Olfactory signals

CNG channels are expressed in retinal photoreceptors and olfactory neurons, and play a key role in visual and olfactory signal transduction. In addition, CNG channels are found at low density in some other cell types and tissues such as brain, testis, and kidney. While the function of CNG channels in sensory neurons has been unequivocally demonstrated, the role of these channels in other cell types, where expression has been observed, remains to be established. Based on their phylogenetic relationship, the six CNG channels... 

Hurst J.L., Robertson D., Tolladay U. and Beynon R. (1998). Proteins in urine scent marks of male house mice extend the longevity of olfactory signals. Anim Behav 55, 1289-1297. 

Menco B. (1997). Ultrastructural aspects of olfactory signaling. Chem Senses 22, 295-311. 

Behavioral bioassays are inextricably linked with chemical studies to decipher the information content of olfactory signals (Albone 1984). As a complement to the experimental approach described above, several research groups have applied chemical approaches, particularly gas chromatography and mass spectrometry (GC-MS),... 

Scordato, E.S. and Drea, C.M. (2007) Scents and sensibility information content of olfactory signals in the ringtailed lemur (Lemur catta). Anim. Behav. 73, 301-314. 

Two olfactory systems have evolved in terrestrial vertebrates which differ in both their peripheral anatomy and central projections. The main olfactory system is usually conceived as a general analyzer that detects and differentiates among complex chemosignals of the environment (Firestein 2001). Odors are detected by olfactory sensory neurons located in the main olfactory epithelium (MOE) these neurons project to glomeruli in the main olfactory bulb (MOB). The mitral and tufted neurons abutting these MOB glomeruli then transmit olfactory signals to various... 

Whereas some species oxidize host terpenes more randomly, producing an array of rather unspecific volatiles with little information, others use highly selective enzyme systems for the production of unique olfactory signals. However, apart from transformations of monoterpene hydrocarbons of host trees, oxygenated monoterpenes may well be biosynthesized de novo by the beetles (see below). 

Evans, C. M., Mackintosh, J. H., Kennedy, J. T., and Robertson, S. M. (1978). Attempts to characterise and isolate aggression-reducing olfactory signals from the urine of female mice Mus musculus. Physiology andBehavior20,129-134. 

Galef, B. G. and Stein, M. (1985). Demonstrator influence on observer diet preference analysis of critical social interactions and olfactory signals. AnimalLearningand Behavior 13,31-38. 

Kendrick, K. M., Levy, E., and Keverne, E. B. (1992). Changes in the sensoiy processing of olfactory signals induced by birth in sheep. Science 256,833-836. 

Gibernau, M., Hossaert-McKey, M Frey, J. and Kjellberg, F. (1998). Are olfactory signals sufficient to attract fig pollinators Ecoscience 5 306-311. 

Ronnett, G.V. Moon, C. (2002) G proteins and olfactory signal transduction. Annu. Rev. Physiol. 64, 189-222. 

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. 

As is the case for all sensory pathways, the capacity to perceive and respond to olfactory cues (odorants) is the combined result of events that take place in both peripheral and central processing centers. These steps, which will be discussed in detail below, begin with the molecular transduction of chemical signals in the form of odorants into electrical activity by olfactory receptor neurons (ORNs) in the periphery whose axonal projections form characteristic synaptic connections with elements of the central nervous system (CNS). Within the CNS, complex patterns of olfactory signals are integrated and otherwise processed to afford recognition and ultimately, the behavioral responses to the insect s chemical environment. Within the context of pheromone recognition these responses would likely be centered on various elements of the insect s reproductive cycle. 

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... 

At first glance, labeled-line coding of olfactory signals may seem in contrast to the ensemble or across-fiber code (Shepherd, 1985) where complex mixtures of odorants or even individual odorant components are perceived as patterns of activity across an ensemble of neurons and AL glomeruli. However, recent experiments examining odor coding of individual ORNs in Drosophila and mammalian olfactory systems demonstrate that individual ORNs are capable of a wide spectrum of responses. In the fly, a particular odor can excite one neuron while inhibiting another, and a particular neuron can be excited by one odor and... 

Given the wealth of breakthrough-level work that has taken place over the past several years (in part detailed above), there seems little doubt that our overall understanding of the chemoreception has entered a robust period of growth and maturation. At first glance, it should be noted that the primacy of the conservation of general principles of olfactory signal transduction has now been... 

Krieger J., Mameli M. and Breer H. (1997) Elements of the olfactory signaling pathways in insect antennae. Invert. Neurosci. 3, 137-144. 

Breer H., Boekhoff I., Krieger J., Raming K., Strotmann J. and Tareilus E. (1992) Molecular mechanism of olfactory signal transduction. In Sensory Transduction, eds D. P. Corey and S. D., Roper, pp. 94-108. The Rockfeller University Press, New York. 

Vogt R. G. and Riddiford L. M. (1986) Pheromone reception a kinetic equilibrium. In Seminar on Mechanisms in Perception and Orientation to Insect Olfactory Signals, eds T. L. Payre, M. C. Birch, and C. E. J. Kennedy, pp. 201-208, Clarendon Press, Oxford. 

This chapter describes some of the principles and mechanisms underlying the primary processes of olfactory signaling, the chemo-electrical signal transduction. We will focus on molecular events that follow the interaction of odorants with olfactory sensory neurons, and leave aside perireceptor events including odorant... 

While experimental evidence concerning the molecular mechanisms and the diversity of reaction cascades involved in olfactory signal transduction in antennal cells of insects is still fragmentary, a much more detailed picture has been established for signal transduction in chemosensory cells of the lobster, another member of the arthropod phyla. The bipolar chemosensory neurons of the lobster antennule respond to stimulation with odorous compounds either with an excitation or an inhibition i.e. cells are equipped to respond to one odor with a depolarization and excitation as well as to another odor with a hyperpolarization and inhibition. 

Enormous progress has been made over the last decade towards an understanding of the olfactory signal transduction process in vertebrate olfactory neurons. A... 

However, mechanisms involved in olfactory signaling seem much more diverse than hitherto expected. Recently, a subset of olfactory neurons has been described that lacks most of the elements for the AC/cAMP cascade these cells rather express distinct subtypes of guanylyl cyclase (GC-D) and phosphodiesterase (PDE2) (Juilfs et al., 1997), as well as a characteristic channel subtype (Meyer et al., 2000). These sensory neurons, which project to the so-called necklace... 

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