Lake char (<Emphasis Type="Italic">Salvelinus namaycush</Emphasis>) olfactory neurons are highly sensitive and specific to bile acids

Bile acids have been implicated as chemical signals in spawning behaviour of lake char (Salvelinus namaycush). In this study, we investigated olfactory responses of lake char to bile acids by using the electro-olfactogram recording. Lake char detected 9 out of 38 bile acids tested at thresholds 0.02–0.5 nM. The most stimulatory included chenodeoxycholic acid, cholic acid, taurochenodeoxycholic acid, taurocholic acid, and taurolithocholic acid 3α-sulphate. Structure–activity analysis indicated that substituents in the side chain or hydroxyl sulphation were determinant elements for the recognition of individual bile acid receptors, while the position and orientation of hydroxyls or the type of amidation were important for effective stimulation. Three distinct types of concentration–response relationships were found, representing free, taurine- or glycine-amidated, and 3α-sulphated bile acids. Cross-adaptation and binary mixture experiments revealed the presence of multiple olfactory receptors for bile acids. Lake char were also capable of detecting petromyzonol sulphate at 1 nM, possibly via its own receptors. Our study further showed that the olfactory responses to bile acids were independent of those of known odorants including amino acids, prostaglandins and gonadal steroids. We conclude that lake char possess multiple olfactory receptors capable of discriminating bile acids produced and released by conspecifics.     

Transient and persistent tetrodotoxin-sensitive sodium currents in squid olfactory receptor neurons

Squid olfactory receptor neurons are primary bipolar sensory neurons capable of transducing water-born odorant signals into electrical impulses that are transmitted to the brain. In this study, we have identified and characterized the macroscopic properties of voltage-gated Na⁺ channels in olfactory receptor neurons from the squid Lolliguncula brevis. Using whole-cell voltage-clamp techniques, we found that the voltage-gated Na⁺ channels were tetrodotoxin sensitive and had current densities ranging from 5 to 169 pA pF⁻¹. Analyses of the voltage dependence and kinetics revealed interesting differences from voltage-gated Na⁺ channels in olfactory receptor neurons from other species; the voltage of half-inactivation was shifted to the right and the voltage of half-activation was shifted to the left such that a “window-current” occurred, where 10–18% of the Na⁺ channels activated and did not inactivate at potentials near action potential threshold. Our findings suggest that in squid olfactory neurons, a subset of voltage-gated Na⁺ channels may play a role in generating a pacemaker-type current for setting the tonic levels of electrical activity required for transmission of hyperpolarizing odor responses to the brain. Accepted: 1 October 1998     

The rodent accessory olfactory system

The accessory olfactory system contributes to the perception of chemical stimuli in the environment. This review summarizes the structure of the accessory olfactory system, the stimuli that activate it, and the responses elicited in the receptor cells and in the brain. The accessory olfactory system consists of a sensory organ, the vomeronasal organ, and its central projection areas: the accessory olfactory bulb, which is connected to the amygdala and hypothalamus, and also to the cortex. In the vomeronasal organ, several receptors—in contrast to the main olfactory receptors—are sensitive to volatile or nonvolatile molecules. In a similar manner to the main olfactory epithelium, the vomeronasal organ is sensitive to common odorants and pheromones. Each accessory olfactory bulb receives input from the ipsilateral vomeronasal organ, but its activity is modulated by centrifugal projections arising from other brain areas. The processing of vomeronasal stimuli in the amygdala involves contributions from the main olfactory system, and results in long-lasting responses that may be related to the activation of the hypothalamic–hypophyseal axis over a prolonged timeframe. Different brain areas receive inputs from both the main and the accessory olfactory systems, possibly merging the stimulation of the two sensory organs to originate a more complex and integrated chemosensory perception.     

A neural mechanism of hierarchical discrimination of odors in the olfactory cortex based on spatiotemporal encoding of odor information

We propose a neural mechanism for discrimination of different complex odors in the olfactory cortex based on the dynamical encoding scheme. Both constituent molecules of the odor and their mixing ratios are encoded simultaneously into a spatiotemporal activity pattern (limit cycle attractor) in the olfactory bulb [Hoshino O, Kashimori Y, Kambara T (1998) Biol Cybern 79:109–120]. We present a functional model of the olfactory cortex consisting of some dynamical mapping modules. Each dynamical map is represented by itinerancy among the limit cycle attractors. When a temporal sequence of spatial activity patterns corresponding to a complex odor is injected from the bulb to the network of the olfactory cortex, the neural activity state of each mapping module is fixed to a relevant spatial pattern injected. Recognition of an odor is accomplished by a combination of firing patterns fixed in all the mapping modules. The stronger the response strength of the component, the earlier the component is recognized. The hierarchical discrimination of an odor is made by recognizing the components in order of decreasing response strengths. Received: 28 November 1998 / Accepted in revised form: 17 December 1999     

Modifications of EEG Related to Directed Perception and Analysis of Olfactory Information in Humans

We recorded EEG in adult volunteers in the course of perception of smells of plant essential oils under conditions of directed attention. It was found that perception of olfactory information, even in the case of mild intensity of the smells inducing no aversive effects, correlates with noticeable changes in the EEG characteristics mostly typical of the reaction of nonspecific EEG activation induced by sensory stimulation and manifested in a decrease in the spectral power, SP, of low-frequency EEG components (6–10 Hz)). In addition, the SP of relatively high-frequency EEG components (11–25 Hz) increased; this effect was most pronounced in the occipital regions of the neocortex. Perception of the smells of essential oils was also accompanied by increases in the coherence of EEG oscillations, most intense in the β2 range (20–25 Hz). Such modifications were maximum in the left temporal/parietal region; this is interpreted as an indication of the special role of these cortical areas in the processes of interaction between the neocortical part of the olfactory analyzer and the respective structures of other analyzer systems. It is hypothesized that such interaction is necessary for the formation of a semantic image of the analyzed stimuli. Neirofiziologiya/Neurophysiology, Vol. 41, No. 1, pp. 70–78, January–February, 2009.     

Water temperature and pH influence olfactory sensitivity to pre-ovulatory and post-ovulatory ovarian pheromones in male Barilius bendelisis

The attractive response and sexual activity elicited by pre-ovulatory steroid sulphate and post-ovulatory 15K-PGF pheromones are greater in wild caught tubercular males and immature males which express breeding tubercles on the snout (at 12–13 days post androgen implant) than in non-tubercular and non-androgen implanted males of freshwater fishBarilius bendelisis. This shows that circulatory androgens exert an activational effect on olfactory receptors of male fish. Wild caught tubercular males and androgen implanted juvenile males exhibit a high responsiveness to steroid sulphate at the water temperature and pH which fish experience during the pre-spawning phase. The male’s sensitivity to 15K-PGF is almost equally high at the water temperature and pH which they experience in wild during the both pre-spawning and spawning periods. This suggests that the differential olfactory sensitivity to the two classes of pheromones in androgen implanted males is due to the varied temperature and pH of water, and that during the breeding season the male’s olfactory sensitivity to PGF pheromone is more widespread than to the steroidal pheromone. An increased and decreased olfactory sensitivity in mature males to sex pheromones and L-alanine respectively during the breeding phase is in agreement with the hypothesis that pheromonal stimuli dominate over feeding stimuli to promote spawning success.     

Olfactory sensitivity to amino acids in the blackspot sea bream (<Emphasis Type="Italic">Pagellus bogaraveo</Emphasis>): a comparison between olfactory receptor recording techniques in seawater

The current study investigated the olfactory sensitivity of the blackspot sea bream to amino acids, odorants associated with food detection in fish, and compared the efficacy of two different experimental methods: multi-unit recording from the olfactory nerve and the electro-olfactogram (EOG). Twenty essential amino acids plus l-DOPA evoked clear, concentration-dependent olfactory responses using both methods, with estimated thresholds of 10^−8.5–10^−6.2 M (nerve recording) and 10^−7.5–10^−4.8 M (EOG). The most potent amino acids were l-cysteine, l-methionine (both sulphur-containing), l-alanine, l-leucine (both neutral), l-glutamine (amide-containing) and l-serine (hydroxyl-containing). The least potent were l-proline (secondary α-amino group), the aromatic amino acids and glycine (simplest). Although the rank order of olfactory potency was similar for the two methods used, and the calculated thresholds given by the two methods were positively correlated, the sensitivity of the EOG was consistently lower than multi-unit recording by approximately one order of magnitude, presumably due to the electrical shunting effect of seawater. As in freshwater, the EOG could be a valid method for comparing olfactory potency of different odorants in stenohaline marine fish; however, for absolute ‘biological’ thresholds, a more invasive recording technique, such as multi-unit recording from the olfactory nerve, should be used.     

Effect of B2m gene disruption on MHC-determined odortypes

 Major histocompatibility complex (MHC) genes confer individual olfactory identity that can be detected with exquisite accuracy by mice. The fact that MHC genes themselves generate the characteristic odortype, rather than dedicated odor-determining genes, was supported in studies of point mutations in H2K and HLA transgenic mice, which evinced distinct odor profiles in olfactory assays. In this article we provide further evidence for a central role of MHC genes themselves in odortype specification by demonstrating that mice that are unable to express their genomic class I MHC genes because they lack β₂-microglobulin are distinguishable by scent from otherwise identical mice which possess an intact B2m gene. This odortype disparity appears at 9–12 days of gestational age, the period in which the MHC is first detectable in fetal cells of normal mice. Received: 15 October 1999 / Revised: 30 December 1999     

Effects of bemitil and benzimidazole on behavior of rats in open-field test

Under conditions of the open-field test, we demonstrated that bemitil and benzimidazole injected intraperitoneally into rats in doses of 50 to 150 mg/kg suppress horizontal and vertical (motor and research) activities, as well as decrease the frequencies of episodes of grooming, defecation, and urination. Possible mechanisms underlying modifications of behavioral phenomena triggered by the above agents are discussed. Neirofiziologiya/Neurophysiology, Vol. 38, No. 1, pp. 85–90, January–February, 2006     

Space proton flux and the temporal distribution of cardiovascular deaths

 The influence of solar activity (SA) and geomagnetic activity (GMA) on human homeostasis has long been investigated. The aim of the present study was to analyse the relationship between monthly proton flux (>90 MeV) and other SA and GMA parameters and between proton flux and temporal (monthly) distribution of total and cardiovascular-related deaths. The data from 180 months (1974–1989) of distribution in the Beilinson Campus of the Rabin Medical Centre, Israel, and of 108 months (1983–1991) from the Kaunas Medical Academy, were analysed and compared with SA, GMA and space proton flux (>90 MeV). It was concluded: (1) monthly levels of SA, GMA and radiowave propagation (Fof2) are significantly and adversely correlated with monthly space proton flux (>90 MeV); (2) medical-biological phenomena that increase during periods of low solar and/or geomagnetic activity may be stimulated by physical processes provoked by the concomitant increase in proton flux; (3) the monthly number of deaths related (positively or negatively) to SA are significantly and adversely related to the space proton flux (>90 MeV). Received: 14 January 1996 / Accepted: 14 October 1996     

Identification of carbonic anhydrase activity in bullfrog olfactory receptor neurons: histochemical localization and role in CO2 chemoreception

The objectives of this study were to determine: (1) the frequency and distribution of carbonic anhydrase (CA) activity in the bullfrog nasal cavities, and (2)␣whether inhibition of nasal CA affects the olfactory receptor response to CO₂ or other odorants. It was found, using Hansson's staining technique, that some olfactory receptor neurons exhibited CA activity and that these CA-positive receptors were distributed throughout the nasal cavity with peak densities in the dorsal and ventral sensory epithelial regions. To test for the role of CA in olfactory transduction, electro-olfactograms (EOGs) were recorded from the surface of the ventral sensory epithelium in response to 2-s pulses of 5% CO₂ and amyl acetate before and after topical CA inhibition with acetazolamide (10⁻³mol · l⁻¹). In 52 bullfrogs, 1222 sites on the ventral epithelium were tested resulting in 23 locations that exhibited a response to 5% CO₂. Inhibition of CA caused an immediate 65% reduction in the EOG response to CO₂ while the response to amyl acetate was not affected. These results, along with the histochemical localization of CA in some olfactory receptor neurons, indicate that CA plays a role in the detection of CO₂ in frog olfactory neurons and that only a small population of olfactory receptor neurons are CO₂ sensitive. Accepted: 31 July 1997     

Functionality of divergence and convergence in a model of the insect olfactory system

Recent studies have shown that the insect olfactory system uses a spatio-temporal encoding of odours in the population of projection neurons in the antennal lobe, and suggest that the information thus coded is spread across a large population of Kenyon cells in the mushroom bodies. At this stage, the temporal part of the code might be transformed into a spatial code, especially via the temporally sensitive mechanisms of paired–pulse facilitation and feedback inhibition with its possible associated rebound. We explore here a simple model of the olfactory system using a three–layer network of formal neurons, comprising a fixed number (three) of projection and inhibitory neurons, but a variable number of Kenyon cells. We show how enlarging the divergence of the network (i.e. the ratio between the number of Kenyon cells to the number of input – projection – neurons) alters the number of different output spatial states in response to a fixed set of spatio-temporal inputs, and may therefore improve its effectiveness in discriminating between these inputs. Such enlarged divergence also reduces the variation of this effectiveness among random realisations of the network connectivity. Our model shows that the discriminative effectiveness first increases with the divergence, and then plateaus for a divergence factor of ∼20. The maximal average number of different outputs was 470.2, which was computed from some simulations with random realisations of connectivity and with a set of 512 possible inputs. The discriminative effectiveness of the network is sensitive to paired-pulse facilitation, and especially to inhibition with rebound. Received: 6 April 2001 / Accepted in revised form: 8 April 2002     

The effect of learning and search images on predator–prey interactions

In dealing with the spatial and temporal variability of prey species, predators may be able to forage optimally if they have flexible and rapid behavioral plasticity rather than predetermined responses. For predators that learn to focus attention on the cryptic prey type most frequently encountered during recent searching (termed a “search image”), rare prey types may be overlooked because of a focus on more common prey. Search imaging reflects biased searching for one of a number of available prey types, and has been studied widely in birds and mammals. Here we discuss the significant implications of this phenomenon for insect predator–prey systems, particularly with respect to parasitic wasps searching for host species using learned olfactory cues. We (1) review studies about perceptual development through individual ontogeny, (2) define the term “search image” and discuss the cognitive mechanisms involved in search-image formation, (3) discuss the role of search images and frequency-dependent predation as a proximate mechanism in the maintenance of prey diversity, (4) examine data on host–parasitoid olfactory search imaging, and (5) conclude by identifying important research areas for future studies in the field of olfactory search images.     

The effect of olfactory deprivation on the thresholds of sensitivity of skin chemoreceptors of carp <Emphasis Type="Italic">Cyprinus carpio</Emphasis>

Using method of registration of electrical potentials caused by chemical stimulation of the skin surface of the head of the carp Cyprinus carpio, the effect of prolonged olfactory deprivation (3, 9, and 12 months after operation) and partial blinding of anosmiated fish (9 months) on the sensitivity thresholds of external chemoreceptors was studied. It was found that, 3 months following anosmiation, the thresholds decreased by orders of 0.1–0.5, and, after 9 and 12 months, they decreased by orders of 0.1–0.8 depending on the kind of the chemical stimulus and the zone of registration. The highest increase in the sensitivity of skin chemoreceptors was recorded in anosmiated fish deprived also of object vision, by orders of 0.3–1.5. The results obtained indicate the existence of a close functional relationship between the olfactory and visual systems, on the one hand, and the skin chemosensory system, on the other hand. The compensatory processes taking place in these systems in the case of the loss of one of them have an adaptive pattern and are directed at provision of reliability of behavioral contacts and survival of fish in the environment.     

Sporadic sustained nonperiodic oscillations in the activities of organismic sets

In combining the author's theories of organismic sets (Rashevsky,Bull. Math. Biophysics,31, 159–198, 1969a) and Robert Rosen's theory of (M, R)-systems (Bull. Math. Biophysics,20, 245–265, 1958), a conclusion is reached that the number of either normal or pathological phenomena in organismic sets may occur. Those phenomena are characterized by occurring spontaneously once in a while but are not exactly periodic. Some epilepsies are an example of such pathological phenomena in the brain.     

Identification,release and olfactory detection of bile salts in the intestinal fluid of the Senegalese sole (<Emphasis Type="Italic">Solea senegalensis</Emphasis>)

Olfactory sensitivity to bile salts is wide-spread in teleosts; however, which bile salts are released in sufficient quantities to be detected is unclear. The current study identified bile salts in the intestinal and bile fluids of Solea senegalensis by mass spectrometry–liquid chromatography and assessed their olfactory potency by the electro-olfactogram. The main bile salts identified in the bile were taurocholic acid (342 mM) and taurolithocholic acid (271 mM) plus a third, unidentified, bile salt of 532.3 Da. These three were also present in the intestinal fluid (taurocholic acid, 4.13 mM; taurolithocholic acid, 0.4 mM). In sole-conditioned water, only taurocholic acid (0.31 μM) was released in sufficient quantities to be measured (release rate: 24 nmol kg⁻¹ min⁻¹). Sole had high olfactory sensitivity to taurocholic acid but not to taurolithocholic acid. Furthermore, olfactory sensitivity was higher in the upper (right) olfactory epithelium than the lower (left). These two bile acids contribute about 40% of the olfactory potency of intestinal fluid and account for the difference in potency at the two epithelia. Taurocholic acid (but not taurolithocholic acid), and possibly other types of bile acid not tested, could be used as chemical signals and the upper olfactory epithelium is specialised for their detection.     

Renewing olfactory receptor neurons in goldfish do not require contact with the olfactory bulb to develop normal chemical responsiveness

This study investigated whether contact with the olfactory bulb was necessary for developing and renewing olfactory receptor neurons (ORNs) to attain normal odorant responsiveness, and whether the anatomical and functional recoveries of the olfactory epithelium were similar in both bulbectomized (BE) and bilaterally axotomized (AX) preparations. In vivo electrophysiological recordings were obtained in response to amino acids, a bile acid [taurolithocholic acid sulfate(TLCS)] and a pheromonal odorant [17α, 20β,-dihydroxy-4-pregnen-3-one (17,20P)] from sexually immature goldfish. Both transmission and scanning electron microscopy indicated that the olfactory epithelium degenerated in BE and AX goldfish. Within 1–2 weeks subsequent to the respective surgeries, responses to high concentrations (>0.1 mmol · l⁻¹) of the more stimulatory amino acids remained, whereas responses were no longer obtainable to TLCS and 17,20P. At 4 weeks, responses to amino acid stimuli recovered to control levels, while responses to TLCS and 17,20P were minimal. By 7 weeks post bilateral axotomy, the olfactory epithelium recovered to a condition similar to control sensory epithelium; however, the rate of degeneration and proliferation of receptor neurons in BE preparations appeared to remain in balance, thus blocking further recovery of the olfactory epithelium. At 7 weeks post surgery, odorant responses of AX and BE goldfish to TLCS and 17,20P were still recovering. Accepted: 14 June 1997     

Amitriptyline reduces olfactory neuron adenylyl cyclase activity

Adenylyl cyclase plays an important role in olfactory signaltransduction. Recently, a novel type III adenylyl cyclase hasbeen localized in olfactory neurons (Pfeuffer et al., 1989;Bakalyar and Reed, 1990). Because amitriptyline (AMI), a tricyclicantidepressant, appears to have an inhibitory effect on adenylylcyclase activity in other in other neuronal tissue (Yamaokaet al., 1988; Wong et al., 1991), we measured the effect ofAMI on forskolin-stimulated adenylyl cyclase activity in membranepreparations of olfactory mucosa from adult rats. In the presenceof 5'-guanylyl-imidodiphosphate, AMI (0.5–8.0 µM)inhibited forskolin-stimulated adenylyl cyclase activity ina dose-dependent manner. To determine whether this effect wasspecific for olfactory neurons, as opposed to other cells inthe olfactory epithelium, rats were unilaterally bulbectomizedin order to reduce selectively the number of olfactory neuronson the side ipsilateral to the bulbectomy. In membrane preparationsfrom unilaterally bulbectomized animals we saw significantlylower adenylyl cyclase activity in ipsilateral olfactory mucosa,compared with adenylyl cyclase activity from non-bulbectomizedmucosa. These results indicate that AMI inhibition of adenylylcyclase activity is primariy localized in olfactory neurons.     

A nonlinear dynamical mechanism for bruit generation by an intracranial saccular aneurysm

 Intracranial saccular aneurysms have been clinically observed to emit a transient sound, a bruit, on each heartbeat. The mechanism causing the bruits has been a matter of contention. A qualitative analysis of the nonlinear dynamical properties of the Shah-Humphrey model for periodic pressure forcing of a thin-necked saccular aneurysm, using the Fung nonlinear constitutive model for the aneurysm material, shows that a small blood pressure jump on each beat, whether the pressure is weakly aperiodic or periodic, induces transients in the radial deformation response of the aneurysmal wall on each heartbeat. These transient vibrations, which have a component with frequency near the natural frequency of the system but are not resonant phenomena and which decay rapidly to a limit cycle during each distinct forcing pressure cycle, can generate the bruits. Received: 21 November 2000 / Revised version: 9 August 2001 / Published online: 23 August 2002 Mathematics Subject Classification (2000): 92B99, 70K40, 70K05 Key words or phrases: Intracranial saccular aneurysm – Bruit – Spectrum – Nonlinear dynamics – Transients – Vortex shedding – Fung model