Understanding the Human Sensory Conduction of Smell / 한양의대학술지

The olfactory epithelium is the main end organ for the sense of smell in humans and vertebrates. Specially differenciated neuronal cells called olfactory receptor neurons (ORNs) play a key role in the olfactory epithelium by expressing the olfactory receptors (ORs) on their apical surface membrane. The ORs are G-protein coupled receptors that transmit signals from odorants to ORNs by molecular cascades using cyclic adenosine monophosphate, calcium ions and other molecules, which result in the depolarization of ORN. Unlike other mammalian animals, only about 30% of OR genes in the human genome are expressed. The Nobel Prize was awarded to the scientists who cloned these ORs for the first time. Each ORN expresses only a single type of OR, and ORNs which express the same type of OR converge together into the same glomeruli in the olfactory bulb. A single OR recognizes multiple odorants, and a single odorant is recognized by multiple ORs with varying affinities. At the higher neurons beyond the bulb, neuronal connections are divergent. The combinatorial model of odor identification and discrimination is well established at the convergence level, but little is known about the action mechanisms of neuronal divergence for odor identification and discrimination and further study is required.

Interplay of Signaling Molecules in Olfactory Sensory Neuron toward Signal Amplification / 한양의대학술지

Over the last decades, piles of data have been accumulated to understand the olfactory sensation in every aspect, ranging from the intracellular signaling to cognitive perception. This review focuses on the ion conduction through multiple ion channels expressed in olfactory sensory neurons (OSNs) to describe how odorant binding to olfactory receptors is transduced into an electrical signal. Olfactory signal transduction and the generation of the depolarizing receptor current occur in the cilia, where the unique extraciliary environment of the nasal mucosa assists in the neuronal activation. Upon contacting with odorants, OSNs dissociate G protein-coupled receptors, initiating a signal transduction pathway that leads to firing of action potential. This signaling pathway has a unique, two step organization: a cAMP-gated Ca2+ (CNG) channel and a Ca2+-activated Cl- channel (CACC), both of which contribute to signal amplification. This transduction mechanism requires an outward-directed driving force of Cl- established by active accumulation of Cl- within the lumen of the sensory cilia. To permit Cl- accumulation, OSNs avoid the expression of the 'Chloride Sensor: WNK3', that functions as the main Cl- exclusion co-transporter in neurons of the central nervous system (CNS). Cl- accumulation provides OSNs with the driving force for the depolarization, increasing the excitatory response magnitude. This is an interesting adaptation because of the fact that the olfactory cilia reside in the mucus, outside the body, where the concentrations of ions are not as well regulated as they are in normal interstitial compartments.

Preputial gland activates olfactory receptor neurons in rat: Calcium imaging study using laser scanning confocal microscopy.

The rodent preputial gland is one of the major sources of odours and is reported to be involved in several behavioural activities. However, how the preputial gland initiates the olfactory response to manifest the effects is not known. Olfactory receptor neurons (ORNs) present in the olfactory epithelium are involved in the perception of odorant/pheromonal compounds. In the present study, the response of rat ORNs to preputial gland extract was evaluated by calcium imaging analysis. We found that some rat ORNs responded to the preputial gland extract by exhibiting an intracellular calcium response. By contrast, the ORNs did not respond at all to the foot pad extract (control). The results indicated that the substances contained in the preputial gland might interact with a type of receptor expressed in the female rat ORNs, suggested to manifest the behavioural responses, such as social and sexual interactions. This study provided the first evidence of activation of ORNs by the preputial gland extract.

Sensopercepción olfatoria: una revisión / Olfactory sensory perception

The five senses have had a fundamental importance for survival and socialization of human beings. From an evolutionary point of view the sense of smell is the oldest. This sense has a strong representation within the genome, allowing the existence of many types of receptors that allow us to capture multiple volatile odor producing molecules, sending electrical signals to higher centers to report the outside world. Several cortical areas are activated in the brain, which are interconnected to form an extensive and complex neural network, linking for example, areas involved with memory and emotions, thus giving this sense of perceptual richness. While the concept of fl avor is largely related to the sense of taste, smell provides the necessary integration with the rest of the senses and higher functions. Fully understanding the sense of smell is relevant to health professionals. Knowing the characteristics of the receptors, the transduction processes and convergence of information in the higher centers involved, we can properly detect olfactory disorders in our patients.

Effects of steroid hormone on the expression of cyclic nucleotide-gated channels of olfactory receptor neurons / 中国耳鼻咽喉头颈外科

OBJECTIVE To observe the effects of Dexamethasone on the expression of cyclic nucleotide-gated channels (CNG channels) mRNA of olfactory receptor neurons (ORNs) by real-time quantitative reverse transcription-polymerase chain reaction(RT-PCR). METHODS Forty Wistar rats were randomly divided into four groups: 24-hours Dexamethasone treated group and its control group; 2-weeks Dexamethasone treated group and its control group. Dexamethasone was injected i.p. (1 mg/kg for 24-hours group, 0.2 mg/d for 2-weeks group). Control group rats were injected with the same volume of normal saline. Real-time quantitative RT-PCR was performed to evaluate mRNA production of CNGA2 subunits. RESULTS In Dexamethasone-injected rats, the up-regulation of CNGA2 mRNA was observed in 2-weeks group(P

The Effect of Superior Cervical Ganglionectomy on Recovery of Olfaction in Induced Anosmic Mice / 대한이비인후과학회지

BACKGROUND AND OBJECTIVES: This study was undertaken to evaluate the effect of superior cervical ganglionectomy (SCG) on anosmia, which is peripherally induced in the mice. MATERIALS AND METHOD: Three groups of mice (BCF1) were studied: normal control (nasal instillation of saline, n=6); zinc sulfate group (nasal instillation of 64 mM zinc sulfate, n=25); SCG group (superior cervical ganglionectomy after nasal instillation of 64 mM zinc sulfate, n=25). Tissues of olfactory mucosa were obtained at 1, 2, 3, 4 and 7 weeks after instillation of zinc sulfate, and processed for immunohistochemistry using antisera to olfactory marker protein (OMP) to evaluate the olfactory regeneration. RESULTS: No OMP-positive cells were observed in the first two weeks after the instillation of zinc sulfate in both zinc sulfate group and the SCG group. However, the OMP-positive cells appeared first at 3 weeks after the instillation in both groups, and gradually increased in number at 4 and 7 weeks. In the SCG group, the increase of OMP-positive cells was significantly greater than those of the zinc sulfate group. The number of OMP-positive cells in the SCG group at 7 weeks was almost similar to that of the normal control group. CONCLUSION: SCG enhances regeneration of olfactory receptor cells at 3 weeks after injury. It was inferred from the above results that SCG has a significant effect on the regeneration of olfactory receptor cells and we suggest that SCG could be an effective treatment modality for olfactory dysfunction.