Olfactory system cells

Eggan K, Baldwin K, Tackett M, Osborne J, Gogos J, Chess A, Axel R, Jaenisch R (2004) Mice cloned from olfactory sensory neurons. Nature 428(6978) 44-49 Feinstein P, Mombaerts P (2004) A contextual model for axonal sorting into glomeruli in the mouse olfactory system.Cell 117(6) 817—831... 

Zhao H, Reed RR (2001) X inactivation of the OCNC1 channel gene reveals a role for activity-dependent competition in the olfactory system. Cell 104(5) 651-660... 

Eeinstein, P., Mombaerts, P. A contextual model for axonal sorting into glomeruli in the mouse olfactory system. Cell 117, 817-831 (2004)... 

The mechanisms by which the taste (and also the olfactory) system senses chemical compounds is assumed to occur by way of a chemoreceptory system that interacts effectively with a broad, structural variety of stimulant molecules, by means of a receptor epithelium consisting of the mosaic of adjacent, peripheral membranes of many receptor cells, exposed to a medium carrying stimulus molecules. A receptor cell is conveniently and, for our present purpose, sufficiently defined as a cell equipped to interact, according to some mechanism, with stimulus molecules, to convert the effect of this interaction into a signal, and to project this signal into the system. The taste receptor is thus a differentiated, epithelial cell synaptically contact-... 

Petti M.A., Matheson S.F. and Burd G.D. (1999). Differential antigen expression during metamorphosis in the tripartite olfactory system of the African clawed frog, Xenopus laevis. Cell Tiss Res 297, 383-396. 

Ressler, K. ]., Sullivan, S. L. and Buck, L. B. Information coding in the olfactory system evidence for a stereotyped and highly organized epitope map in the olfactory bulb. Cell 79 1245-1255,1994. 

By contrast, the accessory olfactory system is thought to be involved in the detection of odors that influence a variety of reproductive and aggressive behaviors (Keverne 1999). Sensory neurons are located in the vomeronasal organ (VNO) and detect pheromones which gain access to the VNO by a pumping mechanism (Meredith and O Connell, 1979). VNO neurons send projections to the accessory olfactory bulb (AOB). Mitral cells of the AOB project in turn to the medial nucleus of the amygdala olfactory information is then dispatched to several hypothalamic regions such as the bed nucleus of the stria terminalis, the medial preoptic area and the ventromedial hypothalamus (Scalia and Winans 1975). 

Comparative and phylogenetic considerations such as those outlined in the preceding paragraphs readily lead to speculation that the olfactory systems of modern animals share common antecedents and therefore probably also share common principles of functional organization and information processing. We might ask, What attributes of chemical stimuli do olfactory systems analyze and encode How are those features mapped in "neural space" at various levels of the olfactory pathway How are cells of the pathway organized, and what mechanisms do they use, to accomplish this analysis of odors in the environment ... 

Information coding in the olfactory system evidence for a stereotyped and highly organized epitope map in the olfactory bulb. Cell 79 1245-1255. 

Differential sensory sensitivity. The insect s perception of plant odours differs essentially from their discrimination of non-volatile taste substances, as phytophagous insects may already perceive the odour at some distance from the plant. In adult phytophagous insects the antennae bear a large number of olfactory sensilla in order to detect the minute concentrations of the leaf odour components in the air downwind from a plant. The overall sensitivity of the antennal olfactory receptor system can be measured by making use of the electroantennogram technique (17). An electroantennogram (EAG) is the change in potential between the tip of an antenna and its base, in response to stimulation by an odour component. Such an EAG reflects the receptor potentials of the olfactory receptor cell population in the antenna. 

Recently, a putative olfactory receptor from Drosophila, Or43a (Clyne et al., 1999 Vosshall et al., 1999), has been expressed in Xenopus laevis oocytes (Wetzel et al., 2001). The receptor expressed in a heterologous cell system was activated by four odorants, i.e. cyclohexanone, cyclohexanol, benzaldehyde, and benzyl alcohol (Wetzel et al., 2001). These experiments not only provided direct evidence for the function of the Or gene, but also demonstrated that the olfactory receptor can be stimulated without an odorant-binding protein. It was demonstrated earlier that PBP was not necessary to obtain pheromone-dependent responses in cultured olfactory receptor neurons of Manduca sexta (Stengl et al., 1992). The possibility that OBPs have been produced in vitro and were present in cultured ORNs could not be excluded. The same argument can not be raised for the heterologous expression of the Drosophila olfactory receptor. While the evidence that Xenopus oocytes responded to odorants in the absence of OBPs does not support the OBP-odorant complex model, it also demonstrated that OBPs are essential for the kinetics of the olfactory system (see below). 

Binding of hydrophobic molecules by specific protein carriers appears to be a very efficient mechanism to increase both solubility and transport of these molecular messengers in a hydrophilic medium. OBPs and CSPs may represent a successful application of this principle. In particular, the molecular mechanisms of transport of hydrophobic molecules may be more ancient than that most ancient of senses, olfaction. The olfactory system may have developed to extract the hydrophobic odorants from the air environment and optimize their transport and delivery to sensory cells. 

Figure 20.1 Olfactory sensory cells of both insects and vertebrates are primary sensory cells, i.e. they are bipolar neurons extending a sensory dendritic process towards the odorous environment and projecting an unbranched axon directly to specialized target regions in the central nervous system.

Figure 5.9 The human olfactory system. (A) Section through the nose. (B) Section through the cribriform plate. (C) The olfactory pathway to the cerebrum (forebrain). This shows the pathway of olfactory sensation. Nasal stimulation begins at the cilia of the olfactory receptor cells located at the ends of the olfactory nerves. The olfactory nerves then carry the impulse to the cerebrum, resulting in the sense of smell.

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