Abstract: Myriads of odorous molecules that vary widely in structure are nevertheless readily detected and discriminated by the sense of smell, but how this is achieved by the olfactory system has been a long-standing puzzle. Several different models have been proposed, and previous observations indicate that the recognition sites for odorous molecules could be G-protein-coupled receptor proteins, an idea supported by the discovery of a new gene family that probably encodes a diversity of odorant receptors. Here we report the identification of new members of the gene family encoding putative odorant receptors and demonstrate that they are indeed transcribed in olfactory receptor neurons. Furthermore, the receptor-encoding complementary DNA is expressed in non-neuronal surrogate cells, which generate second messenger responses upon stimulation with appropriate odorants, indicating that the receptors recognize odorants and couple to G proteins of the host cells.

Abstract: 1. Sensitization and classical odor conditioning of the proboscis extension reflex were functionally analyzed by repeated intracellular recordings from a single identified neuron (PE1-neuron) in th...

Abstract: Olfactory dysfunction occurs in most patients with idiopathic Parkinson9s disease (PD). In this study, we sought to determine whether such dysfunction is also present in progressive supranuclear palsy (PSP), a condition which shares a number of motor symptoms with PD and is commonly misdiagnosed as PD. We administered the University of Pennsylvania Smell Identification Test, a standardized test of odor identification ability, to 21 PSP patients; 17 also received a forced-choice odor detection threshold test. We compared the olfactory test scores to those obtained from PD patients and normal controls matched to the PSP patients on the basis of age, sex, and smoking habits. Overall, the olfactory function of the PSP patients was markedly superior to that of the PD patients and did not differ significantly from that of the normal controls. There was no association in either the PSP or PD patient groups between (1) the olfactory test scores and (2) measures of motor symptom severity, disease stage, and medication usage. These findings demonstrate that patients with PSP and PD differ markedly in their ability to smell and suggest that olfactory testing may be useful in their differential diagnosis.

Abstract: The development of the olfactory organ of the zebrafish, from the forming of early placode to the adult organ, was investigated by electron microscopy and DiI labeling. The olfactory placode is formed by a subepidermal layer of cells. These cells differ from those of the epidermis as well as from brain cells, and they do not mingle either with epidermal or with brain cells. No migration of cells from the brain or the epidermis towards the subepidermal cell layer has been observed. The cells of the subepidermal layer seem to form all cell types of the olfactory mucosa, i.e., basal cells, ciliated and microvillous receptor cells, supporting cells, and ciliated nonsensory cells. Axons grow into the forebrain at a very early stage when the epidermis still covers the placode completely. Dendrites grow out when the epidermis separates, building the olfactory pit. This process implicates neither cell lysis nor cell degeneration. The olfactory pit forms a rosette with a midline raphe and olfactory lamellae. The incurrent nostril is separated from the excurrent nostril by a funnel-shaped structure. Differentiation of the olfactory placode in the embryo is accomplished very quickly, whereas the development into the adult organ during larval stages is a slow process.

Abstract: in spatial orientation and learning during dance communication, but the mechanisms of this kind of learning are little understood. In associative learning, stimuli experienced immediately before the reward (usually sucrose solution) are memorized for the guidance of future behavior. Well-established paradigms have been used to characterize operant and classical conditioning. The classical conditioning of olfactory stimuli is a very effective form of learning in bees and has helped to describe the behavioral and physiological basis of memory formation. It is concluded that memory needs time to be established and is processed in sequential phases. The neuronal compartments of the brain involved in the chemosensory pathway appear to participate differently in the sequential memory phases. A model is developed which assigns the strong non-associative components in olfactory conditioning to the antennal lobes, and the associative components to the mushroom bodies and the lateral output region of the protocerebrum. It is speculated that the amnesia-sensitive memory resides in the mushroom bodies and the amnesia-resistant memory in certain structures (eg the lateral protocerebrum) perhaps together with the mushroom bodies.

Abstract: IntraceLlular responses to olfactory signals (three components and the combination of mixtures which they can provide) of 90 morphological identified local and output interneurones of the bee antennal lobe (the so-called Homo LIN, Hetero LIN, Pluri ON and Uni ON) were analysed and classified into eight main categories of response profiles. The different morphological types exhibit differences m (i) background activity; (ii) response patterns; and (iii) selectivity and responsiveness to pure odours and mixtures. The results demonstrate that the responses to mixtures are unpredictable from the responses to the single components. Olfactory integration includes inhibitory processes. Results of the present work considered together with those related to the morphological and spatial aspects demonstrate that the antennal lobe layer of the bee olfactory neuronal network is characterized by a complex architecture and connectivity underlying highly complex and somewhat unpredictable intracellular responses.

Abstract: Odor discrimination is mediated via dendritic cilia of olfactory receptor neurons. Odorants traverse the aqueous mucous interphase that lines the surface of the olfactory neuroepithelium and interact with odorant receptors, which are members of the superfamily of G-protein-linked receptors. These interactions trigger synthesis of second messengers, including cyclic AMP and inositol triphosphate. Cyclic AMP opens a cation channel to elicit the generator current, which depolarizes the cell and, ultimately, leads to action potentials. Inositol triphosphate opens a calcium channel in the ciliary plasma membrane. Calcium entering through both this channel and the cyclic nucleotide-gated channel modulates the response to odorants by amplifying the generation of cyclic AMP after binding to calmodulin. Calcium also is essential for desensitization of olfactory receptor neurons. Differential expression of odorant receptors of diverse ligand specificities by different olfactory neurons ensures that the structures and concentrations of odorants that reach the chemosensory surface are encoded as distinct patterns of neuronal activity, which are relayed to the brain where they take shape as characteristic odor sensations.

Abstract: Rats with horizontal diagonal band of Broca (HDBB) lesions were trained in a successive-cue olfactory discrimination using different intertrial intervals (ITIs). They learned the paradigm of the task, but substantial impairment in performance of odor-reward associations was observed when the ITIs were longer than 15 s. They performed as well as control animals with short ITIs when they were trained previously with long ITIs, but forgetting appeared very soon thereafter (24 hr later). The finding is that the HDBB is an essential relay between the hippocampal system and the olfactory cortex: The HDBB allows associative memory storage when a limited-duration short-memory system located elsewhere is overloaded.

Abstract: Whether a system of imagery for olfaction exists is currently an unsettled issue. Moreover, the dimensions underlying odor perception have eluded researchers for many years. Two experiments bearing on these issues are presented. In one experiment, a group of 32 undergraduates rated the similarity of pairs of 16 commonplace odorants (e.g., chocolate and leather) they perceived using scratch and sniff stimuli; in another, a different group of 44 undergraduates was asked to imagine and then rate the similarity of the same pairs of odors. Multidimensional scaling of the data suggests that three-dimensional solutions with similar stimulus dimensions, such as fruitiness, strength, and familiarity, underlied the ratings of both perceived and imagined odors. By finding that similar dimensions define the psychological space of both the imagery and the perception tasks, this study suggests that imagery does indeed exist for olfaction.

Abstract: Subordinate female marmoset monkeys remain anovulatory and have low plasma concentrations of luteinizing hormone (LH) when maintained with their dominant females. Olfactory cues from the dominant female have been implicated in maintaining this reproductive suppression. Subordinate females that received either ablation of the vomeronasal organ (an accessory olfactory organ; n = 3), ablation of the main olfactory epithelium (n = 4), or both lesions (n = 5) did not ovulate in the following 7 weeks while housed with their dominant female. Plasma LH concentrations following either or both lesions were similar to pre-lesion concentrations. Olfactory lesions (verified by histological and behavioural trials) did not impair reproductive activity, as olfactory-lesioned dominant females underwent ovarian cycles of similar duration to intact dominant females. Lesioned subordinate females (n = 6), maintained in visual-only contact with their dominant female and group ovulated 29.1 +/- 9.3 days (mean +/- SEM) after physical separation from their dominant females; this first onset of ovulation was significantly delayed (P < 0.05) compared with intact subordinate females completely isolated from their dominant females and group (10.8 +/- 1.3 days, n = 8). Behavioural and visual cues together with olfaction all appear to play important roles in maintaining the suppression of ovulation in subordinate female marmoset monkeys.

Abstract: Two different techniques were used to assess the role of olfaction in the preference rats show for dilute nutrient suspensions and solutions. Removal of the olfactory bulbs reduced but did not abolish preference for 1% starch and oil emulsions. Removal of the olfactory bulbs also reduced preference for sucrose, Polycose, and saccharin. In another experiment, rats were rendered anosmic with intranasal zinc sulfate. The degree of anosmia was evaluated by measuring preference for an aqueous solution of citral and vanillin. Rats whose avoidance of citral plus vanillin had been abolished by zinc sulfate continued to prefer a 1% starch suspension over vehicle, although starch preference was significantly reduced. It is concluded that starch and oil preference is mediated by both olfactory and nonolfactory cues.

Abstract: The effect of stimulating olfactory cilia from the channel catfish (Ictalurus punctatus) with odorant amino acids on the formation of adenosine 3',5'-cyclic monophosphate, guanosine 3',5'-cyclic monophosphate, and inositol 1,4,5-trisphosphate (IP3) was studied in the subsecond time scale using a quenched flow technique. L-Alanine (L-Ala) and L-cysteine (L-Cys) (100 microM) elicited a transient elevation in IP3 levels that peaked at 25 ms. In contrast, even at high concentration a mixture of odorant amino acids (1 mM L-Ala, L-Cys, L-norleucine, L-glutamate, L-proline, and L-arginine) did not elicit a change in cAMP levels in this time scale and caused only relatively slow and minor increases in cGMP. The dose-response relationship for the IP3 response of L-Cys and L-Ala in the range from 10 nM to 1 mM is consistent with previous electrophysiological and ligand binding experiments. Odorant amino acid-stimulated IP3 formation was GTP dependent and was inhibited by guanosine 5'-O-(2-thiodiphosphate), suggesti...

Abstract: Olfaction plays a significant role in the perception of foods. For the most part, taste is limited to sweet, sour, bitter, and salty. The sensory experiences during consumption of complex foods and drinks cannot be constructed from these units. Indeed, much of the taste of a meal derives from olfactory stimulation. Hence, factors that influence olfactory perception should affect treatment of food-related odors. This article initially reviews previously published observations on the effects of age on olfaction and food preferences and then presents the results of original analyses of data derived from a substantial database formed as a result of the National Geographic Smell Survey. Included in the Survey form were topics relevant to the present article. They include the following question: Would you eat something that smelled like this? Two of the odors in the Survey were food related and two were fragrance related. Hence, in addition, we assessed responses to the following question: Would you apply something that smelled like this to your body? Answers were affected in part by the age and gender of the respondent and by the perceived pleasantness and intensity of the odor.

Abstract: To determine whether wild common carp (Cyprinus carpio) employ as pheromones the same gonadal hormones as goldfish, and whether their olfactory sensitivity is influenced by gonadal condition, the o...

Abstract: Olfactory neurons respond to odors with a change in conductance that mediates an influx of cations including Ca2+. The concomitant increase in [Cai] has been postulated to play a role in the adaptation to maintained odorant stimulation (Kurahashi, T., and T. Shibuya. 1990. Brain Research. 515:261-268. Kramer, R. H., and S. A. Siegelbaum. 1992. Neuron. 9:897-906. Zufall, F., G. M. Shepherd, and S. Firestein. 1991. Proceedings of the Royal Society of London, B. 246:225-230.) We have imaged the distribution of [Cai] in rat olfactory neurons (RON) using the Ca2+ indicator fura-2. A large percentage of the RON (42%, n = 35) responded to odorants with an increase in [Cai]. About half of the responding neurons displayed an increase in [Cai] at the apical end of the cell, but not at the soma. Moreover, in those cells that responded to odors with a standing [Cai] gradient, the gradient could be maintained for long periods of time (minutes) provided that the cells were continuously stimulated. In contrast, K(+)-induced depolarization elicited a more homogeneous increase in [Cai]. The spatially inhomogeneous increase in [Cai] elicited by odorants in some cells has important implications for the role of Ca2+ in adaptation because channels and enzymes regulated by Ca2+ will be affected differently depending on their location.

Abstract: Complete understanding of the role of the mammalian main olfactory bulb in sensory processing has remained elusive despite many detailed studies on its anatomy and physiology. Several lines of recent evidence viewed in the context of earlier knowledge have provided new insights into the bulbar mechanisms of olfactory coding. The output cells of the olfactory bulb receive a localized olfactory nerve input and interneuronal input via dendrodendritic synapses on distinct sets of dendrites. The spatial arrangement of granule cell contacts on output cell basal dendrites suggests that lateral inhibitory interactions may occur between neighboring output cells. The input from olfactory receptor cell axons to the bulb also has spatial order, but does not represent a precise map of the receptor surface. Recent studies with antibodies and lectins suggest that different groups of axons from chemically similar receptor cells collect into certain glomeruli, even if the axons originate from cells that are not contiguous in the mucosa. Electrophysiological studies have begun to explore the participation of spatially organized circuits in olfactory processing. The degree to which neighboring output cells respond similarly to odor stimulation, for example, depends on the distance between the cells, with those further apart showing complementary responses. Also, a single output cell can show 2 or more different temporal response patterns when different odors are presented. Intracellular recordings indicate that these responses are shaped by IPSPs. Electrical stimulation during such recordings shows that some mitral cells are excited by nerve inputs close to their glomerular tufts, while they are inhibited by nerve inputs to other parts of the bulb. Finally, recordings from granule and periglomerular cells indicate their potential in mediating components of output cell odor responses. These considerations suggest that the olfactory bulb performs a spatially based analysis on the information coming from the receptor cells. While the spatial organization of the olfactory bulb is probably not faithfully represented in the projections to the olfactory cortex, bulbocortical projections are not random. The fact that spatial factors exist at each of these levels in the olfactory system must be considered in developing models of central olfactory processing. © 1993 Wiley-Liss, Inc.

Abstract: Prominent, odor-evoked, fast (40–60 Hz) oscillations have been reported in the olfactory bulb and piriform (primary olfactory) cortex of both awake-behaving and anesthetized animals. The present study used current source-density analysis to examine the origin of the fast oscillations evoked by single weak shocks to afferent fibers. These shock-evoked oscillations closely resemble those evoked by odor. The results revealed that each cycle of the oscillatory field potential was generated by a stereotyped series of membrane currents similar to those previously characterized in the nonoscillatory response to strong afferent fiber shocks. Each cycle began with a strong inward current in layer la identified as an EPSC mediated by afferent fibers in distal apical dendrites of pyramidal cells. This afferent input was followed by a strong inward current in layer Ib identified as an EPSC mediated by intrinsic association fibers in middle apical dendritic segments. These excitatory events were followed by a smaller inward current at the depth of pyramidal cell somata (layers II and superficial III) that may be the depolarizing Cl(-)-mediated IPSC previously identified in the strong-shock response. Based on an analysis of the timing of the EPSCs it was concluded that the weak shock-evoked oscillation is generated in the olfactory bulb and that the resulting periodic activity in afferent fibers drives the oscillation in the piriform cortex.(ABSTRACT TRUNCATED AT 250 WORDS)

Abstract: Although olfactory associative conditioning in newborn rats produces marked structural and functional changes in the olfactory bulb, recent evidence suggests that extrabulbar circuits must be involved in storing these early memories. The present experiments examined the role of the amygdala complex on early olfactory learning. Bilateral amygdala lesions or sham lesions were performed on Postnatal Day (PN) 5. On PN6, pups were trained in a standard classical conditioning paradigm associating odor with tactile stimulation. Behavioral testing on PN7 revealed that amygdala lesions blocked odor preferences but had no effect on conditioned behavioral activation. Similar sized neocortical lesions did not impair odor preferences. Importantly, amygdala lesion effects on learned odor preferences could be reversed by extensive overtraining. These results suggest that the amygdala complex plays a critical role in modulating associative learning as early as the first postnatal week in the rat.

Abstract: Solitary fathead minnows (Pimephales promelas) were rendered anosmic and exposed to chemical stimuli from a predatory northern pike (Esox lucius) to determine the role of olfaction in the minnow's ability to recognize predators on the basis of chemical stimuli. Anosmic fish did not respond to the pike stimuli with a typical fright reaction, while control fish, with intact olfactory receptors, did. These results demonstrate that the olfactory system is necessary for the ability of fathead minnows to recognize northern pike as a predator and that the gustatory and single-celled chemosensory systems are not sufficient for this recognition in the absence of olfactory input. Olfactory impairment was behaviorally confirmed by exposing minnows to alarm substance (Schreckstoff).

Abstract: Gekkonid lizards are shown to have well-developed nasal chemical senses. It is argued that they are unique among squamates so far studied in the degree of their olfactory (as opposed to vomeronasal) development. This contention is supported by evidence from the brain, nasal capsule, tongue, and experimental studies of behaviour. Limited evidence suggests that olfaction functions in food-finding and predator detection; vomerolfaction during investigation of novel stimuli and in reproduction. The conception of gekkonids as members of a ‘visual Ascalabota’ is not supported by these findings. Olfactory specialization makes geckos ideal subjects for tests of the Cowles and Phelan hypothesis of olfactory function and suggests that they might be better subjects than snakes for future studies of dual olfactory form, function and evolution in a nonmammalian lineage.

Abstract: The glomerulus of the olfactory bulb may serve as a fundamental organizational unit for odor representation. In this context, the axons of olfactory receptor cells with similar response spectra may converge in specific glomeruli. While the topography between the olfactory epithelium and the olfactory bulb glomeruli has been explored, the characteristics of primary afferent terminal fields within glomeruli are poorly understood. To explore this issue, reconstructions of the terminal arbors of single olfactory nerve (ON) fibers within glomeruli were carried out in the rat olfactory bulb at the light microscopic level. Tissue samples prepared with the Golgi-EM technique resulted in distinct impregnation of limited subsets of individual ON fibers. Following camera lucida reconstruction, quantitative analyses were made on selected sets of ON fibers and on the glomeruli they invaded. Most ON fibers began to arborize only after penetrating the glomeruli to a mean depth of approximately 35.9 microns. The fibers gave rise to a complex arbor of branches that was limited in total length (mean 157.7 microns) and the number of en passant varicosities or terminal enlargements (mean = 8.1). The number of varicosities and terminal boutons was proportional to the total length of branches. Also, there was a statistically significant correlation between the total branch length and the area (microns2) encompassed by the total arbor. The intraglomerular region supplied by the terminal arbor of an individual ON fiber was generally restricted. Given the recent molecular specificity attributed to olfactory receptor cells, this may provide a morphological basis for selective processing of signals encoded by specific receptors in the olfactory epithelium.