Showing papers on "Olfaction published in 1993"

Nonlinear amplification by calcium-dependent chloride channels in olfactory receptor cells

Abstract: The sense of smell is highly evolved in mammals, allowing discrimination between a vast number of odorants, with detection thresholds as low as 10(-17) M (ref. 1). Although several features of mammalian olfactory transduction have been revealed by biochemical and molecular biological studies, the odorant-induced membrane current has remained elusive. In amphibians this current is mediated by cyclic-nucleotide-gated channels, which depolarize the cell by Na+ and Ca+ influx and consequent Cl- efflux through Ca(2+)-dependent Cl- channels. The Cl- current may be absent in mammals, however, because its proposed role is linked to the aquatic habitat of amphibians. Here we show that the transduction current in rat olfactory receptor cells is initiated by cyclic-nucleotide-gated channels. The Cl- current is also present and endows the transduction current with a steep sigmoidal dependence on cyclic AMP concentration in both rat and in an amphibian, indicating a new function for the Cl- channel: nonlinear amplification of the transduction signal, whereby suprathreshold responses are boosted relative to basal transduction noise.

Cloning and expression of odorant receptors

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.

Odor-induced increases in c-fos mRNA expression reveal an anatomical "unit" for odor processing in olfactory bulb.

Abstract: Expression of the immediate-early gene c-fos was used to evaluate the coordinate activation of olfactory bulb neurons by brief exposure to specific odors in the alert rat. In situ hybridization to c-fos mRNA was compared to regional increases in 2-deoxy-D-[14C]glucose incorporation in an adjacent section analysis. Levels of c-fos mRNA in olfactory bulb were high in rats recently removed from their home cage but were low in animals placed in a relatively odor-free chamber for 30 min. Presentation of specific odors to alert rats for as little as 5 min increased c-fos mRNA in radially distributed neuronal ensembles that spanned the lamina of the main olfactory bulb. The complementary RNA (cRNA)-labeled neuronal collectives consisted of cells in the glomerular layer that precisely defined the borders of individual glomeruli and underlying tufted, mitral, and granule cells. The activated fields were much broader in the granule cell layer than in the overlying glomerular layer and thus exhibited a flask-like, as opposed to a columnar, contour. The bulbar distribution of cRNA-labeled cell arrays differed with different odors and, in the glomerular layer, corresponded to focal regions of high 2-deoxy-D-[14C]glucose uptake. Administration of the noncompetitive N-methyl-D-aspartate receptor antagonist MK801 did not attenuate the odor induction of c-fos but, instead, increased c-fos mRNA levels throughout the bulb. We propose that the neuronal ensembles expressing increased c-fos mRNA with odor stimulation represent principal functional units of sensory processing in the main olfactory bulb of the behaving rat.

Neural correlates of olfactory learning paradigms in an identified neuron in the honeybee brain

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...

β-Adrenergic Receptor Kinase-2 and β-Arrestin-2 as Mediators of Odorant-Induced Desensitization

Abstract: beta-Adrenergic receptor kinase (beta ARK) and beta-arrestin function in the homologous or agonist-activated desensitization of G protein-coupled receptors. The isoforms beta ARK-2 and beta-arrestin-2 are highly enriched in and localized to the dendritic knobs and cilia of the olfactory receptor neurons where the initial events of olfactory signal transduction occur. Odorants induce a rapid and transient elevation of adenosine 39,59-monophosphate (cAMP), which activates a nonspecific cation channel and produces membrane depolarization. Preincubation of rat olfactory cilia with antibodies raised against beta ARK-2 and beta-arrestin-2 increased the odorant-induced elevation of cAMP and attenuated desensitization. These results suggest that beta ARK-2 and beta-arrestin-2 mediate agonist-dependent desensitization in olfaction.

Synaptic organization and development of the antennal lobe in insects

Abstract: Many insects possess a highly developed sense of smell. This paper summarizes the cellular and synaptic organization of the antennal (olfactory) lobe of the insect brain and then reviews morphological and fine-structural aspects of the development of the lobe. Visualization of synapses between classes of neurons identified by physiological, morphological, or transmitter-cytochemical properties has provided insights into arrangements of contacts and their possible roles in information processing. Studies of development have revealed the requirement for afferent axons from the antenna for the formation of olfactory glomeruli, where virtually all of the synapses in the lobe occur, and have suggested the possibility that glial cells play a role in the instructive influence of the axons on their target neurons in the lobe. The findings reviewed in this paper are primarily from one representative hemimetabolous insect, the American cockroach, and one representative holometabolous insect, a hawkmoth, and comparisons are made with vertebrate systems when appropriate. © 1993 Wiley-Liss, Inc.

Olfactory testing differentiates between progressive supranuclear palsy and idiopathic Parkinson's disease

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.

Nutrition and chemosensory perception in the elderly

Abstract: The elderly person's perception of foods and food flavor is affected by age‐associated changes in the chemical senses (taste, smell, and trigeminal sensation). Both classic and modern psychophysical techniques have been applied to achieve some understanding of these changes. Taste threshold sensitivity declines with age; however, the magnitude of the decline and the degree to which taste qualities are differentially affected remains to be understood. Suprathreshold taste intensity perception is affected by age, but there is a differential effect of taste quality. Experiments with blended foods have indicated that both olfactory and taste deficits contribute to older people's difficulty with food identification. Experiments assessing threshold sensitivity, suprathreshold intensity, and suprathreshold identification have all demonstrated significant impairment in olfaction in old age. In fact, these effects are far greater than in the taste system. Patients with Alzheimer's disease show even greate...

Development of the olfactory organ in the zebrafish, Brachydanio rerio

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.

Parabrachial nucleus lesions and conditioned taste aversion: evidence supporting an associative deficit.

Abstract: Three experiments examined the conditioned taste aversion (CTA) deficit that occurs following electrolytic lesions of the parabrachial nucleus (PEN). In Experiment 1, lesioned rats failed to avoid either a gustatory or an olfactory stimulus that had been paired with lithium chlorideinduced toxicosis. In Experiment 2, however, all rats learned a conditioned flavor preference. Finally, in Experiment 3, all controls and 7 of the 12 lesioned rats learned a conditioned place aversion. Together, these results demonstrate that the disruption of CTA in lesioned rats cannot be ascribed to an inability to process either gustatory or visceral afferent information per se. Rather, the data suggest that PBN-lesioned rats are unable to form a specific association between gustatory and visceral cues. Using electrophysiological and tract tracing techniques, researchers have identified the major components of the central gustatory system in the rat. The first synapse of this system occurs in the nucleus of the solitary tract (NST; Hamilton & Norgren, 1984), which, in turn, projects to the parabrachial nucleus (PEN) of the pons (Norgren & Leonard, 1971,1973). From the PBN gustatory information follows two routes to the forebrain. First, PBN axons synapse on cells in the ventroposteromedial nucleus of the thalamus (Cechetto & Saper, 1987; Norgren, 1974); the thalamic neurons then

Ramification pattern and ultrastructural characteristics of the serotonin‐immunoreactive neuron in the antennal lobe of the moth Manduca sexta: A laser scanning confocal and electron microscopic study

Abstract: The two antennal lobes, the primary olfactory centers of the brain, of the moth Manduca sexta each contain one neuron that displays serotonin immunoreactivity. The neuron projects out of the antennal lobe and sends branches into ipsi- and contralateral protocerebral areas. An axon-like process extends from the contralateral protocerebrum to, and terminates in, the contralateral antennal lobe. In order to begin to investigate the possible role of this unique neuron in olfactory information processing, we have used laser scanning confocal microscopic and electron microscopic immunocytochemical techniques to study the ramification pattern, ultrastructural characteristics, and synaptic connections of the neuron in the antennal lobes of female adult Manduca sexta. The neuron ramifies extensively in the antennal lobe contralateral to the cell body. The ramifications, mainly in the base and center of each glomerulus, do not overlap with those of the sensory axons from the antenna. This finding suggests that the serotonin-immunoreactive neuron may not receive direct input from sensory neurons, and that it may modulate the activity of the neurons of the antennal lobe rather than that of the sensory neurons. In the electron microscope, the neuron exhibits large dense-cored vesicles and small, clear round vesicles. In the antennal lobe ipsilateral to the cell body, the primary neurite of the serotonin-immunoreactive neuron is unbranched and lacks detectable synaptic connections. The ramifications in the contralateral antennal lobe, however, participate in synaptic connections. At very low frequency, contralateral branches form synapses onto unlabeled processes and also receive synapses from unidentified neurons in the glomeruli, indicating that the neuron may participate directly in synaptic processing of olfactory information. The high ratio of output to input synapses made by the serotonin-immunoreactive processes in the contralateral antennal lobe is consistent with the idea that this neuron may receive synaptic input via its bilateral branches in the protocerebrum and then send information to the contralateral antennal lobe where the neuron may exert feedback or modulatory influences on olfactory information processing in the glomeruli. © 1993 Wiley-Liss, Inc.

Morphological study of the effects of intranasal zinc sulfate irrigation on the mouse olfactory epithelium and olfactory bulb

Abstract: The effects of intranasal zinc sulfate (ZnSO4) irrigation on the morphology of the olfactory epithelium and olfactory bulb were studied in mice with short survival times (as early as 1 day) and with long survival times (up to 593 days) after the irrigation procedure. As in several previous studies, the olfactory epithelium was completely destroyed within a few days after the ZnSO4 treatment. Within 2-4 days, the septum and turbinates were covered by a new, cuboidal epithelium, the cells of which differed significantly from any cells normally seen in the olfactory epithelium. Slowly, over several months, small areas of the olfactory epithelium regenerated in many of the animals. The ultrastructural changes occurring in the olfactory bulb from 1 to 25 days (the reactive stage) were characterized by degenerating olfactory axons and axon terminals, hypertrophy of astroglial cell processes, and proliferation of or extravasation by phagocytic cells. By 25 days after intranasal ZnSO4 irrigation, the number of reactive glial processes and phagocytic cells returned to normal. In some mice with survival times of 150 days or longer, there was reinnervation of small areas of the olfactory bulb by regenerated olfactory axons. These new olfactory axons innervated only superficial glomeruli or the outer portions of deeper glomeruli, but they formed synaptic contacts with mitral/tufted cells and periglomerular cells that did not differ from control animals. These findings were supported by tract-tracing experiments with 3H-amino acids and by behavioral analysis. In summary, the ultrastructural changes observed in the olfactory bulb in this study were not significantly different from those observed after surgical lesions of the olfactory epithelium or nerve.(ABSTRACT TRUNCATED AT 250 WORDS)

Associative learning in honey bees

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.

Tracing neural pathways in snail olfaction: From the tip of the tentacles to the brain and beyond

Abstract: The anatomical organization of the olfactory system of terrestrial snails and slugs is described in this paper, primarily on the basis of experiments using the African snail Achatina fulica. Behavioral studies demonstrate the functional competence of olfaction in mediating food finding, conspecific attraction, and homing. The neural substrate for olfaction is characterized by an extraordinarily large number of neurons relative to the rest of the nervous system, and by the fact that many of them are unusually small. There exist multiple serial and parallel pathways connecting the olfactory organ, located at the tip of the tentacle, with integrative centers in the central nervous system. Our methods of studying these pathways have relied on the selective neural labels horseradish peroxidase and hexamminecobaltous chloride. One afferent pathway contains synaptic glomeruli whose ultrastructure is similar to that of the glomeruli seen in the mammalian olfactory bulb and the insect olfactory lobe. All of the olfactory neuropils, but especially the tentacle ganglion, contain large numbers of morphologically symmetrical chemical synapses. The procerebrum is a unique region of the snail brain that possesses further features analogous with olfactory areas in other animal groups. Olfactory axons from the tentacle terminate in the procerebrum, but the intrinsic neurons do not project outside of it. An output pathway from the procerebrum to the pedal ganglion has been identified and found to consist of inter-ganglionic dendrites. The major challenge for future studies is to elucidate the pattern of connectivity within, rather than between, the various olfactory neuropils. © 1993 Wiley-Liss, Inc.

Are there structural and functional modules in the vertebrate olfactory bulb

Abstract: A number of different recording methods have shown that odorants elicit patterns of neuronal activity widely distributed across cells of the olfactory receptor epithelium, olfactory bulb, and piriform cortex in the vertebrate olfactory system. These findings suggest that the physicochemical properties of odorant molecules are processed by distributed coding mechanisms activated in parallel in olfactory circuits in order to characterize a single, "monomolecular" odorant. These findings also suggest that the response patterns seen at higher levels are set up by differential responses in peripheral receptor cells of the olfactory epithelium. One requirement for understanding the details of this proposed encoding scheme is correlation of odor-generated patterns with the components of these circuits. In this paper, results from 2-deoxyglucose and voltage-sensitive dye studies suggest that certain components of these responses may relate to patterns established in reproducibly identifiable aggregates of bulbar cells. These findings are consistent with previous observations suggesting that columnar groups of periglomerular, mitral/tufted and granule cells, oriented perpendicular to the laminae of the bulb, are functionally related to one another. Such cell groups or modules, when activated in parallel, could serve as building block components of the complete ensemble response. According to this hypothesis, different sets of such modules would be activated with different odorant stimuli and modules could be shared to the degree to which the physicochemical properties of the different stimuli overlap.

Timing of odor stimulation does not alter patterning of olfactory bulb unit activity in freely breathing rats.

Abstract: 1. The effect of the timing between nasal airflow and ongoing tracheal respiration on single-unit activity in the olfactory bulb (OB) of the rat was examined. Nasal and tracheal breathing were dissociated with the use of a double tracheal cannulation technique that allowed independent control of nasal airflow and control of the synchronization of nasal airflow and tracheal breathing. 2. When amyl acetate-saturated air was presented to the nose, OB units showed a distinct reorganization of activity known as respiratory patterning. Of 43 cells examined, 29 fired maximally after inspiration, and 14 fired maximally after expiration. In all 43 cells the patterning of OB activity was synchronized with the time course of the nasal stimulation. This synchronization was independent of the point in the ongoing respiratory cycle (tracheal breathing) at which the odor stimulation was applied. 3. Patterning of OB single-unit activity was also observed when odor was applied as a series of "inspirations" without intervening expirations. Patterning was observed to follow the time course of the odor stimulation even when this was considerably longer and slower than normal breathing. No patterning of activity was observed during continuous odor stimulation or in the absence of odor stimulation. 4. It is concluded that respiratory patterning of OB single-unit activity in the rat is not directly dependent on centrifugal inputs synchronized to respiration. Rather, the observed pattern of neural activity reflects the phasic stimulation of the olfactory receptors with each inspiration and the dynamics of the circuitry intrinsic to the bulb itself.

Molecular neurobiology of olfaction.

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.

Learning and memory of odor-reward association: selective impairment following horizontal diagonal band lesions.

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.

Odour quality processing by bee antennal lobe interneurones

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.

Response of olfactory receptor neurons in honeybees to odorants and their binary mixtures

Abstract: Recordings were made from single sensilla placodea of the worker honeybee (Apis mellifera). The sensilla were stimulated with one of two sets of four compounds and their binary mixtures, at two dosage levels. Aromatic compounds comprised one set, and saturated n-octane derivatives comprised the other set. Correlation, principal component, and cluster analyses indicate that responses to binary mixtures are not linear combinations of responses to the component compounds. The first principal component indicated that neuronal units had either more excitatory or more inhibitory responses to all odorants than would be expected from a model where inhibitory and excitatory responses are randomly distributed among the neuronal units. When compared to the responses to the component odorants, synergistic responses to binary odors occurred more often than would be expected by chance. Clear inhibitory responses to binary odors were less prevalent. This study agrees with an earlier study employing aromatic odorants in that most of the aromatic odorants each had groups of receptor neurons that were relatively selective for it, and each odorant had a distinctly different number of receptor neurons selective for it. Among the octane derivatives, receptor neurons were selective for the level of oxidation of the functional group or its site of attachment, rather than specific compounds.

Olfactory perception and olfactory imagery: a multidimensional analysis

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.

Presynaptic co-localization of carnosine and glutamate in olfactory neurones

Abstract: Olfaction plays a dominant role in modulating behaviour in most vertebrate species and the olfactory bulb is considered a model system for characterizing principles of neural computation. Nevertheless, although the physiology and neurochemistry of the olfactory circuits have been widely studied, the neurotransmitter released by olfactory receptor neurones remains unknown. We now describe the ultrastructural localization of the dipeptide carnosine and the excitatory amino acid glutamate in the glomerular layer of the mouse olfactory bulb. We demonstrate that both carnosine-like and glutamate-like immunoreactivities are selectively co-localized in the olfactory neurone boutons. These observations, taken with the recent findings of glutamate-receptor subunit expression in rodent olfactory bulb, argue compellingly for a role of glutamate in olfactory neurotransmission and suggest a modulatory effect of carnosine.

Sensory cues and the suppression of reproduction in subordinate female marmoset monkeys, Callithrix jacchus

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.

Coherent network oscillations by olfactory interneurons: modulation by endogenous amines

Abstract: 1. The procerebral (PC) lobe of the terrestrial mollusk Limax maximus contains a highly interconnected network of local olfactory interneurons that receives direct axonal projections from the two pairs of noses. This olfactory processing network generates a 0.7-Hz oscillation in its local field potential (LFP) that is coherent throughout the network. The oscillating LFP is modulated by natural odorants applied to the neuroepithelium of the superior nose. 2. Two amines known to be present in the PC lobe, dopamine and serotonin, increase the frequency of the PC lobe oscillation and alter its waveform. 3. Glutamate, another putative neurotransmitter known to be present in the lobe, suppresses the PC lobe oscillation by a quisqualate-type receptor and appears to be used by one of the two classes of neurons in the PC lobe to generate the basic LFP oscillation. 4. The known activation of second messengers in Limax PC lobe by dopamine and serotonin together with their effects on the oscillatory rhythm suggest the hypothesis that these amines augment mechanisms mediating synaptic plasticity in the olfactory network, similar to hypothesized effects of amines in vertebrate olfactory systems. 5. The use of a distributed network of interneurons showing coherent oscillations may relate to the highly developed odor recognition and odor learning ability of Limax.