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PubMed2002

Olfactory sensitivity for aliphatic alcohols in squirrel monkeys and pigtail macaques.

The view that primates are microsmatic animals is based mainly on an interpretation of neuroanatomical features, whereas physiological evidence of a poorly developed sense of smell in this order of mammals is largely lacking. Using a conditioning paradigm, we therefore assessed the olfactory sensitivity of three squirrel monkeys (Saimiri sciureus) and of four pigtail macaques (Macaca nemestrina) for a homologous series of aliphatic alcohols (ethanol to 1-octanol) and isomeric forms of some of these substances. In the majority of cases, the animals of both species significantly discriminated concentrations below 1 part per million from the odourless solvent, and with 1-hexanol individual monkeys even demonstrated thresholds below 10 parts per billion. The results showed (i) that both primate species have a well-developed olfactory sensitivity for aliphatic alcohols, which for the majority of substances matches or even is better than that of species such as the rat, (ii) that both species generally show very similar olfactory detection thresholds for aliphatic alcohols, and (iii) that a significant negative correlation between perceptibility in terms of olfactory detection threshold and carbon chain length of both the aliphatic 1- and 2-alcohols exists in both species. These findings support the idea that across-species comparisons of neuroanatomical features are a poor predictor of olfactory performance and that general labels such as 'microsmat' or 'macrosmat', which are usually based on allometric comparisons of olfactory brain structures, are inadequate to describe the olfactory capabilities of a species. Further, our findings suggest that olfaction may play an important and hitherto underestimated role in the regulation of behaviour in the species tested.

1-Butanol↗
PubMed1984

Anatomical evidence for convergence of olfactory, gustatory, and visceral afferent pathways in mouse cerebral cortex.

Flavor perception requires the neural integration of olfactory, gustatory and, possibly, visceral afferent information. Presently, it is not known where, or how this integration takes place in the brain. Neuroanatomical data presented here suggest that pathways subserving these sensory modalities converge in mouse insular cortex after surprisingly few synaptic relays. Orthograde transport of wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP) was used to label main olfactory bulb (MOB) efferents. A projection into layer I of insular cortex was present in every case. Bulb transections were made to provoke anterograde degeneration and EM analysis confirmed that the olfactory projection to insular cortex was a terminal pathway. WGA-HRP injections in the MOB-recipient zone of insular cortex resulted in ortho and retrograde labeling of ascending and descending gustatory-visceral afferent pathways. It is concluded that in the mouse, there is a remarkably direct convergence of olfactory and gustatory-visceral sensory pathways in insular cortex. Together with the descending connections from insular cortex to the amygdala and to brainstem autonomic structures, it is possible that the cortical integration of olfactory and gustatory-visceral information could modulate mechanisms involved in food selection and autonomic reactions relating to the chemical senses. Basic mechanisms subserving flavor perception might be usefully modelled in mouse insular cortex.

Afferent Pathways↗
PubMed1990

Stud male protection of implantation in food-deprived mice: evaluation of the involvement of olfactory-vomeronasal systems.

The protection of implantation in food-deprived females provided by exposure to the stud males was not abolished following surgical ablation of the vomeronasal organ (VNO) from females. By contrast, stud males failed to protect implantation in food-deprived females made peripherally anosmic by intranasal irrigation with ZnSO4. The results suggest that the main olfactory system, and not the accessory olfactory system, is involved in the perception of the stud male-originating olfactory cue that protects implantation in nutritionally-stressed females. The findings also provide circumstantial evidence that the study male-originating olfactory cue involved in the protective effect is volatile (air-borne).

Animals↗
PubMed1985

[Origin of olfactory and rhinosensory evoked cortical potentials in diseases of the central nervous system].

This is the first report to be published on olfactory evoked potentials in patients with well-defined lesions of the central nervous system and the trigeminal nerve. Absence of olfactory evoked potentials is seen in post-central and parietotemporal lesions. The first peak of the so-called olfactory evoked twin potential is absent in lesions of the basal nuclei and sectioning of the trigeminal or ophthalmic nerve, whereas there is no second peak in subcortico-frontal and cortico-temporal lesions. Tumours of the corpus callosum and sectioning of the maxillary and mandibular nerves do not disturb the olfactory evoked potentials. The anatomically different localisation and the functional synergism of the olfactory and trigeminal systems in the perception of odours and the processing of olfactory evoked potentials are pointed out.

Adolescent↗
PubMedDate not supplied

[The effect of age on the sense of smell in health individuals].

INTRODUCTION: A need for research of the olfactory function exists in everyday clinical work. The aim of this study was to determine standards for perception and identification thresholds regarding olfactory substances in healthy subjects in regard to their age. MATERIAL AND METHODS: The research included 120 healthy examinees (60 women and 60 men) classified according to age into three age groups (20-30, 31-40, 41-50 years of age). This examination was done using Fortunato-Niccolini's method. RESULTS AND DISCUSSION: The results of this work show that olfactory function becomes significantly weaker after the age of forty. Thresholds of perception in correlation with thresholds of identification for examined olfactory substances are significantly lower in older age groups. CONCLUSION: A gradual loss of olfactory capability with age can be explained by gradual destruction of olfactory cells and fibres of olfactory nerves during life.

Adult↗
PubMed2002

Imaging of brain activation by odorants in humans.

Application of positron emission tomography and magnetic resonance imaging has provided several new insights into various olfactory functions. One is that sniffing and smelling engage separate subsystems in the human olfactory cortex. Another is that perception of odorous compounds (odorants) is mediated by a set of core regions, which are partly different for pure olfactory than for olfactory plus trigeminal odorants. Depending on the task associated with odor perception, the core regions are recruited together with other circuits, in a parallel and hierarchical manner. The sense of smell seems, therefore, to be organized similarly to other sensory modalities, and the specific psychophysical characteristics of olfaction should be attributed to an early involvement of the limbic system rather than to a conceptually different mode of processing.

Brain↗
PubMed1998

Sniffing and smelling: separate subsystems in the human olfactory cortex.

The sensation and perception of smell (olfaction) are largely dependent on sniffing, which is an active stage of stimulus transport and therefore an integral component of mammalian olfaction. Electrophysiological data obtained from study of the hedgehog, rat, rabbit, dog and monkey indicate that sniffing (whether or not an odorant is present) induces an oscillation of activity in the olfactory bulb, driving the piriform cortex in the temporal lobe, in other words, the piriform is driven by the olfactory bulb at the frequency of sniffing. Here we use functional magnetic resonance imaging (fMRI) that is dependent on the level of oxygen in the blood to determine whether sniffing can induce activation in the piriform of humans, and whether this activation can be differentiated from activation induced by an odorant. We find that sniffing, whether odorant is present or absent, induces activation primarily in the piriform cortex of the temporal lobe and in the medial and posterior orbito-frontal gyri of the frontal lobe. The source of the sniff-induced activation is the somatosensory stimulation that is induced by air flow through the nostrils. In contrast, a smell, regardless of sniffing, induces activation mainly in the lateral and anterior orbito-frontal gyri of the frontal lobe. The dissociation between regions activated by olfactory exploration (sniffing) and regions activated by olfactory content (smell) shows a distinction in brain organization in terms of human olfaction.

Adult↗
PubMed2003

Olfactory coding in the mammalian olfactory bulb.

There have been a number of recent approaches to the study of olfactory coding, each of which has its advantages and disadvantages. In the present review, we discuss our own work on this topic, which has involved mapping uptake of [14C]2-deoxyglucose across the entire glomerular layer of the rat main olfactory bulb in response to systematically selected pure odorant molecules. Our strategy to understand the olfactory code has involved four approaches. In the first, we determined whether the system encodes odorants in their entirety, or whether it encodes odorants by representing combinations of molecular features that add together to comprise a neural picture of each odorant. Multiple odorant features appeared to be coded by multiple receptors. Our second strategy examined the ways that such features are represented. We stimulated rats with odorants that differed greatly in their molecular structure to be able to identify a set of odorant feature response domains. Our third approach asked how odorants with very small differences in molecular structure are coded, and we found systematic differences in the representation of such features within response domains. Finally, we were able to predict odor perception from the neural representations of odorants that differed in only a single aspect of their structure. Using these strategies, we have been able to learn some of the rules by which the olfactory code operates. These rules have allowed us to predict where previously unmapped molecules would be represented and how differences in molecular representations affect olfactory perceptions.

Animals↗
PubMed2002

Odor discrimination and odor quality perception in rats with disruption of connections between the olfactory epithelium and olfactory bulbs.

Rats were trained using olfactometry and operant conditioning to discriminate among homologous fatty acids, homologous aldehydes, and a series of unrelated odors. Their memory for the positive and negative assignment of each odor (tested under extinction) was assessed before and after they had received selective lesions of the olfactory bulbs or injection of the olfactory epithelial toxin 3-methyl indole (3-MI). Response accuracy on the memory test provided a measure of the extent to which treatments altered the remembered perceptual quality of the odors. The degree of deafferentation of the bulb by treatment with 3-MI was assessed using anterograde transport of horseradish peroxidase applied to the olfactory epithelium. Rats treated with 3-MI had a detectable reaction product only in varying numbers of glomeruli on the lateral and, in some cases, posterior medial walls of the olfactory bulb. Bulbar lesions destroyed the dorsal and dorsomedial bulbar areas that have been identified in optical and electrophysiological studies as showing responses to fatty acids. Rats with bulbar lesions had good to near perfect retention on their post-treatment memory test on all odor pairs, as did 3-MI-treated rats that still had substantial input to glomeruli on the lateral or posterior medial wall of the bulb. 3-MI-treated rats with substantially fewer afferent connections had severe retention deficits, particularly for the aldehyde and fatty acid odors, but this loss was secondary to deficits in the ability to discriminate among these odors. The results indicate that input to bulbar areas that are activated by a series of homologous odors may not be essential for odor discrimination and that deafferentation of the majority of bulbar glomeruli may be primarily without effect on odor quality perception as assessed by the memory test. These outcomes point to a much higher degree of redundancy within the olfactory bulb than that envisioned by current combinatorial or odotopic hypotheses of odor quality coding or, alternatively, to mechanisms of odor coding used in the awake behaving animal that have not yet been elucidated.

Afferent Pathways↗
PubMed1991

Molecular reaction cascades in olfactory signal transduction.

Odorant induced second messenger signals in ciliary preparations from rat olfactory epithelia were monitored in the subsecond time range using a rapid kinetic methodology. Application of micromolar concentrations of odorants induced a rapid and transient elevation of second messenger concentrations. The odorous compounds analyzed induced in a mutually exclusive way the formation of either cyclic adenosine monophosphate or inositol-triphosphate. The activating effects of odorants on intracellular signalling cascades appear to be mediated via different G-proteins. Thus, at least two different second messenger pathways appear to be involved in olfactory signal transduction. Selective inhibition of odor-induced second messenger responses by certain lectins indicate that glycoproteins appear to be involved in the perception or transduction of olfactory signals. In the presence of protein kinase inhibitors the odorant-induced second messenger response is no longer transient but persistent over a longer time period, suggesting that termination of the signal is realized via feedback phosphorylation of functional elements in the reaction cascade.

Adenylyl Cyclases↗
PubMed1999

Temporal processing reveals a mechanism for limiting the capacity of humans to analyze odor mixtures.

Humans have great difficulty in analyzing odor mixtures. The present study investigates the role of temporal processing in mixture perception and its impact on human performance. The results indicate that in contrast to binary mixtures, the temporal order of the perception of components and their identity cannot be discerned in ternary mixtures. It is proposed that the primary cause of this inability is slow processing in olfactory working memory which limits the analysis of mixtures to about three components.

Adolescent↗
PubMed2006

Cross-modal interactions between olfaction and touch.

We report two experiments designed to investigate the nature of any cross-modal interactions between olfactory and tactile information processing. In Experiment 1, we assessed the influence of olfactory cues on the tactile perception of fabric softness using computer-controlled stimulus presentation. The results showed that participants rated fabric swatches as feeling significantly softer when presented with a lemon odor than when presented with an animal-like odor, demonstrating that olfactory cues can modulate tactile perception. In Experiment 2, we assessed whether this modulatory effect varied as a function of the particular odors being used and/or of the spatial coincidence between the olfactory and tactile stimuli. The results replicated those reported in Experiment 1 thus further supporting the claim that people's rating of tactile stimuli can be modulated by the presence of an odor. Taken together, the results of the two experiments reported here support the existence of a cross-modal interaction between olfaction and touch.

Adolescent↗
PubMed2003

Olfactory sensitivity for aliphatic aldehydes in squirrel monkeys and pigtail macaques.

Using a conditioning paradigm, the olfactory sensitivity of three squirrel monkeys and three pigtail macaques for a homologous series of aliphatic aldehydes ( n-butanal to n-nonanal) was assessed. With only few exceptions, the animals of both species significantly discriminated concentrations below 1 ppm from the odorless solvent, and with n-butanal and n-hexanal individual pigtail macaques even demonstrated thresholds below 1 ppb. The results showed (1). both primate species to have a well-developed olfactory sensitivity for aliphatic aldehydes, (2). pigtail macaques to generally perform better than squirrel monkeys in detecting members of this class of odorants, and (3). no significant correlation between perceptibility in terms of olfactory detection thresholds and carbon chain length of the aliphatic aldehydes in both species tested. These findings lend further support to the growing body of evidence suggesting that between-species comparisons of the number of functional olfactory receptor genes or of neuroanatomical features are poor predictors of olfactory performance. Further, our findings suggest that olfaction may play an important and hitherto underestimated role in the regulation of behavior in the species tested.

Administration, Inhalation↗
PubMed2000

'Microsmatic' primates revisited: olfactory sensitivity in the squirrel monkey.

Using a conditioning paradigm, the olfactory sensitivity of three squirrel monkeys to nine odorants representing different chemical classes as well as members of a homologous series of substances was investigated. The animals significantly discriminated dilutions as low as 1:10,000 n-propionic acid, 1:30,000 n-butanoic acid and n-pentanoic acid, 1:100,000 n-hexanoic acid, 1:1Mio n-heptanoic acid, 1:30, 000 1-pentanol, 1:300,000 1,8-cineole, 1:1Mio n-heptanal and 1:30Mio amyl acetate from the near-odorless solvent, with single individuals scoring even slightly better. The results showed (i) the squirrel monkey to have an unexpectedly high olfactory sensitivity, which for some substances matches or even is better than that of species such as the rat or the dog, and (ii) a significant negative correlation between perceptibility in terms of olfactory detection thresholds and carbon chain length of carboxylic acids. These findings support the assumptions that olfaction may play a significant and hitherto underestimated role in the regulation of primate behavior, and that the concept of primates as primarily visual and 'microsmatic' animals needs to be revised.

Aldehydes↗
PubMed2006

Olfactory sensitivity for aliphatic alcohols and aldehydes in spider monkeys (Ateles geoffroyi).

Using a conditioning paradigm, the olfactory sensitivity of five spider monkeys for homologous series of aliphatic 1-alcohols (1-propanol to 1-octanol) and n-aldehydes (n-butanal to n-nonanal) was investigated. With the exception of 1-propanol, the animals significantly discriminated concentrations below 1 ppm from the odorless solvent, and in several cases, individual monkeys even demonstrated detection thresholds below 10 ppb. The results showed 1) spider monkeys to have a well-developed olfactory sensitivity for both substance classes, which for the majority of alcohols tested matches or even is better than that of the rat, and 2) a significant negative correlation between perceptibility in terms of olfactory detection thresholds and carbon chain length of the alcohols, but not of the aldehydes tested. These findings lend further support to the growing body of evidence suggesting that between-species comparisons of the number of functional olfactory receptor genes or of neuroanatomical features are poor predictors of olfactory performance, and that general labels such as "microsmat" or "macrosmat" (which are usually based on allometric comparisons of olfactory brain structures) are inadequate to describe a species' olfactory capabilities.

Aldehydes↗