Interactions of odorants with olfactory receptors and receptor neurons match the perceptual dynamics observed for woody and fruity odorant mixtures.

The present study aimed to create a direct bridge between observations on peripheral and central responses to odorant mixtures and their components. Three experiments were performed using mixtures of fruity (isoamyl acetate; ISO) and woody (whiskey lactone; WL) odorants known to contribute to some of the major notes in Burgundy red wine. These experiments consisted of (i) calcium imaging of human embryonic kidney cells (HEK293T) transfected with olfactory receptors (ORs); (ii) single-unit electrophysiological recordings from olfactory receptor neurons (ORNs) and analyses of electro-olfactogram (EOG) responses in the rat nose in vivo; and (iii) psychophysical measurements of the perceived intensity of the mixtures as rated by human subjects. The calcium imaging and electrophysiological results revealed that ISO and WL can act simultaneously on single ORs or ORNs and confirm that receptor responses to mixtures are not the result of a simple sum of the effects of the individual mixture compounds. The addition of WL to ISO principally suppressed the ORN activation induced by ISO alone and was found to enhance this activation in a subset of cases. In the human studies, the addition of high concentrations of WL to ISO decreased the perceived intensity of the ISO. In contrast, the addition of low concentrations of WL enhanced the perceived intensity of the fruity note (ISO) in this mixture, as it enhanced EOG responses in ORNs. Thus, both OR and ORN responses to ISO + WL mixtures faithfully reflected perceptual response changes, so the odour mixture information is set up after the peripheral stage of the olfactory system.

[Building and validation of a test evaluating verbal recognition memory: The Forty test (f40)]. / Mise au point et validation d'une épreuve d'évaluation de la mémoire de reconnaissance verbale: le Forty test (f40).

INTRODUCTION: Neuropsychologic evaluation is a primordial diagnostic tool. Numerous tests explore episodic memory but few tests exist to assess incidental verbal episodic memory or verbal recognition memory. This memory is however impaired early in certain neurodegenerative diseases such as Alzheimer's disease. Our objective was to create a test sensitive and specific to this cognitive dysfunction. METHOD: Our test was performed by 33 healthy volunteers and 51 patients (19 with idiopathic Parkinson's disease, 16 with Alzheimer's disease at the prodromal stage and 16 with Alzheimer's disease). RESULTS AND DISCUSSION: Independently of age, education level and global cognitive impairment, the young and old healthy volunteers and the patients with idiopathic Parkinson's disease displayed results significantly better than the group of Alzheimer's disease at the prodromal stage and Alzheimer's disease patients. Our test appears to be sensitive to dysfunction of verbal recognition memory. A score of 30/40 or less on the Forty test discriminates 91% of subjects with a cortical pattern of memory. This test could be recommended for clinical neuropsychological practice.

Changes in rat olfactory detection performance induced by orexin and leptin mimicking fasting and satiation.

Numerous peripheral and hypothalamic peptides control food intake. Among these signals are orexin, an orexigenic molecule released into the olfactory bulb by centrifugal hypothalamic fibres and leptin, an anorexigenic molecule that is released peripherally and can pass through the blood-brain barrier. In the present study, we injected either orexin or leptin, intracerebroventricularly, and their effect on olfactory performance was evaluated in two groups of rats, using a behavioral paradigm based on conditioned olfactory aversion. Rats were made aversive to water odorized with isoamyl acetate (ISO) at 10(-5) (1microl in 100ml of water). One group was injected with orexin versus saline and the other with leptin versus saline. They were then presented with different concentrations (lower than 10(-5)) of ISO-odorized water to compare their ability to avoid the ISO-drink. Orexin decreased ISO-drink consumption, showing increased avoidance of the ISO concentrations tested which ranged from 10(-9) to 10(-7). Conversely, the administration of leptin resulted in a dose dependant increase in the odorized-drink consumption for ISO 10(-10). Orexin therefore increases and leptin decreases olfactory sensitivity. Orexin and leptin modulate the olfactory performance in a similar way as do physiological induced fasting and satiation and appear to be important factors in the interdependency of olfaction and food intake.

Fasting increases and satiation decreases olfactory detection for a neutral odor in rats.

Olfaction plays a fundamental role in feeding behavior, but changes in olfactory acuity according to feeding states have never been precisely demonstrated in animals. The present study assesses the olfactory detection performance of fasted or satiated rats placed under a strictly controlled food-intake regimen. We did this using a conditioned odor aversion (COA) protocol which induced in rats an almost total aversion to an ISO-odorized drink at 10(-5) (1 microl in 100 ml of water). The rats (either fasted or satiated) were then presented with different concentrations of ISO-odorized water to compare their ability to detect and so avoid the ISO drink. In both states, the rats consumed significantly larger volumes of ISO at 10(-10), 10(-9) and 10(-8) than at 10(-5), suggesting lower detection at these three concentrations, although the fasted rats consumed significantly less ISO drink than did the satiated ones, showing better ISO detection at these concentrations. These experiments provide original data demonstrating the expected fact that olfactory sensitivity increases in fasted animals. Since these results were obtained using a neutral odor, we suggest that olfactory acuity increases during fasting, enabling animals to more easily detect both food and environmental odors such as those of predators. This would have an obvious eco-ethological role by increasing the relevance of olfactory inputs when seeking food.

Orexin A effects on the olfactory bulb spontaneous activity and odor responsiveness in freely breathing rats.

The mitral cells (MCs) of the olfactory bulb (OB) are relay neurons between the periphery and the central nervous structures. MCs receive in turn a centrifugal control from several higher brain centers that depends on the nutritional state. In this study, we investigated the effects of orexin A (ORX), a novel molecule known to regulate food intake and whose receptors are present in the OB, on the electrophysiological activity of single MCs. Using icv-injections and direct applications on the OB, we determined the respective central and local effects of this molecule on the MCs' spontaneous firing activity and responsiveness to different odors. Icv-injections and local OB-applications were found to induce a significant decrease in spontaneous firing activity in 14% and 50% of the recorded MCs, respectively. In one case, ORX application on the OB caused a significant firing increase. Effects of OB-applications had shorter delays. The responsiveness of some MCs to food and non-food odors was also changed, but the proportion of changes was not statistically significant. Icv-injection effects likely resulted from a local action of ORX on the OB. Changes of spontaneous firing activity and odor responsiveness are discussed in terms of regulation of the functioning of the olfactory system.

Taurine action on mitral cell activity in the frog olfactory bulb in vivo.

Taurine (TAU) is a free amino acid that is particularly abundant in the olfactory bulb. In the frog, TAU is located in the terminations of the primary olfactory axons and in the granular cell layer. TAU action seems to be associated with gamma amino butyric acid (GABA), the main inhibitory neurotransmitter involved in the processing of the sensory signal. The present study was designed to assess the action of TAU in vivo during the olfactory network's stimulation by odors. It was performed by recording the single-unit activity of mitral cells, the main bulbar output neurons. TAU effects were tested on both their spontaneous and odor-induced firing activity. Interactions between TAU and GABA were examined by analyzing TAU effects under the selective blocking action of GABAA or GABAB antagonists. TAU was found to suppress the spontaneous firing of mitral cells, mainly without altering their odor response properties. By testing GABA antagonists, we further show that TAU action is associated with GABAergic inhibitory mechanisms mainly via GABAB receptors. Thus, TAU action clearly reduces background activity in favor of the emergence of the odor-induced activity in the same manner as GABA action does via GABAB receptors. As a conclusion, we propose that, in the frog olfactory bulb, the joint actions of TAU and GABA may favor the processing of the primary sensory information by increasing the signal to noise ratio.

Rats habituated to chronic feeding restriction show a smaller increase in olfactory bulb reactivity compared to newly fasted rats.

During the 1970s, the multiunit reactivity of the olfactory bulb to food odor was extensively shown to increase before their usual meal in rats habituated to having a single 2 h daily meal compared to the same rats recorded after their usual meal. More recently, we reported dramatic modifications of mitral cell single-unit reactivity in adult rats following a simple a manipulation of the olfactory environment--exposure to an odor. The present study aimed at testing the hypothesis that a simple behavioral change such as habituation to chronic food restriction may induce profound changes in olfactory bulb responsiveness compared to occasional fasting. We compared mitral cell reactivity in non-fasted rats, in rats fasted during 22 h for the very first time, and in rats habituated during 15 days to a chronic 22 h food restriction. Mitral cell single-unit reactivity was found to increase less in rats habituated to fasting than in newly fasted rats. Indeed, the proportion of mitral cell responses to food and non-food odors was significantly higher in rats habituated to fasting than in non-fasted rats, but lower than in newly fasted rats. The proportion of simple unsynchronized and synchronized responses of 1b and 2b types was also lower in habituated rats whereas the proportion of complex synchronized responses of 4b type increased. This decreased responsiveness in habituated rats, similar to that observed in rats repeatedly exposed for 20 min per day to an odor during six consecutive days in our previous studies, is discussed with respect to olfactory bulb plasticity.

EOG responses in anesthetized freely breathing rats.

In mammals, access of odor molecules to the olfactory receptor neurons is controlled by respiratory activity. Thus, anesthetized, freely breathing rats were used to record from the olfactory mucosa in the intact nasal cavity (electroolfactogram or EOG) so as to study global response characteristics to odor stimuli. During alternation of the inspiratory phases of odor sampling and expiratory phases, the response was a succession of individual EOG events synchronized with respiration. These were characterized by a steep decrease that started approximately 100-150 ms after the beginning of inhalation, reached its maximum at the transition between inspiration and expiration and was followed by a slower rise until the next inhalation. They were greater during the first respiratory cycles following odor stimulation onset. Thereafter their amplitudes decreased throughout odor delivery, but a significant EOG signal was still present at the end of short (10 s) and long (60 s) odor presentations. Amplitude increased with odor concentration, but much less than expected from concentration changes. Lastly, for some odors EOG responses persisted well beyond the end of stimulation. These results are in agreement with the respiratory synchronization of mitral cell activities observed during short odor presentations and long duration odor exposures. They underline again the importance of taking into account the respiratory activity in studies on the functioning of the olfactory system.

Peripheral odor coding in the rat and frog: quality and intensity specification.

In mammals, two recent studies have shown recently that one odor molecule can be recognized by several molecular olfactory receptors (ORs), and a single OR can recognize multiple odor molecules. In addition, one olfactory receptor neuron (ORN) may respond to different stimuli chosen as representative of distinct odor qualities. The aim of the present study was to analyze quality and intensity coding abilities of rat single ORNs, comparing them with previous extensive data gathered in the frog to get insight into the generality of olfactory coding mechanisms over vertebrates. Response properties of 90 rat ORNs to different odors or to one odor at different concentrations were analyzed. In the rat and the frog, odor quality appears to be specified through the identity of activated ORNs. However, rat ORNs have higher response thresholds. This lower sensitivity may be interpreted as an increase in selectivity of rat ORNs for low or medium odor intensities. In these conditions, the lower proportion of activated ORNs could be counterbalanced by their number, as well as by their higher glomerular convergence ratio in the olfactory bulb. From amphibians to mammals, the olfactory system appears to use universal mechanisms based on a combinatorial-coding mode that may allow quasi-infinite possibilities of adaptation to various olfactory environments.

Olfactory experience decreases responsiveness of the olfactory bulb in the adult rat.

We recently reported the existence of dramatic modifications of the olfactory bulb reactivity following a very simple manipulation of the olfactory input as an exposure to an odorant. The present study aimed at testing the possibility that such effects could depend on the nature of the exposure odour. For this purpose, rats were exposed 20 min per day during six consecutive days to cineole, methyl-amyl ketone, isoamyl acetate or with no odour in the control group. On day 7, rats were anaesthetized and the spontaneous activity of mitral/tufted cells was recorded along with their responses to the familiar odour and to four novel odours. Results revealed that: (i) the firing frequencies were not significantly different in the four groups; (ii) the proportion of excitatory responses was considerably decreased in the exposed groups while the number of non-responses was significantly enhanced; (iii) excitatory responses were decreased not only to the familiar odour but also to four other novel odours; (iv) this lower responsiveness was long lasting at least for isoamyl acetate exposure; and (v) increasing concentration of test odours was not enough to allow mitral/tufted cells to recover control responsiveness. All of these effects have a differential importance according to the exposure odour. In particular, the more powerful an odour is in activating control cells, the more non-specific the decrease in mitral/tufted cell reactivity is. Hypotheses on the underlying mechanisms are advanced.

Repeating triplets of spikes and oscillations in the mitral cell discharges of freely breathing rats.

The olfactory bulb responses to odours display evident temporal organization, both in the form of high-frequency oscillations and precisely replicating triplets of spikes. In this study, the frequency of replicating triplets in a sample of 118 individual responses from 45 cells was compared with that in simulations of non-homogeneous Poisson processes, constructed from the experimental post-stimulus time histograms (PSTHs). In a large majority of the records, replicating triplets (to a precision of 0.5 ms) are found to be more numerous in the physiological records; in some of them, they are approximately 10 times more abundant. An excess of precisely replicating triplets is also found in records where no oscillations are apparent in the autocorrelograms. Triplet replication thus seems a more robust phenomenon than transient oscillation. Not unlike fast oscillations observed in other preparations, replicating triplets produced by a given mitral cell are generally observed only during a restricted period of time of the respiratory cycle (at least in the case of the responses under olfactory stimulation). No relation was found, however, between the nature and strength of the olfactory stimulus and the frequency of replicating patterns. In the absence of olfactory stimulation, some mitral cell discharges also contain more replicating triplets than the non-homogeneous Poisson simulations. Thus, replicating triplets in single-cell discharges seem to play only an indirect role in the coding of olfactory information at the mitral cell output level.

Cost effectiveness of transbronchial needle aspiration.

OBJECTIVE: To evaluate the yield and cost effectiveness of transbronchial needle aspiration (TBNA) in the assessment of mediastinal and/or hilar lymphadenopathy. DESIGN: Retrospective study. SETTING: A university hospital. POPULATION STUDIED: Ninety-six patients referred for bronchoscopy with computed tomographic evidence of significant mediastinal or hilar adenopathy. RESULTS: Ninety-nine patient records were reviewed. Three patients had two separate bronchoscopy procedures. TBNA was positive in 42 patients (44%) and negative in 54 patients. Of the 42 patients with a positive aspirate, 40 had malignant cytology and two had cells consistent with benign disease. The positive TBNA result altered management in 22 of 40 patients with malignant disease and one of two patients with benign disease, thereby avoiding further diagnostic procedures. The cost of these subsequent procedures was estimated at $27,335. No complications related to TBNA were documented. CONCLUSIONS: TBNA is a high-yield, safe and cost effective procedure for the diagnosis and staging of bronchogenic cancer.

Odor response properties of rat olfactory receptor neurons.

Molecular biology studies of olfaction have identified a multigene family of molecular receptors that are likely to be involved in odor transduction mechanisms. However, because previous functional data on peripheral coding were mainly collected from inferior vertebrates, it has been difficult to document the degree of specificity of odor interaction mechanisms. As a matter of fact, studies of the functional expression of olfactory receptors have not demonstrated the low or high specificity of olfactory receptors. In this study, the selectivity of olfactory receptor neurons was investigated in the rat at the cellular level under physiological conditions by unitary extracellular recordings. Individual olfactory receptor neurons were broadly responsive to qualitatively distinct odor compounds. We conclude that peripheral coding is based on activated arrays of olfactory receptor cells with overlapping tuning profiles.

Evaluation of endoscope sheaths as viral barriers.

OBJECTIVES: Evaluate ENT endoscope sheaths as barriers to virus passage. STUDY DESIGN: "Defective" sheaths covering an endoscope were challenged with virus to determine how many virus particles could be recovered from the endoscope. METHODS: Sheaths with small laser-drilled holes (2 to 30 microm) were challenged with high-titer virus suspensions (10(8) viruses/mL). The inside of the sheath and the endoscope were separately rinsed to recover any virus that penetrated through the hole in the sheath. In an attempt to assess the possible importance of holes in the sheaths, a sequential test was conducted with an initial virus challenge outside a defective sheath (30-micron hole in the sheath), after which the possibly contaminated endoscope was removed and inserted into a second defective sheath (with a 20-micron hole at the same location) to determine whether the contaminating virus would pass outward through the second sheath. RESULTS: Small volumes of virus-containing fluid penetrated through the hole, e.g., 500 virus particles passed through one of three 30-microm holes. A significant fraction of those virus particles was occasionally found on the endoscope after removal from the sheath. Similar results were obtained with sheaths that had small tears (34-84 microm in length, from punctures with fine wires). Although some virus penetration could occur during the initial challenge contaminating the endoscope, no virus was detected passing outward through the second sheath. CONCLUSIONS: Use of a sheath combined with intermediate level disinfection should provide a safe instrument for ENT endoscopy.

Short-lasting exposure to one odour decreases general reactivity in the olfactory bulb of adult rats.

We investigated in adult rats whether a relatively short exposure to a novel odour can lead to changes in reactivity of olfactory bulb principal neurons. Naive rats were exposed to isoamyl acetate for 20 min per day either for 6 consecutive days or for a single 20-min exposure. Control group was non-exposed. Under anaesthesia, responsiveness of each recorded single mitral/tufted cell was tested towards isoamyl acetate and four other odours. Results show that the proportion of responding cells in the exposed groups decreased drastically when compared to controls. In the two experimental groups recorded 24 h following the last exposure, mitral/tufted cells show a significant decrease in the number of excitatory responses. In parallel, the number of non-responsive cells increased by at least a fourfold factor. This decrease in reactivity was not selective towards the odour used during the exposure but concerned any of the five test-odours presented during recordings. Finally, this lower responsiveness was long lasting as it was still observed 10 days after the end of the last exposure. This preliminary study points out the importance of even limited sensory experience in neural representation of odours.

Olfactory bulb output cell temporal response patterns to increasing odor concentrations in freely breathing rats.

This study compares the single-unit responses of 74 mitral/tufted cells recorded in freely breathing rats to step increases of the intensity of five odorants from 2 x 10(-4) to 10(-1) of saturated vapor pressure. It reveals a stability of the responses of these olfactory bulb output cells. Olfactory stimulation has frequently been shown to produce a strong patterning of mitral/tufted cell discharges highly correlated with respiration. In this study, cells were generally found to show the same response type to two consecutive concentrations, and only a few cells switched their response from excitation to suppression or vice versa. Their firing peak and/or trough occupied the same position in a high proportion of respiratory cycles recorded during a stimulation, and they remained significantly time-locked to the same respiratory epoch for the next higher concentration. Increasing odor concentration did not cause the mean firing frequency of individual cells during a peak to change appreciably between successive or extreme concentrations. By contrast, it tended to shift their maximum frequency during this peak towards an earlier respiratory cycle after stimulation onset. These results are compared with data reported in other electrophysiological studies and with results given by olfactory bulb models before being discussed for their implications in odor coding.

Recording the slow potentials evoked by odors in the olfactory mucosa of awake animals.

The aim of this report is to expose several improvements which are essential for obtaining good recordings from the basal side of the olfactory mucosa of awake rats with Ag-AgCl electrodes implanted through holes drilled in the roof of the nasal bone. In a first step, we present how this minimally invasive method was developed and validated in anesthetized rats. We insist particularly on several important points such as the size and form of the electrode tip, the careful deposit of silver chloride on this tip or the location of the implanting site. Then we demonstrate that the recorded signals have the characteristics of an electro-olfactogram (EOG), i.e that they have a local origin, that they change with odors and concentrations, and that they do not appear during pure air delivery, nor after ipsilateral nostril closure. Lastly we show that this method was successfully utilized in awake rats. In provided data demonstrating the rhythmicity of EOGs in freely-breathing animals and allowed us to study their relationships with respiration.

Similarity of granular-induced inhibitory periods in pairs of neighboring mitral/tufted cells.

1. Neighboring mitral/tufted cells have been previously shown to present temporal correlations of their firings related to the respiratory rhythm, particularly under odor stimulation. This occurs despite the existence of a powerful inhibitory control exerted by granule cells onto mitral/tufted cells. In the present study, we hypothesized that neighboring mitral cells can present granular induced inhibitory periods with similar latencies and durations and that such a similarity would preserve them from a possible suppression of their temporal correlations. 2. To test this hypothesis, we analyzed the latencies and durations of the inhibitory periods induced by granular activation in pairs of simultaneously recorded neighboring mitral cells. The activation of granule cells was achieved by electrical stimulation of the different pathways known to directly activate granule cells [lateral olfactory tract (LOT), anterior limb of the anterior commissure (AC), and piriform cortex (PC)]. Data from this group were compared with those of a control group composed of distant cells also recorded simultaneously. 3. Results first show that the latencies to onset of inhibition or to recovery were more frequently similar in neighboring cells than in control cells and that this similarity was enhanced by odor stimulation. Second, the probability that two cells exhibit similar inhibitory periods (i.e., similar latencies to both onset and to recovery) in response to electrical stimulation of LOT, AC, or PC was significantly higher in neighboring than in control cells. Third, only neighboring cells were found to present similar inhibitory periods in response to the stimulation of all of the three structures. 4. Granular activation was also found to modify the temporal patterns of individual mitral cells. However, although these patterns were not systematically modified similarly in neighboring mitral cells, they remained perfectly synchronized with zero delay if they were already synchronous without electrical stimulation. On the contrary, if patterns were spontaneously uncorrelated, electrical stimulation never produced a synchronization of their firings, even if their temporal relationships could be profoundly modified. 5. These results show that neighboring mitral cells can receive granular-induced inhibition with similar latencies and durations with a probability much higher than control cells. Such similarities allow neighboring mitral cells to preserve their temporal correlation despite the powerful inhibitory input from granule cells. Functional hypotheses about the role of the cortical feedback projections onto the bulb are discussed.

Fibreoptic bronchoscopy in the diagnosis of pulmonary disease in the immunocompromised host in northern Alberta.

OBJECTIVES: To determine the diagnostic utility of bronchoscopy in a population of immunocompromised hosts in northern Alberta. PATIENTS AND METHODS: Results from bronchoscopy in 86 immunocompromised patients who underwent a total of 101 procedures were retrospectively reviewed. RESULTS: The overall diagnostic yield was 57% with the highest yield in patients on immunosuppressive drug therapy (80%) and the lowest yield in the group of bone marrow transplant patients (27%). CONCLUSIONS: Bronchoscopy is a valuable tool for the evaluation of pulmonary disease in the immunocompromised host. Overall diagnostic yield of 57% is comparable with that reported in the literature.

GABAergic control of odor-induced activity in the frog olfactory bulb: electrophysiological study with picrotoxin and bicuculline.

In the olfactory bulb, the first relay of the olfactory pathways, GABA, could be largely involved in the information processing since the two main populations of interneurons, periglomerular and granular cells, use it as neurotransmitter through reciprocal synapses with second-order neurons. This study planned to clarify the role of GABAergic inhibition in odor coding and, more precisely, the role of glomerular GABAergic inhibition. To do so, we attempted to specifically block in vivo GABAA receptors with either picrotoxin or bicuculline. The drug was applied at the level of the glomerular layer so that the antagonist could act primarily via periglomerular cells. The analysis of the effects of blocking GABAA on the coding was studied by recording the second-order neuron responses to odor stimuli delivered in a wide concentration range. Under drug treatment, the second-order neuron properties were deeply changed: response thresholds to odors were often lowered and spike bursts were more sustained in frequency and in duration. Thus, the GABAergic control on second-order neurons might be carried out by limiting the neuron excitability. GABAA antagonists applied in this manner could act to suppress the inhibitory effect of either the periglomerular cells or of the granule cells, both of which have been shown to contain enzymes for GABA production. The placement of the drug suggests to us that the action is primarily at the glomerulus. The results are consistent with periglomerular cells exerting a tonic inhibition on second-order neurons, an inhibition whose strength would be modulated by stimulus intensity. As a result, the amplifying role of glomerular convergence might be partly counterbalanced by input inhibition. Nevertheless, due to our procedure of drug application, one cannot rule out the possibility that the effects observed may partly reflect granular cell blocking. It can be concluded that the whole GABAergic inhibition, through GABAA receptors, permits a wide dynamic range of intensity coding.