Inhibition of nitric oxide and soluble guanylyl cyclase signaling affects olfactory neuron activity in the moth, <Emphasis Type="Italic">Manduca sexta</Emphasis>

Nitric oxide is emerging as an important modulator of many physiological processes including olfaction, yet the function of this gas in the processing of olfactory information remains poorly understood. In the antennal lobe of the moth, Manduca sexta, nitric oxide is produced in response to odor stimulation, and many interneurons express soluble guanylyl cyclase, a well-characterized nitric oxide target. We used intracellular recording and staining coupled with pharmacological manipulation of nitric oxide and soluble guanylyl cyclase to test the hypothesis that nitric oxide modulates odor responsiveness in olfactory interneurons through soluble guanylyl cyclase-dependent pathways. Nitric oxide synthase inhibition resulted in pronounced effects on the resting level of firing and the responses to odor stimulation in most interneurons. Effects ranged from bursting to strong attenuation of activity and were often accompanied by membrane depolarization coupled with a change in input resistance. Blocking nitric oxide activation of soluble guanylyl cyclase signaling mimicked the effects of nitric oxide synthase inhibitors in a subset of olfactory neurons, while other cells were differentially affected by this treatment. Together, these results suggest that nitric oxide is required for proper olfactory function, and likely acts through soluble guanylyl cyclase-dependent and -independent mechanisms in different subsets of neurons.     

Proteomic analysis of castor bean tick Ixodes ricinus: a focus on chemosensory organs

In arthropods, the large majority of studies on olfaction have been focused on insects, where most of the proteins involved have been identified. In particular, chemosensing in insects relies on two families of membrane receptors, olfactory/gustatory receptors (ORs/GRs) and ionotropic receptors (IRs), and two classes of soluble proteins, odorant-binding proteins (OBPs) and chemosensory proteins (CSPs). In other arthropods, such as ticks and mites, only IRs have been identified, while genes encoding for OBPs and CSPs are absent. A third class of soluble proteins, called Niemann-Pick C2 (NPC2) has been suggested as potential carrier for semiochemicals both in insects and other arthropods.Here we report the results of a proteomic analysis on olfactory organs (Haller's organ and palps) and control tissues of the tick Ixodes ricinus, and of immunostaining experiments targeting NPC2s. Adopting different extraction and proteomic approaches, we identified a large number of proteins, and highlighted those differentially expressed. None of the 13 NPC2s known for this species was found. On the other hand, using immunocytochemistry, we detected reaction against one NPC2 in the Haller's organ and palp sensilla. We hypothesized that the low concentration of such proteins in the tick's tissues could possibly explain the discrepant results. In ligand-binding assays the corresponding recombinant NPC2 showed good affinity to the fluorescent probe N-phenylnaphthylamine and to few organic compounds, supporting a putative role of NPC2s as odorant carriers.     

The Lepidoptera Odorant Binding Protein gene family: Gene gain and loss within the GOBP/PBP complex of moths and butterflies

Butterflies and moths differ significantly in their daily activities: butterflies are diurnal while moths are largely nocturnal or crepuscular. This life history difference is presumably reflected in their sensory biology, and especially the balance between the use of chemical versus visual signals. Odorant Binding Proteins (OBP) are a class of insect proteins, at least some of which are thought to orchestrate the transfer of odor molecules within an olfactory sensillum (olfactory organ), between the air and odor receptor proteins (ORs) on the olfactory neurons. A Lepidoptera specific subclass of OBPs are the GOBPs and PBPs; these were the first OBPs studied and have well documented associations with olfactory sensilla. We have used the available genomes of two moths, Manduca sexta and Bombyx mori, and two butterflies, Danaus plexippus and Heliconius melpomene, to characterize the GOBP/PBP genes, attempting to identify gene orthologs and document specific gene gain and loss. First, we identified the full repertoire of OBPs in the M. sexta genome, and compared these with the full repertoire of OBPs from the other three lepidopteran genomes, the OBPs of Drosophila melanogaster and select OBPs from other Lepidoptera. We also evaluated the tissue specific expression of the M. sexta OBPs using an available RNAseq databases. In the four lepidopteran species, GOBP2 and all PBPs reside in single gene clusters; in two species GOBP1 is documented to be nearby, about 100 kb from the cluster; all GOBP/PBP genes share a common gene structure indicating a common origin. As such, the GOBP/PBP genes form a gene complex. Our findings suggest that (1) the lepidopteran GOBP/PBP complex is a monophyletic lineage with origins deep within Lepidoptera phylogeny, (2) within this lineage PBP gene evolution is much more dynamic than GOBP gene evolution, and (3) butterflies may have lost a PBP gene that plays an important role in moth pheromone detection, correlating with a shift from olfactory (moth) to visual (butterfly) communication, at least regarding long distance mate recognition. These findings will be clarified by additional lepidopteran genomic data, but the observation that moths and butterflies share most of the PBP/GOBP genes suggests that they also share common chemosensory-based behavioral pathways.     

Role of a tachykinin-related peptide and its receptor in modulating the olfactory sensitivity in the oriental fruit fly,Bactrocera dorsalis (Hendel)

Insect tachykinin-related peptide (TRP), an ortholog of tachykinin in vertebrates, has been linked with regulation of diverse physiological processes, such as olfactory perception, locomotion, aggression, lipid metabolism and myotropic activity. In this study, we investigated the function of TRP (BdTRP) and its receptor (BdTRPR) in an important agricultural pest, the oriental fruit fly Bactrocera dorsalis. BdTRPR is a typical G-protein coupled-receptor (GPCR), and it could be activated by the putative BdTRP mature peptides with the effective concentrations (EC₅₀) at the nanomolar range when expressed in Chinese hamster ovary cells. Consistent with its role as a neuromodulator, expression of BdTRP was detected in the central nervous system (CNS) of B. dorsalis, specifically in the local interneurons with cell bodies lateral to the antennal lobe. BdTRPR was found in the CNS, midgut and hindgut, but interestingly also in the antennae. To investigate the role of BdTRP and BdTRPR in olfaction behavior, adult flies were subjected to RNA interference, which led to a reduction in the antennal electrophysiological response and sensitivity to ethyl acetate in the Y-tube assay. Taken together, we demonstrate the impact of TRP/TRPR signaling on the modulation of the olfactory sensitivity in B. dorsalis. The result improve our understanding of olfactory processing in this agriculturally important pest insect.     

Transient and persistent tetrodotoxin-sensitive sodium currents in squid olfactory receptor neurons

Squid olfactory receptor neurons are primary bipolar sensory neurons capable of transducing water-born odorant signals into electrical impulses that are transmitted to the brain. In this study, we have identified and characterized the macroscopic properties of voltage-gated Na⁺ channels in olfactory receptor neurons from the squid Lolliguncula brevis. Using whole-cell voltage-clamp techniques, we found that the voltage-gated Na⁺ channels were tetrodotoxin sensitive and had current densities ranging from 5 to 169 pA pF⁻¹. Analyses of the voltage dependence and kinetics revealed interesting differences from voltage-gated Na⁺ channels in olfactory receptor neurons from other species; the voltage of half-inactivation was shifted to the right and the voltage of half-activation was shifted to the left such that a “window-current” occurred, where 10–18% of the Na⁺ channels activated and did not inactivate at potentials near action potential threshold. Our findings suggest that in squid olfactory neurons, a subset of voltage-gated Na⁺ channels may play a role in generating a pacemaker-type current for setting the tonic levels of electrical activity required for transmission of hyperpolarizing odor responses to the brain. Accepted: 1 October 1998     

Hunger is the best spice: Effects of starvation in the antennal responses of the blood-sucking bug Rhodnius prolixus

Blood-sucking insects strongly rely on olfactory cues to find their vertebrate hosts. As in other insects with different lifestyles, it has been shown that endogenous and exogenous factors modulate olfactory responses. The triatomine bug Rhodnius prolixus is an important vector of Chagas disease and a classical model for studies of physiology and behavior. In this species, the behavioral response to host-derived odorants is modulated by both the time of the day and the starvation. Here I investigated the peripheral neural mechanisms underlying these modulatory effects. For this, I measured the electroantennogram (EAG) responses of insects towards different concentrations (from 0.5% to 75% vol/vol) of an attractive host-odorant, ammonia. I tested the responses of starved and fed animals during the middle of the day (when insects are inactive and aggregated in refuges) and at the beginning of the night (when insects become active and search for hosts). Regardless of the time of the day and the starvation status, EAG responses systematically increased with odorant concentration, thus accurately reflecting the response of olfactory receptor cells. Interestingly, the EAG responses of starved insects were larger than those of fed insects only during the night, with larger differences (6–7 times) observed at low–middle concentrations. This study is the first reporting modulation of sensory responses at the neural level in triatomines. This modulation, considering that triatomine hosts are mostly diurnal and are also potential predators, has an important adaptive value, ensuring that insects search for hosts only when they are hungry and at appropriate times.     

Using insects to drive mobile robots — hybrid robots bridge the gap between biological and artificial systems

The use of mobile robots is an effective method of validating sensory–motor models of animals in a real environment. The well-identified insect sensory–motor systems have been the major targets for modeling. Furthermore, mobile robots implemented with such insect models attract engineers who aim to avail advantages from organisms. However, directly comparing the robots with real insects is still difficult, even if we successfully model the biological systems, because of the physical differences between them. We developed a hybrid robot to bridge the gap. This hybrid robot is an insect-controlled robot, in which a tethered male silkmoth (Bombyx mori) drives the robot in order to localize an odor source. This robot has the following three advantages: 1) from a biomimetic perspective, the robot enables us to evaluate the potential performance of future insect-mimetic robots; 2) from a biological perspective, the robot enables us to manipulate the closed-loop of an onboard insect for further understanding of its sensory–motor system; and 3) the robot enables comparison with insect models as a reference biological system. In this paper, we review the recent works regarding insect-controlled robots and discuss the significance for both engineering and biology.     

Effect of dietary nickel deprivation on vision,olfaction, and taste in rats

Early studies on dietary nickel deprivation found decreased reproduction rate in pigs and decreased insemination and conception rates in goats. Studies from our laboratory demonstrated that nickel deprivation impaired male reproductive function of rats. A physiological amount of nickel modulates the function of cyclic nucleotide-gated cation channels (CNG channels) in vitro. Thus, because CNG channels have important roles in spermatozoa function, it was speculated that the impairment of reproduction by nickel deprivation was through an effect on CNG channels. Because CNG channels are found in retinal photoreceptor, olfactory receptor, and taste receptor cells, we hypothesized that nickel deprivation would also alter light/dark preference, odor preference to female rat urine, and taste preference/aversion in rats. In the light/dark Y-maze, nickel deprivation significantly decreased time spent in the dark arm by rats. The number of sniffs to estrous female urine was significantly increased only in nickel-supplemented rats. The number of licks at the saccharin bottle was significantly decreased by dietary nickel deprivation. These findings suggest that nickel has a biological role in the special senses: vision, olfaction and taste.     

Expression of a Lipocalin in Human Nasal Mucosa

A 19 kDa soluble protein was purified from human nasal mucus. Its N-terminal amino-acid sequence appeared to be identical to that of a lipocalin synthesised both in lachrymal glands and in von Ebner's glands (VEG) of circumvallate papillae. In order to verify whether this protein was synthesised in the nasal cavity or was the result of tear contamination, we adopted an immunohistochemical approach. Polyclonal antibodies, raised against a primate VEG protein, were used on sections of human nasal mucosa obtained from surgery. The results clearly indicate that the protein is synthesised in sero-mucous glands underlying the respiratory ciliated epithelium. Although ligand-binding experiments with some odorant molecules have given negative results, we cannot exclude a role of odorant solubiliser and carrier for this protein.     

The source of an aggression-promoting olfactory cue,released by α-Melanocyte stimulating hormone,in the male mouse

Earlier experiments demonstrated that the injection of α-melanocyte stimulating hormone into one mouse of a male pair results, 15 minutes later, in the release of an olfactory cue which increases the aggressive behavior of its partner. Because the preputial gland, whose activity is dependent upon testosterone and α-MSH, produces an odor which stimulates aggressive behavior, its relationship with the MSH response was investigated. Preputialectomy failed to prevent the release of the odor by an MSH-treated subordinate mouse of a pair, although preputialectomy of one mouse of a naive pair resulted in it later displaying higher levels of aggression than its intact partner, which then became subordinate. Swabs taken from the perineal region of α-MSH-injected subordinates, contained more aggression-promoting factor than swabs taken from saline injected subordinates. It is concluded that the short-term effects of α-MSH upon aggression are probably via a product of glandular or urinary origin other than the preputial gland and that the latter is more involved in long-term aggression-promoting cues.