Techniques for temporal detection of neural sensitivity to external stimulation

We propose a simple measure of neural sensitivity for characterizing stimulus coding. Sensitivity is defined as the fraction of neurons that show positive responses to n stimuli out of a total of N. To determine a positive response, we propose two methods: Fisherian statistical testing and a data-driven Bayesian approach to determine the response probability of a neuron. The latter is non-parametric, data-driven, and captures a lower bound for the probability of neural responses to sensory stimulation. Both methods are compared with a standard test that assumes normal probability distributions. We applied the sensitivity estimation based on the proposed method to experimental data recorded from the mushroom body (MB) of locusts. We show that there is a broad range of sensitivity that the MB response sweeps during odor stimulation. The neurons are initially tuned to specific odors, but tend to demonstrate a generalist behavior towards the end of the stimulus period, meaning that the emphasis shifts from discrimination to feature learning.     

Mate-odour identification by both sexes of Evarcha culicivora, an East African jumping spider

Evarcha culicivora is an unusual salticid spider because each sex actively courts the other and both sexes make distinctive mate-choice decisions. Here we use olfactometer experiments for investigating the ability of each sex to identify potential mates on the basis of odour alone. Test spiders spent more time in the vicinity of opposite-sex conspecific source spiders, regardless of whether or not these source spiders had previously mated, when the alternatives were conspecific individuals of the same sex, juveniles or a control (no odour source). This trend held regardless of the test spider's and source spider's age after reaching maturity and, for male test spiders, it held regardless of the test spider's mating status. However, after females had mated they no longer expressed a preference for male odour.     

Expression of cGMP signaling elements in the Grueneberg ganglion

The Grueneberg ganglion (GG) is a cluster of neurons localized to the vestibule of the anterior nasal cavity. Based on axonal projections to the olfactory bulb of the brain, as well as expression of olfactory receptors and the olfactory marker protein, it is considered a chemosensory subsystem. Recently, it was observed that in mice, GG neurons respond to cool ambient temperatures. In mammals, coolness-induced responses in highly specialized neuronal cells are supposed to rely on the ion channel TRPM8, whereas in thermosensory neurons of the nematode worm Caenorhabditis elegans, detection of environmental temperature is mainly mediated by cyclic guanosine monophosphate (cGMP) pathways, in which cGMP is generated by transmembrane guanylyl cyclases. To unravel the molecular mechanisms underlying coolness-induced responses in GG neurons, potential expression of TRPM8 in the murine GG was investigated; however, no evidence was found that this ion channel is present in the GG. By contrast, a substantial number of GG neurons was observed to express the transmembrane guanylyl cyclase subtype GC-G. In the nose, GC-G expression appears to be confined to the GG since it was not detectable in other nasal compartments. In the GG, coolness-stimulated responses are only observed in neurons characterized by the expression of the olfactory receptor V2r83. Interestingly, expression of GC-G in the GG was found in this V2r83-positive subpopulation but not in other GG neurons. In addition to GC-G, V2r83-positive GG cells also co-express the phosphodiesterase PDE2A. Thus, in summary, coolness-sensitive V2r83-expressing GG neurons are endowed with a cGMP cascade which might underlie thermosensitivity of these cells, similar to the cGMP pathway mediating thermosensation in neurons of C. elegans. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. J. Fleischer and K. Mamasuew contributed equally to this work.     

Responses of the sea catfish Ariopsis felis to chemical defenses from the sea hare Aplysia californica

Ink secretion of sea hares (Aplysia spp.), which is a mixture of co-released ink from the ink gland and opaline from the opaline gland, protects sea hares from predatory invertebrates through diverse mechanisms. These include both aversive or deterrent compounds and also high concentrations of amino acids that stimulate the predators' chemical senses and divert the attack through phagomimicry or sensory disruption. The aim of the present study was to examine if sea hares also defend themselves from predatory vertebrates by interacting with their chemical senses. We used sea catfish, Ariopsis felis, in behavioral and electrophysiological experiments. Behavioral tests on sea catfish show that ink is aversive: when ink is added to palatable food items (noodles with food flavoring), the noodles are no longer eaten, and when ink is added to noodles without food flavoring, the noodles are avoided more than unflavored noodles. Behavioral tests also show that opaline and the amino acid components of either opaline or ink are appetitive. Electrophysiological recordings of chemosensory neuronal activity in the olfactory epithelium and maxillary barbels show that the olfactory and gustatory systems of sea catfish are highly stimulated by ink and opaline, and that the amino acid components of ink and opaline significantly contribute to these responses. Compounds generated by the activity of escapin, an L-amino acid oxidase in the secretion, are moderately stimulatory to both olfactory and gustatory systems. Taken together, our results support the idea that sea hares are chemically defended from predatory sea catfish largely through unpalatable chemical deterrents in ink, but possibly also through amino acids stimulating olfactory and gustatory systems and thus functioning through phagomimicry or sensory disruption.     

Intranasal Odorant Concentrations in Relation to Sniff Behavior

Knowledge on how odorants are transported through the nasal cavity to the olfactory epithelium is limited. One facet of this is how the sniffing behavior affects the abundance of odorants transferred to the olfactory cleft and in turn influences odor perception. A novel system that couples an online mass spectrometer with an odorant pulse delivery olfactometer was employed to characterize intranasal odorant concentrations of butane‐2,3‐dione (or butanedione, commonly known as diacetyl) at the interior naris and the olfactory cleft. Volunteers (n=12) were asked to perform different modes of sniffing in relation to the sniff intensity that were categorized as ‘normal’, ‘rapid’ and ‘forced’. The highest concentrations of butanedione at both positions in the nose were observed during normal sniffing, with the lowest concentrations correlating with periods of forced sniffs. This corresponded to the panelists' ratings that normal sniffing elicited the highest odor intensities. These feasibility assessments pave the way for more in‐depth analyses with a variety of odorants of different chemical classes at various intranasal positions, to investigate the passage and uptake of odorants within the nasal cavity.     

Deorphanization and Characterization of Human Olfactory Receptors in Heterologous Cells

Olfaction plays an indispensable role in human and animals in self and environmental recognition, as well as intra‐ and interspecific communication. Following the discovery of a family of olfactory receptors (ORs) by Buck and Axel in 1991, it has been established that the sense of smell begins with the molecular recognition of a chemical odorant by one or more ORs expressed in the olfactory sensory neurons. Therefore, characterization of the molecular interactions between odorant molecules and ORs is a key step in the elucidation of the general properties of the olfactory system and in the development of applications, i.e., design of new odorants, search for blockers, etc. The process putted in place at ChemCom to improve the expression of ORs at the cytoplasmic membrane of the HEK293 cell and assays enabling large‐scale deorphanization, and to characterize the interaction between chemical odorants and ORs is described. The family of human ORs includes ca. 400 putatively functional ORs which are GPCRs (G protein‐coupled receptors); to date over 100 human ORs have been deorphanized.     

Morphology,ultrastructure and functional role of antennal sensilla in off-host aggregation by the bed bug,Cimex lectularius

After blood feeding on a host, bed bugs, Cimex lectularius, assemble in aggregation sites away from the host. Off-host aggregation is mediated by a combination of mechanical and chemical stimuli associated with bug feces. Partial antennectomies indicated removal of flagellomeres did not affect aggregation, but removal of the whole pedicel or its distal half significantly reduced (P < 0.01) aggregation, suggesting that sensilla related to off-host aggregation occur on the distal half of the pedicel. Scanning electron microscopy (SEM) revealed that serrated hairs were distributed throughout the pedicel, but newly described smooth hairs were present mainly on the distal half, and a distinct patch of grooved pegs, smooth pegs and immersed cones was present on the posterior edge of the distal half of the pedicel in adults, but not in nymphs. Numbers of different types of sensilla increased significantly during metamorphosis from first instar to adult (P < 0.05), but were similar between genders (P = 0.11) and between females from a laboratory and field strain of bugs (P = 0.19). Transmission electron microscopy (TEM) revealed that cuticular pores were present in the two types of pegs, indicating that the pegs have an olfactory function. The smooth hairs resembled gustatory sensilla previously described in Cimex hemipterus F. The existence of both olfactory and gustatory sensilla on the distal half of the pedicel suggests those sensilla may be the sensory basis of off-host aggregation behavior.     

Mixture interactions of glutamate and betaine in single squid olfactory neurons

We used nystatin-patch techniques to characterize the responses of squid olfactory receptor neurons to the attractive odorant, L-glutamate, and to study mixture interactions between glutamate and the aversive odorant, betaine. We report that glutamate activates a cation-selective conductance that is permeable to Ca²⁺, K⁺, and Na⁺ and which would depolarize squid olfactory receptor neurons under physiological conditions. The responses to glutamate were concentration dependent. The EC₅₀ of individual cells ranged from 0.3 mmol · l⁻¹ to 85.0 mmol · l⁻¹. We found that individual cells were capable of responding to both glutamate and betaine, and that the relative magnitudes of these responses varied from cell to cell. Finally, we report that current responses to binary mixtures of glutamate and betaine are suppressed relative to the sum of the responses to the individual odors in single squid olfactory receptor neurons. Accepted: 20 October 1999     

Responses of olfactory receptor neurons in Utetheisa ornatrix to gender-specific odors

We recorded the electrophysiological responses of individual olfactory receptor neurons in sensilla trichodea on the antennae of adult arctiid moths, Utetheisa ornatrix, to stimulation with volatiles associated with both sexes. All trichoid sensilla contain at least two receptor neurons, each with distinct action potential amplitudes and waveforms, that respond dichotomously to male and female odors. Although, neither female neuron responds to extracts of coremata or the male-produced pheromone hydroxydanaidal, they do respond in a gender-specific manner to the volatiles emanating from whole pupae, hemolymph, thoracic froth, and adult animals of several ages. Thoracic froth, which contains pyrrolizidine alkaloids, is thought to play a role in defense. Froth from moths reared on diets, with or without added pyrrolizidine alkaloids, were equally effective in eliciting gender-specific patterns of response. Male trichoid receptor neurons respond to these same materials with similar patterns of activation. These receptor neurons provide information about substances, which we have termed “gender odors,” that are persistently emitted by nearby animals. These substances do not appear to be the same as those already known to be involved in defense or the sexual dialog between individuals. Accepted: 16 March 2000     

Feeding-deterrent substance in cattle feces: its effects on ingestive behavior in goats

A feeding-deterrent substance was isolated from cattle feces and its effects on ingestive behavior were examined in goats. The substance was added to alfalfa hay and presented to the goats in the following experiments. In a two-choice test, between control fodder and the fodder treated with the substance, animals avoided eating treated fodder. This food-deterrent effect was strengthened in a dose-dependent manner. The results of ingestive behavior analysis suggested that this substance affected the goats through olfaction. However, in a single-presentation test, where the goats had no choice, no effect on ingestive behavior was noticed. It is therefore suggested that the preference induced by the substance is relative rather than absolute in the ingestive behavior of goats.