Stage Of Olfactory Processing Research Articles

Long-range GABAergic projections contribute to cortical feedback control of sensory processing

In the olfactory system, the olfactory cortex sends glutamatergic projections back to the first stage of olfactory processing, the olfactory bulb (OB). Such corticofugal excitatory circuits — a canonical circuit motif described in all sensory systems— dynamically adjust early sensory processing. Here, we uncover a corticofugal inhibitory feedback to OB, originating from a subpopulation of GABAergic neurons in the anterior olfactory cortex and innervating both local and output OB neurons. In vivo imaging and network modeling showed that optogenetic activation of cortical GABAergic projections drives a net subtractive inhibition of both spontaneous and odor-evoked activity in local as well as output neurons. In output neurons, stimulation of cortical GABAergic feedback enhances separation of population odor responses in tufted cells, but not mitral cells. Targeted pharmacogenetic silencing of cortical GABAergic axon terminals impaired discrimination of similar odor mixtures. Thus, corticofugal GABAergic projections represent an additional circuit motif in cortical feedback control of sensory processing.

Olfactory shifts linked to postpartum depression

Postpartum Depression (PPD) is the most common non-obstetric complications associated with childbearing, but currently has poor diagnostic regimes. Sensory symptoms of PPD are understudied, particularly with regard to the sense of olfaction. The present study addresses this research gap by assessing differences in olfactory abilities between 39 depressed mothers, who were within the perinatal period (i.e., during pregnancy and up to 1-year post pregnancy) and assessed with Edinburgh Postnatal Depression Scale, and their case-matched healthy volunteers. The assessments include two olfactory testing sessions conducted 4-weeks apart, each comprising a standard odour detection threshold test (i.e., Snap & Sniff Olfactory Test System), and intensity and valence ratings for 3 “pleasant” and 3 “unpleasant” odorants. The results revealed no difference between patients (M = 5.6; SE = 0.3) and control group (M = 5.7; SE = 0.4) in terms of olfactory detection threshold. However, the patients group perceived the 3 “unpleasant” odours as significantly less pleasant (p < 0.05), and 2 odorants (1 “pleasant” and 1 “unpleasant”) as less intense. Additionally, these results did not appear to be significantly interacted with the individual’s perinatal stage. The present study is the first to evaluate associations between olfactory function and PPD. Findings from the study suggest that, while PPD has little effect on the early stages of olfactory processing, these conditions may have stronger influence on higher-order olfactory perception, including both hedonic and intensity perception. These novel findings add knowledge to sensory symptoms of PPD.

Dynamics of Electrical Activity of Olfactory Structures under Conditions of Calypsol / Ketamine Anesthesia

Introduction. In this study, we have characterized high-frequency and low-frequency oscillations at several stages of olfactory processing under calypsol anesthesia in albino rats. While monitoring the animal's respiration, we also obtained field potentials from the olfactory bulb and piriform (olfactory) cortex and simultaneously recorded membrane potentials in piriform cortex pyramidal cells. Manifestations of the considered specific high-frequency components of electrical activity of rhinencephaly structures, in particular olfactory-amygdala rhythm and high-frequency synchronized activity, are obviously the resultof complex interaction of peripheral and central excitation mechanisms at the level of olfactory bulbs. We believe this finding has important functional as well as evolutionary implications.Purpose. To investigate the temporal dynamics of the manifestations of the phenomena of electrical activity of the olfactory bulb of rats and its changes under calypsol anesthesia.Methods.Stereotactic and electroencephalographic methods, correlation-spectral and coherent analysis of the obtained records of electricalactivity of the brain structures were used to study the bioelectrical activity of olfactory structures of the brain of experimental animals.The work was performed in a chronic experiment on 12 outbred white rats, males weighing 200 g. A premedication cocktail and calypsol at a rate of 25 mg / kg of animal weight were used for anesthesia. Implantation control was carried out according to specific patterns of electrical activity of the studied structures.The bioelectrical activity of the brain of each animal was studied for 10-20 days, followed by morphological control.Results. Olfacto-amygdala rhythm is registered against the background of polymorphic activity on the peak of respiratory waves in the form of spindle-shaped flashes of high-frequency oscillations in the range of 52-95 Hz, variable in amplitude. Simulation of the sustained suppression state of olfacto-amygdala rhythm in rhinencephalic structures was achieved using the technique of transferring animals to a state of deep ketamine (calypsol) anesthesia. This allowed not only to "exclude" flashes of olfactory-amygdala rhythm, but also to significantly suppress the high-frequency components of the spectra of electrical activity of olfactory bulbs, to increase the manifestation of low-frequency components (p &lt;0.01-0.05) and to probably reduce the index of high-frequency waves (р&lt;0.05). ISSN 2076-5835. Вісник Черкаського університету. 2021 No247Deep calypsol anesthesia caused differences in the spectra of electrical activity of olfactory bulbs at different depths of discharge only in terms of the spectral power density of the slow-wave range. At the same time, identical probable (p &lt;0.05) suppression of high-frequency components of electrical activity of olfactory bulbs was observed.Under these conditions, the preservation of high-frequency components of the spectrum (unformed in spindles) in the electrical activity of olfactory bulbs at the border of mitral and granular cells was observed even under conditions of sharp depression of -activity in ECoG and identical dominance of high-amplitude low-frequency oscillations in the amygdala.Originality. The influence of narcotic substances on the dynamics of manifestations of the phenomena of electrical activity of rhinencephalic structures: respiratory waves, olfacto-amygdala rhythm, polymorphic activity, is revealed.Conclusions.It is expedient to use the following amplitude-time patterns for objective characterization of total electrical activityof olfactory structures of rats, whichprobably differ in power-frequency characteristics: polymorphic desynchronized activity, respiratory waves, olfacto-amygdala synchronous rhythm and high-frequency synchronous rhythm.Polymorphic activity is normally represented by low-amplitude oscillations (10-200 μV) in a wide frequency range (10-150 Hz) with a set of dominant extremes. Оlfactory-amygdala rhythmis registered against the background of polymorphic activity on the peak of respiratory waves in the form of spindle-shaped flashes of high-frequency oscillations in the range of 52-95 Hz, variable in amplitude.Experimental modeling of the state of stable suppression of olfacto-amygdala rhythm and high-frequency synchronized activity in the electrical activity of olfactory bulbs (under colipslol / ketamine anesthesia) revealed suppression of manifestations of high-frequency components of the spectrum, indicating the important role of centrifugal effects inthe mechanisms of olfactory rhythm generation.Key words:electrical activity, olfactory bulb, fast oscillations, slow oscillations, excitation, anesthesia

Intraglomerular lateral inhibition promotes spike timing variability in principal neurons of the olfactory bulb.

The activity of mitral and tufted cells, the principal neurons of the olfactory bulb, is modulated by several classes of interneurons. Among them, diverse periglomerular (PG) cell types interact with the apical dendrites of mitral and tufted cells inside glomeruli at the first stage of olfactory processing. We used paired recording in olfactory bulb slices and two-photon targeted patch-clamp recording in vivo to characterize the properties and connections of a genetically identified population of PG cells expressing enhanced yellow fluorescent protein (EYFP) under the control of the Kv3.1 potassium channel promoter. Kv3.1-EYFP(+) PG cells are axonless and monoglomerular neurons that constitute ∼30% of all PG cells and include calbindin-expressing neurons. They respond to an olfactory nerve stimulation with a short barrage of excitatory inputs mediated by mitral, tufted, and external tufted cells, and, in turn, they indiscriminately release GABA onto principal neurons. They are activated by even the weakest olfactory nerve input or by the discharge of a single principal neuron in slices and at each respiration cycle in anesthetized mice. They participate in a fast-onset intraglomerular lateral inhibition between principal neurons from the same glomerulus, a circuit that reduces the firing rate and promotes spike timing variability in mitral cells. Recordings in other PG cell subtypes suggest that this pathway predominates in generating glomerular inhibition. Intraglomerular lateral inhibition may play a key role in olfactory processing by reducing the similarity of principal cells discharge in response to the same incoming input.

Odorant recognition using biological responses recorded in olfactory bulb of rats

In this study we applied pattern recognition (PR) techniques to extract odorant information from local field potential (LFP) signals recorded in the olfactory bulb (OB) of rats subjected to different odorant stimuli. We claim that LFP signals registered on the OB, the first stage of olfactory processing, are stimulus specific in animals with normal sensory experience, and that these patterns correspond to the neural substrate likely required for perceptual discrimination. Thus, these signals can be used as input to an artificial odorant classification system with great success. In this paper we have designed and compared the performance of several configurations of artificial olfaction systems (AOS) based on the combination of four feature extraction (FE) methods (Principal Component Analysis (PCA), Fisher Transformation (FT), Sammon NonLinear Map (NLM) and Wavelet Transform (WT)), and three PR techniques (Linear Discriminant Analysis (LDA), Multilayer Perceptron (MLP) and Support Vector Machine (SVM)), when four different stimuli are presented to rats. The best results were reached when PCA extraction followed by SVM as classifier were used, obtaining a classification accuracy of over 95% for all four stimuli.

Chapter 1 - Olfactory Habituation in Drosophila—Odor Encoding and its Plasticity in the Antennal Lobe

A ubiquitous feature of an animal's response to an odorant is that it declines when the odorant is frequently or continuously encountered. This decline in olfactory response, termed olfactory habituation, can have temporally or mechanistically different forms. The neural circuitry of the fruit fly Drosophila melanogaster's olfactory system is well defined in terms of component cells, which are readily accessible to functional studies and genetic manipulation. This makes it a particularly useful preparation for the investigation of olfactory habituation. In addition, the insect olfactory system shares many architectural and functional similarities with mammalian olfactory systems, suggesting that olfactory mechanisms in insects may be broadly relevant. In this chapter, we discuss the likely mechanisms of olfactory habituation in context of the participating cell types, their connectivity, and their roles in sensory processing. We overview the structure and function of key cell types, the mechanisms that stimulate them, and how they transduce and process odor signals. We then consider how each stage of olfactory processing could potentially contribute to behavioral habituation. After this, we overview a variety of recent mechanistic studies that point to an important role for potentiation of inhibitory synapses in the primary olfactory processing center, the antennal lobe, in driving the reduced response to familiar odorants. Following the discussion of mechanisms for short- and long-term olfactory habituation, we end by considering how these mechanisms may be regulated by neuromodulators, which likely play key roles in the induction, gating, or suppression of habituated behavior, and speculate on the relevance of these processes for other forms of learning and memory.

Precise and Fuzzy Coding by Olfactory Sensory Neurons

The exact nature of the olfactory signals that arrive in the brain from the periphery, and their reproducibility, remain essentially unknown. In most organisms, the sheer number of olfactory sensory neurons (OSNs) makes it impossible to measure the individual responses of the entire population. We measured the individual in situ electrophysiological activity of OSNs in Drosophila larvae, in response to stimulation with 10 aliphatic odors (alcohols and esters). We studied control larvae (a total of 296 OSNs) and larvae with a single functional OSN, created using the Gal4-upstream activator sequence system. Most OSNs showed consistent, precise responses (either excitation or inhibition) in response to a given odor. Some OSNs also showed qualitatively variable responses ("fuzzy coding"). This robust variability was an intrinsic property of these neurons: it was not attributable to odor type, concentration, stimulus duration, genotype, or interindividual differences, and was seen in control larvae and in larvae with one and two functional OSNs. We conclude that in Drosophila larvae the peripheral code combines precise coding with fuzzy, stochastic responses in which neurons show qualitative variability in their responses to a given odor. We hypothesize that fuzzy coding occurs in other organisms, is translated into differing degrees of activation of the glomeruli, and forms a key component of response variability in the first stages of olfactory processing.

Glomerular activation patterns and the perception of odor mixtures

Odor mixtures can produce several qualitatively different percepts; it is not known at which stage of processing these are determined. We asked if activity within the first stage of olfactory processing, the glomerular layer of the olfactory bulb, predicts odor mixture perception. We characterized how mice respond to components after training to five different mixture ratios of pentanal and hexanal, and found two types of responses: elemental perception and overshadowing. We then used intrinsic signal imaging to observe glomerular activity in response to the same mixtures and their components. As has been previously described, glomerular activity patterns produced by mixtures resemble the linear combination of responses to components. Mice trained to identify mixtures with more hexanal than pentanal recognized hexanal but not pentanal when the odorants were presented alone (overshadowing). Consistent with these behavioral responses, the imaged activity pattern in response to mixtures was similar to that produced to hexanal alone. Moreover, there was no significant effect of glomerular inhibition in the imaged response. In contrast, the glomerular activity patterns did not predict elemental perception: when trained to identify mixtures with more pentanal than hexanal, mice recognized both components equally well, even with highly overlapping activation patterns. This suggests that spatial activity patterns within the olfactory bulb are not always sufficient to specify component recognition in mixtures.

Component Information Is Preserved in Glomerular Responses to Binary Odor Mixtures in the Moth Spodoptera littoralis

Natural odors are often complex mixtures of different compounds. These mixtures can be perceived to have qualities that are different from their components. Moreover, components can be difficult to distinguish within a blend, even if those components are identifiable when presented individually. Thus, odor components can interact along the olfactory pathway in a nonlinear fashion such that the mixture is not perceived simply as the sum of its components. Here we investigated odor-evoked changes in Ca2+ concentration to binary blends of plant-related substances in individually identified glomeruli in the moth Spodoptera littoralis. We used a wide range of blend ratios and a range of concentrations below the level at which glomerular responses become saturated. We found no statistically significant cases where the mixture response was greater than both component responses at the same total concentration (synergistic interactions) and no statistically significant cases where the mixture response was less than either component presented individually (suppressive interactions). Therefore, we conclude that, for the plant mixtures studied, information of their components is preserved in the neural representations encoded at the first stage of olfactory processing in this moth species.

Understanding the logics of pheromone processing in the honeybee brain: from labeled-lines to across-fiber patterns

Honeybees employ a very rich repertoire of pheromones to ensure intraspecific communication in a wide range of behavioral contexts. This communication can be complex, since the same compounds can have a variety of physiological and behavioral effects depending on the receiver. Honeybees constitute an ideal model to study the neurobiological basis of pheromonal processing, as they are already one of the most influential animal models for the study of general odor processing and learning at behavioral, cellular and molecular levels. Accordingly, the anatomy of the bee brain is well characterized and electro- and opto-physiological recording techniques at different stages of the olfactory circuit are possible in the laboratory. Here we review pheromone communication in honeybees and analyze the different stages of olfactory processing in the honeybee brain, focusing on available data on pheromone detection, processing and representation at these different stages. In particular, we argue that the traditional distinction between labeled-line and across-fiber pattern processing, attributed to pheromone and general odors respectively, may not be so clear in the case of honeybees, especially for social-pheromones. We propose new research avenues for stimulating future work in this area.

Variable Coupling Between Olfactory System Activity and Respiration in Ketamine/Xylazine Anesthetized Rats

In this study, we have characterized slow and fast oscillations at several stages of olfactory processing under light and deep ketamine/xylazine anesthesia in the albino rat. While monitoring the animal's respiration, we also obtained field potentials from the olfactory bulb and piriform (olfactory) cortex and simultaneously recorded membrane potentials in piriform cortex pyramidal cells. Our results demonstrate that oscillations are generally found at higher frequencies under lighter and lower frequencies under deeper anesthesia. In previous studies of cerebral cortex, similar results in ketamine/xylazine anesthetized animals have been interpreted to correspond with the higher frequencies found during waking and lower frequencies found in the sleep state. Correlation and coherence analysis between data obtained in the bulb and cortex reveals a clear difference in coupling depending on the anesthetic state of the animal. Specifically, activity recorded in the whole system is highly correlated with respiration during deep anesthesia, whereas only the olfactory bulb, and not the cortex, is correlated with respiration during light anesthesia. These data suggest that global activity in the piriform cortex is actually more directly tied to peripheral slow respiratory input during slow wave than fast wave states and that the coupling between olfactory structures can be dynamically modulated by the level of anesthesia and therefore presumably by different brain states as well.

Local inhibition modulates odor-evoked synchronization of glomerulus-specific output neurons.

At the first stage of olfactory processing in the brain, synchronous firing across glomeruli may help to temporally bind multiple and spatially distributed input streams activated by a given odor. This hypothesis, however, has never been tested in an organism in which the odor-tuning properties of several spatially identifiable glomeruli are known. Using the sphinx moth, an insect that meets these specific criteria, we recorded odor-evoked responses simultaneously from pairs of projection neurons (PNs) innervating the same or different glomeruli in the macroglomerular complex (MGC), which is involved in processing pheromonal information. PNs that branched in the same glomerulus and were activated by the same pheromone component also showed the strongest coincident responses to each odor pulse. Glomerulus-specific PN pairs were also inhibited by the pheromone component that selectively activated PNs in the neighboring glomerulus, and about 70% of all intraglomerular pairs showed increased synchronization when stimulated with a mixture of the two odorants. Thus, when two adjacent glomeruli receive their inputs simultaneously, the temporal tuning of output from each glomerulus is enhanced by reciprocal and inhibitory interglomerular interactions.

Chemotopic, Combinatorial, and Noncombinatorial Odorant Representations in the Olfactory Bulb Revealed Using a Voltage-Sensitive Axon Tracer

Odor information is first represented in the brain by patterns of input activity across the glomeruli of the olfactory bulb (OB). To examine how odorants are represented at this stage of olfactory processing, we labeled anterogradely the axons of olfactory receptor neurons with the voltage-sensitive dye Di8-ANEPPQ in zebrafish. The activity induced by diverse natural odorants in afferent axons and across the array of glomeruli was then recorded optically. The results show that certain subregions of the OB are preferentially activated by defined chemical odorant classes. Within these subregions, "ordinary" odorants (amino acids, bile acids, and nucleotides) induce overlapping activity patterns involving multiple glomeruli, indicating that they are represented by combinatorial activity patterns. In contrast, two putative pheromone components (prostaglandin F2alpha and 17alpha, 20beta-dihydroxy-4-pregnene-3-one-20-sulfate) each induce a single focus of activity, at least one of which comes from a single, highly specific and sensitive glomerulus. These results indicate that the OB is organized into functional subregions processing classes of odorants. Furthermore, they suggest that individual odorants can be represented by "combinatorial" or "noncombinatorial" (focal) activity patterns and that the latter may serve to process odorants triggering distinct responses such as that of pheromones.

Associative memory and segmentation in an oscillatory neural model of the olfactory bulb.

We discuss the first few stages of olfactory processing in the framework of a layered neural network. Its central component is an oscillatory associative memory, describing the external plexiform layer, that consists of inhibitory and excitatory neurons with dendrodendritic interactions. We explore the computational properties of this neural network and point out its possible functional role in the olfactory bulb. When receiving a complex input that is composed of several odors, the network segments it into its components. This is done in two stages. First, multiple odor input is preprocessed in the glomerular layer via a decorrelation mechanism that relies on temporal independence of odor sources. Second, as the recall process of a pattern consists of associative convergence to an oscillatory attractor, multiple inputs are identified by alternate dominance of memory patterns during different sniff cycles. This could explain how quick analysis of mixed odors is subserved by the rapid sniffing behavior of highly olfactory animals. When one of the odors is much stronger than the rest, the network converges onto it, thus displaying odor masking.

A model for temporal and intensity coding in insect olfaction by a network of inhibitory neurons

Female insects release sex-pheromones which attract their conspecific males. These pheromones are detected through a distinct male-specific olfactory subsystem which resides at the first stage of olfactory processing, and consists of receptor, local and projection (relay) neurons. When male insects were stimulated by female sex-pheromones, some projection neurons could distinguish between different pheromones, following input and code stimulus intensity. Presented here, is a simple biophysical model that described characteristic bursting responses observed for projection neurons. The bursting behavior of the model resulted from a particular cellular mechanism and specific network architecture. At the neuron level, a rapidly activating and slowly inactivating low-threshold calcium channel provided depolarizing current for bursting, while at the network level, inhibitory neurons implementing dis-inhibition which triggered this calcium channel. Also, the network architecture provided a mechanism by which certain projection neurons coded temporal input and stimulus intensity.