Olfactory Organ Research Articles

In situ hybridization analysis of odorant receptor expression in the olfactory organ of the pig-nosed turtle Carettochelys insculpta

The turtle olfactory organ consists of upper (UCE) and lower (LCE) chamber epithelium, which send axons to the ventral and dorsal portions of the olfactory bulbs, respectively. Generally, the UCE is associated with glands and contains ciliated olfactory receptor neurons (ORNs), while the LCE is devoid of glands and contains microvillous ORNs. However, the olfactory organ of the pig-nosed turtle Carettochelys insculpta appears to be a single olfactory system morphologically: there are no associated glands; ciliated ORNs are distributed throughout the olfactory organ; and the olfactory bulb is not divided into ventral and dorsal portions. In this study, we analyzed the expression of odorant receptors (ORs), the major olfactory receptors in turtles, in the pig-nosed turtle olfactory organ, via in situ hybridization. Of 690 ORs, 375 were classified as class I and 315 as class II. Some class II ORs were expressed predominantly in the posterior dorsomedial walls of the nasal cavity, while other class II ORs and all class I ORs examined were expressed in the remaining region. These results suggest that the pig-nosed turtle olfactory organ can be divided into two regions according to the expression of ORs.

Zinc Oxide Nanoparticles (ZnO-NPs) Induce Cytotoxicity in the Zebrafish Olfactory Organs via Activating Oxidative Stress and Apoptosis at the Ultrastructure and Genetic Levels.

Nanotechnology has gained tremendous attention because of its crucial characteristics and wide biomedical applications. Although zinc oxide nanoparticles (ZnO-NPs) are involved in many industrial applications, researchers pay more attention to their toxic effects on living organisms. Since the olfactory epithelium is exposed to the external environment, it is considered the first organ affected by ZnO-NPs. Herein, we demonstrated the cytotoxic effect of ZnO-NPs on the olfactory organ of adult zebrafish after 60 days post-treatment. We opted for this period when fishes stop eating their diet from the aquarium, appear feeble, and cannot swim freely. Our study demonstrated that ZnO-NPs induced significant malformations of the olfactory rosettes at histological, ultrastructural, and genetic levels. At the ultrastructure level, the olfactory lamellae appeared collapsed, malformed, and twisted with signs of degeneration and loss of intercellular connections. In addition, ZnO-NPs harmed sensory receptor and ciliated cells, microvilli, rodlet, crypt, and Kappe cells, with hyper-activity of mucous secretion from goblet cells. At the genetic level, ZnO-NPs could activate the reactive oxygen species (ROS) synthesis expected by the down-regulation of mRNA expression for the antioxidant-related genes and up-regulation of DNA damage, cell growth arrest, and apoptosis. Interestingly, ZnO-NPs affected the odor sensation at 60 days post-treatment (60-dpt) more than at 30-dpt, severely damaging the olfactory epithelium and irreparably affecting the cellular repairing mechanisms. This induced a dramatically adverse effect on the cellular endoplasmic reticulum (ER), revealed by higher CHOP protein expression, that suppresses the antioxidant effect of Nrf2 and is followed by the induction of apoptosis via the up-regulation of Bax expression and down-regulation of Bcl-2 protein.

Resilient conductive membrane synthesized by in-situ polymerisation for wearable non-invasive electronics on moving appendages of cyborg insect

By leveraging their high mobility and small size, insects have been combined with microcontrollers to build up cyborg insects for various practical applications. Unfortunately, all current cyborg insects rely on implanted electrodes to control their movement, which causes irreversible damage to their organs and muscles. Here, we develop a non-invasive method for cyborg insects to address above issues, using a conformal electrode with an in-situ polymerized ion-conducting layer and an electron-conducting layer. The neural and locomotion responses to the electrical inductions verify the efficient communication between insects and controllers by the non-invasive method. The precise “S” line following of the cyborg insect further demonstrates its potential in practical navigation. The conformal non-invasive electrodes keep the intactness of the insects while controlling their motion. With the antennae, important olfactory organs of insects preserved, the cyborg insect, in the future, may be endowed with abilities to detect the surrounding environment.

Immunohistochemical Analysis of Olfactory Sensory Neuron Populations in the Developing Olfactory Organ of the Guppy, Poecilia reticulata (Cyprinodontiformes, Poecilidae).

Olfaction is fundamental for sensing environmental chemicals and has obvious adaptive advantages. In fish, the peripheral olfactory organ is composed of lamellae in which the olfactory mucosa contains three main categories of olfactory sensory neurons (OSNs) as follows: ciliated (cOSNs), microvillous (mOSNs), and crypt cells. We studied the appearance of these different OSNs during development of Poecilia reticulata, given its growing use as animal model system. We performed immunohistochemical detection of molecular markers specific for the different OSNs, carrying out image analyses for marked-cell counting and measuring optical density. The P. reticulata olfactory organ did not show change in size during the first weeks of life. The proliferative activity increased at the onset of secondary sexual characters, remaining high until sexual maturity. Then, it decreased in both sexes, but with a recovery in females, probably in relation to their almost double body growth, compared to males. The density of both cOSNs and mOSNs remained constant throughout development, probably due to conserved functions already active in the fry, independently of the sex. The density of calretinin-positive crypt cells decreased progressively until sexual maturity, whereas the increased density of calretinin-negative crypt cell fraction, prevailing in later developmental stages, indicated their probable involvement in reproductive activities.

Microscopic morphology and distribution of the antennal sensilla in the double-spined bark beetle, Ips duplicatus (Coleoptera: Curculionidae).

The double-spined spruce bark beetle, Ips duplicatus, has become an infamous secondary pest of Norway spruce, causing extensive ecological and economic destruction in many Central European countries. Antennae are the primary olfactory organs that play a fundamental role in insect-host chemical communication; therefore, understanding morphology is crucial before conducting electrophysiological investigations. Here, we present our analysis of sensilla types on the antennal surface of I. duplicatus for the first time, using high-resolution-scanning electron microscopy. We studied the external morphological characteristics of antennae and the types, numbers, and distribution of the antennal sensilla in males and females. Our results revealed the presence of five different types of morphologically distinct sensilla: sensilla chaetica, sensilla basiconica, sensilla trichodea, sensilla coeloconica, and Böhm's sensilla. We observed two subtypes of sensilla chaetica (SChI and SChII), four subtypes of sensilla basiconica (SBI, SBII, SBIII, and SBIV), three subtypes of sensilla trichodea (STrII, STrIII, and STrIV) and two subtypes of sensilla coeloconica (SCoI and SCoII), respectively in I. duplicatus males and females. Minor differences in length and numbers between the sexes for some sensilla types were found. Distribution maps for different sensillar types were constructed, and specific areas for the respective sensilla were found. Possible functions of observed sensilla types are discussed. The present study provides a basis for future electrophysiological studies to understand how I. duplicatus detects ecologically important olfactory cues. RESEARCH HIGHLIGHTS: • The first report of morphology and distribution pattern of the antennal sensilla in Ips duplicatus is discussed. • A total of 6 main types and 11 antennal sensilla subtypes were observed in male and female Ips duplicatus. • Minor sex-specific differences were seen in the length and numbers in several sensilla types.

Pig olfaction: the potential impact and use of odors in commercial pig husbandry

Pigs are widely acknowledged for their olfactory abilities. Research on pigs’ olfactory capacities has focused mainly on aspects of olfaction that directly impact production, such as palatability of feed and pheromones to stimulate reproduction. Several basic research questions remain unanswered, such as which odors do pigs like/dislike, and how may odors enrich their lives? This review aims to explore the currently available literature on pig olfaction to elucidate the current knowns and unknowns within the following topics: chemicals in a pig’s environment, the olfactory organs of pigs, olfactory detection and acuity, behavioral reactions to odors, aversive odors, reaction to novel odors, attractive odors, and odors as a management tool in commercial pig production. The review focuses on complex odors of non-social origin (e.g., ammonia), and when information on this topic is lacking we include information from research on other mammalian species. We found that the olfactory organs of pigs are already functional at birth and that piglets can recognize the smell of the sow within 12h postpartum. Compared with humans and several other mammalian species, the pig’s olfactory system is highly developed, and the use of their sense of smell is incorporated into their natural behavior. While sniffing is a well-known behavior in pigs’ exploratory behavioral repertoire, this review points to a lack of knowledge on pigs’ behavioral reactions specifically when exposed to odors. Some odors appear attractive to pigs, whereas others appear repellent. Depending on the properties of the odor, providing pigs access to odors may be a way to stimulate their sense of smell, and could possibly be used in commercial pig production to enrich their lives. The review lastly highlights potential risks for animal welfare caused from lacking knowledge about how pigs perceive odors in their environment, and proposes future research questions and ways to utilize pigs’ sense of smell in the daily management of these animals. Further research on the olfactory abilities of pigs could help to ensure a more sustainable pig production.

Expression of type 1 vomeronasal receptors in the olfactory organ of the African lungfish, Protopterus dolloi

The vomeronasal organ is an olfactory organ found in amphibians and higher vertebrates. Type 1 vomeronasal receptors, one of the major olfactory receptors in vertebrates, are expressed in the vomeronasal organ in mammals. In amphibians and fish, they are expressed in the olfactory epithelium. The lungfish, which is the species of fish most closely related to amphibians, has a primitive vomeronasal organ: the recess epithelium. Expression of type 1 vomeronasal receptors has been reported in both the olfactory epithelium and the recess epithelium in three species of African lungfish and one species of South American lungfish. However, a previous study suggested that in the African lungfish Protopterus dolloi these receptors are expressed only in the olfactory epithelium. In this study, we identified 21 type 1 vomeronasal receptor genes in P. dolloi and examined the expression sites in the olfactory organ. In P. dolloi, most cells expressing the type 1 vomeronasal receptor were distributed in the olfactory epithelium, but a few were also found in the recess epithelium. This implies that the functions of the olfactory epithelium and the primitive vomeronasal organ are incompletely separated, and that all extant African and South American lungfish share this trait.

In situ hybridization analysis of olfactory receptor expression in the sea turtle olfactory organ.

The olfactory organ of turtles consists of an upper chamber epithelium (UCE) with associated glands, and a lower chamber epithelium (LCE) devoid of glands. The UCE and LCE are referred to as the air-nose and the water-nose, respectively, because the UCE is thought to detect airborne odorants, while the LCE detects waterborne odorants. However, it is not clear how the two are used in the olfactory organ. Odorant receptors (ORs) are the major olfactory receptors in turtles; they are classified as class I and II ORs, distinguished by their primary structure. Class I ORs are suggested to be receptive to water-soluble ligands and class II ORs to volatile ligands. This study analyzed the expression of class I and II ORs in hatchlings of the green sea turtle, Chelonia mydas, through in situ hybridization, to determine the localization of OR-expressing cells in the olfactory organ. Class I OR-expressing cells were distributed mainly in the LCE, implying that the LCE is receptive to waterborne odorants. Class II OR-expressing cells were distributed in both the UCE and LCE, implying that the entire olfactory organ is receptive to airborne odorants. The widespread expression of class II ORs may increase opportunities for sea turtles to sense airborne odorants.

Olfactory sensitivity and threat-sensitive responses to alarm cue in an invasive fish

Establishing how invasive animals perceive and manage the threat of predation improves our understanding of why certain species rapidly invade unfamiliar environs where others do not. The threat-sensitive response hypothesis predicts that prey that modulate their antipredator behavior in response to the perceived intensity of the threat will have a selective advantage. We investigated the behavioral and olfactory antipredator responses of migrating invasive sea lamprey to varying concentrations of a conspecific alarm cue in the laboratory and field. We hypothesized the odor indicates the presence and location of predation risk on river shorelines, allowing sea lamprey to either alter their migratory path and/or movement timing to reduce exposure to the predator. Migratory sea lampreys exhibited threat-sensitivity in space-use both in the laboratory and nature by increasingly avoiding areas as the concentration of alarm cue increased when safe space was available (areas without the alarm cue). The intensity of the avoidance at higher concentrations was greater in the field. Electrophysiological recordings from the olfactory organ confirmed a concomitant increase in signal output to the olfactory bulb of the brain when exposed to increased alarm cue concentrations. However, increasing the alarm cue concentration did not alter the animal’s motivation to move upstream in either avoidable risk or unavoidable risk scenarios. Exposure to alarm cue affected decisions regarding how to move, but not whether to move. Knowledge of how the animal uses the cue in nature reveals ways to use the cue to manipulate movement and achieve conservation goals.

Reduction of Cancer Stem Cells and Invasiveness of Human Melanoma and Breast Cancer by Cucurbitacin B from Lagenaria siceraria

Cucurbitacins are secondary metabolites that are commonly found in the Cucurbitacae family. Many biological properties have been reported for cucurbitacins, including anti-inflammatory, antioxidant, antiviral, anti-malaria, and anticancer properties. While studies for the anticancer property of cucurbitacins focus mostly on the cell-cycle progression and apoptosis, no study has considered the effect of cucurbitacin on other cancer behaviors. Here, we report cell-proliferation-based drug testing on random herbal extracts leading to the identification of cucurbitacin B as an anticancer compound. Interestingly, cucurbitacin B had no effect on the proliferation of rat embryonic myoblast cells. We also found that cucurbitacin B significantly reduced the invasiveness of at least two highly metastatic breast cancer and melanoma cells. Using known cancer stem-cell markers, we observed a significant reduction of the melanoma stem cells. Molecularly, cucurbitacin B caused reduction of the metastasis-promoting gene Snail in melanoma and one of the cancer stem cell markers, ALDH1A1 (aldehyde dehydrogenase 1 A1), in breast cancer. Finally, we report the potential toxicity of cucurbitacin B in developing skin tissue and the olfactory organ using zebrafish embryo. In summary, our study suggests the potential use of cucurbitacin B for cancer metastasis and relapse treatment.

Differential sensitivity of mucosal organs to transient exposure to hydrogen sulphide in post-smolt Atlantic salmon (Salmo salar)

Mortality related to hydrogen sulphide (H2S) has recently become a serious concern in Atlantic salmon (Salmo salar) farming, particularly in saline recirculating aquaculture systems (RASs), where the risk of H2S formation is high. H2S has a distinct odour of rotten eggs, and its production is associated with the anaerobic bacterial decomposition of protein and other sulphur-containing organic matter. Significant advances have been made in elucidating its formation in RAS, but the biological consequences of this toxicant in salmon remain elusive. We report the physiological consequences of transient exposure of post-smolt Atlantic salmon to H2S. The fish were exposed to one of three levels of H2S for 1 h: 0 μM (unexposed), 0.6 μM (low exposure), and 1.2 μM (high exposure). Fish were allowed to recover for 24 h and then sampled for gene expression, histology, and metabolomics analyses. Molecular profiling was performed on a subset of genes with known functions in sulphide detoxification, mucins, immunity, and stress responses, which focused on the gills, olfactory organ, skin, and distal gut. With the exception of interleukin 10, all genes studied were significantly affected in the skin, where high H2S triggered significant upregulation. Stress-related genes were mostly affected in the gills, where the high H2S level also induced significant upregulation. Downregulation of the marker genes was identified in the olfactory organ especially in the low-dose group. The distal gut was less sensitive to H2S, regardless of the dose. Histological health scoring of the four mucosal organs revealed no substantial structural alterations and only sporadic cases of mild-moderate unspecific tissue damage. High-throughput metabolomics revealed that transient H2S exposure had a substantial mucosal impact rather than a systemic impact, as shown by changes in skin mucus metabolome. Functional annotation indicated that 10 metabolomic pathways were significantly affected in the skin mucus, including tRNA charging, the superpathway of branched-chain amino acid biosynthesis, and glucosilinate biosynthesis from phenylalanine. The physiological alterations following transient exposure to H2S showed that the mucosal organs exhibited distinct response profiles, where transcriptional impacts were more pronounced in the skin and gills. The results contribute to a better understanding of the biological functions of exogenous H2S in teleost fish, as well as the development of mitigation strategies for salmon-production facilities and the risk of H2S exposure.

Expression patterns of prosaposin and its receptors, G protein-coupled receptor (GPR) 37 and GPR37L1, in the mouse olfactory organ

Prosaposin is a glycoprotein conserved widely in vertebrates, because it is a precursor for saposins that are required for normal lysosomal function and thus for autophagy, and acts as a neurotrophic factor. Most tetrapods possess two kinds of olfactory neuroepithelia, namely, the olfactory epithelium (OE) and the vomeronasal epithelium (VNE). This study examined the expression patterns of prosaposin and its candidate receptors, G protein-coupled receptor (GPR) 37 and GPR37L1, in mouse OE and VNE by immunofluorescence and in situ hybridization. Prosaposin immunoreactivity was observed in the olfactory receptor neurons, vomeronasal receptor neurons, Bowman’s gland (BG), and Jacobson’s gland (JG). Prosaposin expression was mainly observed in mature neurons. Prosaposin mRNA expression was observed not only in these cells but also in the apical region of the VNE. GPR37 and GPR37L1 immunoreactivities were found only in the BG and/or the JG. Prosaposin was suggested to secrete and facilitate the autophagic activities of the neurons and modulate the mucus secretion in mouse olfactory organ.

Ancient and nonuniform loss of olfactory receptor expression renders the shark nose a de facto vomeronasal organ.

Cartilaginous fishes are renowned for a keen sense of smell, a reputation based on behavioral observations and supported by the presence of large and morphologically complex olfactory organs. At the molecular level, genes belonging to the four families coding for most olfactory chemosensory receptors in other vertebrates have been identified in a chimera and a shark, but it was unknown whether they actually code for olfactory receptors in these species. Here we describe the evolutionary dynamics of these gene families in cartilaginous fishes using genomes of a chimera, a skate, a sawfish and eight sharks. The number of putative OR, TAAR and V1R/ORA receptors is very low and stable whereas the number of putative V2R/OlfC receptors is higher and much more dynamic. In the catshark Scyliorhinus canicula, we show that many V2R/OlfC receptors are expressed in the olfactory epithelium in the sparsely distributed pattern characteristic for olfactory receptors. In contrast, the other three vertebrate olfactory receptor families are either not expressed (OR) or only represented with a single receptor (V1R/ORA and TAAR). The complete overlap of markers of microvillous olfactory sensory neurons with panneuronal marker HuC in the olfactory organ suggests the same cell type specificity of V2R/OlfC expression as for bony fishes, i.e. in microvillous neurons. The relatively low number of olfactory receptors in cartilaginous fishes compared to bony fishes could be the result of an ancient and constant selection in favor of a high olfactory sensitivity at the expense of a high discrimination capability.

Type 1 vomeronasal receptor expression in juvenile and adult lungfish olfactory organ

Lungfish are the most closely related fish to tetrapods. The olfactory organ of lungfish contains lamellae and abundant recesses at the base of lamellae. Based on the ultrastructural and histochemical characteristics, the lamellar olfactory epithelium (OE), covering the surface of lamellae, and the recess epithelium, contained in the recesses, are thought to correspond to the OE of teleosts and the vomeronasal organ (VNO) of tetrapods. With increasing body size, the recesses increase in number and distribution range in the olfactory organ. In tetrapods, the expression of olfactory receptors is different between the OE and VNO; for instance, the type 1 vomeronasal receptor (V1R) is expressed only in the OE in amphibians and mainly in the VNO in mammals. We recently reported that V1R-expressing cells are contained mainly in the lamellar OE but also rarely in the recess epithelium in the olfactory organ of lungfish of approximately 30 cm body length. However, it is unclear whether the distribution of V1R-expressing cells in the olfactory organ varies during development. In this study, we compared the expression of V1Rs in the olfactory organs between juveniles and adults of the African lungfish Protopterus aethiopicus and South American lungfish, Lepidosiren paradoxa. The density of V1R-expressing cells was higher in the lamellae than in the recesses in all specimens evaluated, and this pattern was more pronounced in juveniles than adults. In addition, the juveniles showed a higher density of V1R-expressing cells in the lamellae compared with the adults. Our results imply that differences in lifestyle between juveniles and adults are related to differences in the density of V1R-expressing cells in the lamellae of lungfish.

Strategies of vascularization of the ethmoid labyrinth in selected even-toed ungulates (Artiodactyla) and carnivores (Carnivora).

The anatomy of the nasal cavity and its structures, as well as other elements building a scaffold for olfactory organs, differs significantly among various groups of mammals. Understanding anatomical conditions of quality of olfaction are being studied worldwide and is a complex problem. Among many studies regarding bone and epithelial structures of turbinates and connected anatomical structures, few studies describe the vascularization of turbinates. Ethmoid turbinates are above all covered in olfactory epithelium containing branched axons that receive olfactory stimuli and as olfactory nerves penetrate the cribriform lamina of the ethmoid bone conveying information from smell receptors to the brain. Differences in vascularization of the cribriform plate and turbinates may add crucial information complementing studies regarding the olfactory organ's bone and soft tissue structures. In the study, we describe the vascularization of the cribriform plate of the ethmoid bone of 54 Artiodactyla and Carnivora.

Effects of organophosphate pesticides on the olfactory organ of fish: a comprehensive review

Effects of organophosphate pesticides on the olfactory organ of fish: a comprehensive review

Structure of an antennally-expressed carboxylesterase suggests lepidopteran odorant degrading enzymes are broadly tuned.

Insects rely on the detection of chemical cues present in the environment to guide their foraging and reproductive behaviour. As such, insects have evolved a sophisticated chemical processing system in their antennae comprised of several types of olfactory proteins. Of these proteins, odorant degrading enzymes are responsible for metabolising the chemical cues within the antennae, thereby maintaining olfactory system function. Members of the carboxyl/cholinesterase gene family are known to degrade odorant molecules with acetate-ester moieties that function as host recognition cues or sex pheromones, however, their specificity for these compounds remains unclear. Here, we evaluate expression levels of this gene family in the light-brown apple moth, Epiphyas postvittana, via RNAseq and identify putative odorant degrading enzymes. We then solve the apo-structure for EposCCE24 by X-ray crystallography to a resolution of 2.43Å and infer substrate specificity based on structural characteristics of the enzyme's binding pocket. The specificity of EposCCE24 was validated by testing its ability to degrade biologically relevant and non-relevant sex pheromone components and plant volatiles using GC-MS. We found that EposCCE24 is neither capable of discriminating between linear acetate-ester odorant molecules of varying chain length, nor between molecules with varying double bond positions. EposCCE24 efficiently degraded both plant volatiles and sex pheromone components containing acetate-ester functional groups, confirming its role as a broadly-tuned odorant degrading enzyme in the moth olfactory organ.

The alleged mechanisms of olfactory disorders in the new coronavirus infection

In March 2020, the World Health Organization (WHO) announced the beginning of the COVID-19 pandemic, which continues to the present. A change in the sense of smell, up to the complete disappearance of odors, is regarded as one of the early symptoms of the disease. Sometimes anosmia was the only sign of infection of the patient. As is known, a disturbance of the sense of smell indicates a serious pathology of the brain, such as the consequences of traumatic brain injuries, strokes, Alzheimer's disease, Parkinson's disease, autoimmune diseases, a side-effect of drug therapy. The review is dedicated to the pathogenesis of anosmia in COVID-19. For a better understanding of the pathogenesis, the article presents a brief anatomy and physiology of the olfactory organ as well as the probable mechanisms of anosmia: encephalitis, inflammatory edema of the olfactory cleft, olfactory epithelium damage, apoptosis of bipolar neurons, damage of olfactory cell cilia and damage of olfactory bulbs. Because of the rapid accumulation of information on this topic, there is a need to structure, periodic systematization and presentation to a wide range of specialists.

Antennal and maxillary palp morphology, and sensillar equipment, of the spruce bark beetle predators, Medetera signaticornis and Medetera infumata (Diptera: Dolichopodidae)

Many long-legged Medetera flies are natural enemies of bark beetle pests, which they detect using olfactory cues, likely through olfactory sensilla on the antennae and maxillary palps. Morphological characterisation of olfactory sensilla among insects can provide a basis for future taxonomic, phylogenetic or electrophysiological studies. Scanning electron microscopy was used to describe the morphology of olfactory organs and sensillar equipment of Medetera signaticornis and M. infumata. Three different olfactory sensillum types were found in both fly species, sensilla trichodea, s. basiconica and grooved pegs. Based on size and wall structure, s. trichodea and s. basiconica were categorised into different subtypes. Sharp-tipped curved s. trichodea, and small, large and thin s. basiconica were found on the antennal postpedicel of M. signaticornis adults, while grooved s. basiconica were found in M. infumata. The density of sharp-tipped long s. trichodea was significantly higher in males compared to females, and in M. signaticornis compared to M. infumata. Long-grooved s. basiconica were found grouped in a small pit on the maxillary palps of both species. Comparison of our results with the limited available ecological data suggests that differences in numbers of specific sensillum types may reflect adaptations related to olfactory-driven behaviours such as host seeking.

Identification and analysis of odorant receptors expressed in the two main olfactory organs, antennae and palps, of Schistocerca americana

Locusts depend upon their sense of smell and provide useful models for understanding olfaction. Extending this understanding requires knowledge of the molecular and structural organization of the olfactory system. Odor sensing begins with olfactory receptor neurons (ORNs), which express odorant receptors (ORs). In insects, ORNs are housed, in varying numbers, in olfactory sensilla. Because the organization of ORs within sensilla affects their function, it is essential to identify the ORs they contain. Here, using RNA sequencing, we identified 179 putative ORs in the transcriptomes of the two main olfactory organs, antenna and palp, of the locust Schistocerca americana. Quantitative expression analysis showed most putative ORs (140) are expressed in antennae while only 31 are in the palps. Further, our analysis identified one OR detected only in the palps and seven ORs that are expressed differentially by sex. An in situ analysis of OR expression suggested ORs are organized in non-random combinations within antennal sensilla. A phylogenetic comparison of OR predicted protein sequences revealed homologous relationships among two other Acrididae species. Our results provide a foundation for understanding the organization of the first stage of the olfactory system in S. americana, a well-studied model for olfactory processing.