Olfaction and neurogenesis in the olfactory epithelium

Anosmia was experimentally produced in strain C57BL/6 laboratory mice by treatment with 1% zinc sulfate solution. Structural and functional changes taking place in the olfactory epithelium were investigated during this process and during reinstatement of olfaction. Isoamyl acetate, butyl acetate, and substances present in murine urine were used as olfactory stimuli. Response to these odorants was found to recover from zinc sulfate action at different rates. The highest (both relative and absolute) daily rise in amplitude response was that induced by isoamyl acetate and butyl acetate and lowest in the case of odors of biological origin. Response to olfactory stimuli recovered most rapidly in the areas of the epithelium where maximum response to the same stimuli had been seen in intact animals."Biopharmautomatica" Combined Research and Production Unit, Gor'kii. Translated from Neirofiziologiya, Vol. 22, No. 4, pp. 500–506, July–August, 1990.     

Electroolfactogram study of the unilaterally axotomized frog

Changes of amplitude in the electroolfactogram (EOG) were investigated following unilateral section of the olfactory nerve. A reduction in EOG amplitude was observed during the first two weeks after the operation; electrical activity gradually began to return to normal and reached 80–100% of control level for trial substances by the end of the third week. Complete disappearance of EOG over the entire surface of the olfactory organ was not observed in any of the animals. A reduction in EOG amplitude was also noted on the unoperated side of the olfactory organ. These changes were less pronounced: the decrease in electrical response level began at a later stage, while complete recovery in amplitude was achieved sooner. Findings showed that EOG amplitude changed at different rates in different areas of the olfactory epithelium; it decreased sooner and began to recover at a later stage in the caudal than in the centromedial portion of the olfactory organ.Institute of Applied Mathematics and Cybernetics, N. I. Lobachevskii University, Gor'kii. Translated from Neirofiziologiya, Vol. 18, No. 5, pp. 603–610, September–October, 1986.     

Age-related changes in olfactory sensitivity of laboratory mice

Age-related alterations in the electrical response of olfactory epithelium to odorant-induced stimulation and certain morphometric indices were investigated in male and female laboratory mice of strains C57BL/6 (B6) and AKR (AK). It was found that maximum amplitude of response to odorants characterized young and adolescent animals. Ageing is accompanied by a decline in response level in the olfactory epithelium. Age-related distinctions between morphometric characteristics of the olfactory organ such as overall area and depth of the olfactory epithelium were noted.Applied Mathematics and Cybernetics Research Institute, N. I. Lobachevskii University, Gor'kii. Translated from Neirofiziologiya, Vol. 21, No. 6, pp. 723–729, November–December, 1989.     

Morphofunctional research into the mouse olfactory organ following the action of zinc sulfate

Correlations between morphological and functional changes occurring in the olfactory epithelium after treatment with various concentrations of zinc sulfate were investigated during experiments on mice. Electroolfactogram recordings (EOG) and epithelium morphometry showed that the intensity of damaging effects and the speed of regenerative processes at work in the epithelium are concentration-dependent. Amplitude of EOG and thickness of the olfactory epithelium have almost reached their normal level by the first month after olfactory epithelium treatment with a 1% zinc sulfate solution, while recuperative processes have only just started during this period when higher concentrations were used. It was noted that the capacity for generating EOG recovered well after processes of structural recovery in the olfactory epithelium and that application of higher concentrations of zinc sulfate (3 and 5%) increased the amount by which rise in EOG amplitude lagged behind thickening of the epithelium compared with the 1% solution.Research Institute of Applied Mathematics and Cybernetics, N. I. Lobachevskii University, Gor'kii. Translated from Neirofiziologiya, Vol. 19, No. 6, pp. 796–802, November–December, 1987.     

Integral evoked potentials and single unit activity in the frog olfactory bulb

Integral evoked potentials and intracellular potentials of single units were recorded from the frog olfactory bulb in response to afferent stimulation by two methods: electrical stimulation of the olfactory nerve and natural stimulation with odorous substances. At least four components can be distinguished in the response of the olfactory bulb to single electrical stimulation: an integral action potential of the olfactory nerve fibers, a synaptic glomerular potential, and two polysynaptic components. Responses of mitral and superficial (interglomerular) bulb cells to orthodromic electrical stimulation and antidromic stimulation of the olfactory tract are described. A functional similarity between the mitral cells of frogs and the analogous cells of rabbits is noted. Responses of the bulb to stimulation of olfactory receptors by odorous substances are characterized by regular waves of potentials. Corresponding waves of postsynaptic potentials are observed in the interglomerular cells of the bulb. These latter must, therefore, participate in generation of the rhythmic response. During stimulation by odorous substances, prolonged PSPs, producing excitation or inhibition of the spike discharge, arise in various cells of the bulb. The results of component analysis of the integral response and the functional properties of single bulb units are discussed.Institute of Problems of Information Transmission, Academy of Sciences of the USSR, Moscow; Institute of Biology of Internal Waters, Academy of Sciences of the USSR, Borok, Yaroslavl'Region. Translated from Neirofiziologiya, Vol. 1, No. 3, pp. 269–277, November–December, 1969.     

Olfactory rhythm in the electrical activity of the human amygdaloid nucleus

Summated electrical activity of the human amygdaloid nucleus was investigated in the neurosurgical clinic by chronically implanted electrodes. It was found that odoriferous stimulation of this structure produced bursts of rapid rhythm (20–30 cps, 30–50 µV). The quasisinusoidal waves of olfactory rhythm consist of sinusoidal components which are more pronounced within the 20–30-Hz frequency range. Spindling of 1–3 sec duration occurs at the end of inhalation and the beginning of exhalation in time with breathing. During monorhinal breathing this activity, whose amplitude depends on degree of olfactory stimulation, can only be recorded ipsilaterally. Room air also activates the amygdaloid nucleus, but less strongly than odoriferous substances: No characteristic odor-dependent differences were discovered in the frequency range of the olfactory rhythm within a 20–30-Hz band.Institute of Physiology, Kiev State University, Kiev. Translated from Neirofiziologiya, Vol. 18, No. 1, pp. 61–69, January–February, 1986.     

Electrophysiological evidence for detection and discrimination of pheromonal bile acids by the olfactory epithelium of female sea lampreys (<Emphasis Type="Italic">Petromyzon marinus</Emphasis>)

Electro-olfactograms were used to determine sensitivity and specificity of olfactory organs of female sea lampreys (Petromyzon marinus) to four bile acids: 3-keto petromyzonol sulfate and 3-keto allocholic acid from spermiating males and petromyzonol sulfate and allocholic acid from larvae. Spermiating male bile acids are thought to function as a mating pheromone and larval bile acids as a migratory pheromone. The response threshold was 10^–12 mol l^–1 for 3-keto petromyzonol sulfate and 10^–10 mol l^–1 for the other bile acids. At concentrations above 10^–9 mol l^–1, the sulfated bile acids showed almost identical potency, as did the non-sulfated bile acids. The two sulfated bile acids were more potent than the two non-sulfated ones. In addition, 3-keto petromyzonol sulfate and water conditioned with spermiating males induced similar concentration-response curves and response thresholds. Cross-adaptation experiments demonstrated that the sulfated and non-sulfated bile acids represent different odors to the olfactory epithelium of females. Further exploration revealed that 3-keto petromyzonol sulfate represents a different odor than petromyzonol sulfate, while 3-keto allocholic acid and allocholic acid represent the same odor. Results indicate that male-specific bile acids are potent and specific stimulants to the female olfactory organ, supporting the previous hypothesis that these bile acids function as a pheromone.Abbreviations 3kACA 3-keto allocholic acid - 3kPZS 3-keto petromyzonol sulfate - ACA allocholic acid - ANOVA analysis of variance - ELISA enzyme-linked immunosorbent assay - EOG electro-olfactogram - PIR percent initial response - PZS petromyzonol sulfate - SMW spermiating male washings     

Pharmacological study of inhibited frog olfactory bulb glomerular input produced by a puff of air on the olfactory mucosa

The effects of applying 4-aminopyridine (10^–2 M), aminooxyacetic acid (AOAA — 10^–4–10^–3 M), -alanine (10^–3–10^–2 M), and bicuculline (10^–5, 10^–4 M) to the intact frog olfactory bulb were investigated. Having measured inhibition of orthodromic potential postsynaptic components produced either by a puff of air on the olfactory mucosa (OB input inhibition) or by single electrical stimulation of the olfactory nerve (postsynaptic inhibition) or by single electrical stimulation of the olfactory nerve (postsynaptic inhibition), it was found that 4-aminopyridine greatly intensified postsynaptic inhibition but strongly reduced that of OB input; inhibition of the latter was raised by AOAA or bicuculline and decreased by -alanine. These substances failed to exert any consistent, clear-cut effects on postsynaptic inhibition. Findings would support the hypothesis that OB input inhibition produced by a puff of air on the olfactory mucosa could occur as a result of GABA release from glial cells and subsequent binding of GABA to presynaptic GABA_B-receptors in glomeruli.M. V. Lomonosov Moscow State University. Translated from Neirofiziologiya, Vol. 19, No. 1, pp. 12–20, January–February, 1987.     

Receptive fields of second-order neurons in the olfactory bulb of the hamster

Electrical stimulation of nerve fibers emerging from different positions of the olfactory epithelium was used to determine the receptive fields for 52 olfactory bulb neurons in the hamster. The responses of olfactory bulb neurons were recorded extracellularly with metal-filled micropipettes. Suprathreshold stimuli (500 microA) were applied to each of eight standard epithelial positions spaced approximately 250 microns apart, and the position, or positions, which, when stimulated, produced a response in the bulb were taken as an index of the neuron's receptive field. The results indicate that most bulb neurons have very localized receptive fields limited to only one or two stimulating positions. Furthermore, there was a statistically significant correlation between the location of a neuron's receptive field in the olfactory epithelium and the recording depth of the neuron in the olfactory bulb (Spearman rank correlation coefficient, rs, 0.67, P < 0.001). These findings demonstrate that in the mammalian olfactory system there exists a topographical projection of input from localized regions in the epithelium onto the second-order neurons in the olfactory bulb.     

Developmental expression of the calcium‐activated chloride channels TMEM16A and TMEM16B in the mouse olfactory epithelium

Calcium‐activated chloride channels are involved in several physiological processes including olfactory perception. TMEM16A and TMEM16B, members of the transmembrane protein 16 family (TMEM16), are responsible for calcium‐activated chloride currents in several cells. Both are present in the olfactory epithelium of adult mice, but little is known about their expression during embryonic development. Using immunohistochemistry we studied their expression in the mouse olfactory epithelium at various stages of prenatal development from embryonic day (E) 12.5 to E18.5 as well as in postnatal mice. At E12.5, TMEM16A immunoreactivity was present at the apical surface of the entire olfactory epithelium, but from E16.5 became restricted to a region near the transition zone with the respiratory epithelium, where localized at the apical part of supporting cells and in their microvilli. In contrast, TMEM16B immunoreactivity was present at E14.5 at the apical surface of the entire olfactory epithelium, increased in subsequent days, and localized to the cilia of mature olfactory sensory neurons. These data suggest different functional roles for TMEM16A and TMEM16B in the developing as well as in the postnatal olfactory epithelium. The presence of TMEM16A at the apical part and in microvilli of supporting cells is consistent with a role in the regulation of the chloride ionic composition of the mucus covering the apical surface of the olfactory epithelium, whereas the localization of TMEM16B to the cilia of mature olfactory sensory neurons is consistent with a role in olfactory signal transduction. © 2013 Wiley Periodicals, Inc. Develop Neurobiol 74: 657–675, 2014     

Feinstruktur des Riechepithels von Calamoichthys calabaricus J. A. Smith (Pisces,Brachiopterygii)

Zusammenfassung Die vorliegende Untersuchung befaßt sich mit der Feinstruktur der Riechfalten von Calamoichthys calabaricus unter besonderer Berücksichtigung des Riech- und Flimmerepithels. — Das Flimmerepithel ist aus 3 Zelltypen aufgebaut: Flimmerzellen, wenigen Stützzellen und Basalzellen. Die Flimmerzellen sind mitochondrienreich und tragen bis zu 160 Flimmerhärchen pro Zelle. Diese Kinocilien besitzen an ihren Basalkörpern Zilienwurzeln, von denen ein Teil ins Zellinnere bis in Kernnähe zieht, während der andere Teil parallel zur Oberfläche verläuft und benachbarte Basalapparate verbindet. — Auch das Riechepithel, das gegen das Flimmerepithel scharf abgesetzt ist, besteht aus 3 Zelltypen: Rezeptoren, Stützzellen und Basalzellen. Die Rezeptoren haben eine einheitliche Gestalt und Struktur. Sie sind schlank keulenförmig und überragen mit einer kleinen Vesicula olfactoria die Epitheloberfläche. Seitlich sitzen an der Vesicula — unter konstant 25–27° Ablenkung von der Senkrechten — in der Regel 12 sensorische Cilien, die alle auf gleicher Höhe entspringen. Basal setzt sich das Rezeptorperikaryon in ein Axon fort. Die Axone mehrerer Rezeptoren vereinigen sich noch innerhalb des Epithels zu Bündeln, die durch die Basalmembran ins Bindegewebe ziehen. Die stark osmiophilen Stützzellen des Riechepithels durchziehen das Riechepithel von der Basalmembran bis zur Epitheloberfläche und tragen einzelne Cilien. Der verbreiterte Apikalteil der Stützzellen enthält zahlreiche Schleimvesikel, die auf eine sezernierende Funktion dieser Zellen hinweisen. Die präparative Behandlung von Riechepithelien wird kritisch diskutiert.

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Ultrastructure of the olfactory epithelium of Calamoichthys calabaricus J. A. Smith (Pisces, Brachiopterygii)

Summary The ciliary epithelium of the olfactory folds in Calamoichthys calabaricus is composed of ciliary cells, supporting cells, and basal cells. All ciliary cells contain numerous mitochondria and bear up to 160 kinocilia. Some rootlets of the basal bodies of the kinocilia, project towards the nucleus, while others run parallel to the epithelial surface and connect with neighbouring basal bodies. Ciliary and olfactory epithelia are separated from each other. — The olfactory epithelium contains olfactory receptor cells, supporting cells, and basal cells. The club shaped olfactory receptor cells have a uniform ultrastructure. The terminal portions of the olfactory dendrites form small olfactory vesicles which are seen above the olfactory surface. 12 sensory cilia project constantly to the more basal portion of the olfactory vesicles, each cilium forming a 25–27° angle with the vertical cell axis. Basally, an axon originates from each olfactory receptor cell. Axons from a number of olfactory receptor cells may combine to form bundles within the epithelium. The supporting cells of the olfactory epithelia are strongly osmiophilic. Supporting cells occur in all parts of the olfactory epithelium and bear few cilia. Numerous mucous vesicles, located within the apical region of the supporting cells, probably have a secretory function.

Mit Unterstützung durch die Deutsche Forschungsgemeinschaft.     

Characteristics of odorant elicited calcium fluxes in acutely-isolated chick olfactory neurons

To understand avian olfaction, it is important to characterize the peripheral olfactory system of a representative bird species. This study determined the functional properties of olfactory receptor neurons of the chicken olfactory epithelium. Individual neurons were acutely isolated from embryonic day-18 to newborn chicks by dissection and enzymatic dissociation. We tested single olfactory neurons with behaviorally relevant odorant mixtures and measured their responses using ratiometric calcium imaging; techniques used in this study were identical to those used in other studies of olfaction in other vertebrate species. Chick olfactory neurons displayed properties similar to those found in other vertebrates: they responded to odorant stimuli with either decreases or increases in intracellular calcium, calcium increases were mediated by a calcium influx, and responses were reversibly inhibited by 100 M L–cis–diltiazem, 1 mM Neomycin, and 20 M U73122, which are biochemical inhibitors of second messenger signaling. In addition, some cells showed a complex pattern of responses, with different odorant mixtures eliciting increases or decreases in calcium in the same cell. It appears that there are common features of odorant signaling shared by a variety of vertebrate species, as well as features that may be peculiar to chickens.     

Timberol? Inhibits TAAR5-Mediated Responses to Trimethylamine and Influences the Olfactory Threshold in Humans

In mice, trace amine-associated receptors (TAARs) are interspersed in the olfactory epithelium and constitute a chemosensory subsystem that is highly specific for detecting volatile amines. Humans possess six putative functional TAAR genes. Human TAAR5 (hTAAR5) is highly expressed in the olfactory mucosa and was shown to be specifically activated by trimethylamine. In this study, we were challenged to uncover an effective blocker substance for trimethylamine-induced hTAAR5 activation. To monitor blocking effects, we recombinantly expressed hTAAR5 and employed a commonly used Cre-luciferase reporter gene assay. Among all tested potential blocker substances, Timberol®, an amber-woody fragrance, is able to inhibit the trimethylamine-induced hTAAR5 activation up to 96%. Moreover, human psychophysical data showed that the presence of Timberol® increases the olfactory detection threshold for the characteristic fishy odor of trimethylamine by almost one order of magnitude. In conclusion, our results show that among tested receptors Timberol® is a specific and potent antagonist for the hTAAR5-mediated response to trimethylamine in a heterologous system. Furthermore, our data concerning the observed shift of the olfactory detection threshold in vivo implicate that hTAAR5 or other receptors that may be inhibited by Timberol® could be involved in the high affinity olfactory perception of trimethylamine in humans.     

Inhibition in the fish olfactory bulb

Inhibition in the olfactory bulb of the carp was studied by recording potentials from secondary neurons intracellularly. Three types of inhibition — trace, early, and late — can arise in neurons of the olfactory bulb. Trace inhibition corresponds to hyperpolarization about 20 msec in duration, which is closely connected with the spike, but it is not after-hyperpolarization but an IPSP. Early and late inhibition correspond to IPSPs of different parameters. The first has a latency of 0–50 msec (relative to the spike) and a duration of 60–400 msec; the corresponding values for the second are 100–400 msec and 0.5–3 sec. The possible mechanisms of these types of inhibition are discussed.M. V. Lomonosov Moscow State University. Translated from Neirofiziologiya, Vol. 3, No. 6, pp. 650–656, November–December, 1971.     

Functional Architecture of the Vomeronasal Organ of the Frog (Genus Rana)

Abstract The vomeronasal organ in the frog, genus Rana, is composed of three interconnected cavities; superior, middle and inferior, which are separated from and anterior to the principal olfactory cavity. The superior cavity is found just underneath the external naris and forms a vestibule both for the principal olfactory organ and the vomeronasal organ. The vomeronasal sensory epithelium is located in the medial region of the inferior cavity and contains ciliated cells and microvillous receptor cells. Inspection of microscopic sections of frogs that had been swimming in fluorescent colorants revealed fluorescence on the surface of the vomeronasal organ, but not on that of the olfactory organ. Observations in vivo show that water enters via the external naris by two fissures, one on each side of the movable nasal lid, passes the middle cavity to flow via the sensory epithelium of the inferior cavity. The design of the frog nose makes it possible for this amphibious animal to sample the chemical composition of its environment; above water the frog can inhale air and expose its olfactory organ to volatile substances; in water the vomeronasal organ samples water-borne substances. These new findings are discussed in relation to the air/water interface and the position of the amphibians in the evolution of terrestrial vertebrates.     

Lesion of the Olfactory Epithelium Accelerates Prion Neuroinvasion and Disease Onset when Prion Replication Is Restricted to Neurons

Natural prion diseases of ruminants are moderately contagious and while the gastrointestinal tract is the primary site of prion agent entry, other mucosae may be entry sites in a subset of infections. In the current study we examined prion neuroinvasion and disease induction following disruption of the olfactory epithelium in the nasal mucosa since this site contains environmentally exposed olfactory sensory neurons that project directly into the central nervous system. Here we provide evidence for accelerated prion neuroinvasion and clinical onset from the olfactory mucosa after disruption and regeneration of the olfactory epithelium and when prion replication is restricted to neurons. In transgenic mice with neuron restricted replication of prions, there was a reduction in survival when the olfactory epithelium was disrupted prior to intranasal inoculation and there was >25% decrease in the prion incubation period. In a second model, the neurotropic DY strain of transmissible mink encephalopathy was not pathogenic in hamsters by the nasal route, but 50% of animals exhibited brain infection and/or disease when the olfactory epithelium was disrupted prior to intranasal inoculation. A time course analysis of prion deposition in the brain following loss of the olfactory epithelium in models of neuron-restricted prion replication suggests that neuroinvasion from the olfactory mucosa is via the olfactory nerve or brain stem associated cranial nerves. We propose that induction of neurogenesis after damage to the olfactory epithelium can lead to prion infection of immature olfactory sensory neurons and accelerate prion spread to the brain.     

Composition and Biological Activity of Submerged Mycelium of the Xylotrophic Basidiomycete Lentinus edodes

The composition of submerged mycelium of Lentinus edodesgrown in laboratory fermenters was studied. The mycelium contained 23–24% proteins, 8–9% lipids, up to 1.8% phenolic substances, and a significant amount of inorganic substances, including calcium and iron. The fungus produced up to 5.0% intracellular and 3.5–4.0 g/l extracellular polysaccharides. The submerged mycelium stimulated the development of humoral immune response elicited by sheep red blood cells.     

Heterogeneity of molecular mechanisms the olfactor reception

In experiments on the frog isolated olfactory epithelium by using vital fluorescent microscope, odorants with fruit, rank, flower and camphor smell were shown to involve intracellular signaling systems in olfactory transduction. The odorants with different qualitative smells have different messenger and activity mechanisms. Intracellular messengers do not participate in reception of odorants with piquant and rotten smells. Thus the perception of different odour substances is maintained by physical and chemical processes. Hence, not only taste, carotid, medullar, but olfactory reception as well are characterised by heterogeneity of biophysical mechanisms.     

Olfaction in Three Genetic and Two MPTP-Induced Parkinson’s Disease Mouse Models

Various genetic or toxin-induced mouse models are frequently used for investigation of early PD pathology. Although olfactory impairment is known to precede motor symptoms by years, it is not known whether it is caused by impairments in the brain, the olfactory epithelium, or both. In this study, we investigated the olfactory function in three genetic Parkinson’s disease (PD) mouse models and mice treated with MPTP intraperitoneally and intranasally. To investigate olfactory function, we performed electro-olfactogram recordings (EOGs) and an olfactory behavior test (cookie-finding test). We show that neither a parkin knockout mouse strain, nor intraperitoneal MPTP treated animals display any olfactory impairment in EOG recordings and the applied behavior test. We also found no difference in the responses of the olfactory epithelium to odorants in a mouse strain over-expressing doubly mutated α-synuclein, while this mouse strain was not suitable to test olfaction in a cookie-finding test as it displays a mobility impairment. A transgenic mouse expressing mutated α-synuclein in dopaminergic neurons performed equal to control animals in the cookie-finding test. Further we show that intranasal MPTP application can cause functional damage of the olfactory epithelium.     

Development of the Olfactory Epithelium and Nasal Glands in TMEM16A-/- and TMEM16A+/+ Mice

TMEM16A/ANO1 is a calcium-activated chloride channel expressed in several types of epithelia and involved in various physiological processes, including proliferation and development. During mouse embryonic development, the expression of TMEM16A in the olfactory epithelium is dynamic. TMEM16A is expressed at the apical surface of the entire olfactory epithelium at embryonic day E12.5 while from E16.5 its expression is restricted to a region near the transition zone with the respiratory epithelium. To investigate whether TMEM16A plays a role in the development of the mouse olfactory epithelium, we obtained the first immunohistochemistry study comparing the morphological properties of the olfactory epithelium and nasal glands in TMEM16A^-/- and TMEM16A^+/+ littermate mice. A comparison between the expression of the olfactory marker protein and adenylyl cyclase III shows that genetic ablation of TMEM16A did not seem to affect the maturation of olfactory sensory neurons and their ciliary layer. As TMEM16A is expressed at the apical part of supporting cells and in their microvilli, we used ezrin and cytokeratin 8 as markers of microvilli and cell body of supporting cells, respectively, and found that morphology and development of supporting cells were similar in TMEM16A^-/- and TMEM16A^+/+ littermate mice. The average number of supporting cells, olfactory sensory neurons, horizontal and globose basal cells were not significantly different in the two types of mice. Moreover, we also observed that the morphology of Bowman’s glands, nasal septal glands and lateral nasal glands did not change in the absence of TMEM16A. Our results indicate that the development of mouse olfactory epithelium and nasal glands does not seem to be affected by the genetic ablation of TMEM16A.