Neurons, olfactory

The future in research will certainly lead to a better understanding of how odors are recognized, sorted, and classified. Studies promise, among other things, to determine whether perceptually similar, but stmcturaHy different, odors share the same class of receptor proteins, whether responses to odors can be modified, and possibly why olfactory neurons regenerate but other neurons do not. 

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... 

The chemosensory stem cells give rise to several types of neuronal and non-neuronal cell lines under the influence of multiple organisers. From a ventro-lateral infolding, the olfactory pit is produced and this invagination soon becomes separated into two areas which will produce the main and accessory olfactory neurones [Figs. 4.2(a)-(d)]. 

The lateral diverticulum cells in semi-terrestrial species such as toads can still detect a wide range of amino acids, comparable to the properties of fish neuroepithelium. Both water-soluble and volatile odourants are discriminated by the olfactory neurones of the Clawed toad (Xenopus) (Iida and Kashiwayanagi, 1999). When single olfactory neurones were tested with acidic, neutral and basic amino acids, over 50% of the receptors gave some excitatory response. 

Ebrahimi F.A. and Chess A. (2000). Olfactory neurons are interdependent in maintaining axonal projections. Curr Biol 10, 219-222. 

Iida A. and Kashiwayanagi M. (2000). Responses to putative second messengers and odorants in water nose olfactory neurons of Xenopus laevis. Chem Senses 25, 55-59. 

Strotmann J., Wanner I., Helfrich T. and Breer H. (1995). Receptor expression in olfactory neurons during rat development in situ hybridization studies. Eur J Neurosci 7, 492-500. 

Tanaka M., Treloar H., Kalb R.G., Greer C.A., et al. (1999). G(o) protein-dependent survival of primary accessory olfactory neurons. Proc Natl Acad Sci 96, 14106-14111. 

Identical olfactory neurons are located in different places in the cavity, and therefore occupy different positions in the flow path. By using a nasal cavity model, we investigated the influence of the dynamic flow on the sensors response14. The responses from identical fiber optic sensors located... 

FIGURE 29-5 In the adult rodent brain, dividing cells in the subventricular zone adjacent to the lateral ventricle migrate in the rostral migratory stream (RMS) and differentiate into olfactory neurons in the olfactory bulb (OB). This is one site of neuronal turnover in the adult that appears to result from persistent generation of neurons from adult CNS stem cells. CIS, cerebellum NC, neocortex. 

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. 

Serizawa, S. et al. Negative feedback regulation ensures the one receptor-one olfactory neuron rule in mouse. Science 302 2088-2094,2003. 

Fritschy, J. M., Johnson, D. K., Mohler, H., and Rudolph, U. (1998) Independent assembly and subcellular targeting of GABAa receptor subtypes demonstrated in mouse hippocampal and olfactory neurons in vivo. Neurosci. Lett. 249, 99-102. 

In vertebrates the neurons for olfaction are located in the nose mucosa and consist of short neurons with a peripheral ending endowed with odorant receptors for a large number of molecules in the environment. Each receptor neuron only contains one odorant receptor and is connected directly with the olfactory lobe of the brain. The vertebrate olfactory system must cope with a staggering developmental problem how to connect millions of olfactory neurons expressing different odorant receptors to appropriate targets in the brain. 

All animals exhibit innate behaviors in response to specific sensory stimuli that are likely to result from the activation of developmentally programmed neural circuits. Even the activation of single classes of olfactory neurons can trigger complex behaviors [10]. The authors observed that Drosophila exhibit robust avoidance to odors released by stressed flies. When stressed, the flies emit an odorant mixture that elicits avoidance in other flies. C02 is the active component of this mixture. Specific blockade of the activation of a particular odorant receptor... 

Earlier experiments based on EAG and SSR highlighted the inordinate specificity and sensitivity of the insect olfactory system. While minimal structural modifications to pheromone molecules render them inactive [12], a single molecule of the native ligand is estimated to be sufficient to activate an olfactory neuron in male antennae [14]. The large number of detectors certainly contributes to the sensitivity of the olfactory system, but selectivity is a matter of... 

In humans and other mammals, the sense of smell begins when we inhale some odorant through our nose. The inhaled air enters the nasal cavity where it encounters a large number of olfactory neurons located in the nasal epithelium associated with bony structures located at the rear of this cavity. These bony structures are known as turbinates. In a human, these turbinates create a surface area of a few square inches. In a medium-size dog, in contrast, the turbinates have a surface area several times larger. It is small wonder that dogs have a more acute sense of smell than we do. 

The olfactory epithelium of mammals contains many types of olfactory neurons, each expressing a specific odorant receptor. Linda Buck has shown that an odorant can activate multiple distinct receptors and that a receptor can be activated by multiple odorants. Thus, there must exist a combinatorial mechanism for odor detection some sort of pattern recognition. The axons of olfactory neurons converge on glomeruli in the olfactory bulb. There, incoming signals are integrated and the sense of smell is created. 

In the olfactory epithelium, each olfactory neuron expresses a specific odorant receptor. Each may be activated by multiple odorants. 

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 olfactory bulb contains glomeruli where the dendrites of mitral cells and tufted cells concentrate. The mouse has about 1800 glomeruli in its olfactory bulb. In the rabbit, the input from 5 x 10 receptor cells converges on 1900 glomeruli (Fig. 5.7). In some bats, 900 receptor cells converge on each secondary olfactory neuron. 

FIGURE 5.7 Projection ofreceptor input from olfactory epithelium onto glomeruli in the main olfactory bulb in mice. The epithelium is organized into four zones defined by expression of odorant receptors. Olfactory neurons of a particular zone project to a corresponding zone in the bulb. Axons of these olfactory neurons that express the same odorant receptor (such as those shown in black) converge to a small number of glomeruli. AOB, accessory olfactory bulbs, NC, nucleus coeruleus. (From Mori etal, 1999.)... 

Ghanbari, H. A., Ghanbari, K., Harris, P. L. R., Jones, P. K., Kubat, Z., Castellani, R. J., Wolozin, B. L., Smith, M. A., and Perry, G. (2004). Oxidative damage in cultured human olfactory neurons from Alzheimer s disease patients. Aging Cell 3,41-44. 

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