Vertebrate Olfactory System Research Articles

A Putative Cyclic Nucleotide–Gated Channel Is Required for Sensory Development and Function in C. elegans

In vertebrate visual and olfactory systems, a cyclic nucleotide–gated channel couples receptor activation to electrical activity of the sensory neurons. The Caenorhabditis elegans tax-2 gene is required for some forms of olfaction, for chemosensation of salts, and for thermosensation. We show here that tax-2 encodes a predicted subunit of a cyclic nucleotide–gated channel that is expressed in olfactory, gustatory, and thermosensory neurons, implicating this channel in multiple sensory modalities. Some sensory neurons display axon outgrowth defects in tax-2 mutants. Thus, the channel has an unexpected role in sensory neuron development in addition to its role in sensation. Consistent with this proposed dual function, a Tax-2::GFP fusion protein is present both in sensory cilia and in sensory axons.

A chemical-detecting system based on a cross-reactive optical sensor array.

The vertebrate olfactory system has long been recognized for its extraordinary sensitivity and selectivity for odours. Chemical sensors have been developed recently that are based on analogous distributed sensing properties, but although an association between artificial devices and the olfactory system has been made explicit in some previous studies, none has incorporated comparable mechanisms into the mode of detection. Here we describe a multi-analyte fibre-optic sensor modelled directly on the olfactory system, in the sense that complex, time-dependent signals from an array of sensors provide a 'signature' of each analyte. In our system, polymer-immobilized dye molecules on the fibre tips give different fluorescent response patterns (including spectral shifts, intensity changes, spectral shape variations and temporal responses) on exposure to organic vapours, depending on the physical and chemical nature (for example, polarity, shape and size) of both the vapour and the polymer. We use video images of temporal responses of the multi-fibre tip as the input signals to train a neural network for vapour recognition. The system is able to identify individual vapours at different concentrations with great accuracy. 'Artificial noses' such as this should have wide potential application, most notably in environmental and medical monitoring.

Rapid Analyte Recognition in a Device Based on Optical Sensors and the Olfactory System

We report here the development of a new vapor sensing device that is designed as an array of optically based chemosensors providing input to a pattern recognition system incorporating artificial neural networks. Distributed sensors providing inputs to an integrative circuit is a principle derived from studies of the vertebrate olfactory system. In the present device, primary chemosensing input is provided by an array of fiber-optic sensors. The individual fiber sensors, which are broadly yet differentially responsive, were constructed by immobilizing molecules of the fluorescent indicator dye Nile Red in polymer matrices of varying polarity, hydrophobicity, pore size, elasticity, and swelling tendency, creating unique sensing regions that interact differently with vapor molecules. The fluorescent signals obtained from each fiber sensor in response to 2-s applications of different analyte vapors have unique temporal characteristics. Using signals from the fiber array as inputs, artificial neural networks were trained to identify both single analytes and binary mixtures, as well as relative concentrations. Networks trained with integrated response data from the array or with temporal data from a single fiber made numerous errors in analyte identification across concentrations. However, when trained with temporal information from the fiber array, networks using "name" or "characteristic" output codes performed well in identifying test analytes.

Nitric oxide synthase activity in the olfactory bulb of anuran and urodele amphibians

Nitric oxide synthase activity was studied by means of NADPH-diaphorase activity and nitric oxide synthase immunoreactivity in the main and accessory olfactory bulbs of the frog Rana perezi and the newt Triturus marmoratus. In both species, NADPH-diaphorase staining was observed in all olfactory fibers. Vomeronasal fibers were NADPH-diaphorase-positive in Triturus but they were NADPH-diaphorase-negative in Rana. Nitric oxide synthase immunoreactivity was not observed in the primary afferents in any case. Granule cells were NADPH-diaphorase-positive and nitric oxide synthase-immunopositive in the main and accessory olfactory bulb of Rana, and in the main olfactory bulb of Triturus. The homogeneous NADPH-diaphorase staining of olfactory fibers is similar to what has been reported in teleosts, and it contrasts with the spatial segregation of NADPH-diaphorase-positive and -negative olfactory projections in rodents. These results confirm the interspecies variability of the NADPH-diaphorase/nitric oxide synthase distribution in the olfactory system of vertebrates.

Information coding in the vertebrate olfactory system.

The olfactory systems of vertebrates are able to discriminate a vast array of structurally diverse odorants. This perceptual acuity derives from a series of information-processing events that occur within distinct neural structures through which olfactory sensory information flows. This review discusses current knowledge concerning the mechanisms by which olfactory stimuli are initially detected and transduced into electrical signals that are transmitted to the olfactory bulb of the brain. It also reviews how information may initially be organized, or encoded, and then reorganized as it flows through the system.

Cyclic Nucleotide-Gated Channels, Nitric Oxide, and Neural Function

Cyclic nucleotide-gated (CNG) channels are nonselective cation channels that are activated by direct interaction of the second messengers cAMP and cGMP. Once activated, they provide for membrane depolarization and Ca2+ influx into cells. The functions of CNG channels are tightly coupled to the mechanisms by which cAMP and cGMP are regulated in neurons, namely through activation of G-protein–coupled membrane receptors and through the nitric oxide/guanylyl cyclase signaling system. These functions are best understood in sensory neurons of the vertebrate visual and olfactory system, where CNG channels are critical components of the signal transduction apparatus. The family of known CNG channels is expanding, and there is now increasing evidence that these channels are also present in many other areas of the nervous system. Based on their role in sensory neurons, a functional framework for the role of CNG channels in the CNS is provided.

The olfactory memory of the honeybee Apis mellifera. II. Blocking between odorants in binary mixtures.

Proboscis extension conditioning of honeybee workers was used to study the processing of odorants when bees were conditioned to binary mixtures. Responses to a set of pure floral odors and pheromones after conditioning have already been described. When bees are conditioned to certain mixtures of odorants, the response to both components is equal to that when they are tested alone. However, mixtures of an aliphatic aldehyde and an alcohol elicit asymmetric response patterns; that is, the response to the aldehyde is much stronger than that to the alcohol. A bee's response to the alcohol after it had been trained in an aldehyde background is significantly lower than when the bee is trained to respond to the same alcohol in the background of another odorant. Such response patterns are not necessarily caused by a behavioral decrement resulting from a compound-unique perceptual effect produced by the mixture. Furthermore, studies of blocking show that behavioral acquisition in response to one component can be hindered or blocked by pretraining with the other component. These results suggest that honeybees can perceive the individual components of some binary mixtures. The similarities in neural processing in olfactory systems of vertebrates and invertebrates mean that such studies could elucidate behavioral mechanisms of olfaction in a wide phylogenetic spectrum of animals.

Coherent network oscillations by olfactory interneurons: modulation by endogenous amines.

1. The procerebral (PC) lobe of the terrestrial mollusk Limax maximus contains a highly interconnected network of local olfactory interneurons that receives direct axonal projections from the two pairs of noses. This olfactory processing network generates a 0.7-Hz oscillation in its local field potential (LFP) that is coherent throughout the network. The oscillating LFP is modulated by natural odorants applied to the neuroepithelium of the superior nose. 2. Two amines known to be present in the PC lobe, dopamine and serotonin, increase the frequency of the PC lobe oscillation and alter its waveform. 3. Glutamate, another putative neurotransmitter known to be present in the lobe, suppresses the PC lobe oscillation by a quisqualate-type receptor and appears to be used by one of the two classes of neurons in the PC lobe to generate the basic LFP oscillation. 4. The known activation of second messengers in Limax PC lobe by dopamine and serotonin together with their effects on the oscillatory rhythm suggest the hypothesis that these amines augment mechanisms mediating synaptic plasticity in the olfactory network, similar to hypothesized effects of amines in vertebrate olfactory systems. 5. The use of a distributed network of interneurons showing coherent oscillations may relate to the highly developed odor recognition and odor learning ability of Limax.

Historical aspects of research on the vertebrate olfactory system.

The historical review concentrates on M. Schultzes ingenious investigations in the 19th century. His work contains numerous methodological details, vigorous defense against theoretical and experimental criticism, and precise descriptions of the olfactory mucosa throughout the vertebrate kingdom, and left little for further investigations for many years; practically all of his careful observations proved to be correct.

Are there structural and functional modules in the vertebrate olfactory bulb?

A number of different recording methods have shown that odorants elicit patterns of neuronal activity widely distributed across cells of the olfactory receptor epithelium, olfactory bulb, and piriform cortex in the vertebrate olfactory system. These findings suggest that the physicochemical properties of odorant molecules are processed by distributed coding mechanisms activated in parallel in olfactory circuits in order to characterize a single, "monomolecular" odorant. These findings also suggest that the response patterns seen at higher levels are set up by differential responses in peripheral receptor cells of the olfactory epithelium. One requirement for understanding the details of this proposed encoding scheme is correlation of odor-generated patterns with the components of these circuits. In this paper, results from 2-deoxyglucose and voltage-sensitive dye studies suggest that certain components of these responses may relate to patterns established in reproducibly identifiable aggregates of bulbar cells. These findings are consistent with previous observations suggesting that columnar groups of periglomerular, mitral/tufted and granule cells, oriented perpendicular to the laminae of the bulb, are functionally related to one another. Such cell groups or modules, when activated in parallel, could serve as building block components of the complete ensemble response. According to this hypothesis, different sets of such modules would be activated with different odorant stimuli and modules could be shared to the degree to which the physicochemical properties of the different stimuli overlap.

Morphology of olfactory epithelium in humans and other vertebrates.

Human olfactory epithelium is similar in organization and cell morphology to that of most vertebrate species. The epithelium has a pseudostratified columnar organization and consists of olfactory neurons, supporting and basal cells. Near the mucosal surface there are also microvillar cells. These cells have neuron-like features and may be chemoreceptors. Human olfactory epithelium is not a uniform sensory sheet. Patches of non-sensory tissue often appear in what was thought to be a purely olfactory region. The significance of these patches has not been determined, but they could reflect exposure to environment agents or changes that occur during the normal aging process. In order to better understand the human olfactory system, further knowledge of the normal structure is necessary. This review addresses the morphology of the human olfactory epithelium and the remarkable plasticity of the vertebrate olfactory system.

Odour-modulated collective network oscillations of olfactory interneurons in a terrestrial mollusc

Determination of the dynamical structure of neural circuits--the general principles of how neural activity varies with time and manipulates information--is a prerequisite to understanding their computational function. Rhythmically active or oscillating neural circuits are particularly interesting dynamical structures, as rhythms and oscillations are a prominent feature of mammalian central nervous system electrophysiology. Coherent oscillations by networks of interneurons are observed in the vertebrate olfactory system and have recently been described in mammalian visual cortex. These interneuronal networks display oscillations in local field potential (LFP) and probability of producing action potentials that are highly correlated between subcircuits sharing the same stimulus features. Much less is known about the existence and importance of network oscillations in the higher centres of invertebrates. Here we report that a network of olfactory interneurons in the cerebral ganglion of the terrestrial mollusc Limax maximus also displays coherent oscillations in LFP which are modified by odour input. This dynamical structure could be central to the odour recognition and odour learning ability of Limax.

Carnosine-like Immunoreactivity in Human Olfactory Mucosa

By means of immunohistochemical techniques it is demonstrated for the first time ever that carnosine (beta-alanyl-L-histidine)-like immunoreactivity (LI) is localized in the olfactory receptor neuron in human olfactory mucosa. Carnosine-LI was found in all regions of the receptor cells, i.e. in dendrites, olfactory vesicles, soma and axons. Supporting cells and basal cells were not immunoreactive. The present results suggest that carnosine play a major role in the human olfactory neuron and supports the concept that this peptide is a putative neurotransmitter in vertebrate olfactory systems.

Central pattern generating and recognizing in olfactory bulb: A correlation learning rule

A learning rule called an input correlation rule that can simplify exploration of the behavior of learning, generating, and classifying patterns in the vertebrate olfactory system is proposed. We apply this correlation rule to a set of fully interconnected coupled oscillators that comprises a dynamical model of the olfactory bulb so as to form “templates” of oscillators with strengthened interconnection in respect to inputs classed as “learned.” We obtain a content addressable memory in which phase coherent oscillation provides for central pattern generation and recognition. We use this analog model neural network to simulate dynamic features of the olfactory bulb in detail by numerical integration and multivariate analysis. The model classifies 100% correctly for incomplete inputs, testing inputs about their training centroids, and distortion by noise that is defined as input to nontemplate elements. The model also allows substantially overlapping templates, which implies that it possesses a large information capacity. For multiple inputs the model gives correct output of the forms A and B, A and not B, B and not A, or neither. The initial conditions of the model at the time of onset of input play no role in classification. Classification is achieved within 20 to 50 ms of simulated run time, even though convergence to a limit cycle requires up to 10 cycles (200 ms). The repetition rate of convergence from one pattern to the next in the model exceeds 10 patterns/s.

Maturation and plasticity in the olfactory system of vertebrates.

Maturation and plasticity in the olfactory system of vertebrates.

Responses to odors mapped in snail tentacle and brain by [14C]-2- deoxyglucose autoradiography

The method of 2-deoxyglucose (2-DG) autoradiography has been widely used to map functional neuronal systems in vertebrates, but in invertebrate species, where morphological dimensions favor its use, the applications have been minimal. This study uses [14C]-2-DG to map the olfactory system of a terrestrial snail, Achatina fulica. The olfactory organ in the snail's tentacles bears a striking resemblance to the vertebrate olfactory mucosa. There are also complex neural structures in the tentacle and brain that are devoted to subsequent processing. These facts make the molluscan olfactory system a suitable complement to the traditional vertebrate and insect models in olfaction. The experiments utilized intact snails in which one tentacle was exposed to a controlled odor environment while the contralateral tentacle was held in a retracted position. The dose of [14C]-2-DG (2 microCi/gm) was injected into the hemocele. Tissue processing involved freeze-substitution with acetone, dry sectioning, and the preparation of liquid film autoradiographs. Optical density measurements permitted quantitative comparisons between experimental conditions. The natural odors of conspecific snails and of carrots elicited significantly more uptake of 2-DG in the exposed tentacle than in the unexposed tentacle and, in the exposed tentacle, significantly more label over the axons of the primary sensory neurons than was elicited by exposure to clean air. Amyl acetate and octanol were less effective. A small number of superficially placed sensory neurons were labeled in all stimulus conditions, including clean air, and may represent the mechanosensors. Stimulus-dependent labeling in the brain was limited to the procerebrum and included both neuropilar and cellular parts. In contrast to vertebrate and insect olfactory systems, there was no evidence of spatial coding for odor quality.

Regeneration in the olfactory system of vertebrates

The olfactory sensory neurons, which are of placodal origin, maintain in adult vertebrates, including mammals, a neurogenetic matrix that allows for their replacement without impairment of function, both in normal circumstances (turnover) and after experimental intervention. The unique characteristics of these "disposable" neurons have recently led to a number of experiments whose results may have some importance in our understanding of the olfactory system and of the nervous system as a whole.

The Origin and Development of Reflexes in the Cat during the Third Fetal Week

Previous articleNext article No AccessThe Origin and Development of Reflexes in the Cat during the Third Fetal WeekW. F. Windle, D. W. Orr, and W. L. MinearW. F. Windle Search for more articles by this author , D. W. Orr Search for more articles by this author , and W. L. Minear Search for more articles by this author PDFPDF PLUS Add to favoritesDownload CitationTrack CitationsPermissionsReprints Share onFacebookTwitterLinkedInRedditEmail SectionsMoreDetailsFiguresReferencesCited by Volume 7, Number 4Oct., 1934 Article DOIhttps://doi.org/10.1086/physzool.7.4.30151235 Views: 2Total views on this site Citations: 25Citations are reported from Crossref Journal History This article was published in Physiological Zoology (1928-1998), which is continued by Physiological and Biochemical Zoology (1999-present). PDF download Crossref reports the following articles citing this article:R. Nieuwenhuys Histogenesis, (Jan 1998): 229–271.https://doi.org/10.1007/978-3-642-18262-4_5T. Nakao, A. 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