Olfactory system transduction

Buck L. (1993). Receptor diversity and spatial patterning in the mammalian olfactory system. In The Molecular Basis of Smell and Taste Transduction (Chadwick D., et al., eds). John Wiley, London, Ciba Symposium 179, pp. 51-67. 

The sensitivity of the olfactory system is likely to derive from the capacity of the olfactory transduction apparatus to effectively amplify and rapidly terminate signals 821... 

Cytosolic cGMP can activate CNG channels. These ion channels are not only an important part of the signal transduction pathway in the visual and olfactory system (Biel et al. 1999 Hofmann et al. 2003), but are also expressed in other neurons where they may be involved in the modulation of various functions by NO. The CNG channel family comprises six homologous subunits. Based on phylogenetic relationship, these proteins are classified as A subunits (CNGA1-A4) and B subunits (CNGB1 and CNGB3) (Biel et al. 1999 Bradley et al. 2001). Native CNG channels... 

These are exciting times in the field of chemosensory reception in general and olfaction in particular. In the decade since the landmark identification of a novel class of candidate odorant receptors (ORs) in rats (Buck and Axel, 1991), we have seen an explosion of similar studies involving other vertebrate as well as several insect species. In addition to an ever-increasing wealth of behavioral and physiological studies, insect systems provide arguably the most robust experimental system for the study of olfaction as well as a profound demonstration of the universal conservation of olfactory signal transduction mechanisms. 

In all systems studied thus far, olfactory-stimulated signal transduction is mediated by G-protein-coupled receptor (GPCR) pathways involving the synthesis of second messengers such as cyclic AMP (cAMP) and/or inositol 1,4,5-triphosphate (IP3) (Boekhoff et al., 1994 Reed, 1992). Moreover, several proteins that are involved in fundamental aspects of olfactory signal transduction have... 

Michel WC, Sanderson MJ, Olson JK, Lipschitz DL (2003) Evidence of a novel transduction pathway mediating detection of polyamines by the zebrafish olfactory system. J Exp Biol 206 1697-1706... 

Michel WC (1999) Cyclic nucleotide-gated channel activation is not required for activity-dependent labeling of zebrafish olfactory receptor neurons by amino adds. Biol Signals Recept 8 338-347 Michel WC, Derbidge DS (1997) Evidence of distinct amino acid and bile salt receptors in the olfactory system of the zebrafish, Danio rerio. Brain Res 764 179-187 Michel WC, Sanderson MJ, Olson JK, Lipschitz DL (2003) Evidence of a novel transduction pathway mediating detection of polyamines by the zebrafish olfactory system. J Exp Biiol 206 1697-1706... 

Olfactory Marker Protein ORNs express high levels of olfactory marker protein (OMP), which is unique in the olfactory system to ORNs (Margolis, 1972 Keller and Margolis, 1975). OMP is found in a number of mammalian species and it appears to be expressed in all mature ORNs. Studies in mice containing a null mutation for OMP suggest that this protein may play a role in ORN adaptation to odors (Ivic et al., 2000), signal amplification, and transduction (Youngentob et al., 2004). 

However, the solution of these fundamental problems will not bring a complete understanding of the olfactory code any more than the elucidation of retinal receptor transduction events has been able to clarify the neural mechanisms that underlie visual perception. The ORN is but the first element in a complex neural network. The operations of central olfactory networks are also poorly understood and the anatomical organization of the olfactory system appears in some respects to be fundamentally different from the familiar topographically organized circuits of the other major sensory systems. Thus, much remains to be discovered before we will approach the kind of understanding we currently have of visual, auditory and somatosensory neural network function. 

Impedimetric measurements are inherently nonselective, but the modification of electrode surfaces with selective recognition agents has resulted in selective sensing devices based on impedimetric transducers. Reviews of immunosensors and cell-based biosensors include sections on impedance transduction [177, 250, and references therein]. A review of bioelec-tronic noses, devices intended to mimic the human olfactory system in detecting and identifying odors, includes interdigital structures for complex impedance measurements and arrays of capacitive sensor elements [251]. 

Even though well-characterized at a biophysical level, the mechanical transduction mechanism of hair cells is still not fully understood in molecular terms. This discrepancy is in part due to the extreme scarcity of hair cells instead of the millions or even hundreds of millions of receptor cells that the olfactory and visual systems possess, only a few tens of thousands of hair cells are found in the internal ears of most vertebrate species. The small number of hair cells and the direct transduction mechanism has greatly impeded molecular biological and... 

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