Functional identification of a goldfish odorant receptor.
(25/2509)
The vertebrate olfactory system utilizes odorant receptors to receive and discriminate thousands of different chemical stimuli. An understanding of how these receptors encode information about an odorant's molecular structure requires a characterization of their ligand specificities. We employed an expression cloning strategy to identify a goldfish odorant receptor that is activated by amino acids-potent odorants for fish. Structure-activity analysis indicates that the receptor is preferentially tuned to recognize basic amino acids. The receptor is a member of a multigene family of G protein-coupled receptors, sharing sequence similarities with the calcium sensing, metabotropic glutamate, and V2R class of vomeronasal receptors. The ligand tuning properties of the goldfish amino acid odorant receptor provide information for unraveling the molecular mechanisms underlying olfactory coding. (+info)
Optical imaging of odorant representations in the mammalian olfactory bulb.
(26/2509)
We adapted the technique of intrinsic signal imaging to visualize how odorant concentration and structure are represented spatially in the rat olfactory bulb. Most odorants activated one or more glomeruli in the imaged region of the bulb; these optically imaged responses reflected the excitation of underlying neurons. Odorant-evoked patterns were similar across animals and symmetrical in the two bulbs of the same animal. The variable sensitivity of individual glomeruli produced distinct maps for different odorant concentrations. Using a series of homologous aldehydes, we found that glomeruli were tuned to detect particular molecular features and that maps of similar molecules were highly correlated. These characteristics suggest that odorants and their concentrations can be encoded by distinct spatial patterns of glomerular activation. (+info)
Long-term effects on the olfactory system of exposure to hydrogen sulphide.
(27/2509)
OBJECTIVE: To study chronic effects of hydrogen sulphide (H2S) on cranial nerve I (nervi olfactorii), which have been only minimally described. METHODS: Chemosensations (smell and taste) were evaluated in eight men who complained of continuing dysfunction 2-3 years after the start of occupational exposure to H2S. Various bilateral (both nostrils) and unilateral (one nostril at a time) odour threshold tests with standard odorants as well as the Chicago smell test, a three odour detection and identification test and the University of Pennsylvania smell identification test, a series of 40 scratch and sniff odour identification tests were administered. RESULTS: Six of the eight patients showed deficits of various degrees. Two had normal scores on objective tests, but thought that they continued to have problems. H2S apparently can cause continuing, sometimes unrecognised olfactory deficits. CONCLUSION: Further exploration into the extent of such problems among workers exposed to H2S is warranted. (+info)
Environmental signals modulate olfactory acuity, discrimination, and memory in Caenorhabditis elegans.
(28/2509)
Caenorhabditis elegans uses a variety of attractive olfactory cues to detect food. We show here that the responses to olfactory cues are regulated in a dynamic way by behavioral context and the animal's previous experience. Prolonged exposure to an odorant leads to a decreased response to that odorant, a form of behavioral plasticity called olfactory adaptation. We show that starvation can increase the extent of olfactory adaptation to the odorant benzaldehyde; this effect of starvation persists for several hours after the animals have been returned to food. The effect of starvation is antagonized by exogenous serotonin, which induces many of the same behavioral responses in C. elegans as are induced by food. Starvation also inhibits recovery from adaptation to a different odorant, 2-methylpyrazine, thus enhancing olfactory memory. In addition to its effects on adaptation, starvation modulates olfactory discrimination in C. elegans; starved animals discriminate more classes of odorants than fed animals. Increased olfactory discrimination is also seen in the adaptation-defective mutant adp-1 (ky20). These various forms of behavioral plasticity enhance the ability of starved animals to respond to novel, potentially informative odorants. (+info)
Association of visual objects and olfactory cues in Drosophila.
(29/2509)
Context-dependent preferences in a choice between an upper and a lower visual object of otherwise identical appearance were recorded during stationary flight of the fruitfly, Drosophila melanogaster, in a flight simulator. The test animal was held in a fixed orientation at the center of a wing-beat processor that converts attempted turns into counter-rotations of a surrounding cylindrical panorama. This allowed the fly to maneuver the preferred object into the actual direction of flight. Single flies were trained to avoid a course toward the visual object that had been associated with the aversive odor benzaldehyde (BAL). Conditioned object avoidance was investigated in different treatment groups by collective evaluation of the scores from 80 long-lasting flights (> 1 hr). In addition to a significant cross-modal association, we found a striking long-term effect of transient exposure to BAL both in the embryonic and larval states. The preimaginal experience significantly increased the indifference to BAL in the adult flies. Disturbed vision does not account for this effect: Neither the perception nor the discrimination of the visual objects was significantly impaired in the investigated flies. Disturbed olfaction could explain the present results. Recently, however, preimaginal BAL uptake has been found to interfere directly with the retention of heat-shock-conditioned object avoidance. (+info)
The Drosophila mutation turnip has pleiotropic behavioral effects and does not specifically affect learning.
(30/2509)
The Drosophila mutant turnip (tur) was isolated on the basis of its poor performance in an olfactory learning task, and also has a reduction in protein kinase C (PKC) activity. PKC has been found in the nervous systems of a wide range of organisms and appears to have an important role in learning and memory-related processes. Unfortunately, previous reports documenting the learning defect of tur lacked the controls required to assess the origins of the poor performance of the mutant. We have analyzed the effects of the tur mutation on both associative and nonassociative learning as well as on PKC activity. Additionally, the effects of the mutation on the task-relevant sensorimotor abilities of the flies were assessed. Although we were able to replicate previous behavioral and biochemical results obtained with tur, we discovered that the tur mutation also affected response to electric shock and caused a drastic reduction in the locomotor ability of the flies. Because locomotion is an essential component of the learning assays, this result makes it impossible to conclude that tur specifically affects learning and demonstrates the crucial importance of sensorimotor controls in conditioning experiments. (+info)
Olfactory dysfunction in schizophrenia: a qualitative and quantitative review.
(31/2509)
Olfactory dysfunction in patients with schizophrenia has been a topic of increasing interest, with deficits in odor identification, detection threshold sensitivity, discrimination, and memory being reported. Despite increasing knowledge, controversy has existed about possible differential deficits among olfactory tests as well as the influences of gender, smoking, and medication status on olfactory measures. To help elucidate some of this controversy, we conducted a qualitative and quantitative (meta-analytic) review of the English language literature on olfaction in schizophrenia. Moderator variables such as gender, medication status, and smoking history were also examined. Results indicated that substantial olfactory deficits, across all domains, are observed in patients with schizophrenia. No differential deficits were observed across domains of odor identification, detection threshold sensitivity, discrimination, and memory. The influences of gender, medication status, and smoking on effect sizes were not significant across studies. This supports the hypothesis of primary dysfunction in the olfactory system that is regulated by brain regions where structural and functional abnormalities have also been reported in neuroimaging studies. (+info)
Cognitive decline associated with normal aging in rats: a neuropsychological approach.
(32/2509)
The effects of aging on cognitive capacities were examined by comparing the performance of young and old rats on tasks characterized as dependent on different brain systems. This neuropsychological approach was employed to determine the extent to which multiple neural systems are compromised in aging and whether deterioration of one system correlates with that of another. The two tasks used in the present study were an odor-guided recognition memory task, for which different aspects of performance have been shown to be dependent on the integrity of the orbital prefrontal and perirhinal-entorhinal cortex, and the Morris water maze, for which performance depends on the medial prefrontal cortex and hippocampus. Rats were trained on the recognition memory task under minimal memory load and then challenged with longer memory delays and higher levels of inter-item interference. Considerable variation was observed in the performance of aged rats on acquisition of the recognition memory task, and unlike young rats, some aged rats could not acquire the task. Nevertheless, those aged rats who did acquire the cDNM task performed as well as young animals when the memory delay was extended and interference was elevated. In addition, consistent with previous findings, the performance of the same aged rats was highly variable in the Morris water maze task. Furthermore, although correlations between scores on the two tasks for individual aged rats were not reliable, only those aged rats that performed outside the performance range of young rats in the water maze were impaired on acquisition of the recognition memory task. This pattern of findings is consistent with age-related dysfunction in multiple subdivisions of the prefrontal cortex as well as the hippocampus and suggests that these brain regions may deteriorate in the same subgroup of aged rats. (+info)