve in nourishing the cells of the olfactory system. Taken together, GLUT1 and occludin may serve as part of the machinery for the specific transfer of glucose in the olfactory system while preventing the non-specific entry of substances.     

Frequency of mast cells in the olfactory mucosa of rhesus monkeys

During studies of the olfactory mucosa and its response to the different levels of circulating sex hormones, considerable numbers of mast cells have been observed in its epithelia and subepithelial regions. The number of these cells in the olfactory mucosa of male monkeys differs greatly from that found in females. The frequency of these cells in the olfactory mucosa of females fluctuates significantly during the menstrual cycle. These fluctations stimultaneously correspond to the well known changes in olfactory sensitivity: around ovulation, when the olfactory sensitivity for certain odorants is high, the number of mast cells in the olfactory mucosa also increases.     

嗅鞘细胞的不同纯化方法及结果

培养的嗅鞘细胞的最终纯度受到多种因素的影响,如嗅鞘细胞的取材来源、分离方法等等;对培养的嗅鞘细胞进行纯化可获得高纯度的嗅鞘细胞。纯化嗅鞘细胞的方法有许多种,主要有单纯差速贴壁法、免疫吸附法、化学药物抑制法、无血清饥饿法等,现在的实验研究更趋向于以上2-3种方法联合应用对嗅鞘细胞进行纯化,这些联合纯化方案主要是在采用单纯差速贴壁方法的基础上再次运用其他一种或几种方法进行嗅鞘细胞的纯化。就获取的嗅鞘细胞的最终纯度而言,许多方法取得了可观的效果。但不同的纯化方法各有利弊,除了价格不同外,不同的纯化方法对嗅鞘细胞的生物活性造成不同程度的影响。因此在选择纯化方法时,应综合考虑各方面因素,根据研究目的和实际需要选择合理的方案进行纯化。本文通过查阅各数据库中与嗅鞘细胞的分离培养及纯化有关的文献和其他相关书籍,来探讨纯化嗅鞘细胞的不同方法以及这些纯化方法对嗅鞘细胞最终纯度的影响。     

Receptor cells of different types and quantitative relations between them in the organ of smell of larval and adult specimens of acipenserid fishes]

Three types of olfactory cells: rod-like and cone-like (flagellar olfactory cells) and filamentous (microvillar olfactory cells), which have been described previously in adult Acipenseridae were found in the olfactory organ of the ten-days larval sturgeons (Acipenser güldenst?dti), sevrugas (Acipenser stellatus) and sterlets (Acipenser ruthenus). The flagellar olfactory receptors appeared to predominate in both ten-days larvae and adults of the anadromous sturgeons and sevrugas, while the microvillar olfactory receptors predominate in freshwater sterlets in ten-days larvae as well in adults. The facts obtained confirm the idea that the rod-like, cone-like and filamentous olfactory cells are independent types of olfactory receptors. The different ratios of these cells in the olfactory organs of anadromous and fresh-water Acipenseridae may be a result of their ecological adaptations.     

Olfactory ensheathing cells: their role in central nervous system repair

The olfactory system is an unusual tissue in that it can support neurogenesis throughout life; permitting the in-growth and synapse formation of olfactory receptor axons into the central nervous system (CNS) environment of the olfactory bulb. It is thought that this unusual property is in part due to the olfactory glial cells, termed olfactory ensheathing cells (OECs), but also due to neuronal stem cells. These glial cells originate from the olfactory placode and possess many properties in common with the glial cells from the peripheral nervous system (PNS), Schwann cells. Recent data has suggested that olfactory ensheathing cells are a distinct glial cell type and possess properties, which might make them more suitable for transplant-mediated repair of central nervous system injury models. This paper reviews the biological properties of these cells and illustrates their use in central nervous system repair.     

Immunocytochemical localization of S-100 beta beta protein in olfactory and supporting cells of lamb olfactory epithelium

By immunocytochemistry, we have identified two novel cell types, olfactory and supporting cells of lamb olfactory epithelium, expressing S-100 beta beta protein. S-100 immune reaction product was observed on ciliary and plasma membranes, on axonemes and in the cytoplasm adjacent to plasma membranes and to basal bodies of olfactory vesicles. A brief treatment of olfactory mucosae with Triton X-100 before fixation is necessary for detection of S-100 beta beta protein within olfactory vesicles. In the absence of such a treatment, the immune reaction product is restricted to ciliary and plasma membranes. On the other hand, irrespective of pre-treatment of olfactory mucosae, S-100 beta immune reaction product in supporting cells is restricted to microvillar and plasma membranes. The anti-S-100 beta antiserum used in these studies does not bind to basal cells of the olfactory epithelium or to cells of the olfactory glands, whereas it binds to Schwann cells of the olfactory nerve. An anti-S-100 alpha antiserum does not bind to cellular elements of the olfactory mucosa, Schwann cells, or axons of the olfactory nerve. The present data provide, for the first time, evidence for the presence of S-100 beta beta protein in mammalian neurons (olfactory cells).     

Progress in defining heterogeneity and modeling periglomerular cells in the olfactory bulb

In recent years the evolution of olfactory bulb periglomerular cells, as well as the function of periglomerular cells in olfactory encoding, has attracted increasing attention. Studies of neural information encoding based on the analysis of simulation and modeling have given rise to electrophysiological models of periglomerular cells, which have an important role in the understanding of the biology of these cells. In this review we provide a brief introduction to the anatomy of the olfactory system and the cell types in the olfactory bulb. We elaborate on the latest progress in the study of the heterogeneity of periglomerular cells based on different classification criteria, such as molecular markers, structure, ion channels and action potentials. Then, we discuss the several existing electrophysiological models of periglomerular cells, and we highlight the problems and defects of these models. Finally, considering our present work, we propose a future direction for electrophysiological investigations of periglomerular cells and for the modeling of periglomerular cells and olfactory information encoding.     

Dynamic expression of Pax6 in the shark olfactory system: evidence for the presence of Pax6 cells along the olfactory nerve pathway

Pax6 is involved in the control of neuronal specification, migration, and differentiation in the olfactory epithelium and in the generation of different interneuron subtypes in the olfactory bulb. Whether these roles are conserved during evolution is not known. Cartilaginous fish are extremely useful models for assessing the ancestral condition of brain organization because of their phylogenetic position. To shed light on the evolution of development of the olfactory system in vertebrates and on the involvement of Pax6 in this process, we analyzed by in situ hybridization and immunohistochemistry the expression pattern of Pax6 in the developing olfactory system in a basal vertebrate, the lesser spotted dogfish Scyliorhinus canicula. This small shark is becoming an important fish model in studies of vertebrate development. We report Pax6 expression in cells of the olfactory epithelium and olfactory bulb, and present the first evidence in vertebrates of strings of Pax6-expressing cells extending along the developing olfactory nerve. The results indicate the olfactory epithelium as the origin of these cells. These data are compatible with a role for Pax6 in the development of the olfactory epithelium and fibers, and provide a basis for future investigations into the mechanisms that regulate development of the olfactory system throughout evolution.     

Reciprocal interactions between olfactory receptor axons and olfactory nerve glia cultured from the developing moth Manduca sexta

In olfactory systems, neuron-glia interactions have been implicated in the growth and guidance of olfactory receptor axons. In the moth Manduca sexta, developing olfactory receptor axons encounter several types of glia as they grow into the brain. Antennal nerve glia are born in the periphery and enwrap bundles of olfactory receptor axons in the antennal nerve. Although their peripheral origin and relationship with axon bundles suggest that they share features with mammalian olfactory ensheathing cells, the developmental roles of antennal nerve glia remain elusive. When cocultured with antennal nerve glial cells, olfactory receptor growth cones readily advance along glial processes without displaying prolonged changes in morphology. In turn, olfactory receptor axons induce antennal nerve glial cells to form multicellular arrays through proliferation and process extension. In contrast to antennal nerve glia, centrally derived glial cells from the axon sorting zone and antennal lobe never form arrays in vitro, and growth-cone glial-cell encounters with these cells halt axon elongation and cause permanent elaborations in growth cone morphology. We propose that antennal nerve glia play roles similar to olfactory ensheathing cells in supporting axon elongation, yet differ in their capacity to influence axon guidance, sorting, and targeting, roles that could be played by central olfactory glia in Manduca.     

Synaptic transmission: a new kind of inhibition

Periglomerular cells in the olfactory bulb are the 'gatekeepers' of the olfactory system. A recent study shows that these cells inhibit themselves by releasing GABA from their own dendrites.     

The Embryonic Septum and Ventral Pallium, New Sources of Olfactory Cortex Cells

The mammalian olfactory cortex is a complex structure located along the rostro-caudal extension of the ventrolateral prosencephalon, which is divided into several anatomically and functionally distinct areas: the anterior olfactory nucleus, piriform cortex, olfactory tubercle, amygdaloid olfactory nuclei, and the more caudal entorhinal cortex. Multiple forebrain progenitor domains contribute to the cellular diversity of the olfactory cortex, which is invaded simultaneously by cells originating in distinct germinal areas in the dorsal and ventral forebrain. Using a combination of dye labeling techniques, we identified two novel areas that contribute cells to the developing olfactory cortices, the septum and the ventral pallium, from which cells migrate along a radial and then a tangential path. We characterized these cell populations by comparing their expression of calretinin, calbindin, reelin and Tbr1 with that of other olfactory cell populations.     

Primary culture of lobster (Homarus americanus) olfactory sensory neurons

Lobster olfactory sensory neurons have contributed to a number of advances in our understanding of olfactory physiology. To facilitate further study of their function, we have developed conditions allowing primary culture of the olfactory sensory neurons in a defined medium. The most common cells in the culture were round cell bodies with diameters of 10-15 micro m that often extended fine processes, features resembling olfactory sensory neurons. We discovered that acetylcholinesterase acted as a growth factor for these cells, improving their survival in culture. We also confirmed previous evidence from spiny lobsters that poly-D-lysine was a superior substrate for olfactory cells of this size and morphology. We then identified olfactory sensory neurons in the culture in two ways. Almost half the cells tested responded to application of a complex odorant with an inward current. An even more rigorous test was made possible by the development of an antiserum to OET-07, an ionotropic glutamate receptor homolog specifically expressed by Homarus americanus olfactory sensory neurons. It labeled a majority of the round cells in the culture, unequivocally identifying them as olfactory sensory neurons.     

Organization of olfactory system of the Indian major carp Labeo rohita (Ham.): a study using scanning and transmission microscopy

Catla catla, Labeo rohita, and Cirrhinus mrigala are important alimentary fish in India. Their reproduction (breeding) depends on season. The fish perceive external factors-stimuli and chemical signals through the olfactory system that plays the key role in the central regulation of reproduction. However, in the available literature, any electron microscopy data on organization of olfactory elements in these fish are absent. We have studied ultrastructure of the olfactory organ in male L. rohita by using scanning (SEM) and transmission electron microscopy (TEM). The olfactory organ consists of olfactory epithelium, a short nerve, and olfactory bulb. The organ has oval shape and consists of approximately 47-52 lamellae in adult fish and of 14-20 lamellae in fish at the stage of fingerling. These lamellae originate from the midline raphe. By using SEM, the presence of microvillar sensory and ciliated non-sensory cells in these lamellae is shown. By using TEM, a microvillar receptor cell is revealed, which has rough endoplasmic reticulum and Golgi apparatus towards the apical end. Basal cells are found at the base of the receptor cell; supporting cells are located adjacent to olfactory receptor neurons, while epithelial cells--in the non-sensory part of olfactory epithelium. Mast, blastema and macrophages cells are also found in the basal lamina. This work is the first publication on structural organization of olfactory system of the Indian major carp, which provides information about morphological and ultrastructural organization of olfactory system and opens new opportunities for study of chemical neuroanatomy, sensory signal processing, and nervous regulation of reproduction of the Indian major carp.     

High correlation between microvillous olfactory receptor cell abundance and sensitivity to pheromones in olfactory nerve-sectioned goldfish

1. To determine whether microvillous olfactory receptor cells mediate responses to pheromonal cues, the olfactory nerves of mature male goldfish were axotomized and both the olfactory and behavioral sensitivity of these animals to olfactory stimuli investigated after which the histological condition of their olfactory epithelia was determined. 2. Behavioral responsiveness to food odor returned within 2 weeks but responsiveness to sexually-active females (pheromones) took 4–10 weeks to return. 3. Electro-olfactogram recordings from the olfactory epithelium of axotomized fish found that olfactory responsiveness to amino acids and pheromones changed little during the first week subsequent to axotomy. However, olfactory sensitivity decreased rapidly during the second week. During the course of the third week, electro-olfactogram sensitivity to amino acids remained while exposure to pheromones evoked no recordable electro-olfactogram. During week 4, sensitivity to amino acids increased further, and weak sensitivity to some pheromones became evident. Further recovery of electro-olfactogram sensitivity to all odorants was slow and erratic over the next 6 months, particularly to the pheromones. 4. Histological examination of the olfactory epithelia of axotomized fish demonstrated that while ciliated receptor cells were present within 2 weeks, microvillous receptor cells took approximately 4 weeks to regenerate. 5. Together these data suggest that microvillous receptor cells mediate responsiveness to pheromones in this species. Accepted: 22 August 1996     

Truncation Releases Olfactory Receptors from the Endoplasmic Reticulum of Heterologous Cells

Olfactory receptors are difficult to express functionally in heterologous cells. We found that olfactory receptors traffic poorly to the plasma membrane even in cells with neuronal phenotypes, including cell lines derived from the olfactory epithelium. Other than mature olfactory receptor neurons, few cells appear able to traffic olfactory receptors to the plasma membrane. In human embryonic kidney 293 cells and Xenopus fibroblasts, olfactory receptor immunoreactivity overlapped with a marker for the endoplasmic reticulum (ER) but not with markers for the Golgi apparatus or endosomes. Except for the ER, olfactory receptors were therefore absent from organelles normally involved in the plasma membrane trafficking of receptors. Olfactory receptors truncated prior to transmembrane domain VI were expressed in the plasma membrane, however. Co-expression of the missing C-terminal fragment with these truncated receptors prevented their expression in the plasma membrane. Intramolecular interactions between N- and C-terminal domains joined by the third cytoplasmic loop appear to be responsible for retention of olfactory receptors in the ER of heterologous cells. Our results are consistent with misfolding of the receptors but could also be explained by altered trafficking of the receptors.     

Cell dynamics in the olfactory mucosa

By means of ultrastructural and autoradiographic observations from the olfactory mucosa of frog, it has been shown that olfactory receptor neurons as well as supporting cells are continuously replaced during the adult life of the animal. The severing of the olfactory nerve in adult frogs results in rapid degeneration of all mature olfactory neurons. An increased mitotic activity of the basal cells accompanies the degeneration of the mature neurons and precedes the regeneration of new neurons. The capability of these newly formed neurons to re-establish their connections in the olfactory bulb has been ascertained and the modalities of the process will be dealt with in a further report.     

The Efferent Connections of the Olfactory Bulb and Accessory Olfactory Bulb in the Snakes,Thamnophis sirtalis and Thamnophis radix

The efferent connections of the olfactory bulb and accessory olfactory bulb of two species of garter snakes, Thamnophis sirtalis and T. radix were studied with experimental anterograde degeneration techniques. Axons of cells located in the olfactory bulb terminate ipsilaterally in all parts of the anterior olfactory nucleus, olfactory tubercle and lateral pallium. In addition, some axons enter the ipsilateral stria medullaris thalami, cross the midline in the habenular commissure, enter the contralateral stria medullaris thalami and terminate in the contralateral lateral pallium. The axons of cells in the accessory olfactory bulb course through the telencephalon completely separated from the fibers of olfactory bulb origin and terminate predominantly in the nucleus sphericus. These results confirm previous reports of the separation between the central projections of the olfactory and vomeronasal systems in a variety of vertebrates. The totality of the separation between these two systems coupled with the extensive development of the vomeronasal-accessory bulb system in these snakes suggests that they may be ideal subjects for further research on the functional significance of the vomeronasal system.     

The ultrastructural organization of olfactory epithelium of two species of gadoid fish

The untrastructural organization of the olfactory epithelium of the cod Gadus morhua (L.) and the haddock Melanogrammus aeglefinus (L.) was studied using both transmission and scanning electron microscopy. The olfactory rosette was found to exhibit regional differences; the faces of the olfactory lamella were composed of sensory epithelium, the edges were non-sensory. The cellular organization of the olfactory epithelium was determined and consisted of bi-polar sensory neurones, supporting cells, mucous cells and basal cells. The ultrastructure of the sensory cells was consistent, having an elongate cell, the free surface of which terminated in an olfactory vesicle from which arose either four olfactory cilia or numerous microvilli. Ciliary aggregations have been found in the two species of gadoid fish studied; it is suggested that these structures aid in the separation and in the circulation of fluid between the lamellae. The surface structure of the supporting cells was found to be of two types: either ciliated or ridged; the former presenting distinct ciliated tufts, the latter showing definite, but unorganized, ridges over the epithelium surface.     

Regeneration of olfactory flagella and restoration of the electroolfactogram following application of triton X-100 to the olfactory mucosa of frogs]

A short-tern (1-1.5 min.) irrigation of the olfactory mucose of the frog Rana temporaria with 0.1-0.15% Triton X-100 in Ringer's solution led to the destroying of olfactory flagella but did not damage the olfactory knob and its flagellar basal bodies. Simultaneously, the generator potential of the olfactory cells-elecroolfactogram (EOG)-disappears. The olfactory cells deprived of fragella were able to produce these organelles. This process begins 2 or 3 hours following theflagellum removal, proceeds in some stages and completes within 2 or 3 days. During the flagellum regeneration the ability of olfactory cells to generate EOG is seen to resotre. The data obtained confirm the presence of receptive sites on flagellar surface.     

Joint migration of gonadotropin-releasing hormone (GnRH) and neuropeptide Y (NPY) neurons from olfactory placode to central nervous system

The olfactory epithelium in vertebrates generates the olfactory sensory neurons and several migratory cell types. Prominent among the latter are the gonadotropin-releasing hormone (GnRH) neurons that differentiate within the olfactory epithelium during embryogenesis and migrate along the olfactory nerve to the central nervous system. We initiated studies to characterize additional neuronal phenotypes of olfactory epithelial derivation. Neuropeptide Y (NPY) neurons are functionally related to the reproductive axis, modulating the release of GnRH and directly enhancing GnRH-induced luteinizing hormone (LH) secretion from gonadotrophs. We demonstrate that a population of migratory NPY neurons originates within the olfactory epithelium of the chick. At stage 25, NPY-positive fibers, but not cells, were detected in the epithelium and the nerve. By stages 28–34, NPY neurons and processes were present in the olfactory epithelium, olfactory nerve, and at the junction of the olfactory nerve and forebrain. In these regions the number of NPY neurons increased until stage 30 and then declined as development progressed. Electron microscopic immunocytochemistry confirmed the neuronal phenotype of the NPY-positive cells. The origin and migratory nature of some of these NPY cells was confirmed by double-label immunocytochemical detection of NPY and GnRH. A large percentage of the NPY-cells coexpressed the GnRH peptide. Between stages 28 and 34 single- and double-labeled NPY and GnRH neurons were found side by side along the GnRH migratory route emanating from the nasal epithelium, along the olfactory nerve, and into the ventral forebrain. These data suggest that an NPY population originates in the olfactory epithelium and migrates into the central nervous system during embryogenesis. By stage 42, no NPY/GnRH double-labeled cells were detected. © 1996 John Wiley & Sons, Inc.