Spatial scale influences the distribution of viral diversity in the eukaryotic virome of the mosquito Culex pipiens

Our knowledge of the diversity of eukaryotic viruses has recently undergone a massive expansion. This diversity could influence host physiology through yet unknown phenomena of potential interest to the fields of health and food production. However, the assembly processes of this diversity remain elusive in the eukaryotic viromes of terrestrial animals. This situation hinders hypothesis-driven tests of virome influence on host physiology. Here, we compare taxonomic diversity between different spatial scales in the eukaryotic virome of the mosquito Culex pipiens. This mosquito is a vector of human pathogens worldwide. The experimental design involved sampling in five countries in Africa and Europe around the Mediterranean Sea and large mosquito numbers to ensure a thorough exploration of virus diversity. A group of viruses was found in all countries. This core group represented a relatively large and diverse fraction of the virome. However, certain core viruses were not shared by all host individuals in a given country, and their infection rates fluctuated between countries and years. Moreover, the distribution of coinfections in individual mosquitoes suggested random co-occurrence of those core viruses. Our results also suggested differences in viromes depending on geography, with viromes tending to cluster depending on the continent. Thus, our results unveil that the overlap in taxonomic diversity can decrease with spatial scale in the eukaryotic virome of C. pipiens. Furthermore, our results show that integrating contrasted spatial scales allows us to identify assembly patterns in the mosquito virome. Such patterns can guide future studies of virome influence on mosquito physiology.

One Health surveillance of West Nile and Usutu viruses: a repeated cross-sectional study exploring seroprevalence and endemicity in Southern France, 2016 to 2020

BackgroundWest Nile virus (WNV) and Usutu virus (USUV), two closely related flaviviruses, mainly follow an enzootic cycle involving mosquitoes and birds, but also infect humans and other mammals. Since 2010, their epidemiological situation may have shifted from irregular epidemics to endemicity in several European regions; this requires confirmation, as it could have implications for risk assessment and surveillance strategies.AimTo explore the seroprevalence in animals and humans and potential endemicity of WNV and USUV in Southern France, given a long history of WNV outbreaks and the only severe human USUV case in France in this region.MethodsWe evaluated the prevalence of WNV and USUV in a repeated cross-sectional study by serological and molecular analyses of human, dog, horse, bird and mosquito samples in the Camargue area, including the city of Montpellier, between 2016 and 2020.ResultsWe observed the active transmission of both viruses and higher USUV prevalence in humans, dogs, birds and mosquitoes, while WNV prevalence was higher in horses. In 500 human samples, 15 were positive for USUV and 6 for WNV. Genetic data showed that the same lineages, WNV lineage 1a and USUV lineage Africa 3, were found in mosquitoes in 2015, 2018 and 2020.ConclusionThese findings support existing literature suggesting endemisation in the study region and contribute to a better understanding of USUV and WNV circulation in Southern France. Our study underlines the importance of a One Health approach for the surveillance of these viruses.

A library preparation optimized for metagenomics of RNA viruses

Our understanding of the viral communities associated to animals has not yet reached the level attained on the bacteriome. This situation is due to, among others, technical challenges in adapting metagenomics using high-throughput sequencing to the study of RNA viromes in animals. Although important developments have been achieved in most steps of viral metagenomics, there is yet a key step that has received little attention: the library preparation. This situation differs from bacteriome studies in which developments in library preparation have largely contributed to the democratisation of metagenomics. Here, we present a library preparation optimized for metagenomics of RNA viruses from insect vectors of viral diseases. The library design allows a simple PCR-based preparation, such as those routinely used in bacterial metabarcoding, that is adapted to shotgun sequencing as required in viral metagenomics. We first optimized our library preparation using mock viral communities and then validated a full metagenomic approach incorporating our preparation in two pilot studies with field-caught insect vectors; one including a comparison with a published metagenomic protocol. Our approach provided a fold increase in virus-like sequences compared to other studies, and nearly-full genomes from new virus species. Moreover, our results suggested conserved trends in virome composition within a population of a mosquito species. Finally, the sensitivity of our approach was compared to a commercial diagnostic PCR for the detection of an arbovirus in field-caught insect vectors. Our approach could facilitate studies on viral communities from animals and the democratization of metagenomics in community ecology of viruses.

A Citrus Based Sensory Functional Food Ingredient Induces Antidepressant-like Effects: Possible Involvement of an Interplay between the Olfactory and the Serotonergic Systems

In the present study, we examined the neurobehavioral effects of a sensory functional food ingredient mainly based on Citrus sinensis extracts (D11399) using a battery of tests recapitulating various endophenotypes of depression such as anxiety in the open field (OF), the elevated plus-maze (EPM), and the novelty suppressed feeding (NSF), self-care in the splash test (ST), despair in the forced swimming task (FST) but also anhedonia in the sucrose preference test (SPT) in mice. A one-week oral administration of D11399 promoted anxiolytic- and antidepressant-like responses in naïve mice subjected to the NSF and FST. In a marked contrast, the administration of D11399 by oral gavage or the inhibition of olfaction by methimazole prevented such beneficial effects. We further investigated the neurobehavioral properties of a ten-week oral administration of D11399 in the corticosterone (CORT) mouse model of depression. Interestingly, D11399 also elicited anxiolytic- and antidepressant-like effects in various paradigms. To characterize the putative underpinning neurobiological mechanisms in CORT mice, we investigated whether cellular and molecular processes commonly associated with antidepressant responses such as monoaminergic neurotransmission and neuronal maturation in the hippocampus were impacted. Although D11399 did not modify the hippocampal extracellular levels of monoamines (i.e. serotonin and norepinephrine), it reversed the ability of CORT to decrease serotonin neurons firing rate in the dorsal raphe and neuronal maturation in the hippocampus. These findings suggest that the anxiolytic- and antidepressant-like effects of this sensory functional food ingredient are closely related with olfaction and likely a concomitant change in the activity of the central serotonergic system. Further experiments are warranted to precise the neuronal circuits linking sensorial and emotional modalities and identify innovative therapeutic strategies aimed to relieve depressive endophenotypes.

Decreased motivational properties of morphine in mouse models of cancerous- or inflammatory-chronic pain: implication of supraspinal neuropeptide FF(2) receptors

Our main purpose was to evaluate the influence of cancer pain on the rewarding properties of morphine. Opioids are very addictive when used by healthy persons, conversely the occurrence of an opioid addiction seems very low when patients suffering from cancer are treated with morphine. We investigated the reinforcing properties of morphine in the place preference paradigm on a new model of mice suffering from a cancer pain induced by syngenic melanoma cells injected in the hind paw. These data were compared with mice suffering either from a short-term- or a chronic-inflammatory pain induced respectively by injection of carrageenan or complete Freund's adjuvant. Remarkably, mice suffering from cancer pain or chronic inflammatory pain did not develop any preference for the environment associated with the injection of morphine. In mice injected with melanoma cells, the specific binding of [(125)I]EYWSLAAPQRF-NH(2), an agonist of neuropeptide FF(2) receptors, was increased in several brain areas involved in the rewarding properties of opiates, including the shell of the nucleus accumbens, the major islands of Calleja, the ventral endopiriform nucleus and the amygdaloid area. Our study is the first to reveal a modification of morphine rewarding properties under cancer pain in rodents. We postulate that anti-opioid neuropeptides might contribute to the suppression of morphine rewarding effects in this murine model of cancer pain.

Characterization of the binding of a potent, selective, radioiodinated antagonist to the human neurokinin-1 receptor

We have synthesized a potent, selective, radioiodinated antagonist of the human neurokinin-1 (NK1) receptor and have characterized its binding to the cloned receptor expressed in Chinese hamster ovary cells. (cis)-2-(Diphenylmethyl)-N-[(2-iodophenyl)-methyl]-1- azabicyclo[2.2.2]octan-3-amine (L-703606) inhibits binding of 125I-Tyr8-substance P to the human NK1 receptor with an IC50 of 2 nM. This compound is a competitive antagonist of substance P-induced inositol phosphate generation, with a Kb of 29 nM. [125I]L-703606 binds to a single class of high affinity binding sites in human NK1/Chinese hamster ovary cell membranes (Kd = 0.3 nM). Substance P inhibits the binding of [125I]L-703606 to 65% of the NK1 receptor sites with a Kd of 0.04 +/- 0.03 nM and to the remaining 35% of the sites with a Kd of 1.5 +/- 0.7 nM. Addition of the nonhydrolyzable GTP analog guanylyl-5'-(beta, gamma-imido)diphosphate [Gpp(NH)p] shifts greater than 90% of the binding sites to the lower affinity state. In addition, Gpp(NH)p markedly alters the dissociation of substance P from the NK1 receptor by increasing the number of sites in the low affinity, rapidly dissociating state. However, Gpp(NH)p does not affect the rate of dissociation of [125I]L-703606. These data suggest that the pharmacological properties of [125I]L-703606 binding to the human NK1 receptor are similar to those of antagonists of nonpeptide guanine nucleotide-binding protein-coupled receptors and that this ligand will be useful for the biochemical and pharmacological characterization of the human NK1 receptor.

Further evidence that morphine-6 beta-glucuronide is a more potent opioid agonist than morphine

The antinociceptive properties of morphine-6 beta-glucuronide (M6G) and morphine (oral, i.c.v. and s.c.) were examined in two tests involving different nociceptive stimuli [i.e., cutaneous-thermal (tail-flick) and chemical-visceral (acetic acid-writhing)] in both naive and chronically treated mice. Twenty min after i.c.v. injection, M6G was 47 and 360 times more potent than morphine in the writhing and tail-flick tests, respectively. This difference was not due to differences in affinity because M6G displayed lower apparent affinities (Ki) for mu and kappa binding sites in vitro. After systemic injection, the two opiates were equieffective, although M6G produced a 10-fold longer antinociceptive effect. These differences with route of administration partially result from the hydrophilic nature of M6G because its inflow into the brain compartment was at least 10-fold lower than that of morphine, whereas the rate of elimination of the parent molecule was 3 times greater. After chronic treatment, mice readily develop tolerance and marked physical dependence to the antinociceptive effects of M6G. In vivo binding studies showed that M6G exerts its antinociceptive effect at low (less than 1%) fractional occupancy of [3H]diprenorphine-specific binding sites. In contrast, morphine needs to occupy 9.5 (writhing) to 47 (tail-flick) times more opioid binding sites to produce the same antinociceptive activity. M6G thus appears to have greater pharmacological potency than morphine, which in comparison possesses a low intrinsic efficacy.

Apparent precoupling of kappa- but not mu-opioid receptors with a G protein in the absence of agonist

Rabbit and guinea-pig cerebellum membranes contain a very high (greater than 80%) proportion of mu- and kappa-opioid receptors, respectively. Rabbit (mu) and guinea-pig (kappa) cerebellum membranes were (i) labeled either with the opiate agonist, [3H]etorphine (Kd = 0.1-0.2 nM), or with the opiate antagonist, [3H]diprenorphine (Kd = 0.1 nM), in the absence or presence of Na+ and/or 5'-guanylylimidodiphosphate (GppNHp), (ii) solubilized with digitonin (1%, w:v) and (iii) the radioactivity in the soluble extracts analyzed by ultracentrifugation in sucrose gradients. In the soluble extracts from rabbit cerebellum (mu) membranes, bound [3H]etorphine sedimented faster (S20,w congruent to 12S) than bound [3H]diprenorphine (10S), while in those from guinea-pig cerebellum (kappa) membranes, bound [3H]etorphine and bound [3H]diprenorphine sedimented at the same position (12S). Na+ selectively decreased recovery of the bound tritiated agonist in the two soluble preparations. When they had been generated in the presence of GppNHp but in the absence of Na+, the [3H]etorphine complexes of the mu- and kappa-opioid receptors as well as the [3H]diprenorphine complex of the kappa-opioid receptor were all recovered at position 10S, indicating that GppNHp had induced a decrease of the apparent molecular size of the two types of opioid receptors. These data are interpreted in terms of mu- and kappa-opioid receptors being capable of physically interacting with a G protein (GTP binding regulatory protein) yet, unlike the mu-opioid receptor which does so only in the presence of an agonist, the kappa-opioid receptor appears to be precoupled with a G protein.

Differential regulation of two molecular forms of a mu-opioid receptor type by sodium ions, manganese ions and by guanyl-5'-yl imidodiphosphate

The rabbit cerebellum contains a very high proportion (up to 80%) of mu-opioid receptor sites (Meunier, J.C., Kouakou, Y., Puget, A. and Moisand, C., Mol. Pharmacol. 24, 23-29, 1983). A membrane fraction derived therefrom is labeled either with the opioid agonist, 3H-etorphine or with the opioid antagonist, 3H-diprenorphine, and solubilized with digitonin. Centrifugation of the soluble extracts in linear sucrose gradients reveals that bound 3H-etorphine sediments faster than does bound 3H-diprenorphine: 12S vs 10S. Pre-incubation of membranes and radioligand in the presence of 120 mM NaCl results in considerably decreased recovery of the 3H-agonist in 12S form while recovery of the 3H-antagonist in 10S form is substantially increased. The opposite situation is observed when the membranes have been prelabeled with radioligand in the presence of 1 mM MnCl2. Guanyl-5'-yl imidodiphosphate, a metabolically stable structural analog of GTP is found to selectively reduce recovery of labeled 12S receptors while it does not affect that of labeled 10S receptors. These data indicate that the mu-opioid receptor from rabbit cerebellum is capable of existing in two forms which differ in apparent molecular size: an "antagonist" (10S) form of apparent Mr approximately 230,000 which is stabilized in the presence of sodium ions and an "agonist" (12S) form of apparent Mr approximately 300,000 which, unlike the antagonist one, is sensitive to guanyl-5'-yl imidodiphosphate. It is thought that the form of larger apparent size represents the mu-opioid receptor associated with a guanine nucleotide regulatory protein.

Na+ ions and Gpp(NH)p selectively inhibit agonist interactions at mu- and kappa-opioid receptor sites in rabbit and guinea-pig cerebellum membranes

Rabbit and guinea-pig cerebellum membrane preparations contain a high proportion (greater than 80%) of mu- and of kappa-opioid binding sites, respectively. These preparations were therefore used to compare the regulation of binding of mu- and of kappa-opioid agonists and antagonists by sodium ions and by guanyl-5'-yl imidodiphosphate. We report here that Na+ ions, Gpp(NH)p and most efficiently, the two agents in association selectively inhibited binding of opioid agonists not only in the mu preparation (rabbit cerebellum) but also in the kappa preparation (guinea-pig cerebellum). These allosteric effectors did not inhibit equilibrium binding of antagonists (naloxone, Mr 2266 or diprenorphine) in the two preparations. Taken together these results suggest that occupancy either of the mu-receptor by a mu-agonist or of the kappa-receptor by a kappa-agonist may be accompanied by similar if not identical molecular events. They also suggest a method to rapidly screen newly designed drugs as mu- or kappa-opioid agonists or antagonists.

Solubilization of two molecular forms of the frog brain opioid receptor

In equilibrium binding studies, using 3H-etorphine and 3H-diprenorphine, digitonin extracts of frog brain membranes are found to contain two classes of sites, one of which is seen only in the presence of Na+ ions. Centrifugation of the extracts in sucrose gradients separates two macromolecular components (10S and 12S) which display specific opiate binding activity. The 12S component appears to carry the site that binds opiates in the absence of Na+ ions while the 10S component would carry the other site, i.e. the one which is seen only in the presence of Na+ ions in equilibrium binding studies. Preliminary evidence is also given that in extracts of frog brain membranes which have been pre-incubated with 120 mM NaCl, the balance of the two components is shifted in favor of the slower sedimenting (10S) one. These results are discussed in terms of the regulation of the state of equilibrium between an agonist (12S) and an antagonist (10S) form of the opioid receptor.

Divalent cations: do they stabilize the agonist (12S) form of the mu opioid receptor?

In rabbit cerebellum membranes, millimolar concentrations of Mn++ ions while slightly reducing the Kd of 3H-etorphine counteract, to a large extent, sodium inhibition of equilibrium binding of the tritiated agonist to the mu opioid receptor. In digitonin extracts of membranes which have been incubated either with 3H-etorphine or with 3H-diprenorphine in the presence of Mn++ ions, recovery of radioligand bound to the agonist form of the receptor (sedimenting at position 12S) is substantially increased while, at the same time, recovery of radioligand bound to the antagonist form of the receptor (10S) is markedly reduced. Taken together these results suggest that Mn++ ions stabilize the agonist (12S) form of the mu opioid receptor. Mn++ ions may do so by promoting association of the receptor and of a guanine nucleotide regulatory protein.