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PubMed1975

Olfaction in the development of social preferences in the human neonate.

Olfactory perception in the human neonate has been largely ignored. The present experiments examine the possibility that neonates can use smell to locate a food source and that they can differentiate between their own mother and another mother on the basis of smell. Head-turning to breast pads was used in perference tests. Although the neonate did not appear to be able to use smell to localize a food source, significantly more babies spent more time turning towards their own mother's breast pad than towards a clean breast pad at five days of age. By six days of age babies were showing a differential response between their own mother's breast pad and another mother's breast pad, although this differentiation was not present at two days of age.

Age Factors↗
PubMed2004

Comparative analysis of the role of olfaction and the neocortex in primate intrasexual competition.

In strepsirrhine primates, the accessory olfactory system plays an important role in intrasexual competition. However, it does not play the same role in most haplorhines. In these primates, the main olfactory system and neocortex may have evolved to serve similar functions as the accessory olfactory system in strepsirrhines. To test these hypotheses, the relative size of the main olfactory bulb and neocortex were analyzed for associations with male and female competition frequency and intensity (categorized as low or high). Because neocortex size and competition intensity are associated with diet, only frugivorous species were analyzed (catarrhines, n = 7; platyrrhines, n = 8). Neither the size of the main olfactory bulb nor the neocortex was significantly associated with intrasexual competition among males. However, neocortex size was related to the frequency of female competition. Because the main olfactory system and neocortex both serve multiple purposes, there may not be a single behavioral variable that has selected for their size. Furthermore, categorization of male and female competition intensity reflects physically aggressive behavior. Use of the neocortex for social manipulation may allow males to obtain copulations and females to obtain food resources despite poor physical fighting abilities and low dominance rank.

Animals↗
PubMed2004

Molecular and cellular basis of human olfaction.

The human olfactory systems recognize and discriminate a large number of different odorant molecules. The detection of chemically distinct odorants begins with the binding of an odorant ligand to a specific receptor protein in the ciliary membrane of olfactory neurons. To address the problem of olfactory perception at a molecular level, we have cloned, functionally expressed, and characterized some of the human olfactory receptors from chromosome 17. Our results show that a receptor protein is capable of recognizing the particular chemical substructure of an odor molecule and, therefore, is able to respond only to odorants that have a defined molecular structure. These findings represent the beginning of the molecular understanding of odorant recognition in humans. In the future, this knowledge could be used for the design of synthetic ideal receptors for specific odors (biosensors), or the perfect odor molecule for a given receptor.

Humans↗
PubMed2001

A new subdivision of anterior piriform cortex and associated deep nucleus with novel features of interest for olfaction and epilepsy.

The anterior part of the piriform cortex (the APC) has been the focus of cortical-level studies of olfactory coding and associative processes and has attracted considerable attention as a result of a unique capacity to initiate generalized tonic-clonic seizures. Based on analysis of cytoarchitecture, connections, and immunocytochemical markers, a new subdivision of the APC and an associated deep nucleus are distinguished in the rat. As a result of its ventrorostral location in the APC, the new subdivision is termed the APC(VR). The deep nucleus is termed the pre-endopiriform nucleus (pEn) based on location and certain parallels to the endopiriform nucleus. The APC(VR) has unique features of interest for normal function: immunostaining suggests that it receives input from tufted cells in the olfactory bulb in addition to mitral cells, and it provides a heavy, rather selective projection from the piriform cortex to the ventrolateral orbital cortex (VLO), a prefrontal area where chemosensory, visual, and spatial information converges. The APC(VR) also has di- and tri-synaptic projections to the VLO via the pEn and the submedial thalamic nucleus. The pEn is of particular interest from a pathological standpoint because it corresponds in location to the physiologically defined "deep piriform cortex" ("area tempestas") from which convulsants initiate temporal lobe seizures, and blockade reduces ischemic damage to the hippocampus. Immunostaining revealed novel features of the pEn and APC(VR) that could alter excitability, including a near-absence of gamma-aminobutyric acid (GABA)ergic "cartridge" endings on axon initial segments, few cholecystokinin (CCK)-positive basket cells, and very low gamma-aminobutyric acid transporter-1 (GAT1)-like immunoreactivity. Normal functions of the APC(VR)-pEn may require a shaping of neuronal activity by inhibitory processes in a fashion that renders this region susceptible to pathological behavior.

Animals↗
PubMed2002

Cell and molecular biology of human olfaction.

Progress in our understanding of olfactory receptor physiology has progressed greatly over the past 10 years. It has become clear that many anatomical and molecular features of the peripheral aspect of the olfactory system have remained highly conserved across diverse species. Yet, this structure is responsible for conveying a wide variety of information about the environment that is necessary to the successful location of food, mates, and avoidance of danger, and it is thus not surprising that specializations have also evolved to suit the differing needs of different species. While the basic anatomical features reflect those of other mammals, functional studies of human olfactory receptor neurons have revealed physiological features both similar to and differing from those of other mammalian species. This review presents an overview of both the anatomical and physiological data describing the cell and molecular biology of the peripheral human olfactory system and how it functions in health and disease.

Humans↗
PubMed1992

Experimental morphology of insect olfaction: tracer studies, X-ray microanalysis, autoradiography, and immunocytochemistry with silkmoth antennae.

The general morphology and methodological peculiarities of insect sensilla are briefly reviewed. The stimulus conducting pore-tubule systems of pheromone-sensitive sensilla of the silkmoths Bombyx mori and Antheraea polyphemus are described. Lipophilic tracers readily enter the hair lumen, while hydrophilic tracers do so only after prolonged extraction with lipid solvents and/or pronase. X-ray microanalysis demonstrates a high potassium content of the sensillum lymph; calcium was only found in the haemolymph above detection limit. Auxiliary cells rapidly take up radioactive leucine administered via the haemolymph. Antibodies against pheromone-binding protein of Antheraea polyphemus label the sensillum lymph of sensilla trichodea, but not of sensilla basiconica in A. polyphemus as well as in B. mori. The cytoplasm of auxiliary cells of the sensilla trichodea is also labelled. The results are discussed in context with present hypotheses on the role of sensillum lymph in stimulus transport and inactivation.

Animals↗
PubMed2001

Recent advances in insect olfaction, specifically regarding the morphology and sensory physiology of antennal sensilla of the female sphinx moth Manduca sexta.

The antennal flagellum of female Manduca sexta bears eight sensillum types: two trichoid, two basiconic, one auriculate, two coeloconic, and one styliform complex sensilla. The first type of trichoid sensillum averages 34 microm in length and is innervated by two sensory cells. The second type averages 26 microm in length and is innervated by either one or three sensory cells. The first type of basiconic sensillum averages 22 microm in length, while the second type averages 15 microm in length. Both types are innervated by three bipolar sensory cells. The auriculate sensillum averages 4 microm in length and is innervated by two bipolar sensory cells. The coeloconic type-A and type-B both average 2 microm in length. The former type is innervated by five bipolar sensory cells, while the latter type, by three bipolar sensory cells. The styliform complex sensillum occurs singly on each annulus and averages 38-40 microm in length. It is formed by several contiguous sensilla. Each unit is innervated by three bipolar sensory cells. A total of 2,216 sensilla were found on a single annulus (annulus 21) of the flagellum. Electrophysiological responses from type-A trichoid sensilla to a large panel of volatile odorants revealed three different subsets of olfactory receptor cells (ORCs). Two subsets responded strongly to only a narrow range of odorants, while the third responded strongly to a broad range of odorants. Anterograde labeling of ORCs from type-A trichoid sensilla revealed that their axons projected mainly to two large female glomeruli of the antennal lobe.

Animals↗
PubMed2005

Odorant-specific requirements for arrestin function in Drosophila olfaction.

The ability to modulate olfactory sensitivity is necessary to detect chemical gradients and discriminate among a multitude of odor stimuli. Desensitization of odorant receptors has been postulated to occur when arrestins prevent the activation of downstream second messengers. A paucity of in vivo data on olfactory desensitization prompts use of Drosophila melanogaster genetics to investigate arrestins' role in regulating olfactory signaling pathways. Physiological analysis of peripheral olfactory sensitivity reveals decreased responsiveness to a host of chemically distinct odorants in flies deficient for arrestin1 (arr1), arrestin2 (arr2), or both. These phenotypes are manifest in odorant- and dose- dependent fashions. Additionally, mutants display altered adaptive properties under a prolonged exposure paradigm. Behaviorally, arr1 mutants are impaired in olfactory-based orientation towards attractive odor sources. As the olfactory deficits vary according to chemical identity and concentration, they indicate that a spectrum of arrestin activity is essential for odor processing depending upon the particular olfactory pathway involved. Arrestin mutant phenotypes are hypothesized to be a consequence of down-regulation of olfactory signaling to avoid cellular excitotoxicity. Importantly, phenotypic rescue of olfactory defects in arr1(1) mutants is achieved through transgenic expression of wild-type arr1. Taken together, these data clearly indicate that arrestins are required in a stimulus-specific manner for wild type olfactory function and add another level of complexity to peripheral odor coding mechanisms that ultimately impact olfactory behavior.

Acetates↗
PubMed2002

Maternal olfaction differentially modulates oxytocin and prolactin release during suckling in goats.

In postparturient goats, olfactory recognition of the young allows the establishment of a selective bond between the mother and her kids. Once this bond is formed, the mother rejects alien young that attempt to suckle. We tested whether the development of the maternal selective bond in goats modulates prolactin (PRL) and oxytocin (OT) release in response to suckling. On day 37 of lactation, serial blood samples were taken during nursing of the mother's own or alien kid(s) in 10 intact/selective goats and in 10 goats rendered anosmic/nonselective through prepartum peripheral ZnSO(4) irrigation. Spontaneous nursing behavior was also studied weekly from day 7 to 30 of lactation, at which time milk production was measured. Maternal selectivity had no effect on PRL release, in contrast to OT release, which was significantly affected by this factor. Intact mothers released OT only when nursing their own kids, but not with aliens, while anosmic/nonselective dams showed an increase in OT levels regardless of the identity of the kids. In addition to these effects on maternal selectivity, the amplitude of the response of both hormones was lower in anosmic mothers than in intact mothers. Finally, nursing behavior and milk production were not significantly affected by anosmia. We conclude that maternal selective behavior in goats, which relies on the individual olfactory signature of the kid, modulates the OT, but not the PRL, response to suckling. In addition, perception of the smell of the young appears to have a general facilitatory effect, independent of the kid's identity, on the release of both hormones.

Animals↗
PubMed1997

A numerical model of nasal odorant transport for the analysis of human olfaction.

The transport and uptake of inspired odorant molecules in the human nasal cavity were determined using an anatomically correct three-dimensional finite element model. The steady-state equations of motion and continuity were first solved to determine laminar flow patterns of odorous air at quiet breathing flow rates. The air stream entering the ventral tip of the naris traveled to the olfactory slit, and then passed through the slit in nearly a straight path without forming separated recirculating zones. The fraction of volumetric flow passing through the olfactory airway was about 10%, and remained nearly constant with variation in flow rate. The three-dimensional inspiratory velocity field was used in the solution of the uncoupled steady convective-diffusion equation to determine the concentration field in the airways and odorant mass flux at the nasal walls. The mass-transfer boundary condition used at the nasal cavity wall included the effects of solubility and diffusivity of odorants in the mucosal lining, and the thickness of the mucus layer. The total olfactory flux of odorants, that is highly correlated with perceived odor intensity, was determined as a function of all transport parameters in our model. Increase in nasal flow rate at a constant inlet concentration resulted in an increase in total olfactory uptake for all odorants. However, with increase in flow rate, the fractional uptake, i.e., total olfactory flux normalized by convective flux at the inlet, decreased for poorly soluble odorants, while it increased for highly soluble odorants. The pattern of flux (or imposed patterning) across the olfactory mucosa, that carries information concerning odor identity, was also determined as a function of transport parameters. There was an overall decrease in odorant flux as the location on the olfactory surface was varied from the anterior towards the posterior and from the inferior towards the superior ends. The flux pattern became more uniform, i.e., the steepness of the flux gradients across the olfactory surface decreased, as the mucus solubility of the odorants decreased. Different odorants generated discernibly different flux patterns across the olfactory mucosa that may contribute to the encoding of odor quality. Variation of total olfactory flux with time after cessation of airflow was determined by solving the unsteady diffusion equation in the air-phase. The flux decreased approximately exponentially with time. The rate of decay decreased as solubility and diffusivity decreased, but was very rapid over a wide range of the parameters, with time constants of less than 0.5 s for most odorants, implying a rapid decrease in perceived odor intensity with cessation of nasal airflow.

Absorption↗
PubMed2001

Activation and habituation in olfaction--an fMRI study.

This study investigated human BOLD responses in primary and higher order olfactory cortices following presentation of short- and long-duration odorant stimuli using a 3-T MR scanner. The goal was to identify temporal differences in the course of the response that might underlie habituation. A short-duration stimulus (9 s) consistently activated the primary olfactory cortex (POC). After a long stimulus (60 s), the temporal form of the response differed in different parts of the olfactory network: (1) The POC (piriform, entorhinal cortex, amygdala) and, interestingly, the hippocampus and, to a certain degree, the anterior insula show a short, phasic increase in the signal, followed by a prolonged decrease below baseline. (2) In the orbitofrontal cortex a sustained increase in activation was seen. This increase lasted approximately as long as the duration of odorant presentation ( approximately 60 s). (3) The mediodorsal nucleus of the thalamus and the caudate nucleus responded with an increase in signal which returned to baseline after approximately 15 to 30 s. The correlated biphasic hemodynamic response in the POC, hippocampus, and anterior insula during prolonged olfactory stimulation suggests that these three areas may interact closely with each other in the control of habituation. These results extend recent data which showed habituation of the rat piriform cortex and dissociation between the POC and the orbitofrontal cortex.

Adult↗
PubMed2003

Olfaction and depth of word processing: a magnetoencephalographic study.

Using a whole-cortex magnetoencephalograph, magnetic field changes were recorded to describe brain activities related to simultaneous visual and olfactory processing and to detect odor-related influences on verbal information processing. Words had to be either shallowly (nonsemantic) or deeply (semantic) encoded by healthy young subjects, each of these tasks under two different kinds of olfactory stimulation. After each encoding phase, word recognition performance was tested. First, the odor was randomly associated with some of the study words (simultaneous stimulation; same duration as for words) for both depths of word processing conditions, and second, continuous olfactory stimulation (permanent stimulation) was provided during the whole study phases of both depths of word processing conditions. The statistical analysis of the physiological data revealed evidence of a specific odor-induced effect depending on depth of word processing and kind of olfactory stimulation. Brain activity between about 250 and 450 ms as well as between about 650 and 1000 ms after stimulus onset was found to vary as a function of odor delivery and depth of word processing. In addition, a significant effect of odor stimulation on subsequent word recognition performance occurred in case of simultaneous odor stimulation and semantic word encoding. It is interpreted that in this case, word recognition performance significantly decreased because of the presence of the odor during prior word encoding. Such a behavioral effect was missing in all other conditions. The present psychological and physiological findings support the idea that semantic word encoding is specifically affected by simultaneous olfactory information processing. It is concluded that this phenomenon is due to a competition with cortical regions related to language and olfactory information processing, as suggested by T. S. Lorig (1999, Neurosci. Biobehav. Rev. 23, 391-398).

Adult↗
PubMed2002

A role for olfaction in object recognition by normal and hippocampal-damaged rats.

To examine how olfactory and visual factors affect object discriminations in rats with and without hippocampus damage, the authors trained Long-Evans rats on simple object discriminations. They then examined how these discriminations were affected by rotations of the objects, by coating the objects in a transparent acrylic coating, or by both rotating and coating the objects in acrylic. The rats displayed no impairments when the objects were only sprayed in acrylic, and they displayed minor impairments when the objects were rotated. However, when the objects were both rotated and acrylic coated, the rats displayed severe impairments. This suggests that the rats are solving the rotated-only phase based on surface features of the objects (probably odor) and not based on the visual information. Such species' biases for obtaining object information are important factors to consider when designing and interpreting visual memory experiments across species. There was no difference in performance between the rats with hippocampus damage and the sham rats, and this is consistent with the literature on similar tasks.

Animals↗
PubMed1999

Olfaction and symptoms in the multiple chemical sensitivities syndrome.

Whereas most idiosyncratic environmental sensitivity complaints do not fit known diagnoses, the multiple chemical sensitivities syndrome (MCS) is an extreme presentation that has defined diagnostic criteria. MCS symptomatics claim that they acquired a sensitized state as the result of a chemical exposure, usually to a solvent or pesticide, but not to a fragrance. Before this exposure, they did not experience symptoms. Following sensitization, symptoms increasing in number and severity with time are attributed by the MCS symptomatic to various exposures that are innocuous to most individuals. Although phenomenological studies have provided no evidence that particular odors elicit MCS symptoms, low levels of fragrances and perfumes are frequently associated with the reporting of MCS symptoms. This evaluation examines proposed mechanisms by which odorants and fragrances might cause either sensitization or elicitation of MCS symptoms, including altered odor sensitivity, primary irritancy or irritancy-induced upper airway reactivity, neurogenic switching of trigeminal irritancy signals, time-dependent sensitization and limbic kindling, CNS toxicity, and various psychiatric conditions. In no case was there persuasive evidence that any olfactory mechanism involving fragrance underlies either induction of a sensitized state or the triggering of MCS symptoms. Fragrances and other odorants could, however, be associated with symptoms as claimed by MCS symptomatics, because they are recognizable stimuli, but fragrance has not been demonstrated to be causal in the usual sense.

Environmental Exposure↗