Sensory neuron membrane proteins

Rogers M. E., Krieger J. and Vogt R. G. (2001) Antennal SNMPs (sensory neuron membrane proteins) of Lepidoptera define a unique family of invertebrate CD36-like proteins. J. Neurobiol. 49, 47-61. 

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. 

Some sensory neurons of the VNO express two gene superfamilies, termed Vlr and V2r, that encode over 240 proteins of the seven-transmembrane type (Matsunami and Buck, 1997). These G-protein-linked putative pheromone receptors are distantly related to the main olfactory system s receptors. Receptors of the VNO are linked to different G-proteins, and their extracellular N-terminal domains are longer than those of the receptors in the main olfactory system. (Vi receptors are linked to Gi-proteins and V2 receptors to Go-proteins). The intracellular excitation mechanism in VNO sensory neurons also differs from that in the main olfactory systems instead of linking to adenylyl cyclase, the VNO receptors activate the phosphoinositol second messenger system. This has been demonstrated in several mammalian species. In hamsters, aphrodisin increases inositol 1,4,5-trisphosphate (IP3) levels in VNO membranes. Boar seminal fluid and urine stimulate increases of IP3 in the VNO of the female pig. (However, in the pig, the VNO is not necessarily essential for responses to pheromones [Dorries etal., 1997]). 

Sodium channels are densely expressed in axons, somata and dendrites of neurons. In the rat brain and spinal sensory neurons, sodium channels are heterotrimeric integral membrane proteins consisting of one major poreforming a-subunit which associates with two smaller auxiliary (3-subunits (one (31 or (33 assembled with one (32 subunit Black et al., 1996 Morgan et al., 2000 for review see Catterall, 1992 Denac et al., 2000). The deduced... 

Short-term memory is not affected by inhibitors of protein synthesis, but alteration of synaptic proteins and membranes may be induced by covalent modification of existing macromolecules.1016 One way in which this happens has been described for Aplysia. As the snail learns a simple gill-withdrawal reflex, the duration of the action potentials in sensory neurons is increased, and there is a greater release of transmitters. This change comes about because stimulation of the sensory neuron causes simultaneous activation of... 

As noted above, Passmore et al. (2003) were the first to demonstrate that Kv7.2, 7.3 and 7.5 are expressed at the protein level in sensory neurons and also that functional M-currents can be measured under voltage-clamp. They were further able to demonstrate that pharmacological activation of Kv7 channels by direct application of retigabine to the spinal cord inhibited both C fiber and AS fiber-mediated signaling. This was true when the afferent fibers were excited by either electrical or tactile stimuli. Moreover, wind-up , an increased sensitivity of the stimulus/response relationship to repetitive stimuli, is also inhibited. These results demonstrate a clear role of Kv7 channels in sensory neuron processing. Gerlach et al. (2006, 2007) have also reported direct effects of ICA-27243 on both M-currents and membrane potential in isolated DRG neurons. Activation of the M-current by ICA-27243... 

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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