Postnatal development of centrifugal inputs to the olfactory bulb

Processing in primary sensory areas is influenced by centrifugal inputs from higher brain areas, providing information about behavioral state, attention, or context. Activity in the olfactory bulb, the first central processing stage of olfactory information, is dynamically modulated by direct projections from a variety of areas in adult mice. Despite the early onset of olfactory sensation compared to other senses, the development of centrifugal inputs to the olfactory bulb remains largely unknown. Using retrograde tracing across development, we show that centrifugal projections to the olfactory bulb are established during the postnatal period in an area-specific manner. While feedback projections from the piriform cortex are already present shortly after birth, they strongly increase in number during postnatal development with an anterior-posterior gradient. Contralateral projections from the anterior olfactory nucleus are present at birth but only appeared postnatally for the nucleus of the lateral olfactory tract. Numbers of olfactory bulb projecting neurons from the lateral entorhinal cortex, ventral hippocampus, and cortical amygdala show a sudden increase at the beginning of the second postnatal week and a delayed development compared to more anterior areas. These anatomical data suggest that limited top-down influence on odor processing in the olfactory bulb may be present at birth, but strongly increases during postnatal development and is only fully established later in life.

Chemotactic and temperature-dependent responses of the Strongyloidoidea superfamily of nematodes

Host-seeking behaviour and how a parasite identifies the correct host to infect remains a poorly understood area of parasitology. What is currently known is that host sensation and seeking behaviour is formed from a complex mixture of chemo-, thermo- and mechanosensory behaviours, of which chemosensation is the best studied. Previous studies of olfaction in parasitic nematodes suggested that this behaviour appears to be more closely related to target host and infection mode than phylogeny. However, there has not yet been a study comparing the chemotactic and temperature-dependent behaviours of very closely related parasitic and non-parasitic nematodes. To this end, we examined the temperature-dependent and chemotactic responses of the Strongyloidoidea superfamily of nematodes. We found differences in temperature response between the different species and within infective larvae. Chemotactic responses were highly divergent, with different attraction profiles between all species studied. When examining direct stimulation with fur, we found that it was insufficient to cause an attractive response. Overall, our results support the notion that olfactory sensation is more closely related to lifestyle and host range than phylogeny, and that multiple cues are required to initiate host-seeking behaviour.

Understanding the sensory characteristics of edible insects to promote entomophagy: A projective sensory experience among consumers

In recent years, a remarkable number of studies have investigated sensory characteristics, such as flavor and texture, of edible insect and insect-based foods, their contribution to consumers’ attitudes toward edible insects are important in consumer appeal and their willingness to try eating insects in the future. This paper addresses the problem of describing the sensory characteristics aof edible insect and insect-based foods in terms of preferences. To this end, we conducted a study to explore the representations of sensory experiences related to an insect-based dish involving a voluntary sample of 154 consumers. The quasi-experiment, which we have called projective sensory experience (PSE), follows a two-step procedure. In the first step, we asked the participants to imagine tasting an insect-based dish and then to rate, from 1 (imperceptible) up to 10 (very perceptible), the following taste-olfactory sensations: Sapidity, Bitter tendency, Acidity, Sweet, Spiciness, Aroma, Greasiness-Unctuosity, Succulence, Sweet, Fatness, Persistence. In the second step, we asked our interviewees to indicate, through a specific check-list, which was the most disturbing and least disturbing taste-olfactory sensation imagined. We collected data from May to July 2020 by using an anonymous on-line questionnaire. Results could help understand the sensory characteristics of “insects as food” that should be used or avoided, for example, in communication aimed at promoting familiarity with edible insects and improving the acceptability of insects as a novel food.

Sensate regimes of war: Smell, tracing and violence

This article explores the fabrication of ‘sensate regimes of war’, concentrating on the typically under-analysed sense of smell. Smell is a sensory mode capable of apprehending potential threat and enmity in ways that are orthogonal to other ways of sensing. Accordingly, the organization and interpretation of olfactory sensation occupies a distinctive place in war. The article details a particular genealogy of martial olfaction, exploring the olfactory capacities of soldiers and their augmentation through various non-human and technological means in specific milieus of combat. It notes how the distinctive affordances of smell have underpinned numerous wartime practices, from tracing improvised explosive devices to militarized manhunting. These developments supplement and trouble ocularcentric accounts of martial sensation and power that concentrate on the increasingly abstracted co-production of vision and violence in wartime. They highlight rather the significance of an alternative ontology of the signature or trace of enmity, and emphasize how in particular warscapes to smell is to kill. The article concludes by arguing that critical inquiry into war would benefit from a broader theorization of all its sensate regimes right across a sensorium that is itself being continuously transformed through war.

Orange Fragrance with Sustained-Release Properties Prepared by Nanoethosomal Encapsulation of Natural Orange Essential Oil

There is an upsurge of interest in improving the stability and prolong the scent holding time of fragrances in cosmetic industry. In this study, to encapsulate the orange essential oils (OEO), nanoethosomes were constructed with optimized proportions of ethanol, water, soybean phosphatidylcholine (SPC), Tween 80, and palm oil sucrose esters (PSE). The controlled-release behavior of nanoethosomes was then studied concerning physicochemical stability, microstructure, and olfactory sensation. The sustained-release effectiveness of the nanoethosomal fragrances was influenced by particle size and OEO amount of specific formula. Herein, there was a positive correlation between particle size and sustained-release effectiveness. In particular, the mean diameter of nanoethosomal orange fragrances (nano-OFs)–prepared by EO-ethanol-water-SPC-Tween 80-PSE (3–7:25:72–68:2:1.0:0.1) and 3%, 5%, and 7% OEO–was 68.6±3.6, 79.5±4.5 and 87.3±6.9 nm, respectively. The results of olfactory sensation and GC-MS analysis showed that these fragrances could sustainedly release the aromatic compounds to yield satisfactory smell longer than that of the conventional orange fragrance. Furthermore, the nano-OF made of 5% EO yield a satisfactory smell more than 3 h, which was 3 times of that of the conventional orange fragrance. This fragrance was stable when stored at 4 °C (>1 year) and 25 °C (>10 months). The knowledge gained from this study will be helpful to develop nanoethosomal fragrances or perfumes for commercial use.

Histology and surface morphology of the olfactory epithelium in the freshwater teleost Clupisoma garua (Hamilton, 1822)

The anatomical structure of the olfactory organ and the organization of various cells lining the olfactory mucosa of Clupisoma garua (Siluriformes; Schilbeidae) were investigated with light and scanning electron microscopy. The olfactory organ was composed of numerous lamellae of various sizes, radiating outward from both sides of the narrow midline raphe, forming an elongated rosette. Each lamella consisted of the olfactory epithelium and a central lamellar space, the central core. The epithelium covering the surface of the rosette folds was differentiated into zones of sensory and indifferent epithelia. The sensory part of epithelium was characterized by three types of morphologically distinct receptor neurons: ciliated receptor cells, microvillous receptor cells, and rod receptor cells for receiving olfactory sensation from the aquatic environment. The indifferent epithelium comprising a large surface area of the lamella, was covered with compact non-sensory cilia. The non-sensory epithelium contained stratified epithelial cells with microridges, mucin secreting mucous cells, labyrinth cells, and basal cells, which were arranged in a layer at the base of the epithelium. Various cells on the olfactory epithelium were correlated with the functional significance of the fish concerned.

Gravid females of Cephalcia chuxiongica (Hymenoptera, Pamphiliidae) are attracted to egg-carrying needles of Pinus yunnanensis

Cephalciachuxiongica Xiao is one of the most dangerous defoliators of Pinusyunnanensis and other pine species in Yunnan province, resulting in serious losses. Its distinguishing characteristics are the females’ aggregation oviposition and larvae’s aggregation feeding. In order to explore the mechanism of aggregation oviposition in this sawfly, preliminary olfactory bioassay was conducted in laboratory. In in-cage choice tests, on average vast majority gravid females selected the shoots that had been loaded and oviposited by a ‘pioneer’ female. In one-choice tests in laboratory by a Y-tube olfactometer, the gravid females were attracted by the odors of eggs-carrying shoots (PE), shoots with one delivering female and her eggs (PGE), needles’ extract (NE), and fresh eggs’ eluent (EL); the virgin females were attracted by odors of fresh needles (P), PE, PGE, and NE, but repelled by odors of virgin and gravid females. In two-choice tests, the odors were tested in pairs for gravid females. When compared with odors of gravid females (G) or P, gravid females showed significantly more tendency to odors of PE or PGE. When given odors EL vs. NE, gravid females preferred the odors of NE, but they did not make obvious selection between G vs. P, and PE vs. PGE. Based on the results, our conjectures were: (1) Delivery female, as a pioneer, can summon her conspecific gravid females to aggregate in the same pine shoot; (2) Pine needles’ odors were attractive for both the virgin and gravid females; (3) Gravid females could be attracted by odors released by the pioneer gravid females; (4) The olfactory sensation of the females may be changed by mating.

Inhalation frequency controls reformatting of mitral/tufted cell odor representations in the olfactory bulb

In mammals olfactory sensation depends on inhalation, which controls activation of sensory neurons and temporal patterning of central activity. Odor representations by mitral and tufted (MT) cells, the main output from the olfactory bulb (OB), reflect sensory input as well as excitation and inhibition from OB circuits, which may change as sniff frequency increases. To test the impact of sampling frequency on MT cell odor responses, we obtained whole-cell recordings from MT cells in anesthetized male and female mice while varying inhalation frequency via tracheotomy, allowing comparison of inhalation-linked responses across cells. We characterized frequency effects on MT cell responses during inhalation of air and odorants using inhalation pulses and also ‘playback’ of sniffing recorded from awake mice. Inhalation-linked changes in membrane potential were well-predicted across frequency from linear convolution of 1 Hz responses and, as frequency increased, near-identical temporal responses could emerge from depolarizing, hyperpolarizing or multiphasic MT responses. However, net excitation was not well predicted from 1 Hz responses and varied substantially across MT cells, with some cells increasing and others decreasing in spike rate. As a result, sustained odorant sampling at higher frequencies led to increasing decorrelation of the MT cell population response pattern over time. Bulk activation of sensory inputs by optogenetic stimulation affected MT cells more uniformly across frequency, suggesting that frequency-dependent decorrelation emerges from odor-specific patterns of activity in the OB network. These results suggest that sampling behavior alone can reformat early sensory representations, possibly to optimize sensory perception during repeated sampling.Significance statementOlfactory sensation in mammals depends on inhalation, which increases in frequency during active sampling of olfactory stimuli. We asked how inhalation frequency can shape the neural coding of odor information by recording from projection neurons of the olfactory bulb while artificially varying odor sampling frequency in the anesthetized mouse. We found that sampling an odor at higher frequencies led to diverse changes in net responsiveness, as measured by action potential output, that were not predicted from low-frequency responses. These changes led to a reorganization of the pattern of neural activity evoked by a given odorant that occurred preferentially during sustained, high-frequency inhalation. These results point to a novel mechanism for modulating early sensory representations solely as a function of sampling behavior.

Caenorhabditis elegans Olfaction

To survive, animals must properly sense their surrounding environment. The types of sensation that allow for detecting these changes can be categorized as tactile, thermal, aural, or olfactory. Olfaction is one of the most primitive senses, involving the detection of environmental chemical cues. Organisms must sense and discriminate between abiotic and biogenic cues, necessitating a system that can react and respond to changes quickly. The nematode, Caenorhabditis elegans, offers a unique set of tools for studying the biology of olfactory sensation. The olfactory system in C. elegans is comprised of 14 pairs of amphid neurons in the head and two pairs of phasmid neurons in the tail. The male nervous system contains an additional 89 neurons, many of which are exposed to the environment and contribute to olfaction. The cues sensed by these olfactory neurons initiate a multitude of responses, ranging from developmental changes to behavioral responses. Environmental cues might initiate entry into or exit from a long-lived alternative larval developmental stage (dauer), or pheromonal stimuli may attract sexually mature mates, or repel conspecifics in crowded environments. C. elegans are also capable of sensing abiotic stimuli, exhibiting attraction and repulsion to diverse classes of chemicals. Unlike canonical mammalian olfactory neurons, C. elegans chemosensory neurons express more than one receptor per cell. This enables detection of hundreds of chemical structures and concentrations by a chemosensory nervous system with few cells. However, each neuron detects certain classes of olfactory cues, and, combined with their synaptic pathways, elicit similar responses (i.e., aversive behaviors). The functional architecture of this chemosensory system is capable of supporting the development and behavior of nematodes in a manner efficient enough to allow for the genus to have a cosmopolitan distribution.