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PubMed2001

Ovarian steroid sulphate functions as priming pheromone in male Barilius bendelisis (Ham.).

The study reveals that pre-ovulatory females of the fish Barilius bendelisis (Ham.) release sex steroids and their conjugates into the water and that a steroid sulphate of these compounds functions as a potent sex pheromone which stimulates milt production in conspecific males prior to spawning. Since males exposed to the purified subfraction III of the steroid sulphate fraction have increased milt volume and more spermatozoa with greater motility, the function of this priming pheromone appears to be to enhance male spawning success. High turbulence and faster water currents render the hillstream ecosystem extremely challenging for chemical communication. Therefore, ovulatory female fish secrete highly water soluble steroid sulphates for rapid pheromonal action in males. Inhibited milt volume in olfactory tract lesioned (OTL) males exposed to the steroid sulphate fraction and 17alpha,20 beta-dihydroxy-4-pregnen-3-one supports the concept that the pheromonally induced priming effect in male fish is mediated through olfactory pathways.

Animals↗
PubMed2006

Parallel processing of social signals by the mammalian main and accessory olfactory systems.

The mammalian olfactory system has evolved complex mechanisms to detect a vast range of molecular cues. In rodents, the olfactory system comprises several distinct subsystems. Current interest has focused on the exact role that each of these subsystems plays in detecting molecular information and regulating chemosensory-dependent behaviors. Here, we summarize recent results showing that the mouse main and accessory olfactory systems detect, at least in part, overlapping sets of social chemosignals. These findings give rise to a model that involves parallel processing of the same molecular cues in both systems. Together with previous work, this model will lead to a better understanding of the general organization of chemical communication in mammals and give a new direction for future experiments.

Animals↗
PubMed2001

Ligand-receptor interaction under periodic stimulation: a modeling study of concentration chemoreceptors.

The first step of chemosensory transduction consists in the association of ligand molecules with receptor proteins borne by the cell membrane. In this article, the time evolution of ligand-receptor complexes is studied in the presence of a periodically changing ligand concentration. This type of stimulation is a close approximation to some natural situations, for example in olfaction. The transient and steady-state periodic levels of the complexes, resulting from a single-step (binding) or double-step (binding and activation) reaction, are determined. When possible, analytical solutions are given, if not for the complete model, at least for its simplified version at low ligand concentration. Otherwise, solutions are found numerically and both the complete and simplified versions of the model are compared. The results obtained are discussed with respect to actual experimental data based on the moth sex-pheromone receptor. Periodic steady states are achieved very quickly and their amplitude decreases when the stimulation frequency increases. We show that the simplified description is adequate if only a fraction of activated receptors is sufficient to produce the maximum response, as is actually the case in the example treated. The role of the frequency of stimulation is investigated and it is shown to possess an optimal range between 2 and 5 Hz.

Animals↗
PubMed2003

(-)-Germacrene D receptor neurones in three species of heliothine moths: structure-activity relationships.

Specificity of olfactory receptor neurones plays an important role in food and host preferences of a species, and may have become conserved or changed in the evolution of polyphagy and oligophagy. We have identified a major type of plant odour receptor neurones responding to the sesquiterpene germacrene D in three species of heliothine moths, the polyphagous Heliothis virescens and Helicoverpa armigera and the oligophagous Helicoverpa assulta. The neurones respond with high sensitivity and selectivity to (-)-germacrene D, as demonstrated by screening via gas chromatography with numerous mixtures of plant volatiles. Germacrene D was present in both host and non-host plants, but only in half of the tested species. The specificity of the neurones was similar in the three species, as shown by the "secondary" responses to a few other sesquiterpenes. The effect of (-)-germacrene D was about ten times stronger than that of the (+)-enantiomer, which again was about ten times stronger than that of (-)-alpha-ylangene. Weaker effects were obtained for (+)-beta-ylangene, (+)-alpha-copaene, beta-copaene and two unidentified sesquiterpenes. The structure-activity relationship shows that the important properties of (-)-germacrene D in activating the neurones are the ten-membered ring system and the three double bonds acting as electron-rich centres, in addition to the direction of the isopropyl-group responsible for the different effects of the germacrene D enantiomers.

Action Potentials↗
PubMed2004

Representation of binary pheromone blends by glomerulus-specific olfactory projection neurons.

An outstanding challenge in olfactory neurobiology is to explain how glomerular networks encode information about stimulus mixtures, which are typical of natural olfactory stimuli. In the moth Manduca sexta, a species-specific blend of two sex-pheromone components is required for reproductive signaling. Each component stimulates a different population of olfactory receptor cells that in turn target two identified glomeruli in the macroglomerular complex of the male's antennal lobe. Using intracellular recording and staining, we examined how responses of projection neurons innervating these glomeruli are modulated by changes in the level and ratio of the two essential components in stimulus blends. Compared to projection neurons specific for one component, projection neurons that integrated information about the blend (received excitatory input from one component and inhibitory input from the other) showed enhanced ability to track a train of stimulus pulses. The precision of stimulus-pulse tracking was furthermore optimized at a synthetic blend ratio that mimics the physiological response to an extract of the female's pheromone gland. Optimal responsiveness of a projection neuron to repetitive stimulus pulses therefore appears to depend not only on stimulus intensity but also on the relative strength of the two opposing synaptic inputs that are integrated by macroglomerular complex projection neurons.

Action Potentials↗
PubMed2005

Physiology and glomerular projections of olfactory receptor neurons on the antenna of female Heliothis virescens (Lepidoptera: Noctuidae) responsive to behaviorally relevant odors.

The neurophysiology and antennal lobe projections of olfactory receptor neurons housed within short trichoid sensilla of female Heliothis virescens F. (Noctuidae: Lepidoptera) were investigated using a combination of cut-sensillum recording and cobalt-lysine staining techniques. Behaviorally relevant odorants, including intra- and inter-sexual pheromonal compounds, plant and floral volatiles were selected for testing sensillar responses. A total of 184 sensilla were categorized into 25 possible sensillar types based on odor responses and sensitivity. Sensilla exhibited both narrow (responding to few odors) and broad (responding to many odors) response spectra. Sixty-six percent of the sensilla identified were stimulated by conspecific odors; in particular, major components of the male H. virescens hairpencil pheromone (hexadecanyl acetate and octadecanyl acetate) and a minor component of the female sex pheromone, (Z)-9-tetradecenal. Following characterization of the responses, olfactory receptor neurons within individual sensilla were stained with cobalt lysine (N=39) and traced to individual glomeruli in the antennal lobe. Olfactory receptor neurons with specific responses to (Z)-9-tetradecenal, a female H. virescens sex pheromone component, projected to the female-specific central large female glomerulus (cLFG) and other glomeruli. Terminal arborizations from sensillar types containing olfactory receptor neurons sensitive to male hairpencil components and plant volatiles were also localized to distinct glomerular locations. This information provides insight into the representation of behaviorally relevant odorants in the female moth olfactory system.

Animals↗
PubMed2005

The chemosensory basis for behavioral divergence involved in sympatric host shifts II: olfactory receptor neuron sensitivity and temporal firing pattern to individual key host volatiles.

The Rhagoletis species complex has been a key player in the sympatric speciation debate for much of the last 50 years. Studies indicate that differences in olfactory preference for host fruit volatiles could be important in reproductively isolating flies infesting each type of fruit via premating barriers to gene flow. Single sensillum electrophysiology was used to compare the response characteristics of olfactory receptor neurons from apple, hawthorn, and flowering dogwood-origin populations of R. pomonella, as well as from the blueberry maggot, R. mendax (an outgroup). Eleven volatiles were selected as stimuli from behavioral/electroantennographic studies of the three R. pomonella host populations. Previously, we reported that differences in preference for host fruit volatile blends are not a function of alterations in the general class of receptor neurons tuned to key host volatiles. In the present study, population comparisons involving dose-response trials with the key volatiles revealed significant variability in olfactory receptor neuron sensitivity and temporal firing pattern both within and among Rhagoletis populations. It is concluded that such variability in peripheral sensitivity and temporal firing pattern could influence host preference and contribute to host fidelity and sympatric host shifts in the Rhagoletis complex.

Action Potentials↗
PubMed2005

The chemosensory basis for behavioral divergence involved in sympatric host shifts. I. Characterizing olfactory receptor neuron classes responding to key host volatiles.

The recent shift of Rhagoletis pomonella from its native host hawthorn to introduced, domestic apple has been implicated as an example of sympatric speciation. Recent studies suggest that host volatile preference might play a fundamental role in host shifts and subsequent speciation in this group. Single sensillum electrophysiology was used to test a proposed hypothesis that differences in R. pomonella olfactory preference are due to changes in the number or odor specificity of olfactory receptor neurons. Individuals were analyzed from apple, hawthorn, and flowering dogwood-origin populations, as well as from the blueberry maggot, Rhagoletis mendax Curran (an outgroup). Eleven compounds were selected as biologically relevant stimuli from previous electroantennographic/behavioral studies of the three R. pomonella populations to host fruit volatiles. Cluster analysis of 99 neuron responses showed that cells from all tested populations could be grouped into the same five classes, ranging from those responding to one or two volatiles to those responding to several host volatiles. Topographical mapping also indicated that antennal neuron locations did not differ by class or fly taxa. Our results do not support the hypothesis that differences in host preference among Rhagoletis populations are a result of alterations in the number or class of receptor neurons responding to host volatiles.

Animals↗
PubMed2005

Interactions of mechanical stimuli and sex pheromone information in antennal lobe neurons of a male moth, Spodoptera littoralis.

Male moths respond to sex pheromone sources with up-wind flight behaviour. Localization of the odour source requires not only detection of the olfactory stimulus, but also other sensory input regarding, e.g. visual and mechanical stimuli. Thus, integration of different types of sensory input is necessary. It is, however, not known where in the central nervous system the integration of information regarding different sensory modalities takes place. Using intracellular recording and staining techniques, we investigated neurons in the antennal lobe of Spodoptera littoralis, during stimulation with a mechanical stimulus and a sex pheromone. Fifteen percent of all the neurons investigated responded to the mechanical stimulus and the majority of these neurons showed altered responses if the olfactory stimulus was added. A receptor neuron responding only to the wind stimulus was found to arborise in the antennal lobe. Most projection neurons responded with an enhanced action potential frequency to the combined stimulus. In local interneurons, enhancement, depression, or no change of the responses to the wind stimulus was found when the olfactory stimulus was added. The results suggest that neurons present in the antennal lobe integrate mechanosensory and olfactory input, possibly assisting the moths to orient during up-wind flight towards an odour source.

Action Potentials↗
PubMed2001

Mutations affecting the cAMP transduction pathway modify olfaction in Drosophila.

The rutabaga and dunce genes, encode two enzymes of the cyclic adenosine monophosphate transduction pathway in Drosophila, adenylyl cyclase and cyclic adenosine monophosphate phosphodiesterase, respectively. Two main second messenger systems, depending on inositol 1,4,5-triphosphate and cyclic adenosine monophosphate, have been associated with olfaction in vertebrates as well as invertebrates. A relationship between the cyclic adenosine monophosphate signaling pathway and olfactory reception in Drosophila is suggested by the presence of cyclic nucleotide gated channels and cyclic-nucleotide modulated K+ channels in the antennae, the main olfactory organs. In this report, molecular, electrophysiological and behavioral data support the role of cyclic adenosine monophosphate in olfactory function for this species. Expression of both genes in the antennae has been shown by messenger ribonucleic acid analysis. Changes in the electroantennogram kinetics have been observed specifically on the slope of the initial rising phase, as predicted for processes that affect cyclic adenosine monophosphate concentration. Olfactory behavior changes due to both mutations were coherent with a functional meaning of the reported electrophysiological phenotype in olfactory perception. Sensitivity level increases or decreases for the mutants compared to the control line depending on the odorant. These results are compatible with some olfactory coding at the reception level by differential activation of a dual transduction system involving the inositol 1,4,5-triphosphate and cyclic adenosine monophosphate cascades.

Acetates↗
PubMed2003

The alteration of odor-induced c-Fos immunoreactivity in the rat olfactory bulb after olfactory nerve transection.

We used the rats in which one olfactory nerve had been transected and observed the odor (Propionic acid) -induced c-Fos immunoreactivity in the bulb at different times (2, 4, 8 weeks) after nerve transection. The exposure to odor produced a strong cluster of c-Fos positive cells in the mediodorsal region of the intact bulb. On the other hand, the transected bulb showed much less reactivity 2 weeks after neurectomy; however, a large number of positive cells were observed in the whole of the bulb from 4 weeks after neurectomy. Furthermore, we measured the levels of mRNA for tyrosine hydroxylase (TH), which was the marker of odor-induced olfactory nerve activity in the bulb, by using real-time PCR. The level of TH mRNA decreased on the transected side at 2 weeks but recovered to the level of the contralateral side at 4 weeks after neurectomy. We firstly demonstrated that projection mapping of odor receptors was altered after olfactory nerve transection by using an immunohistochemical method.

Animals↗
PubMed2003

Three-dimensional organization of the glomeruli in the antennal lobe of the parasitoid wasps Cotesia glomerata and C. rubecula.

Two closely related parasitoid wasp species, Cotesia glomerata and C. rubecula, differ in their use of associative learning. To investigate the neural basis underlying these differences, it is necessary to describe the olfactory pathway of both wasp species. This paper focuses on the organization of the glomeruli in the antennal lobe. Glomeruli were stained by retrograde axon tracing of all axons in the antennal nerve and observed by confocal laser scanning microscopy. Stacks of optical sections were processed with AMIRA software, and 3D digital models of the glomeruli were produced. The combined use of 2D images and 3D surface models of the antennal lobes enabled the identification of a set of corresponding glomeruli in both wasp species. This offers unique opportunities for the study of subtle differences involved in synaptic plasticity that may occur at the glomerular level and factors regulating this plasticity.

Animals↗
PubMed2001

Comparative pathogenesis of acute and latent infections of calves with bovine herpesvirus types 1 and 5.

This study was conducted to compare the pathogenesis of acute and latent infections with closely related bovine herpesvirus types 1 (BHV-1) and 5 (BHV-5) in their natural host. Two groups of eight calves were inoculated intranasally with BHV-1 or BHV-5. Although BHV-1 and BHV-5 similarly replicate in the nasal mucosa after inoculation, both viruses differ markedly in their ability to cause disease, BHV-5 being responsible of some fatal encephalitis while BHV-1 inducing rhinotracheitis. Virus isolation and immunohistochemistry demonstrated that BHV-5 replicates extensively in neurons of the central nervous system (CNS) and in respiratory cells of lungs, tracheal and nasal mucosae. Invasion of the CNS likely occurs through the trigeminal and olfactory pathways. Both groups developed cross-neutralising antibodies during this experiment suggesting partial clinical cross-protection afforded by the two infections. Three months after primary infection, experimental reactivation showed that BHV-5 was able to establish latency in the trigeminal ganglia but also the CNS of surviving calves. Moreover, laboratory findings suggested that BHV-5 could also persist in the tracheal and nasal mucosae. These results indicate that, after primary infection, BHV-1 and BHV-5 displayed similar biological features and consequently need to be considered together for the control of BHV-1 infection.

Acute Disease↗
PubMed2002

Cloning and characterization of SLP3: a novel member of the stomatin family expressed by olfactory receptor neurons.

The detection of odorants with high sensitivity and specificity utilizes specialized transduction proteins that may be assembled into complexes to afford enhanced speed and efficiency in olfactory neurons. We have used a differential cDNA screening technique to identify novel gene products that display restricted expression within the olfactory epithelium. Here we report the characterization of an olfactory neuronal protein, SLP3, which shares extensive homology with the stomatin family of membrane proteins. Other stomatin family members have been implicated in specific interactions with ion channels and G protein-coupled receptors. The pattern of SLP3 mRNA expression during embryonic development and the subcellular localization of the SLP3 protein in mature olfactory neurons observed here is consistent with a specific role for this protein in the assembly, translocation, or function of the odorant transduction complex in olfactory neurons.

Amino Acid Sequence↗
PubMed1984

Processing of olfactory information at three neuronal levels in the spiny lobster.

Odor quality coding was analyzed at three neuronal levels, receptor cells and two levels of chemosensory interneurons, in the olfactory system of the spiny lobster Panulirus argus . Responses to three of the most stimulatory compounds for this animal - taurine, glutamate and betaine - were recorded at each level in order to compare basic neuronal response properties, single cell and population response spectra, and across-neuron patterns. Mean response specificity increased for cells at each successive neuronal level. The increase in breadth of tuning between receptor cells and low-order interneurons was paralleled by an increase in interstimulus across-neuron correlations. However, in high-order interneurons, there was a relative decline in across-neuron correlations, indicating that the more broadly-tuned high-order interneurons are better able to discriminate between any two compounds than are the more narrowly-tuned low-order interneurons. Although stimulus quality appears to be coded by interneurons as an across-fiber pattern, the fact that some low-order and high-order interneurons retained the narrow specificity of receptor cells suggests that labeled lines may have an important function in coding throughout the olfactory pathway of the spiny lobster.

Animals↗