Decrease of blood anti-α1,3 Galactose Abs levels in multiple sclerosis (MS) and clinically isolated syndrome (CIS) patients

The etiology of multiple sclerosis (MS) remains elusive. Among the possible causes, the increase of anti-Neu5Gc antibodies during EBV primo-infection of Infectious mononucleosis (IMN) may damage the integrity of the blood-brain barrier facilitating the transfer of EBV-infected B cells and anti-EBV T cell clones in the brain. We investigated the change in titers of anti-Neu5Gc and anti-α1,3 Galactose antibodies in 49 IMN, in 76 MS, and 73 clinically isolated syndrome (CIS) patients, as well as age/gender-matched healthy individuals. Anti-Gal and anti-Neu5Gc are significantly increased during IMN (p=0.02 and p<1.10^-4 respectively), but not in acute CMV primo-infection. We show that, whereas there was no change in anti-Neu5Gc in MS/CIS, the two populations exhibit a significant decrease in anti-Gal (combined p=2.7.10^-3), in contrast with patients with non-MS/CIS central nervous system pathologies. Since anti-Gal result from an immunization against α1,3 Gal, lacking in humans but produced in the gut, our data suggest that CIS and MS patients have an altered microbiota or an altered response to this microbiotic epitope.

Transgenerational effect of infection in Plasmodium-infected mosquitoes

Transgenerational effects of infection have a huge potential to influence the prevalence and intensity of infections in vectors and, by extension, disease epidemiology. These transgenerational effects may increase the fitness of offspring through the transfer of protective immune factors. Alternatively, however, infected mothers may transfer the costs of infection to their offspring. Although transgenerational immune protection has been described in a dozen invertebrate species, we still lack a complete picture of the incidence and importance of transgenerational effects of infection in most invertebrate groups. The existence of transgenerational infection effects in mosquito vectors is of particular interest because of their potential for influencing parasite prevalence and intensity and, by extension, disease transmission. Here we present what we believe to be the first study on transgenerational infection effects in a mosquito vector infected with malaria parasites. The aim of this experiment was to quantify both the benefits and the costs of having an infected mother. We find no evidence of transgenerational protection in response to a Plasmodium infection. Having an infected mother does, however, entail considerable fecundity costs for the offspring: fecundity loss is three times higher in infected offspring issued from infected mothers than in infected offspring issued from uninfected mothers. We discuss the implications of our results and we call for more studies looking at transgenerational effects of infection in disease vectors.

Plasmodium infection brings forward mosquito oviposition

Invertebrate hosts often bring forward their reproductive effort in response to a parasitic infection. This is widely interpreted as a host-driven response aimed at compensating for the expected losses in future fitness as a result of parasitism. Here we report that mosquitoes bring forward their oviposition schedule when they are infected with Plasmodium, a parasite known to severely curtail mosquito fecundity. This response could aim at compensating for a negative time-dependent effect of the parasite on mosquito fitness, as infected mosquitoes seem to display a strong and progressive decrease in the quality of the eggs they lay. In addition, we show that this shift in oviposition date is dependent on mosquito strain: a comparison of several isogenic mosquitoes strains, one insecticide-susceptible and two insecticide-resistant ones, reveals that only the former shift their oviposition strategy when infected. This pattern suggests the existence of a costly host-driven response to parasitism, as insecticide-resistant mosquitoes have been shown to be in generally poorer condition.

Wolbachia increases susceptibility to Plasmodium infection in a natural system

Current views about the impact of Wolbachia on Plasmodium infections are almost entirely based on data regarding artificially transfected mosquitoes. This work has shown that Wolbachia reduces the intensity of Plasmodium infections in mosquitoes, raising the exciting possibility of using Wolbachia to control or limit the spread of malaria. Whether natural Wolbachia infections have the same parasite-inhibiting properties is not yet clear. Wolbachia-mosquito combinations with a long evolutionary history are, however, key for understanding what may happen with Wolbachia-transfected mosquitoes after several generations of coevolution. We investigate this issue using an entirely natural mosquito-Wolbachia-Plasmodium combination. In contrast to most previous studies, which have been centred on the quantification of the midgut stages of Plasmodium, we obtain a measurement of parasitaemia that relates directly to transmission by following infections to the salivary gland stages. We show that Wolbachia increases the susceptibility of Culex pipiens mosquitoes to Plasmodium relictum, significantly increasing the prevalence of salivary gland stage infections. This effect is independent of the density of Wolbachia in the mosquito. These results suggest that naturally Wolbachia-infected mosquitoes may, in fact, be better vectors of malaria than Wolbachia-free ones.

Plasmodium infection decreases fecundity and increases survival of mosquitoes

Long-lived mosquitoes maximize the chances of Plasmodium transmission. Yet, in spite of decades of research, the effect of Plasmodium parasites on mosquito longevity remains highly controversial. On the one hand, many studies report shorter lifespans in infected mosquitoes. On the other hand, parallel (but separate) studies show that Plasmodium reduces fecundity and imply that this is an adaptive strategy of the parasite aimed at redirecting resources towards longevity. No study till date has, however, investigated fecundity and longevity in the same individuals to see whether this prediction holds. In this study, we follow for both fecundity and longevity in Plasmodium-infected and uninfected mosquitoes using a novel, albeit natural, experimental system. We also explore whether the genetic variations that arise through the evolution of insecticide resistance modulate the effect of Plasmodium on these two life-history traits. We show that (i) a reduction in fecundity in Plasmodium-infected mosquitoes is accompanied by an increase in longevity; (ii) this increase in longevity arises through a trade-off between reproduction and survival; and (iii) in insecticide-resistant mosquitoes, the slope of this trade-off is steeper when the mosquito is infected by Plasmodium (cost of insecticide resistance).

Infection with Wolbachia protects mosquitoes against Plasmodium-induced mortality in a natural system

In recent years, there has been a shift in the one host-one parasite paradigm with the realization that, in the field, most hosts are coinfected with multiple parasites. Coinfections are particularly relevant when the host is a vector of diseases, because multiple infections can have drastic consequences for parasite transmission at both the ecological and evolutionary timescales. Wolbachia pipientis is the most common parasitic microorganism in insects, and as such, it is of special interest for understanding the role of coinfections in the outcome of parasite infections. Here, we investigate whether Wolbachia can modulate the effect of Plasmodium on what is, arguably, the most important component of the vectorial capacity of mosquitoes: their longevity. For this purpose, and in contrast to recent studies that have focused on mosquito-Plasmodium and/or mosquito-Wolbachia combinations not found in nature, we work on a Wolbachia-mosquito-Plasmodium triad with a common evolutionary history. Our results show that Wolbachia protects mosquitoes from Plasmodium-induced mortality. The results are consistent across two different strains of Wolbachia and repeatable across two different experimental blocks. To our knowledge, this is the first time that such an effect has been shown for Plasmodium-infected mosquitoes and, in particular, in a natural Wolbachia-host combination. We discuss different mechanistic and evolutionary explanations for these results as well as their consequences for Plasmodium transmission.

Energetic cost of insecticide resistance in Culex pipiens mosquitoes

The extensive use of insecticides to control vector populations has lead to the widespread development of different mechanisms of insecticide resistance. Mutations that confer insecticide resistance are often associated to fitness costs that prevent them from spreading to fixation. In vectors, such fitness costs include reductions in preimaginal survival, adult size, longevity, and fecundity. The most commonly invoked explanation for the nature of such pleiotropic effects of insecticide resistance is the existence of resource-based trade-offs. According to this hypothesis, insecticide resistance would deplete the energetic stores of vectors, reducing the energy available for other biological functions and generating trade-offs between insecticide resistance and key life history traits. Here we test this hypothesis by quantifying the energetic resources (lipids, glycogen, and glucose) of larvae and adult females of the mosquito Culex pipiens L. resistant to insecticides through two different mechanisms: esterase overproduction and acetylcholinesterase modification. We find that, as expected from trade-off theory, insecticide resistant mosquitoes through the overproduction of esterases contain on average 30% less energetic reserves than their susceptible counterparts. Acetylcholinesterase-modified mosquitoes, however, also showed a significant reduction in energetic resources (20% less). We suggest that, in acetylcholinesterase-modified mosquitoes, resource depletion may not be the result of resource-based trade-offs but a consequence of the hyperactivation of the nervous system. We argue that these results not only provide a mechanistic explanation for the negative pleiotropic effects of insecticide resistance on mosquito life history traits but also can have a direct effect on the development of parasites that depend on the vector's energetic reserves to fulfil their own metabolic needs.

Regulation of neuroblast mitosis is determined by PACAP receptor isoform expression

Although neurogenesis in the embryo proceeds in a region- or lineage-specific fashion coincident with neuropeptide expression, a regulatory role for G protein-coupled receptors (GPCR) remains undefined. Pituitary adenylate cyclase activating polypeptide (PACAP) stimulates sympathetic neuroblast proliferation, whereas the peptide inhibits embryonic cortical precursor mitosis. Here, by using ectopic expression strategies, we show that the opposing mitogenic effects of PACAP are determined by expression of PACAP receptor splice isoforms and differential coupling to the phospholipase C (PLC) pathway, as opposed to differences in cellular context. In embryonic day 14 (E14) cortical precursors transfected with the hop receptor variant, but not cells transfected with the short variant, PACAP activates the PLC pathway, increasing intracellular calcium and eliciting translocation of protein kinase C. Ectopic expression of the hop variant in cortical neuroblasts transforms the antimitotic effect of PACAP into a promitogenic signal. Furthermore, PACAP promitogenic effects required PLC pathway function indicated by antagonist U-73122 studies in hop-transfected cortical cells and native sympathetic neuroblasts. These observations highlight the critical role of lineage-specific expression of GPCR variants in determining mitogenic signaling in neural precursors.

Effects of an intrahypothalamic injection of antisense oligonucleotides for preproenkephalin mRNA in female rats: evidence for opioid involvement in lordosis reflex

Previous studies in female rats have shown that estrogen increases preproenkephalin (PPE) mRNA levels in the ventrolateral part of the ventromedial nucleus of the hypothalamus (VMHVL), an area implicated in the modulation of sexual behavior. In order to assess the physiological role of hypothalamic opioid expression in lordosis reflex 16-mer oligodeoxynucleotide (ODN) directed towards the PPE mRNA were acutely microinjected above the VMH of estradiol-primed ovariectomized rats. Estradiol-induced lordosis behavior was observed in response to a stud male 2 days thereafter. Antisense (without or with 4 mismatches) ODN injections near the VMHVL resulted in a significant reduction in lordosis quotient compared to control (reverse sense) ODN treatment or to antisense ODN injections targeted anterior or posterior to the VMHVL. In contrast, locomotor activity of these animals in the open-field test was not affected by ODN treatments. Enkephalin immunoreactive levels were determined by radioimmunoassay in the preoptic area, a major terminal field of the VMHVL. Estradiol-induced enkephalin levels were greatly reduced in antisense-treated groups. Using the in situ hybridization technique, PPE mRNA levels in the VMHVL were also determined. A 1.5-2-fold increase in PPE mRNA levels was observed in estradiol-treated rats compared to ovariectomized rats as previously described. This increase in PPE mRNA levels was not affected by ODN treatment, suggesting that the reduction of enkephalin expression was mainly due to physical blockade of PPE mRNA translation and not to its degradation. Taken together, these data further support the behavioral role of PPE expressing VMHVL neurons. They also highlight the in vivo potency of acute administration of antisense phosphorothioate ODNs in blocking neuronal target gene expression.

Central administration of the neurotensin receptor antagonist, SR48692, modulates diurnal and stress-related hypothalamic-pituitary-adrenal activity

Previous studies in our laboratory suggest that neurotensin (NT) acts centrally to modulate adrenocorticotropin hormone (ACTH) and corticosterone release. In the present studies, we examined hypothalamic-pituitary-adrenal (HPA) function under basal conditions and during restraint stress following central administration of the highly specific NT receptor antagonist, SR48692. Chronic delivery of SR48692 to the paraventricular nucleus (PVN) of the hypothalamus via indwelling central cannulae attenuated both the diurnal- and stress-induced elevations in HPA activity. Thus, SR48692 decreased the diurnal increase in plasma ACTH and corticosterone during the evening phase of the cycle, but did not affect morning levels. Restraint-induced increases in plasma ACTH and corticosterone levels were also significantly reduced in the SR48692-implanted animals. This suggests that the inhibitory effects of SR48692 were restricted to periods of stimulated HPA activity. A decrease in corticotropin-releasing hormone (CRH)-like immunoreactivity was observed within the PVN following chronic SR48692, and parallel decreases in CRH-like immunoreactivity were observed within the external zone of the median eminence. These findings suggest that endogenous NT serves to increase HPA activity during periods of enhanced stimulation.

Endogenous neurotensin regulates hypothalamic-pituitary-adrenal axis activity and peptidergic neurons in the rat hypothalamic paraventricular nucleus

Adrenocorticotropin (ACTH) secretion depends primarily on hypophysiotrophic factors released from neurons of the paraventricular nucleus of the hypothalamus. However, the neurochemical factors controlling these neurons, in particular neuropeptides, have had little investigation. In this study, we have investigated the role of neurotensin in the regulation of the different components of the hypothalamo-pituitary-adrenal (HPA) axis under basal and stress conditions in rats. For this purpose, animals were implanted with bilateral cannulae filled with crystals of the neurotensin antagonist, SR 48692, and which were located above the paraventricular nucleus. Five days after surgery, the effects of SR 48692 implants were studied on basal and stress-induced secretion of ACTH and corticosterone. Such treatment did not modify plasma levels of ACTH and corticosterone in basal conditions but reduced ACTH but not corticosterone levels after tail cut procedure. After an exposure to a novel environment for 30 min, both ACTH and corticosterone plasma levels were reduced in the SR 48692-treated group. In situ hybridization studies revealed that chronic administration of SR 48692 induced a significant reduction of CRF mRNA levels in the parvocellular division of the paraventricular nucleus of the hypothalamus. In addition, a 2-fold increase in basal levels of plasma vasopressin associated with an increase in vasopressin mRNA levels in the magnocellular neurons of the paraventricular nucleus was also detected. Finally, the basal plasma levels of oxytocin were not affected by the same treatment. Taken together, these findings strongly suggest that endogenous neurotensin in the paraventricular nucleus plays a tonic stimulatory role on HPA axis activity and an inhibitory effect on vasopressin secretion.

Antisense oligodeoxynucleotides as specific tools for studying neuroendocrine and behavioral functions: some prospects and problems

Synthetic antisense oligodeoxynucleotides can inhibit the expression of a gene in a sequence-specific manner at the translational level. Their potential use to understand the role of neuropeptides or neurotransmitters in neuroendocrine and behavioral functions, and perhaps for therapeutic gene suppression, has become of great interest in neuroscience, especially in the cases of absence of available specific antagonists. Whether their action can be fully specific to the target gene and not only sequence-specific is, however, the main question about their application to brain studies. A number of factors such as the mode of action, specificity and chemistry of antisense molecules as well as the carrier vehicle and the time course of antisense treatment, must be carefully considered for the design and successful application of antisense oligonucleotides. Assay systems and controls must be chosen so as to ensure that the observed biological effects of antisense oligodeoxynucleotides do in fact reflect the result of a specific target gene inhibition. This article discusses these biochemical factors with the emphasis on the use of phosphodiester or phosphorothioate oligodeoxynucleotides in neuroendocrine or behavioral studies.

Neurotensin and neuromedin N brain levels after fornix transection: evidence for an efficient neurotensin precursor processing in subicular neurons

High levels of neurotensin/neuromedin N precursor mRNA, but few if any NT-positive perikarya have been detected in the dorsal subiculum of the adult rat or human hippocampus. This apparent discrepancy was tentatively ascribed to a lack of precursor mRNA translation or to a poor precursor posttranslational processing in neurons of the hippocampus. Another hypothesis is that in long neuronal pathways, maturation of neuropeptide precursors and derived peptides occurs during axonal transport to terminals, a process which accounts for the lack of peptide detection in cell bodies. In order to test this hypothesis, we performed surgical transection of the fornix to interrupt axonal transport of putative NT/NN products arising from the dorsal hippocampus and measured NT and NN levels in different brain regions. In the mamillary bodies, the main projection area of the dorsal subiculum, NN and NT levels were highly reduced 4 or 14 days after the septo-hippocampal transection which was correlated with a slight increase in NN and NT levels in the dorsal hippocampus and the retrosplenial cortex of 4 days lesioned animals. An increase in hypothalamic NN levels was also detected 14 days after the lesion. These data suggest that the peptide precursor processing can take place during the axonal transport, as shown here for neurotensin and neuromedin N from subicular neurons to their efferent brain areas such as the mamillary bodies.

Hypercorticism induces neurotensin mRNA in rat periventricular hypothalamus

In vitro studies performed on cell lines or embryonic hypothalamic neuronal cultures suggest that neurotensin gene expression can be stimulated by dexamethasone, a synthetic glucocorticoid agonist. In order to test whether such an action could be observed in vivo, the distribution of neurotensin mRNA in the rat forebrain was analysed by in situ hybridization in rats treated chronically with corticosterone and in control animals. Corticosterone treatment resulted in a selective induction of neurotensin mRNA in both the periventricular and rostral arcuate nuclei of the hypothalamus but not in the paraventricular nucleus of the hypothalamus or the hippocampal CA1-CA2 region. This selective effect of corticosterone could be involved in neuroendocrine changes observed following glucocorticoid administration.

Steroid effects on brain functions: an example of the action of glucocorticoids on central dopaminergic and neurotensinergic systems

It is now clearly established that steroid hormones released from peripheral endocrine glands may, through specific receptors in the brain, directly regulate brain function. These effects may be rapid or involve long-term modifications at the genomic level. Concerning the glucocorticoids, their receptors are found in most neuronal cells, an observation which can be related to their widespread effects on neuronal metabolism. Furthermore, glucocorticoids are often related to stress. We have previously demonstrated that neonatal handling of the rat prevented excessive endocrine response to stress. In adults, this action appeared to protect the animal from potential damaging effects of glucocorticoids and from related impairment of cognitive functions. The effects of glucocorticoids are thought to involve an interaction of several central neurotransmitter systems. One such neurotransmitter is neurotensin, a neuropeptide which was reported to be closely related to central dopaminergic system regulation. This paper presents a rapid overview of the central effects of glucocorticoids and possible evidence for the interrelationship between these steroids, dopamine and neurotensin systems in the regulation of the hypothalamo-pituitary-adrenal axis. It provides a new way to approach stress responses and to develop new substances that may become potential drugs in the treatment of some psychiatric disorders.

Differential expression of neurotensin receptor mRNA in the dopaminergic cell groups of the rat diencephalon and mesencephalon

Several lines of evidence support interactions between neurotensin (NT) and dopaminergic (DAergic) neurons in the brain. In order to obtain further knowledge about the anatomical substrate for such interactions, the distribution of cells expressing the cloned neurotensin receptor (NTR) mRNA was examined in relation to tyrosine hydroxylase (TH) mRNA-expressing cells within different subnuclei of the diencephalon and ventral mesencephalon of the male rat. In situ hybridization was performed on consecutive sections labeled with 33P-labeled oligonucleotide probes. In the hypothalamus, NTR mRNA signals were mostly found in the suprachiasmatic, dorsomedial, dorsal premammillary, and supramammillary nuclei. On the other hand, DAergic cells of the periventricular nucleus of the hypothalamus and dorsal aspect of the arcuate nucleus, revealed by TH in situ hybridization, did not exhibit NTR mRNA even though dense NT binding sites have been previously described in this nuclei. In the zona incerta, TH mRNA-containing cells were concentrated in the medial part, with little overlap with NTR mRNA-expressing cells located mainly in its mediolateral extent. In contrast, the distribution of both markers was superimposable within the different subdivisions of the ventral tegmental area and substantia nigra, as previously suggested, but also in the retrorubral field. These anatomical data further support the NT-dopamine interactions on both mesocorticolimbic and nigrostriatal DAergic systems. Moreover, the results suggest that diencephalic DAergic neurons do not synthesize the cloned NTR mRNA or express it at considerably lower levels than DAergic mesencephalic cells.

Blockade of neurotensin binding in the rat hypothalamus and of the central action of neurotensin on the hypothalamic-pituitary-adrenal axis with non-peptide receptor antagonists

Central administration of neurotensin (NT) has been shown to activate the hypothalamic-pituitary-adrenal axis, an effect which seems dependent upon the release of corticotropin-releasing factor. In this study, we describe the distribution of NT binding sites in the hypothalamus using film and emulsion receptor autoradiography. Among the 125I-NT-labelled hypothalamic nuclei, relatively high densities of neurotensin binding sites were detected over the paraventricular nucleus. Silver grains on emulsion-coated slides overlaid indiscriminately cell bodies and surrounding processes of magnocellular and parvocellular parts of the nucleus. Two newly developed NT receptor antagonists, SR 48692 and its analog SR 48450, competed for 125I-NT binding to hypothalamic tissue sections and membrane preparations with Ki values in the nanomolar range. Moreover, intracerebrally injected SR 48450 was able to block the NT-induced hypothalamic-pituitary-adrenal axis activation in freely moving rats, whereas its administration alone did not significantly affect basal plasma levels of adrenocorticotropin and corticosterone. These data provide anatomical substrate for a potential neurotensin action at the hypothalamus in the hypothalamic-pituitary-adrenal axis activation and highlight the use of new non-peptide NT receptor antagonists to characterize the effects of NT on neuroendrocrine functions.

Increase in neurotensin receptor expression in rat brain induced by chronic treatment with the nonpeptide neurotensin receptor antagonist SR 48692

In the present study, we examined the regulation of neurotensin receptor following a chronic pharmacological blockade of the neurotensin transmission with a nonpeptide neurotensin receptor antagonist, SR 48692. Our results showed that treatment of the rats for five days with SR 48692, at a dose of 1 mg/kg, i.p., induced an increase of both the number of binding sites for 125I-neurotensin to whole brain membrane homogenates and neurotensin receptor mRNA levels in the ventral mesencephalon. This study brings the first evidence for an in vivo up-regulation of neurotensin receptors following their pharmacological blockade, and suggests that endogenous neurotensin exerts a tonic inhibitory control on neurotensin receptor mRNA levels.

Neurotensin receptor expression in the rat forebrain and midbrain: a combined analysis by in situ hybridization and receptor autoradiography

The aim of the present study was to examine the distribution of the levocabastine-insensitive high-affinity neurotensin binding sites in the rat forebrain and midbrain in relation to the distribution of the cloned neurotensin receptor mRNA by using a combination of both high-resolution in vitro receptor autoradiography and in situ hybridization approaches. Groups of cells rich in neurotensin receptor mRNA were observed in the basal forebrain nuclei, the ventral tegmental area, the substantia nigra and in the interfascicular and caudal linear nuclei and the retrorubral field. Cells expressing lower levels of neurotensin receptor mRNA were found in several subdivisions of the cortex; the dentate gyrus; the septofimbrial, suprachiasmatic, medial habenular, and mammillary nuclei; the dorsal part of the lateral septum; the zona incerta; and the dorsomedial and perifornical hypothalamic areas. Most of the brain areas containing neurotensin receptor mRNA demonstrated a selective association of neurotensin binding sites with neuronal cell bodies. In contrast, in several telencephalic and diencephalic structures, the presence of neurotensin binding sites was not correlated with that of neurotensin receptor mRNA, suggesting that neurotensin receptors were mainly located on axon terminals. This study provides a better understanding of the anatomical organization of neurotensin receptor expressing systems in the rat brain and gives further insight into the pre- vs. postsynaptic location of neurotensin receptors in various brain regions. Moreover, it indicates that all neurons expressing the cloned neurotensin receptor harbour neurotensin binding sites on their perikaryal membrane.

Marked variations of the relative distributions of neurotensin and neuromedin N in micropunched rat brain areas suggest differential processing of their common precursor

Neuromedin N (NN) is a hexapeptide that shares a four amino acid identity with the C-terminus of neurotensin (NT) and exhibits NT-like effects in the central nervous system. Both peptides were recently shown to be encoded in the same precursor molecule. By means of specific and sensitive radioimmunoassays, we compared the distribution of immunoreactive NT and NN (iNT and iNN) in micropunched rat brain structures. The data revealed marked regional variations in the ratio of iNT over iNN. For instance, the ratio value was 4.5 in the posterior hypothalamus and 0.8 in the mammillary bodies. Reverse phase HPLC analysis of extracts of several brain regions showed that iNT and iNN coeluted with synthetic NT and NN, respectively. The results suggest that differential processing of the common neurotensin/neuromedin N precursor occurs in various regions of the rat brain.