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PubMed1997

Olfactory discrimination ability for aliphatic esters in squirrel monkeys and humans.

Using a behavioral paradigm designed to simulate olfactory-guided foraging, the ability of five squirrel monkeys to distinguish iso-amyl acetate from n- and iso-forms of other acetic esters (ethyl acetate to decyl acetate) and from other esters carrying the iso-amyl group (iso-amyl propionate to iso-amyl capronate) was investigated. We found (i) that all five animals were clearly able to discriminate between all odor pairs tested; (ii) a significant negative correlation between discrimination performance and structural similarity of odorants in terms of differences in carbon chain length of both the aliphatic alcohol group and the aliphatic acid group of the esters; and (iii) that iso- and n-amyl acetate were perceived as qualitatively similar despite different steric conformation. Using a triple-forced choice procedure, 20 human subjects were tested on the same tasks in parallel and showed a very similar pattern of discrimination performance compared with the squirrel monkeys. Thus, the results of this study provide evidence of well-developed olfactory discrimination ability in squirrel monkeys for aliphatic esters and support the assumption that human and non-human primates may share common principles of odor quality perception.

Adult↗
PubMed1997

Neurogenic inflammation: with additional discussion of central and perceptual integration of nonneurogenic inflammation.

The Working Group on Neurogenic Inflammation proposed 11 testable hypotheses in the three domains of neurogenic inflammation, perceptual and central integration, and nonneurogenic inflammation. The working group selected the term people reporting chemical sensitivity (PRCS) to identify the primary subject group. In the domain of neurogenic inflammation, testable hypotheses included: PRCS have an increased density of c-fiber neurons in symptomatic tissues; PRCS produce greater quantities of neuropeptides and prostanoids than nonsensitive subjects in response to exposure to low-level capsaicin or irritant chemicals; PRCS have an increased and prolonged response to exogenously administered c-fiber activators such as capsaicin; PRCS demonstrate augmentation of central autonomic reflexes following exposure to agents that produce c-fiber stimulation; PRCS have decreased quantities of neutral endopeptidase in their mucosa; exogenous neuropeptide challenge reproduces symptoms of PRCS. In the domain of perceptual and central integration, testable hypotheses included: PRCS have alterations in adaptation, habituation, cortical representation, perception, cognition, and hedonics compared to controls; the qualitative and quantitative interactions between trigeminal and olfactory systems are altered in PRCS; higher integration of sensory inputs is altered in PRCS. In the domain of nonneurogenic inflammation, testable hypotheses included: increased inflammation is present in PRCS in symptomatic tissues and is associated with a heightened neurosensory response; PRCS show an augmented inflammatory response to chemical exposure. The working group recommended that studies be initiated in these areas.

Chemoreceptor Cells↗
PubMed2003

Olfactory function in workers exposed to styrene in the reinforced-plastics industry.

BACKGROUND: Impairment of olfactory function in humans has been associated with occupational exposure to volatile chemicals. To investigate whether exposure to styrene was associated with olfactory impairment, olfactory function was examined in workers with a minimum of 4 years exposure to styrene in the reinforced-plastics industry (current mean exposure: 26 ppm, range: 10-60 ppm; historic mean dose: 156 ppm-years, range: 13.8-328 ppm-years) and in a group of age- and gender-matched, unexposed controls. METHODS: Olfactory function was assessed using a standardized battery that included tests of threshold sensitivity for phenylethyl alcohol (PEA), odor identification ability, and retronasal odor perception. Odor detection thresholds for styrene were also obtained as a measure of specific adaptation to the work environment. RESULTS: No differences were observed between exposed workers and controls on tests of olfactory function. Elevation of styrene odor detection thresholds among exposed workers indicated exposure-induced adaptation. CONCLUSIONS: The present study found no evidence among a cross-section of reinforced-plastics industry workers that current or historical exposure to styrene was associated with impairment of olfactory function. Taken together with anatomical differences between rodent and human airways and the lack of evidence for styrene metabolism in human nasal tissue, the results strongly suggest that at these concentrations, styrene is not an olfactory toxicant in humans.

Adaptation, Physiological↗
PubMed1994

Suppression of odorant responses by odorants in olfactory receptor cells.

Odorants activate an inward current in vertebrate olfactory receptor cells. Here it is shown, in receptor cells from the newt, that odorants can also suppress this current, by a mechanism that is distinct from inhibition and adaptation. Suppression provides a simple explanation for two seemingly unrelated phenomena: the anomalously long latency of olfactory transduction and the existence of an "off response" at the end of a prolonged stimulus. Suppression may influence the perception of odorants by masking odorant responses and by sharpening the odorant specificities of single cells.

Acetophenones↗
PubMed2006

A pheromone receptor mediates 11-cis-vaccenyl acetate-induced responses in Drosophila.

Insect pheromones elicit stereotypic behaviors that are critical for survival and reproduction. Defining the relevant molecular mechanisms mediating pheromone signaling is an important step to manipulate pheromone-induced behaviors in pathogenic or agriculturally important pests. The only volatile pheromone identified in Drosophila is 11-cis-vaccenyl acetate (VA), a male-specific lipid that mediates aggregation behavior. VA activates a few dozen olfactory neurons located in T1 sensilla on the antenna of both male and female flies. Here, we identify a neuronal receptor required for VA sensitivity. We identified two mutants lacking functional T1 sensilla and show that the expression of the VA receptor is dramatically reduced or eliminated. Importantly, we show misexpression of this receptor in non-T1 neurons, normally insensitive to VA, confers pheromone sensitivity at physiologic concentrations. Sensitivity of T1 neurons to VA requires LUSH, an extracellular odorant-binding protein (OBP76a) present in the sensillum lymph bathing trichoid olfactory neuron dendrites. Here, we show LUSH are also required in non-T1 neurons misexpressing the receptor to respond to VA. These data provide new insight into the molecular components and neuronal basis of volatile pheromone perception.

Acetates↗
PubMed1993

Neuronal responses in the ventral striatum of the behaving macaque.

To analyse the functioning of the ventral striatum, the responses of more than 1,000 single neurons were recorded in a region which included the nucleus accumbens and olfactory tubercle in 5 macaque monkeys. While the monkeys performed visual discrimination and related feeding tasks, the different populations of neurons found included neurons which responded to novel visual stimuli; to reinforcement-related visual stimuli such as (for different neurons) food-related stimuli, aversive stimuli, or faces; to other visual stimuli; in relation to somatosensory stimulation and movement; or to cues which signalled the start of a task. The neurons with responses to reinforcing or novel visual stimuli may reflect the inputs to the ventral striatum from the amygdala and hippocampus, and are consistent with the hypothesis that the ventral striatum provides a route for learned reinforcing and novel visual stimuli to influence behaviour.

Amygdala↗
PubMed1997

Piriform cortex ablations block navigational map learning in homing pigeons.

Young homing pigeons were subjected to ablations of the piriform cortex or left intact and allowed to learn a navigational map. Three months later, control and piriform cortex lesioned pigeons were released from three unfamiliar locations. Control pigeons oriented homeward indicating successful navigational map learning. In contrast, piriform cortex ablated pigeons consistently oriented east, took more time to return home and were more likely to get lost. The results demonstrate that piriform cortex ablations in young homing pigeons disrupt navigational learning. The data support the conclusion that participation of the piriform cortex is necessary for navigational map learning, and its role in navigational learning cannot be substituted for by other telencephalic olfactory processing regions. Further, the results show that the role of olfactory cues in building up the navigational map cannot be replaced by other non olfactory environmental stimuli.

Animals↗
PubMed2000

Olfactory based spatial learning in neonatal mice and its dependence on CaMKII.

Spatial learning and memory involves the ability to encode geometric relationships between perceived cues and depends critically on the hippocampus. Visually guided spatial learning has been demonstrated in adult animals. As infant animals rely heavily on olfaction, olfactory based spatial learning was assessed in infant mice. When 12-day-old pups were displaced from their nest, they learned within a few training trials to use the spatial pattern of odor cues to move back to the nest. However, mouse pups that over-expressed Ca2+/calmodulin-dependent protein kinase (CaMKII) in hippocampal neurons were impaired in olfactory based spatial learning.

Age Factors↗
PubMedDate not supplied

Vision affects mushroom bodies and central complex in Drosophila melanogaster.

The brain of Drosophila is structurally altered by sensory stimuli that the flies receive during their adult life. Size and fiber number of the mushroom bodies, central complex, and optic lobes are influenced by social, spatial, or olfactory cues. Recently, the optic lobes have been shown to depend on the light regime that flies experience. Structural plasticity in the brain is thought to be a correlate of functional adaptations and long-term memory. We therefore extend our investigation of volume changes to the calyces of the mushroom bodies and the central complex. We show that rearing flies in constant light for 4 days increases the volume of both structures by up to 15% compared to rearing them in total darkness. Much of this difference develops during the first day. The effect of light is not hormonally mediated, as monocularly deprived flies develop a smaller ipsilateral calyx. Mutant analysis suggests that light generates its effects through known visual pathways. In contrast to the optic lobes, in the calyx and central complex structural changes can be linked to cAMP signaling, as in the mutants dunce1 and amnesiac1 no volume differences are observed. Surprisingly, the mutant rutabaga1 shows a prominent light-dependent volume increase in the calyx and central complex, dissociating structural from behavioral plasticity. In complete darkness wild-type flies grow larger calyces under crowded conditions in their normal culture vials than if kept in small groups on fresh food. This stimulating effect of crowding is not observed in any of the cAMP mutants, including rutabaga1.

Aging↗
PubMed2003

Olfactory input increases visual sensitivity in zebrafish: a possible function for the terminal nerve and dopaminergic interplexiform cells.

Centrifugal innervation of the neural retina has been documented in many species. In zebrafish Danio rerio, the only so-far described centrifugal pathway originates from terminal nerve (TN) cell bodies that are located in the olfactory bulb. Most of the TN axons terminate in the forebrain and midbrain, but some project via the optic nerve to the neural retina, where they synapse onto dopaminergic interplexiform cells (DA-IPCs). While the anatomical pathway between the olfactory and visual organs has been described, it is unknown if and how olfactory signals influence visual system functions. We demonstrate here that olfactory input is involved in the modulation of visual sensitivity in zebrafish. As determined by a behavioral assay and by electroretinographic (ERG) recording, zebrafish visual sensitivity was increased upon presentation of amino acids as olfactory stimuli. This effect, however, was observed only in the early morning hours when zebrafish are least sensitive to light. The effect of olfactory input on vision was eliminated after lesion of the olfactory bulbs or after the destruction of DA-IPCs. Intraocular injections of a dopamine D(2) but not a D(1) receptor antagonist blocked the effect of olfactory input on visual sensitivity. Although we cannot exclude the involvement of other anatomical pathways, our data suggest that the TN and DA-IPCs are the prime candidates for olfactory modulation of visual sensitivity.

Amino Acids↗
PubMed2001

Functional magnetic resonance imaging of human olfaction.

Olfaction is our basic sense phylogenetically and embryologically. Little is known, however, about how the human brain encodes the quality of odors, odor-associated memories, and emotions. Olfactory information is projected from the olfactory bulb to the primary olfactory cortex, which is composed of the anterior olfactory nucleus, the olfactory tubercle, the piriform cortex, the amygdala, the periamygdaloid region, and the entorhinal cortex. From there, the primary olfactory cortex projects to secondary olfactory regions including the hippocampus, ventral striatum and pallidum, hypothalamus, thalamus, orbitofrontal cortex, agranular insular cortex, and cingulate gyrus. Functional MR studies using olfactory stimuli as paradigms show activation of many of these areas and can advance our understanding of odor perception in humans.

Adult↗
PubMedDate not supplied

[Why so many synapses?].

INTRODUCTION AND DEVELOPMENT: Synapses are the most abundant structures in the body of all animals. This number appears to be exceedingly large considering their apparent function: excite or inhibit the postsynaptic cell. In the few cases for which data are available, the number of synapses that two identified cells establish is reasonably constant between individuals although variable during development. Observations in a variety of sensory systems and animal species indicate that synapse number is important for normal physiology. Recent data from the olfactory system in Drosophila show that, if this number increases threefold, the sensitivity of perception increases up to three orders of magnitude. Similarly, the loss of perception sensitivity to a given odorant correlates with a loss of sensory synapses in selected neurons. These changes require proper regulation of the cAMP pathway. CONCLUSIONS: It seems reasonable to assume that the postsynaptic effects in the case of N versus N synapses should be different. Since the action potential parameters in the postsynaptic cell are the same in both cases, we can propose, as a working hypothesis, that the functional differences rely in the differential calcium dynamics throughout the postsynaptic dendritic branches.

Animals↗
PubMed1983

Odor perception in children in relation to nasal obstruction.

To determine whether nasal obstruction in children results in impaired nasal function, olfactory sensitivity was assessed in 65 children with various degrees of nasal obstruction and in 13 children without nasal obstruction. Overall, olfactory detection thresholds were directly related to clinical ratings of degree of nasal obstruction. Of the subjects with nasal obstruction attributable to adenoid hypertrophy, 28 received adenoidectomy; when retested 2 to 28 months later, 20 of the 28 subjects showed generally commensurate reductions in nasal obstruction ratings and olfactory detection thresholds. In a comparison subgroup of 16 subjects retested after intervals of 5 to 13 months without having received intervening adenoidectomy, both the nasal obstruction ratings and the olfactory detection thresholds remained relatively unchanged. These results suggest that, in children, nasal obstruction of varied degree is associated with commensurate impairment of the ability to smell, and that reduction in the degree of nasal obstruction results in commensurate recovery of the ability to smell. Olfactory function, although hitherto accorded little pediatric attention, deserves consideration both in weighing the importance of nasal obstruction in children and in deciding about therapeutic intervention.

Adenoidectomy↗
PubMed2004

Visual memory and visual perception recruit common neural substrates.

This human neuroimaging review aims to determine the degree to which visual memory evokes activity in neural regions that have been associated with visual perception. A visual perception framework is proposed to identify cortical regions associated with modality-specific processing (i.e., visual, auditory, motor, or olfactory), visual domain-specific processing (i.e., "what" versus "where," or face versus visual context), and visual feature-specific processing (i.e., color, motion, or spatial location). Independent assessments of visual item memory studies and visual working memory studies revealed activity in the appropriate cortical regions associated with each of the three levels of visual perception processing. These results provide compelling evidence that visual memory and visual perception are associated with common neural substrates. Furthermore, as with visual perception, they support the view that visual memory is a constructive process, in which features or components from disparate cortical regions bind together to form a coherent whole.

Cerebral Cortex↗
PubMed1995

A study of the test-retest reliability of ten olfactory tests.

Ten tests of olfactory function (including tests of odor identification, detection, discrimination, memory, and suprathreshold odor intensity and pleasantness perception) were administered on two test occasions to 57 subjects ranging in age from 18 to 83 years. The stability of the average test scores was determined across the two test sessions for 14 measures derived from these 10 tests and for subcomponents of the Japanese T&T olfactometer threshold test. In addition, the test-retest reliability (Pearson r) of each test measure was established. With the exception of a response bias measure, the average test scores did not differ significantly across the two test sessions. Statistically, the reliability coefficients of the primary test measures fell into three general classes bound by the following r values: 0.43-0.53; 0.67-0.71; 0.76-0.90. Detection threshold values were more reliable than recognition threshold values; those based upon a single ascending presentation series were much less reliable than those based upon a staircase procedure. The relationship between test length and reliability was examined for several of the tests and mathematically modeled. For example, within the staircase series incorporating the odorant phenyl ethyl alcohol, reliability was related (R2 = 0.984) to the number of reversals included in the threshold estimate by a function derived from the Spearman-Brown formula; namely, reliability = 0.455* # reversals/[1 + 0.455 (# reversals - 1)]. Reversal location, per se, had little influence on reliability. Overall, this study suggests that (i) considerable variation is present in the reliability of olfactory tests, (ii) reliability is a function of test length, and (iii) caution is warranted in comparing results from nominally different olfactory tests in applied settings since the findings may, in some instances, simply reflect the differential reliability of the tests.

Adolescent↗
PubMed2001

That's your left foot and...

Olfaction involves pattern recognition processes: in the olfactory bulb each odor is represented as a specific spatial activity pattern, serving as the basis for downstream spatiotemporal encoding and odor perception. The principle of pattern generation, the general properties of the patterns and new evidence regarding the functions of the patterns are discussed.

Animals↗