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At least 1,477 records · Page 82Linked to original sources
PubMed1995

Divergent seven transmembrane receptors are candidate chemosensory receptors in C. elegans.

Using their senses of taste and smell, animals recognize a wide variety of chemicals. The nematode C. elegans has only fourteen types of chemosensory neurons, but it responds to dozens of chemicals, because each chemosensory neuron detects several stimuli. Here we describe over 40 highly divergent members of the G protein-coupled receptor family that could contribute to this functional diversity. Most of these candidate receptor genes are in clusters of two to nine similar genes. Eleven of fourteen tested genes appear to be expressed in small subsets of chemosensory neurons. A single type of chemosensory neuron can potentially express at least four different receptor genes. Some of these genes might encode receptors for water-soluble attractants, repellents, and pheromones.

1-Octanol↗
PubMed1994

The cellular basis of olfaction.

Smell is one of the most important senses driving basic patterns of behaviour in most of the earth's animal species. It plays a role in food-finding, kin recognition, reproductive behaviour, the predator-prey relationship, mother-infant recognition, homing behaviour, nest-finding, and other behaviours. Students of animal behaviour have studied the role of olfaction extensively, but until recently little detail was known about the biology of the cells that respond to odours. This article describes some recent advances in our understanding of these cells.

Adenylyl Cyclases↗
PubMed1991

Association between chemosensory stimuli and cesarean delivery in rat fetuses: neonatal presentation of similar stimuli increases motor activity.

Recent studies conducted in this laboratory indicated that prenatal chemosensory stimulation followed by cesarean delivery strongly affected postnatal responsiveness to odors derived from the administered substances. The present experiments were performed in order to examine if an associative process was responsible for such effects. In Experiment 1 rat fetuses during Gestational Day 21 were exposed to a tenuous alcohol solution or to a lemon-containing solution either 40 or 10 min prior to cesarean delivery. All subjects were subsequently tested in terms of changes in neonatal motor activity when confronted with the odor of alcohol or lemon. Rats experiencing prenatal cues 10 min prior to delivery exhibited higher and differential responsiveness to the smell of these cues when compared to those experiencing similar solutions 40 min prior to delivery. In Experiment 2 each fetus sequentially experienced both cues. Subsequent tests confirmed that the delay between prenatal sensory experience and birth induction was critical in terms of significantly affecting olfactory-mediated motor responses. The results suggest that consequences related with cesarean delivery act as an unconditioned stimulus capable of being associated with orosensory cues present in the amniotic fluid.

Animals↗
PubMed1987

Hypothyroidism disrupts neural development in the olfactory epithelium of adult mice.

Adult mice made hypothyroid with propylthiouracil (PTU) lose their sense of smell. This is prevented by daily administration of thyroxine. As thyroxine is necessary for the correct development of the nervous system it may also be necessary for the genesis of new olfactory receptor neurones, a process that continues into adulthood. Adult mice were treated with PTU, injected with [3H]thymidine after 54 days and killed 5 or 15 days later. Microscopic analysis of the olfactory epithelium after autoradiography revealed similar numbers of labelled nuclei in the basal cell layer of the olfactory epithelia of Control and Hypothyroid mice 5 days after injection with [3H]thymidine. This indicated similar rates of basal cell division in the two groups. Fifteen days after [3H]thymidine injection, however, there were fewer labelled nuclei in the receptor cell layer of Hypothyroid mice and the olfactory epithelium was thinner than in Controls. Thyroxine therapy which reversed PTU-induced anosmia also reversed the epithelial effects of PTU treatment. Somewhat unexpectedly, there were no differences between the treatment groups in the average diameter of glomeruli in the olfactory bulb, and no differences in the expression of olfactory marker protein. The results indicate that although hypothyroidism disrupts neural development in the olfactory epithelium, it does not lead to a complete loss of mature receptor neurones.

Animals↗
PubMed1981

Role of olfactory cues in the radial maze performance of rats.

Contribution of the smell of food and odor trails to the performance of rats in a 12-arm radial maze was assessed in 12 rats. Choice accuracy was increased rather than decreased by omission of bait (Experiment 1). Maze arms entered during the first 6 choices in the 12-arm radial maze were randomly re-entered during the subsequent 6 choices in a parallel maze assembled from the same maze segments (Experiment 2). Error incidence increased from 1.33 to 1.94 per trial but remained below chance (3.0) when after 6 choices in radial maze A the rat completed the trial in an identical and similarly located maze B (Experiment 3). It is concluded that odor cues alone do not guide the animal's choice, but that they contribute to the complex sensory information essential for correct performance.

Animals↗
PubMed1991

Lower pleasantness of palatable foods in nalmefene-treated human volunteers.

The involvement of endogenous opioids in control of human food intake and appetite was investigated in a double-blind placebo-controlled study using a single, 2.5 mg oral dose of the opioid receptor antagonist, nalmefene. Ratings of the pleasantness of the smell and the taste, but not the appearance, of a number of foods was significantly lower in nalmefene-treated subjects. The magnitude of this effect was greater in food items independently rated as highly palatable. Caloric intake of a buffet-style meal was 20% lower in nalmefene-treated subjects, with the proportional reduction in intake of individual food items also depending on their palatability. These results lend further support to recent suggestions that opioids are involved in reward-related aspects of ingestion.

Adult↗
PubMed1986

Olfaction and Alzheimer's disease.

Disturbances in the sense of smell may be important both clinically and theoretically in Alzheimer's disease. Initial evidence of poor olfactory recognition performance in Alzheimer's and parkinsonian dementias was followed by two reports which corroborated olfactory dysfunction in Alzheimer's disease. The neuroanatomical and neurochemical bases for this disturbance are discussed. Despite an abundance of preclinical and clinical data linking olfaction with acetylcholine, a preliminary study failed to show any effect of scopolamine on olfactory thresholds. Two of the olfaction-Alzheimer's studies found significantly better performance in other demented groups (alcoholics and patients with vascular dementia), suggesting possible utility in the differential diagnostic workup. The effect of aging per se on olfactory performance cannot be assessed without rigorous control for cognitive dysfunction in sampled populations.

Acetylcholine↗
PubMed1983

Narrow-spectrum chemoreceptor cells in the antennules of the American lobster, Homarus americanus.

The present study shows that smell (antennular) receptor cells are as narrowly tuned to single compounds as taste (leg) receptor cells in the lobster. Antennular receptors responded best to hydroxy-L-proline (57% of the 30 cells sampled) and taurine (24%). In the presence of 14 other compounds in equimolar concentrations, the hydroxy-L-proline and taurine receptors showed a suppressed response to their best stimulus. Other cells had best responses to ammonium chloride, betaine, L-glutamate or L-proline. The results have implications for molecular receptor processes and for the neural basis of feeding behavior.

Action Potentials↗
PubMed1994

Olfactory disturbance induced by deafferentation of serotonergic fibers in the olfactory bulb.

The serotonergic neurons of the brain stem project widely throughout the central nervous system, and the olfactory bulb is one of the major forebrain targets of the ascending serotonin pathway. According to physiological studies, neurons of the olfactory bulb were found to reduce their spontaneous discharge rates by electrophoretically applied serotonin. However, roles of the bulbar serotonin in the sense of smell remain unanswered. In the present study, using 5,7-dihydroxytryptamine, a specific neurotoxin for serotonin, we found that the conditioned rats who learned to avoid a repellent by olfaction lost ability of discrimination by deafferentation of the bulbar serotonergic fibers. Such olfactory dysfunction did not occur in the early stage (three days after injection of the toxin) when the serotonergic fibers disappeared in the bulb, but developed a few weeks later. Interestingly, histological examination revealed marked shrinkage of the bulbar glomerulus which is a major termination site of the bulbopetal serotonergic fibers, and also a synaptic site of olfactory receptor cells and bulbar output neurons. The results indicate that depletion of the serotonergic fibers in the olfactory bulb causes glomerular atrophy and olfactory disturbance in the rat.

5,7-Dihydroxytryptamine↗
PubMed1991

Olfactory sensations produced by high-energy photon irradiation of the olfactory receptor mucosa in humans.

During irradiation of volumes that incorporate the olfactory system, a proportion of patients have complained of a pungent smell. A retrospective study was carried out to determine the prevalence of this side-effect. A questionnaire was sent to 40 patients whose treatment volumes included the olfactory region and also to a control group treated away from this region. The irradiated tumor volumes included the frontal lobe, whole brain, nasopharynx, pituitary fossa, and maxillary antrum. Of the 25 patients who replied, 60% experienced odorous symptoms during irradiation. They described the odor as unpleasant and consistent with ozone. Stimulation of olfactory receptors is considered to be caused by the radiochemical formation of ozone and free radicals in the mucus overlying the olfactory mucosa.

Adenoma↗
PubMedDate not supplied

Transection of the lateral olfactory tract does not produce anosmia.

Rats trained in an olfactometer were tested for retention of an odor detection and odor discrimination task after lesions of the olfactory peduncle. Large lesions of the peduncle, including transection of the lateral olfactory tract and anterior commissure resulted in severe deficits in retention and relearning but did not produce anosmia. Discrete lesions of the lateral olfactory tract had little or no effect on retention. The results indicate that the lateral and intermediate olfactory pathways are not essential for smell and suggest that significant olfactory function may be mediated by medial olfactory bulb projections.

Animals↗
PubMed1987

Presence of both odor identification and detection deficits in Alzheimer's disease.

Recent studies of Alzheimer's disease patients have demonstrated (a) marked structural and biochemical alterations in brain regions associated with olfactory function (including the olfactory bulb and entorhinal cortex) and (b) decrements in the ability to identify odorants. In light of such findings, we administered the University of Pennsylvania Smell Identification Test (UPSIT) and a forced-choice phenyl ethyl alcohol odor detection threshold test to a relatively large number of patients diagnosed, on the basis of stringent criteria, as having mild to moderately severe Alzheimer's disease. Compared to age-, gender-, and race-matched normal controls, these individuals evidenced consistent and marked decrements on both types of olfactory tests (ps less than 0.001). Surprisingly few of the patients were aware of their disorder, despite its appearance early in the disease process. These findings indicate that both odor identification and odor detection problems are present in dementia of the Alzheimer's type, and raise the possibility that the odor identification problem may be secondary to the odor detection problem.

Aged↗
PubMed1994

The ability of dogs to recognize and cross-match human odours.

The Dutch police use specially trained dogs, Canis familiaris, to identify criminals from scented objects left at the scene of the crime. As part of a study of the reliability of these identifications, experiments were performed to evaluate whether these dogs could match scents collected from different parts of the body. Dutch police dogs are capable of matching hand scent to scent collected in the crook of the elbow and vice versa, and of matching trouser pocket scent to hand scent. It appears that training and familiarity with the person whose scents have to be matched enhance the performance of the dogs. The reliability for judicial purposes entails further research since our knowledge of the sense of smell is limited.

Animals↗
PubMedDate not supplied

Assessment of olfactory deficits in detoxified alcoholics.

Olfactory functioning was evaluated in 37 male detoxified alcoholics and in 21 age-matched nonalcoholic controls using the University of Pennsylvania Smell Identification Test (UPSIT). Of the original subjects, 23 alcoholics and 14 controls returned for reevaluation 3-4 months following initial testing. The results showed that alcoholics had significantly lower UPSIT scores than did the controls, both at baseline and follow-up testing. Thirty-two percent of the alcoholics' UPSIT scores, in comparison to five percent of the controls' scores, fell into the clinically impaired range. Although current smoking patterns correlated significantly with UPSIT indices, comparisons limited to nonsmokers still indicated that the alcoholics were significantly impaired on this olfactory task. Correlational analyses indicated that olfactory performance was unrelated to alcoholics' scores on visuoconceptual and language tasks. Correlations with MR-derived indices of CSF volume showed a highly significant relationship between UPSIT scores and cortical sulcal volumes. Additionally, alcoholics (N = 15) who remained abstinent had significantly higher scores at follow-up than those who were not abstinent (N = 8). These findings demonstrate that alcoholism is associated with basic olfactory impairments which are only partially reversible with abstinence and that cortical structures play an important role in this sensory loss.

Adult↗
PubMedDate not supplied

Olfactory loss in alcoholics: correlations with cortical and subcortical MRI indices.

The relationship between olfactory identification ability and MRI volumetric indices of specific cortical and subcortical brain regions was investigated in 36 recently detoxified male alcoholics. The results of correlational analyses between MRI indices and score on the University of Pennsylvania Smell Identification Test (UPSIT) revealed that impairment in olfactory identification was associated with elevated cortical and ventricular CSF volumes as well as with reduced tissue volumes in the cortical and subcortical grey matter. The volume of the thalamus was found to be a significant unique predictor of UPSIT score, even after accounting for variance shared with other MRI indices. These findings provide the first empirical support for existing hypotheses that olfactory loss in alcoholic subjects may be mediated by both cortical and subcortical structures.

Alcoholism↗
PubMedDate not supplied

Gustatory and olfactory contributions to alcohol consumption in rats.

To determine the relative contributions of taste and smell in the consumption of alcohol by rats, the present experiment tested normal rats (n = 14) and rats with either gustatory cortex ablations (n = 10), olfactory bulbectomies (n = 11), or combination gustatory cortex and olfactory bulb ablations (n = 12). Rats were tested under mild fluid deprivation using a two-bottle testing procedure. Thirteen concentrations of alcohol (0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, and 12%, v/v) were tested in ascending order. Results showed that at strong alcohol concentrations (7% through 11%) rats with combined gustatory cortex and olfactory bulb ablations consumed significantly more alcohol than normal control rats. Rats lacking gustatory cortex displayed a similar increased level of consumption with strong alcohol concentrations. It is suggested that the high level of consumption of strong alcohol concentrations by rats with central nervous system damage reflects an associative deficit rather than an alteration in taste or odor perception.

Alcohol Drinking↗
PubMedDate not supplied

Sensory neurotoxicology: use of the olfactory system in the assessment of toxicity.

Although many compounds are purported to cause olfactory dysfunction, little experimental research has been done in this area. The nasal epithelium, being one of the first "wet tissues" to come into contact with airborne compounds, should be a good indicator of toxic insult. The same general procedures used to measure visual or auditory function can be applied to the olfactory system, although olfactory stimuli are much more difficult to generate and control. Cadmium exposure, which is frequently cited as causing olfactory dysfunction in humans, did not produce anosmia (loss of smell) in rats, even though there was a large increase in cadmium levels in their olfactory bulbs. Rats exposed to methyl bromide showed a severe disruption in olfactory function as well as in morphology and neurochemical indices. However, functional recovery occurred even in the presence of continuing morphological and neurochemical evidence of damage. A nonsensory function of the olfactory system, transneuronal transport via the primary sensory neurons, may represent a mechanism of entry into the central nervous system for compounds that are normally excluded by the blood-brain barrier.

Administration, Intranasal↗
PubMed1991

Neuropsychological probes of fronto-limbic system dysfunction in schizophrenia. Olfactory identification and Wisconsin Card Sorting performance.

Schizophrenic patients and normal control subjects took the University of Pennsylvania Smell Identification Test (UPSIT) and Wisconsin Card Sorting Test (WCST) as dual neuropsychological 'probes' of orbitofrontal (OF) and dorsolateral (DL) prefrontal function respectively. Patients were significantly impaired on both tasks compared to controls. UPSIT and WCST performance were uncorrelated in patients but were positively correlated in controls. The lack of correlation found in the patients suggests that the tasks may be tapping independent dysfunctions in schizophrenia reflecting differential impairment in fronto-limbic brain systems. Individual profiles of preserved and impaired performance on the UPSIT and WCST suggested that three schizophrenic patients had OF dysfunction, five had DL dysfunction and seven had a generalized (OF and DL) frontal system dysfunction. The reduced ability of schizophrenic patients to identify odors was largely independent of many deficits or confounds typically associated with schizophrenia and did not appear to be simply a function of generalized deficit. These data are preliminary and require replication with larger samples and validation with other measures of fronto-limbic system dysfunction.

Adolescent↗