Olfactory sensory neuron

The epithelium covering the nasal cavity. This epithelium contains numerous cell types including the specialized olfactory sensory neurons which detect the chemical stimuli derived from smells by a specific family of G protein-coupled receptors known as olfactory receptors. 

Buiakova O., Baker H., Scott J., Farbman A., et al. (1996). Olfactory marker protein (OMP) gene deletion causes altered physiological activity of olfactory sensory neurons. Proc Natl Acad Sci 93, 9858-9863. 

The ligands for the other forms of membrane-bound GC are less well characterized. In some cases the functions of these GC forms have not been identified. GC-D is expressed in olfactory sensory neurons but its function has not been determined. GC-E and GC-F are expressed in photoreceptor cells in the retina and play a role in phototransduction. GC-G is widely expressed in peripheral tissues and brain but its ligand binding domain is similar to that for GC-A/GC-B, suggesting that it may be regulated by an ANP/BNP-like ligand [34]. 

FIGURE 50-1 A schematic diagram of the olfactory epithelium. The initial events in odor perception occur in the olfactory epithelium of the nasal cavity. Odorants interact with specific odorant receptors on the lumenal cilia of olfactory sensory neurons. The signals generated by the initial binding events are transmitted along olfactory neuron axons to the olfactory bulb of the brain. 

OSN olfactory sensory neuron PSP progressive supranuclear palsy... 

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... 

G.S.B Suh et al. A single population of olfactory sensory neurons mediates an innate avoidance behaviour in Drosophila. Nature Neurosci 431, 2002. 

Odorants are thought to bind to integral membrane receptors on the cilia of the olfactory sensory neurons. The receptors are thought to he specific different olfactory neuron types recognize different odorants that share certain characteristics (Buck, 1993). The odorant receptors transduce signals via interactions with G-proteins (so-called because guanosine trisphosphate is involved in their activation). These G-protein-coupled exhibit seven hydrophobic domains (Fig. 5.6). Variation in the amino acid sequence of the transmembrane domain may account for specificity and selectivity of odor reception. 

The receptors start a second messenger cascade that is initiated by activation of G-proteins in the cell. These, in turn, interact with membrane-bound adenylyl cyclase, which catalyzes the formation of cyclic adenine monophosphate (cAMP) and opening of cAMP-gated cation channels. Depolarization then brings about an action potential, which travels along the axon of the olfactory sensory neuron. Many of the molecular components of this cascade are olfactoiy specific. 

The specialized olfactory mucosa features olfactory sensory neurons, which span the nose-brain barrier. At the epithelial surface nonmotile cilia extend from swellings, which lead via a dendritic extension to the neuronal cell body, from which an extended axon penetrates the... 

The glomerular layer of the olfactory bulb contains a substantial population of dopaminergic neurons. Dopamine acting at D2-like heteroreceptors inhibits glutamate release from terminals of the olfactory sensory neurons and hence may modulate the olfactory nerve synapse (Table 1). 

Olfactory perception translates abstract chemical features of odorants into meaningful neural information to elicit appropriate behavioral responses (Shepherd, 1994 Buck, 1996). Specialized bipolar olfactory sensory neurons (OSNs) are responsible for the initial events in odor recognition. These have ciliated dendrites exposed to the environment, and a single axon that extends into the brain and forms synapses with second order projection neurons (PNs) (Shepherd, 1994 Buck, 1996). In arthropods and mammals, the first olfactory synapse is organized into glomeruli, spherical structures in which afferent olfactory neuron axons synapse with projection neuron dendrites (Hildebrand and Shepherd, 1997). 

TM, seven transmembrane domain DOR, Drosophila odorant receptor EAG, electroantennogram GFP, green fluorescent protein GPCR, G-protein coupled receptor GR, gustatory receptor nsyb, neuronal synaptobrevin OR, odorant receptor OSN, olfactory sensory neuron PCR, polymerase chain reaction PN, projection neuron RT-PCR, reverse transcription-polymerase chain reaction SOG, subesophageal ganglion. 

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... 

The anosmic phenotypes of mice strains which are deficient in G0if (Belluscio et al., 1998), ACIII (Wong et al., 2000) and functional relevant channel subunits (Brunet et al., 1996 Baker et al., 1999) emphasize the central role of the AC/ cAMP pathway for signal transduction in vertebrate olfactory sensory neurons. These features may be considered as evidence for cAMP as the sole relevant second messenger in vertebrate olfaction. 

Meyer M. R., Angele A., Kremmer E., Kaupp U. B. and Muller F. (2000) A cGMP-signaling pathway in a subset of olfactory sensory neurons. Proc. Natl. Acad. Sci. USA 97, 10595-10600. 

What happens at the instant when an odor-active molecule comes in touch with our nasal cavity 205 The first interaction of odorant molecules takes place in the olfactory receptor neurons, which are embedded in the pseudostratified columnar epithelium (or simply, olfactory epithelium), which is located in the posterior nasal cavity in the case of mammals. Olfactory sensory neurons express receptor proteins on the surface membrane of the cilia, which gain access to the extracellular region covered with mucus. The airborne odorants are dissolved into the mucus, bind with the receptors, and then the receptor protein triggers a signal transduction cascade. This results in the opening of the cation channel that would depolarize the sensory neuron and eventually elicit a train of action potentials in the axon. The olfactory axon leads to the olfactory bulb through basal lamina and lamina propria. 

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