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At least 289 records · Page 16Linked to original sources
PubMed2006

Learning to smell the roses: experience-dependent neural plasticity in human piriform and orbitofrontal cortices.

It is widely presumed that odor quality is a direct outcome of odorant structure, but human studies indicate that molecular knowledge of an odorant is not always sufficient to predict odor quality. Indeed, the same olfactory input may generate different odor percepts depending on prior learning and experience. Combining functional magnetic resonance imaging with an olfactory paradigm of perceptual learning, we examined how sensory experience modifies odor perception and odor quality coding in the human brain. Prolonged exposure to a target odorant enhanced perceptual differentiation for odorants related in odor quality or functional group, an effect that was paralleled by learning-induced response increases in piriform cortex and orbitofrontal cortex (OFC). Critically, the magnitude of OFC activation predicted subsequent improvement in behavioral differentiation. Our findings suggest that neural representations of odor quality can be rapidly updated through mere perceptual experience, a mechanism that may underlie the development of odor perception.

Adult↗
PubMed2002

Functional expression of a mammalian olfactory receptor in Caenorhabditis elegans.

The olfactory system in both vertebrates and invertebrates can recognize and distinguish thousands of chemical signals. Olfactory receptors are responsible for the early molecular events in the detection of volatile compounds and the perception of smell. Recently, candidate olfactory receptor genes have been identified in several organisms, but their characterization is far from been completed due to the difficulty to functionally express them in heterologous systems. To circumvent such difficulty, we expressed a mammalian olfactory gene, rat I7, in the nematode. We generated transgenic worms expressing I7 in AWA or AWB chemosensory neurons and performed behavioural assays using different concentrations of the rat I7 receptor agonist octanal. Pure octanal was repellent for wild-type worms whereas a 1:10 dilution was attractant. Expression of I7 in AWB neurons counteracted the volatile attraction to diluted octanal observed in control wild-type worms. Furthermore, expression of I7 in AWA neurons counteracted the volatile avoidance to pure octanal observed in wild-type worms. These results indicate that it is possible to functionally express mammalian olfactory receptors in providing a research tool to efficiently search for specific olfactory receptor ligands and to extend our understanding of the molecular basis of olfaction.

Animals↗
PubMed2003

Olfactory processing in a changing brain.

The perception of odorant molecules provides the essential information that allows animals to explore their surrounding. We describe here how the external world of scents may sculpt the activity of the first central relay of the olfactory system, i.e., the olfactory bulb. This structure is one of the few brain areas to continuously replace one of its neuronal populations: the local GABAergic interneurons. How the newly generated neurons integrate into a pre-existing neural network and how basic olfactory functions are maintained when a large percentage of neurons are subjected to continuous renewal, are important questions that have recently received new insights. Furthermore, we shall see how the adult neurogenesis is specifically subjected to experience-dependent modulation. In particular, we shall describe the sensitivity of the bulbar neurogenesis to the activity level of sensory inputs from the olfactory epithelium and, in turn, how this neurogenesis may adjust the neural network functioning to optimize odor information processing. Finally, we shall discuss the behavioral consequences of the bulbar neurogenesis and how it may be appropriate for the sense of smell. By maintaining a constitutive turnover of bulbar interneurons subjected to modulation by environmental cues, we propose that adult ongoing neurogenesis in the olfactory bulb is associated with improved olfactory memory. These recent findings not only provide new fuel for the molecular and cellular bases of sensory perception but should also shed light onto cellular bases of learning and memory.

Animals↗
PubMed2005

Integration and segregation of inputs to higher-order neuropils of the crayfish brain.

Information about the input and output pathways of higher-order brain neuropils is essential for gaining an understanding of their functions. The present study examines the connectivity of two higher-order neuropils in the central olfactory pathway of the crayfish: the accessory lobe and its target neuropil, the hemiellipsoid body. It is known that the two subregions of the accessory lobe, the cortex and medulla, receive different inputs; the medulla receives visual and tactile inputs, whereas the cortex receives neither (Sandeman et al. [1995] J Comp Neurol 352:263-279). By using dye injections into the olfactory lobe, we demonstrate that the accessory lobe cortex and medulla also have differing connections with the olfactory lobe. These injections show that local interneurons joining the olfactory and accessory lobes branch primarily within the cortex with only limited branching within the medulla. Injections of different dyes into the two subregions of the hemiellipsoid body, HBI and HBII, show that the accessory lobe cortex and medulla also have separate output pathways. HBI is innervated by the output pathway from the cortex while HBII is innervated by the output pathway from the medulla. These injections also show that HBI and HBII are innervated by separate populations of local interneurons with differing connections to higher-order neuropils in the olfactory and visual pathways. These results suggest a segregation of olfactory and multimodal (including olfactory) inputs within both the accessory lobe and the hemiellipsoid body and provide evidence of important functional subdivisions within both neuropils.

Animals↗
PubMed2007

Odor processing in multiple chemical sensitivity.

Multiple chemical sensitivity (MCS) is characterized by somatic distress upon exposure to odors. As in other idiopathic environmental intolerances, the mechanisms behind the reported hypersensitivity are unknown. Using the advantage of the well-defined trigger (odor), we investigated whether subjects with MCS could have an increased odor-signal response in the odor-processing neuronal circuits. Positron emission tomography (PET) activation studies with several different odorants were carried out in 12 MCS females and 12 female controls. Activation was defined as a significant increase in regional cerebral blood flow (rCBF) during smelling of the respective odorant compared to smelling of odorless air. The study also included online measurements of respiratory frequency and amplitude and heart rate variations by recording of R wave intervals (RR) on the surface electrocardiogram. The MCS subjects activated odor-processing brain regions less than controls, despite the reported, and physiologically indicated (decreased RR interval) distress. In parallel, they showed an odorant-related increase in activation of the anterior cingulate cortex and cuneus-precuneus. Notably, the baseline rCBF was normal. Thus, the abnormal patterns were observed only in response to odor signals. Subjects with MCS process odors differently from controls, however, without signs of neuronal sensitization. One possible explanation for the observed pattern of activation in MCS is a top-down regulation of odor-response via cingulate cortex.

Adult↗
PubMed1994

Possible pheromone-carrier function of two lipocalin proteins in the vomeronasal organ.

We report the molecular cloning and characterization of two secretory proteins specifically expressed in vomeronasal and posterior glands of the nasal septum, the ducts of which open into the lumen of the vomeronasal organ. These two proteins are members of the lipocalin superfamily, consisting of hydrophobic ligand carriers. We immunohistochemically localized one of the proteins in the mucus covering the vomeronasal sensory epithelium, where the primary reception of pheromone takes place. The immunoreactivity on the vomeronasal sensory epithelium was evident in the neonatal and post-pubertal periods, when the close contact between animals plays critical roles in suckling and sexual behaviors, respectively. These results suggest that small lipophilic molecules stimulate the accessory olfactory system to regulate the reproductive behavior of mice.

Amino Acid Sequence↗
PubMed1982

Effects of forebrain lesions on spawning behaviour in the male goldfish.

Lesions were stereotaxically placed in medial nuclei of the ventral telencephalon and preoptic area of male goldfish. Only lesions in the area ventralis telencephali pars supracommissuralis (Vs) and posterior pars ventralis (pVv) were effective in reducing the proportion of males spawning, as compared to sham groups, both 5 days (Experiment 1) and up to 4 weeks (Experiment 2) postoperatively. Spawning consistency over 7 weekly tests was negatively correlated with the volume of Vs-pVv destruction. Two-thirds of Vs-pVv lesioned males spawned on at least one of their weekly tests, with latencies for the onset of each courtship behaviour similar to those of control fish, partial performance of the spawning sequence was rare. These results suggest that lesion of the supracommissural telencephalon (Vs-pVv region) blocks the initiation of spawning behaviour in the male goldfish, perhaps by lowering reproductive motivation specifically or by interfering with the perception of sexual, particularly olfactory, cues.

Animals↗
PubMed1995

Second-order neurones and receptor mechanisms in visual- and olfactory-information processing.

The retina and olfactory bulb are relatively simple in their synaptic operation, and provide insight into the fundamental synaptic mechanisms of brain functions. In the visual system, bipolar cells receive glutamate input from photoreceptors, and segregate visual inputs into parallel ON and OFF responses to light exposure and termination. In the olfactory system, the mitral and tufted cells respond to excitatory inputs from olfactory receptor neurones, and undergo reciprocal regulation through dendrodendritic synapses with their associated granule cells. Recent studies of the synaptic operation and regulation of the bipolar, mitral and tufted cells, at the molecular level, have revealed the detailed synaptic mechanisms of the second-order neurones in the segregation and discrimination of sensory information, as well as the modulatory synaptic mechanism that is involved in olfactory-recognition memory formation.

Animals↗
PubMedDate not supplied

The effects of prenatal alcohol exposure on behavioral and neuroanatomical components of olfaction.

Prenatal alcohol exposure is associated with deficits in odor-associative learning in very young rat pups. One alternative explanation for these findings is that rather than a learning deficit per se, alcohol-exposed pups may display a sensory deficit. The present study was designed to examine the effects of prenatal alcohol exposure on behavioral and neuroanatomical components involved in olfaction. The subjects in this study were pups exposed to 35% ethanol-derived calorie (EDC) liquid diet from gestation days (GD) 6-20. Two control groups were included, a 0% EDC pair-fed and an ad lib lab chow group. In Experiment 1, respiratory response to a novel odor was examined in pups tested at either 3, 4, or 10 days of age. The 35% EDC offspring clearly detected the odor. Furthermore, there was an apparent alcohol-related development delay in respiratory rate as shown by a lower baseline respiratory rate at PN 3 relative to controls which was no longer apparent by PN 4. Experiment 2 examined the volume of two neuroanatomical structures involved in olfaction, the main olfactory bulb (MOB) and the vomeronasal organ (VNO) in 3-day-old pups. Prenatal alcohol exposure was associated with a decreased volume of the MOB although the VNO was unaffected.

Animals↗
PubMed2006

Grading odor similarities in a Go/No-Go task.

Recent studies show that some features of odor perception are predicted by olfactory receptor biophysics and olfactory bulb physiology. Those studies used a behavioral assay in which rodents dig in a dish of scented cage bedding after pretraining to associate a buried reward with an odorant. The advantage of the digging task is an intensity measure of similarity (number of seconds spent digging). The method has the disadvantages of odorant contamination and low control over concentration and timing, making it difficult to use in electrophysiology. We describe an operant task that avoids these disadvantages and provides a reliable intensity-based similarity measure. Odorants can be delivered with a standard air dilution olfactometer, and rats learn to lever press to one odorant and avoid pressing to another in a Go/No-Go (CS+/CS-) task with a partial reinforcement protocol. Generalization tests substitute a portion of the unrewarded CS+ trials with test odorants. The number of generalization trials on which a subject responds to a test odorant is the measure of odor similarity intensity. We present validation tests using mixture component recognition, which show high repeatability, little variability across subjects and no decrease in responding across sessions. The results match those obtained with the digging task in four of five mixtures tested. This method allows optimal control over stimulus parameters and is compatible with simultaneous electrophysiological recording.

Animals↗
PubMed2004

Emerging views on the distinct but related roles of the main and accessory olfactory systems in responsiveness to chemosensory signals in mice.

In rodents, the nasal cavity contains two separate chemosensory epithelia, the main olfactory epithelium, located in the posterior dorsal aspect of the nasal cavity, and the vomeronasal/accessory olfactory epithelium, located in a capsule in the anterior aspect of the ventral floor of the nasal cavity. Both the main and accessory olfactory systems play a role in detection of biologically relevant odors. The accessory olfactory system has been implicated in response to pheromones, while the main olfactory system is thought to be a general molecular analyzer capable of detecting subtle differences in molecular structure of volatile odorants. However, the role of the two systems in detection of biologically relevant chemical signals appears to be partially overlapping. Thus, while it is clear that the accessory olfactory system is responsive to putative pheromones, the main olfactory system can also respond to some pheromones. Conversely, while the main olfactory system can mediate recognition of differences in genetic makeup by smell, the vomeronasal organ (VNO) also appears to participate in recognition of chemosensory differences between genetically distinct individuals. The most salient feature of our review of the literature is that there are no general rules that allow classification of the accessory olfactory system as a pheromone detector and the main olfactory system as a detector of general odorants. Instead, each behavior must be considered within a specific behavioral context to determine the role of these two chemosensory systems. In each case, one system or the other (or both) participates in a specific behavioral or hormonal response.

Animals↗
PubMed2004

Mice (Mus musculus) lacking a vomeronasal organ can discriminate MHC-determined odortypes.

Major histocompatibility complex (MHC) genes in mammals (H-2 in mice) play a major role in regulating immune function. They also bestow individuality in the form of a chemical signature or odortype. At present, the respective contributions of the olfactory epithelium and the vomeronasal organ (VNO) in the recognition of individual odortypes are not well defined. We examined a possible role for the VNO in the recognition of MHC odortypes in mice by first removing the organ (VNX) and then training the mice to distinguish the odors of two congenic strains of mice that differed only in their MHC type. C57BL/6J mice (bb at H-2) and C57BL/6J-H-2(k) (kk at H-2) provided urine for sensory testing. Eight VNX and six sham-operated mice were trained to make the discrimination. Neither the number of training trials-to-criterion nor the rate of learning differed significantly for VNX and sham-operated mice. We conclude that the VNO is not necessary for learning to discriminate between MHC odortypes.

Animals↗
PubMed2003

Olfactory perceptual learning: the critical role of memory in odor discrimination.

The major problem in olfactory neuroscience is to determine how the brain discriminates one odorant from another. The traditional approach involves identifying how particular features of a chemical stimulus are represented in the olfactory system. However, this perspective is at odds with a growing body of evidence, from both neurobiology and psychology, which places primary emphasis on synthetic processing and experiential factors--perceptual learning--rather than on the structural features of the stimulus as critical for odor discrimination. In the present review of both psychological and sensory physiological data, we argue that the initial odorant feature extraction/analytical processing is not behaviorally/consciously accessible, but rather is a first necessary stage for subsequent cortical synthetic processing which in turn drives olfactory behavior. Cortical synthetic coding reflects an experience-dependent process that allows synthesis of novel co-occurring features, similar to processes used for visual object coding. Thus, we propose that experience and cortical plasticity are not only important for traditional associative olfactory memory (e.g. fear conditioning, maze learning, and delayed-match-to-sample paradigms), but also play a critical, defining role in odor discrimination.

Animals↗
PubMed2003

Intensity modulation of olfactory acuity.

Acuity is fundamental to sensory systems, establishing the foundation for detectable differences in stimulus quality and consequently shaping animals' sensory capacities. In the olfactory system, which samples intrinsically high-dimensional chemical information, acuity for odor quality is measurable by means of ad hoc dimensions based on behaviorally confirmed sets of sequentially similar odorants. The authors measure olfactory acuity in mice using a rewarded forced-choice odor generalization task and show that mice exhibit greater olfactory acuity in response to higher concentration (1,0 Pa) odorants than to lower concentration (0.01 Pa) odorants. Results suggest that the dynamic modulation of sensory acuity--not necessarily its maximization--is an important component of olfactory processing and reflects the salience of odorant stimuli.

Animals↗
PubMed1997

Olfaction in migraine.

Olfactory thresholds for acetone and vanillin and the unpleasantness rating of concentrated acetone were measured in 20 migraine sufferers and 21 controls. The olfactory threshold for vanillin was lower in migraine sufferers than in controls. In addition, patients who reported that odours frequently seemed stronger during attacks of migraine were able to detect acetone at a lower concentration than most other patients. No differences were found between migraine sufferers and controls for ratings of the unpleasantness of concentrated acetone. These findings suggest that hyperacuity to odours persists between episodes of migraine. Sensitivity to odours could contribute to the migraine predisposition.

Acetone↗
PubMed2002

Ratings of different olfactory judgements in schizophrenia.

We assessed the influence of schizophrenia on different olfactory tasks. Forty patients with schizophrenia (20 males and 20 females) and 40 control subjects (20 males and 20 females) were tested. The experiment included two sessions. Initially, 12 odorants were presented at a rate of one per minute. The subjects were asked to rate intensity, pleasantness, familiarity and edibility for each odour using linear rating scales. The odorants were then presented a second time and the subjects were asked to identify them. The results showed that the scores for pleasantness, familiarity, edibility and identification but not intensity were disturbed in patients when compared with control subjects. Furthermore, the familiarity judgement of male patients was more often deficient than that of female patients and they rated odorants as being inedible when the women judged them as neutral. Considered together, these data show that our olfactory test may be used in patients with schizophrenia for evidencing various dysfunctions specific to different types of olfactory processing that represent steps in the odour name identification process.

Adult↗