Schistosoma mansoni: influence of infection on mouse behavior

Alternate-day fasting, a high-sucrose/caloric diet and praziquantel treatment influence biochemical and behavioral parameters during Schistosoma mansoni infection in male BALB/c mice

Schistosoma mansoni-induced granulomas result in severe damage to the host's liver, as well as neurological and metabolic disorders. We evaluated the biochemical and behavioral changes during schistosomiasis under three diet protocols: ad libitum (AL), alternate-day fasting (ADF) and a high-sucrose/caloric diet (HSD). Healthy male BALB/c mice were divided into noninfected, matched infected and infected/treated [praziquantel (PZQ)] groups. Caloric intake and energy efficiency coefficients associated with diets were measured. Behavioral (exploratory and locomotor) and biochemical (glucose, triglycerides, total cholesterol, AST, ALT, ALP, and γ-GT) tests and histological analysis were performed. Fifteen weeks postinfection, HSD and PZQ promoted weight gain, with higher caloric consumption than ADF (p < 0.05), reflecting serum glucose levels and lipid profiles. HSD and PZQ prevented liver dysfunction (AST and ALT) and significantly prevented increases in granuloma area (p < 0.05). HSD and PZQ also significantly improved mouse physical performance in exploratory and locomotor behavior (p < 0.05), reversing the impaired motivation caused by infection. These findings showed that ADF worsened the course of S. mansoni infection, while HSD and PZQ, even with synergistic effects, prevented and/or attenuated biochemical and behavioral impairment from infection.

Nerve Growth Factor, Stress and Diseases

Stress is a constant threat for homeostasis and is represented by different extrinsic and intrinsic stimuli (stressors, Hans Selye's "noxious agents"), such as aggressive behavior, fear, diseases, physical activity, drugs, surgical injury, and environmental and physiological changes. Our organisms respond to stress by activating the adaptive stress system to activate compensatory responses for restoring homeostasis. Nerve Growth Factor (NGF) was discovered as a signaling molecule involved in survival, protection, differentiation, and proliferation of sympathetic and peripheral sensory neurons. NGF mediates stress with an important role in translating environmental stimuli into physiological and pathological feedbacks since NGF levels undergo important variations after exposure to stressful events. Psychological stress, lifestyle stress, and oxidative stress are well known to increase the risk of mental disorders such as schizophrenia, major depressive disorders, bipolar disorder, alcohol use disorders and metabolic disorders such as metabolic syndrome. This review reports recent works describing the activity of NGF in mental and metabolic disorders related to stress.

Plasmodium berghei-induced malaria decreases pain sensitivity in mice

Various types of pain were reported by people with Plasmodium falciparum and were mostly attributed to a symptom of malarial infection. Neural processes of pain sensation during malarial infection and their contributions to malaria-related death are poorly understood. Thus, these form the focus of this study. Swiss mice used for this study were randomly divided into two groups. Animals in the first group (Pb-infected group) were inoculated with Plasmodium berghei to induce malaria whilst the other group (intact group) was not infected. Formalin test was used to assess pain sensitivity in both groups and using various antagonists, the possible mechanism for deviation in pain sensitivity was probed. Also, plasma and brain samples collected from animals in both groups were subjected to biochemical and/or histological studies. The results showed that Pb-infected mice exhibited diminished pain-related behaviours to noxious chemical. The observed parasite-induced analgesia appeared to be synergistically mediated via µ-opioid, α2 and 5HT2A receptors. When varied drugs capable of decreasing pain threshold (pro-nociceptive drugs) were used, the survival rate was not significantly different in the Pb-infected mice. This showed little or no contribution of the pain processing system to malaria-related death. Also, using an anti-CD68 antibody, there was no immunopositive cell in the brain to attribute the observed effects to cerebral malaria. Although in the haematoxylin and eosin-stained tissues, there were mild morphological changes in the motor and anterior cingulate cortices. In conclusion, the pain symptom was remarkably decreased in the animal model for malaria, and thus, the model may not be appropriate for investigating malaria-linked pain as reported in humans. This is the first report showing that at a critical point, the malaria parasite caused pain-relieving effects in Swiss mice.

Nerve Growth Factor in Alcohol Use Disorders

The nerve growth factor (NGF) belongs to the family of neurotrophic factors. Initially discovered as a signaling molecule involved in the survival, protection, differentiation, and proliferation of sympathetic and peripheral sensory neurons, it also participates in the regulation of the immune system and endocrine system. NGF biological activity is due to the binding of two classes of receptors: the tropomyosin-related kinase A (TrkA) and the low-affinity NGF pan-neurotrophin receptor p75. Alcohol Use Disorders (AUD) are one of the most frequent mental disorders in developed countries, characterized by heavy drinking, despite the negative effects of alcohol on brain development and cognitive functions that cause individual’s work, medical, legal, educational, and social life problems. In addition, alcohol consumption during pregnancy disrupts the development of the fetal brain causing a wide range of neurobehavioral outcomes collectively known as fetal alcohol spectrum disorders (FASD). The rationale of this review is to describe crucial findings on the role of NGF in humans and animals, when exposed to prenatal, chronic alcohol consumption, and on binge drinking.

Evaluation of nanoselenium and nanogold activities against murine intestinal schistosomiasis

Nanomedicine is one of the most important methods used to treat human diseases including parasitic diseases. Schistosomiasis is a major parasitic disease that affects human health in tropical regions. Whilst Praziquantel is the main classic antischistosomal drug, new drugs are required due to the poor effect of the drug on the parasite juveniles and immature worms, and the emergence of drug resistant strains of Schistosoma. The present study aimed to examine the curative roles of both gold and selenium nanoparticles on jejunal tissues of mice infected with Schistosoma mansoni. Transmission electron microscopy was used for characterization of nanoparticles. Gold nanoparticles of 1 mg/kg mice body weight and selenium nanoparticles 0.5 mg/kg body weight were inoculated separately into mice infected with S. mansoni. The parasite induced a significant decrease in glutathione levels; however, the levels of nitric oxide and malondialdehyde were significantly increased. Additionally, the parasite introduced deteriorations in histological architecture of the jejunal tissue. Treatment of mice with metal nanoparticles reduced the levels of body weight changes, oxidative stress and histological impairment in the jejunal tissue significantly. Therefore, our results revealed the protective role of both selenium and gold nanoparticles against jejunal injury in mice infected with S. mansoni.

Development of an experimental model of schistosomal myeloradiculopathy

Schistosomal myeloradiculopathy (SMR) is a severe form of presentation of schistosomiasis in which Schistosoma spp. affect the spinal cord. The aims of the present study were to develop an animal model of SMR caused by S. mansoni, to characterize both sensory and motor abnormalities in the infected animals, and to investigate the relationship of the sensory, motor and histological findings with the progression of the infection over time. Mechanical sensitivity and behavioral tests were performed followed by euthanasia in male Wistar rats divided into six groups of five animals each, on days 5, 10, 20 and 30 after infection of S. mansoni eggs. The controls were subjected to the same procedure but were administered phosphate-buffered saline (PBS). The spinal cord was removed and subjected to histological analysis. S. mansoni eggs were found in the spinal cord of 25% of the infected animals, which belonged to the groups that exhibited more significant reduction of the superficial mechanical sensitivity, thermal sensitivity and muscle strength. This model proved to be satisfactory to assess functional changes in Wistar rats and might be used in studies investigating the pathogenesis of SMR. To our knowledge, this is the first experimental model of SMR.

Comparative in vivo antioxidant levels in Schistosoma mansoni infected mice treated with praziquantel or the essential oil of Melaleuca armillaris leaves

Plant extracts are continuously investigated for their extensive inclusion of biologically active constituents that exert therapeutic activities against many diseases. The aim of this study was to assess the antioxidant/anti-schistosomal activities of the essential oil of the fresh leaves of Melaleuca armillaris (M. armillaris) compared to Praziquantel (PZQ) on normal and Schistosoma mansoni-infected mice. The oil was isolated by hydrodistillation and analyzed by gas chromatography/mass spectrometry (GC/MS). The oil was rich in 1,8-cineole (33.93%), terpinen-4-ol (18.79%), limonene (10.37%) and B-pinene (6.59%). M. armillaris oil (150 mg kg(-1), orally) was administered from the second week post infection twice per week for six weeks. PZQ (500 mg kg(-1), orally) was administered for two successive days 8 weeks post infection and mice sacrificed one week later. Total protein, Malondialdehyde (MDA), Glutathione (GSH), vitamins C and E, the antioxidant enzymes catalase and superoxide dismutase, as well as liver weights and liver/body weight were determined in the liver tissues. Results showed that, both treatments significantly ameliorated the disturbed levels ofGSH and MDA in infected mice. Both vitamins were significantly elevated after treatment with the oil while a significant increase in catalase accompanied by a pronounced decrease in SOD were obtained after treatment with PZQ. Both treatments markedly improved liver and body weights in infected mice compared to the infected-untreated ones. In conclusion, natural plant sources may be used as promising alternative agents to chemical drugs for schistosomiasis treatment, since the latter may result in drug-induced resistance arising from repeated use.

Plasma bioactive LH and testosterone profiles in male New Zealand rabbits experimentally infected with Schistosoma mansoni

The effects of Schistosoma mansoni (S. mansoni) infection on plasma levels of bioactive luteinising hormone (LH) and testosterone in the New Zealand rabbit model were studied. S. mansoni infection significantly decreased the pulse frequency (P < 0.05), amplitude (P < 0.05), area under LH curve (P < 0.05) and mean plasma LH concentrations (P < 0.05) on days 42 and 70 post-infection, as compared to values for day 14 pre-infection. Areas under the response curves for plasma testosterone levels decreased significantly (P < 0.05) on days 42 and 70 post-infection in infected animals compared to day 14 pre-infection. In the praziquantel-treated group, the levels of LH and testosterone remained unchanged throughout the experimental period. The pulsatile secretion of LH was completely inhibited in S. mansoni-infected animals 70 days post-infection. These results suggest that the effects on reproductive gonadal hormones caused by S. mansoni in the rabbit model may partly be induced by alteration in pituitary synthesis or release of LH.

Experimental models of Schistosoma mansoni infection

Experimental models of Schistosoma mansoni infections in mammals have contributed greatly to our understanding of the pathology and pathogenesis of infection. We consider here hepatic and extrahepatic disease in models of acute and chronic infection. Experimental schistosome infections have also contributed more broadly to our understanding of granulomatous inflammation and our understanding of Th1 versus Th2 related inflammation and particularly to Th2-mediated fibrosis of the liver.

Experimental neuroschistosomiasis: inadequacy of the murine model

Neuroschistosomiasis is rarely observed in human pathology, but it is of considerable importance. To investigate its pathogenesis, consequences and response to treatment, an experimental model would be desirable, but is not yet available, in spite of a few indications of a suitable mouse model in the literature. Severe, recent and late Schistosoma mansoni infections in outbred and inbred strains of mice revealed widespread distribution of parasite eggs in several organs, but only exceptionally did eggs reach the encephalus, thus revealing the inadequacy of the mouse as an experimental model for neuroschistosomiasis.

Parasites and behaviour: an ethopharmacological perspective

Ethopharmacology combines an ethological approach to the understanding of the causes and functions of behaviour with pharmacological analysis of the underlying neuromodulatory mechanisms. Recently, this approach has been applied to the analysis of the responses of animals to parasitized individuals and to the effects of parasites on various host behaviours (eg. host defences, mate responses) and their neurobiological correlates. Martin Kavaliers, Douglas Colwell and Elena Choleris explain here how ethopharmacology can be used to address the mechanisms that underlie the often subtle effects of parasites on host behaviour.

Parasites and behavior: an ethopharmacological analysis and biomedical implications

Parasites and disease are increasingly recognized as agents of behavioral, ecological and evolutionary importance having a variety of influences on their hosts other than the more obvious pathological and immunological changes. Parasites can have significant behavioral effects even when parasitism is sub-clinical with these effects proposed to either benefit the parasite (parasite 'manipulation'), benefit the host, or to simply arise as side-effects of the infection (parasitic 'constraints'). However, until relatively recently little attention has been paid to the neuromodulatory substrates that mediate these behavioral changes. Ethopharmacology incorporates an evolutionary approach to the study of behavior with pharmacological analysis of neuromodulatory mechanisms. As such, this approach is appropriate for, and has been applied to, the analysis of the effects of ectoparasites (e.g. biting and blood-feeding flies) and endoparasites (e.g. protozoa, nematodes) on a number of behaviors (e.g. pain inhibition, learning and memory, responses to predators and anxiety, mate selection) in selected host-parasite systems. Ethopharmacology suggests a promising direction by which neuromodulatory mechanisms that underlie the effects of parasites on behavior, including that of humans, can be addressed.

Infection with Schistosoma mansoni in mice induces changes in nociception and exploratory behavior

In this study, CD-1 mice were infected percutaneously with 1600 cercariae of Schistosoma mansoni and their pain sensitivity and exploratory behavior were analyzed in well-standardized tests (hot-plate, hole-board, open-field, novel object investigation and black/white box). Schistosome infection produced body weight reduction, increased analgesia, induced changes in the number of fecal pellets emitted during the hole-board and the black/white tests, induced decreased locomotion in the open-field, decreased sniffing, rearing, wall-rearing and time spent in exploratory activity. The infection also lengthened the latency time to the first transition from the white into the black compartment in the black/white box, index of enhanced anxiety. The present findings indicate that the analgesia is one of the main effects of the disease suggesting that schistosome infection induces maladaptive response in exploratory behavior and in locomotor activity of the host associated with altered motivational and attentional levels. Furthermore, though mouse behavioral changes appear to be similar to those observed in parasite/host systems where the changes are supposed to be adaptive for the parasite, in the case of Schistosoma/mouse system, the changes in host behavior resulted to be not adaptive for the parasite.

Opioid involvement in behavior modifications of mice infected with the parasitic nematode, Nippostrongylus brasiliensis

Several studies have documented the opiate effects of parasitic infection on experimental animals. The current study examined the relationships between infection with the intestinal nematode, Nippostrongylus brasiliensis with analgesia and activity levels. Male white mice infected with N. brasiliensis displayed a significant increase in thermal latency thresholds that rose through the duration of infection and subsided with its termination. Analgesia first became apparent on day three-post infection but did not reach statistical significance (p < 0.05) until day 7 post infection. The maximum analgesia was reached on day 8-post infection and gradually declined. By day 15 post infection, there was no significant difference in the latency times between control and infected mice. The initial significant difference in latency roughly corresponded with the onset of egg production by the parasite. The peak difference in latency times and their subsequent decline also parallels peak egg production and the decline in egg production as the infection subsided. Both naloxone and naltrindole significantly reduced the latency times (p < 0.05) of infected mice. There was also a significant difference in total ambulatory activity levels between infected and control mice. Activity levels began to decline on the second day post infection but did not reach a statistically significant difference (p < 0.05) from the controls until 9th day post infection. Infected mice that were injected with either naloxone or naltrindole had a significantly higher activity level than the infected mice injected with saline.

Anxiogenic effect of subclinical bacterial infection in mice in the absence of overt immune activation

Challenge of animals with infectious microorganisms is well documented to affect a number of behavioral measures through activation of immune-neural mechanisms. In the present study, the ability of an infectious microorganism to directly alter behavioral responses in the absence of an overt immunologic response was examined. Eight-week-old CF-1 male mice were infected orally with the Gram-negative pathogen Campylobacter jejuni in order to establish a subclinical infection that did not result in immune activation. Microbiological examination of cecal contents revealed the presence of C. jejuni in all infected, but not control, animals 1 and 2 days post-oral challenge. Measurement of interleukin-6 (IL-6) levels and peripheral blood leukocyte populations did not reveal the activation of an overt immune response in 1 or 2 day infected animals as compared to controls. Infected mice demonstrated altered levels of anxiety-like behaviors on the elevated plus-maze as compared to controls on Day 2, but not Day 1, as reflected by a significant decrease in exploratory and an increase in nonexploratory behaviors. The anxiogenic effect of a subclinical infection in the absence of an overt immunologic response suggests that the direct activation of neural pathways by microorganisms may play a role in behavior.

Neuroinflammatory Implications of Schistosoma mansoni Infection: New Information from the Mouse Model

Schistosoma mansoni infection is known to induce granulomas, not only in the liver and intestine, but also in the brain, resulting in neuropathological and psychiatric disorders. In the past, the interaction between Schistosoma mansoni infection and the nervous system has received little attention. Here, Luigi Aloe and Marco Fiore discuss recent findings from experimental Schistosoma mansoni infection in the mouse nervous system showing that brain granulomas are associated with a significant alteration in the constitutive expression of nerve growth factor, a neurotrophic factor that plays an essential role in growth and differentiation and in preventing neuronal damage. These findings suggest that the neuropathological dysfunctions in neuroschistosomiasis may be linked to changes in the basal levels and/or activity of neurotrophic factors caused by local formation of granulomas.