Epigenetic Manipulation of Psychiatric Behavioral Disorders Induced by Toxoplasma gondii.

Toxoplasma gondii is known to have a complex life cycle and infect almost all kinds of warm-blooded animals around the world. The brain of the host could be persistently infected by cerebral cysts, and a variety of psychiatric disorders such as schizophrenia and suicide have been reported to be related with latent toxoplasmosis. The infected animals showed fear reduction and a tendency to be preyed upon. However, the mechanism of this "parasites manipulation" effects have not been elucidated. Here, we reviewed the recent infection prevalence of toxoplasmosis and the evidence of mental and behavioral disorders induced by T. gondii and discussed the related physiological basis including dopamine dysregulation and gamma-aminobutyric acid (GABA) pathway and the controversial opinion of the necessity for cerebral cysts existence. Based on the recent advances, we speculated that the neuroendocrine programs and neurotransmitter imbalance may play a key role in this process. Simultaneously, studies in the evaluation of the expression pattern of related genes, long noncoding RNAs (lncRNAs), and mRNAs of the host provides a new point for understanding the mechanism of neurotransmitter dysfunction induced by parasite manipulation. Therefore, we summarized the animal models, T. gondii strains, and behavioral tests used in the related epigenetic studies and the responsible epigenetic processes; pinpointed opportunities and challenges in future research including the causality evidence of human psychiatric disorders, the statistical analysis for rodent-infected host to be more vulnerable preyed upon; and identified responsible genes and drug targets through epigenetics.

Behavioural factors of Dutch pig producers related to control of toxoplasma gondii infections in pigs.

Toxoplasma gondii (T. gondii) is a food safety hazard which causes a substantial human disease burden. Infected pig meat is a common risk source of toxoplasmosis. Therefore, it is important to control T. gondii infections in pigs. Improving farm management to control the introduction risk likely contributes to that aim. A pig producer only implements control measures when he or she is aware of the underlying problem, wants to solve it, and is able to solve it. If a pig producer is not implementing appropriate control measures, behavioural change interventions can be introduced to overcome constraining behavioural factors. To aid in designing behaviour change interventions, this study analysed behavioural factors of Dutch pig producers in terms of capability, opportunity and motivation to control T. gondii infections in pigs. Key risk sources analysed focused on the life cycle of T. gondii, with cats as primary host, rodents as intermediate host, and uncovered feed as an important risk source. A survey was conducted among Dutch pig producers. Responses were analysed using descriptive and cluster analysis. Results showed that around 80% of the 67 responding pig producers was aware of key risk sources of T. gondii infections in pigs. Respondents also rated risk sources that are not known to increase the risk of T. gondii infections in pigs as somewhat important. Many respondents did not know about potential consequences of a T. gondii infection in pigs on human health. Two third expected some impact on pig performance, which is incorrect because T. gondii generally does not make pigs ill. Most respondents indicated to have the motivation and opportunity to control the risk sources cats, rodents and uncovered feed. Three pig producer clusters were identified: one with higher capability to control rodents, one with lower motivation to control rodents and cats and to cover feed storages, and one with lower scores on the importance of rodent control for pigs, human health and farm profit. We conclude that, although many pig producers have knowledge about risk sources for and consequences of T. gondii infections in pigs, the public health impact and risks of T. gondii infections in pigs are not yet common knowledge among all Dutch pig producers. Furthermore, Dutch pig producers differ in opportunity and motivation to control T. gondii infections. Targeted interventions to address these specific constraining behavioural factors can help to improve the control of T. gondii infections in pigs.

Impaired social behaviour and molecular mediators of associated neural circuits during chronic Toxoplasma gondii infection in female mice.

Toxoplasma gondii (T. gondii) is a neurotropic parasite that is associated with various neuropsychiatric disorders. Rodents infected with T. gondii display a plethora of behavioural alterations, and Toxoplasma infection in humans has been strongly associated with disorders such as schizophrenia, in which impaired social behaviour is an important feature. Elucidating changes at the cellular level relevant to neuropsychiatric conditions can lead to effective therapies. Here, we compare changes in behaviour during an acute and chronic T. gondii infection in female mice. Further, we notice that during chronic phase of infection, mice display impaired sociability when exposed to a novel conspecific. Also, we show that T. gondii infected mice display impaired short-term social recognition memory. However, object recognition memory remains intact. Using c-Fos as a marker of neuronal activity, we show that infection leads to an impairment in neuronal activation in the medial prefrontal cortex, hippocampus as well as the amygdala when mice are exposed to a social environment and a change in functional connectivity between these regions. We found changes in synaptic proteins that play a role in the process of neuronal activation such as synaptophysin, PSD-95 and changes in downstream substrates of cell activity such as cyclic AMP, phospho-CREB and BDNF. Our results point towards an imbalance in neuronal activity that can lead to a wider range of neuropsychiatric problems upon T. gondii infection.

Behavioral evaluation of BALB/c (Mus musculus) mice infected with genetically distinct strains of Toxoplasma gondii.

In relation to behavioral changes in rodents infected with Toxoplasma gondii (T. gondii), it is believed that the genotype of the infecting strain can have some influence. In this sense, the present work has sought to evaluate the effect of chronic infection by genetically distinct cystogenic strains of T. gondii on the behavior of mice. For this, experimental models of infection with ME-49 (type II) and VEG (type III) strains were developed in isogenic BALB/c mice. ELISA test was performed to evaluate the humoral immune response and real-time PCR test to quantify parasites in the CNS. Behavioral tests such as passive avoidance, open-field and Y-maze tests were also used for, respectively, evaluation of learning and memory, locomotor activity and aversion to feline odor. The results showed that mice infected with VEG strain had higher total IgG level of anti-toxoplasma, higher tissue burden of T. gondii in the CNS, reduction in the long-term memory, lower activity (mobility) and lower aversion to cat urine and l-felinine than mice infected with ME-49 strain. The results suggest that different T. gondii genotypes have a differential impact on behavioral changes in infected mice.

Induction of depression-related behaviors by reactivation of chronic Toxoplasma gondii infection in mice.

Although Toxoplasma gondii (T. gondii) infection is relevant to many psychiatric disorders, the fundamental mechanisms of its neurobiological correlation with depression are poorly understood. Here, we show that reactivation of chronic infection by an immunosuppressive regimen caused induction of depressive-like behaviors without obvious sickness symptoms. However, the depression-related behaviors in T. gondii-infected mice, specifically, reduced sucrose preference and increased immobility in the forced-swim test were observed at the reactivation stage, but not in the chronic infection. Interestingly, reactivation of T. gondii was associated with production of interferon-gamma and activation of brain indoleamine 2, 3-dioxygenase, which converts tryptophan to kynurenine and makes it unavailable for serotonin synthesis. Furthermore, serotonin turnover to its major metabolite, 5-hydroxyindoleacetic acid, was also enhanced at the reactivation stage. Thus, enhanced tryptophan catabolic shunt and serotonin turnover may be implicated in development of depressive-like behaviors in mice with reactivated T. gondii.

Infection with Toxoplasma gondii does not elicit predator aversion in male mice nor increase their attractiveness in terms of mate choice.

Behavioral manipulation hypothesis posits that some parasites induce behavioral changes in the host to increase transmission efficiency of the parasite. Protozoan parasite Toxoplasma gondii infecting rats has been widely studied in this context. T. gondii increases attractiveness of infected male rats and reduces innate aversion of rats to cat odor, likely increasing transmission of the parasite by sexual and trophic routes respectively. It is currently unexplored if T. gondii induces gain of male attractiveness in experimental models other than rats. Here we show that laboratory infection of two strains of mice does not induce behavioral manipulation. Moreover, T. gondii infection results in reduction of male attractiveness in one of the strains. In agreement with this observation, T. gondii infection also fails to induce reduction in innate aversion to cat odors in mice. Effects of the parasite on mice mate choice are similar to effects of several other parasites in this animal model. Thus, behavioral change induced by the parasite may be specific to the rodent species.

[Effect of Toxoplasma gondii prugniaud strain infection in pregnant mice on the learning ability of the F1 generation].

OBJECTIVE: To study the effect of Toxoplasma gondii prugniaud strain infection on female reproductive toxicity in mice and learning ability of their F1 generation. METHODS: Thirteen ICR mice were each infected intragastrically with 10 T. gondii cysts on the 15th day of pregnancy (late stage pregnancy). 12 mice were treated with physiological saline as control. The time from conception to birth and the number of offspring were recorded. Three mice from each group were sacrificed when pregnant 20 d, placentas from the sacrificed and output stillbirth mice were examined by using histopathology and immunohistochemistry. DNA extraction was performed from placenta tissue, and then T. gondii B1 gene was amplified by PCR. The F1 generation mice from experiment group and control group were tested by Morris water maze test. Statistical analysis on learning and memory ability was made by SPSS 13.0 software. RESULTS: The time from conception to birth in experiment group [(19.2 +/- 1.751)d] was shorter than that in control group [(21.0 +/- 1.732)d] (P < 0.05). No significant difference was found in the number of offspring between experiment group (70) and control group (85) (P > 0.05). Microscopic examination with HE staining showed multiple T. gondii among placental villi, the increase of the number of Hofbauer cells, blood sinus expansion and hyperemia, and visible nucleated erythrocytes. Immunohistochemically, T. gondii antigen was detected in placenta tissue. T. gondii B1 gene was detected in placenta tissue (194 bp). On the third and fourth day of the Morris water maze test, the latency of experiment group [(29.92 +/- 4.28) s, (27.69 +/- 6.23) s] was longer than that of the control [(24.07 +/- 5.32) s, (22.25 +/- 7.94) s] (P < 0.05). In the spatial probe test, the distance across the platform quadrant of experiment group [(384.66 +/- 41.33) cm] was shorter than that of the control [(426.12 +/- 46.48) cm] (P < 0.05). CONCLUSION: T. gondii Prugniaud strain infection in late stage pregnancy of mice may induce reproductive toxicity and affect the learning and memory capability of the F1 generation.

Toxoplasma gondii and cognitive deficits in schizophrenia: an animal model perspective.

Cognitive deficits are a core feature of schizophrenia. Epidemiological evidence indicates that microbial pathogens may contribute to cognitive impairment in patients with schizophrenia. Exposure to Toxoplasma gondii (T. gondii) has been associated with cognitive deficits in humans. However, the mechanisms whereby the parasite impacts cognition remain poorly understood. Animal models of T. gondii infection may aid in elucidating the underpinnings of cognitive dysfunction. Here, we (1) overview the literature on the association of T. gondii infection and cognitive impairment, (2) critically analyze current rodent models of cognitive deficits resulting from T. gondii infection, and (3) explore possible mechanisms whereby the parasite may affect cognitive function.

Congenital infection of mice with Toxoplasma gondii induces minimal change in behavior and no change in neurotransmitter concentrations.

We examined the effect of maternal Toxoplasma gondii infection on behavior and the neurotransmitter concentrations of congenitally infected CD-1 mice at 4 and 8 wk of age when latent tissue cysts would be present in their brains. Because of sex-associated behavioral changes that develop during aging, infected female mice were compared with control females and infected male mice were compared with control males. Only the short memory behavior (distance between goal box and first hole investigated) of male mice congenitally infected with T. gondii was significantly different (P < 0.05) from that of uninfected control males at both 4 and 8 wk by using the Barnes maze test. The other parameters examined in the latter test, i.e., functional observational battery tests, virtual cliff, visual placement, and activity tests, were not significantly different (P > 0.05) at 4 and 8 wk. Concentrations of neurotransmitters and their metabolites (dopamine; 3,4-dihydroxyphenylacetic acid; homovanillic acid; norepinephrine; epinephrine; 3-methoxy-4-hydroxyphenylglycol; serotonin; and 5-hydroxyindoleacetic acid) in the frontal cortex and striatum were not different (P > 0.05) between infected and control mice at 8 wk of age. The exact mechanism for the observed effect on short-term memory in male mice is not known, and further investigation may help elucidate the molecular mechanisms associated with the proposed link between behavioral changes and T. gondii infection in animals. We were not able, however, to confirm the widely held belief that changes in neurotransmitters result from chronic T. gondii infection of the brain.

The role of parasites and pathogens in influencing generalised anxiety and predation-related fear in the mammalian central nervous system.

Behavioural and neurophysiological traits and responses associated with anxiety and predation-related fear have been well documented in rodent models. Certain parasites and pathogens which rely on predation for transmission appear able to manipulate these, often innate, traits to increase the likelihood of their life-cycle being completed. This can occur through a range of mechanisms, such as alteration of hormonal and neurotransmitter communication and/or direct interference with the neurons and brain regions that mediate behavioural expression. Whilst some post-infection behavioural changes may reflect 'general sickness' or a pathological by-product of infection, others may have a specific adaptive advantage to the parasite and be indicative of active manipulation of host behaviour. Here we review the key mechanisms by which anxiety and predation-related fears are controlled in mammals, before exploring evidence for how some infectious agents may manipulate these mechanisms. The protozoan Toxoplasma gondii, the causative agent of toxoplasmosis, is focused on as a prime example. Selective pressures appear to have allowed this parasite to evolve strategies to alter the behaviour in its natural intermediate rodent host. Latent infection has also been associated with a range of altered behavioural profiles, from subtle to severe, in other secondary host species including humans. In addition to enhancing our knowledge of the evolution of parasite manipulation in general, to further our understanding of how and when these potential changes to human host behaviour occur, and how we may prevent or manage them, it is imperative to elucidate the associated mechanisms involved.

Chronic Toxoplasma infection modifies the structure and the risk of host behavior.

The intracellular parasite Toxoplasma has an indirect life cycle, in which felids are the definitive host. It has been suggested that this parasite developed mechanisms for enhancing its transmission rate to felids by inducing behavioral modifications in the intermediate rodent host. For example, Toxoplasma-infected rodents display a reduction in the innate fear of predator odor. However, animals with Toxoplasma infection acquired in the wild are more often caught in traps, suggesting that there are manipulations of intermediate host behavior beyond those that increase predation by felids. We investigated the behavioral modifications of Toxoplasma-infected mice in environments with exposed versus non-exposed areas, and found that chronically infected mice with brain cysts display a plethora of behavioral alterations. Using principal component analysis, we discovered that most of the behavioral differences observed in cyst-containing animals reflected changes in the microstructure of exploratory behavior and risk/unconditioned fear. We next examined whether these behavioral changes were related to the presence and distribution of parasitic cysts in the brain of chronically infected mice. We found no strong cyst tropism for any particular brain area but found that the distribution of Toxoplasma cysts in the brain of infected animals was not random, and that particular combinations of cyst localizations changed risk/unconditioned fear in the host. These results suggest that brain cysts in animals chronically infected with Toxoplasma alter the fine structure of exploratory behavior and risk/unconditioned fear, which may result in greater capture probability of infected rodents. These data also raise the possibility that selective pressures acted on Toxoplasma to broaden its transmission between intermediate predator hosts, in addition to felid definitive hosts.

Predator cat odors activate sexual arousal pathways in brains of Toxoplasma gondii infected rats.

Cat odors induce rapid, innate and stereotyped defensive behaviors in rats at first exposure, a presumed response to the evolutionary pressures of predation. Bizarrely, rats infected with the brain parasite Toxoplasma gondii approach the cat odors they typically avoid. Since the protozoan Toxoplasma requires the cat to sexually reproduce, this change in host behavior is thought to be a remarkable example of a parasite manipulating a mammalian host for its own benefit. Toxoplasma does not influence host response to non-feline predator odor nor does it alter behavior on olfactory, social, fear or anxiety tests, arguing for specific manipulation in the processing of cat odor. We report that Toxoplasma infection alters neural activity in limbic brain areas necessary for innate defensive behavior in response to cat odor. Moreover, Toxoplasma increases activity in nearby limbic regions of sexual attraction when the rat is exposed to cat urine, compelling evidence that Toxoplasma overwhelms the innate fear response by causing, in its stead, a type of sexual attraction to the normally aversive cat odor.

Manipulation of host behaviour by Toxoplasma gondii: what is the minimum a proposed proximate mechanism should explain?

The behavioural manipulation hypothesis posits that parasites can change the behaviour of hosts to increase the reproductive fitness of the parasite. The protozoan parasite Toxoplasma gondii fits this description well. Sexual reproduction occurs in the cat intestine, from which highly stable oocysts are excreted in faeces. Grazing animals, including rodents, can then ingest these oocysts. The parasite has evolved the capacity to abolish the innate fear that rodents have of the odours of cats, and to convert that fear into an attraction. This presumably increases the likelihood of the rodent being predated, thereby completing the parasite's life cycle. The behavioural syndrome produced by T. gondii does not have any precedent in neuroscience research. This is not a case where the normal functioning of fear system have been altered. This is not even the case of the altering of fear towards predator odours, while leaving other kinds of fear intact. This is an unprecedented example of one component of the fear being eliminated (and replaced by a novel attraction), while appearing to leave other domains unchanged. An understanding of the neurobiological effects of T. gondii is beginning to emerge. One possibility is T. gondii's preferential localisation to, and effects within the amygdala; this is particularly intriguing, given the role of this brain structure in the normal fear response. Obviously, far more must be understood, and the unique behavioural effects of T. gondii put very demanding constraints on any hypothesis we formulate to explain proximate neurobiological mechanisms.

Toxoplasma gondii strain-dependent effects on mouse behaviour.

Toxoplasma gondii reportedly manipulates rodent behaviour to increase transmission to its definitive feline host. We compared the effects of mouse infection by two Type II strains of T. gondii, Prugniaud (PRU) and ME49, on attraction to cat odour, locomotor activity, anxiety, sensorimotor gating, and spatial working and recognition memory 2 months post-infection (mpi). Attraction to cat odour was reassessed 7 mpi. At 2 mpi, mice infected with either strain exhibited significantly more attraction to cat odour than uninfected animals did, but only PRU-infected mice exhibited this behaviour 7 mpi. PRU-infected mice had significantly greater body weights and hyperactivity, while ME49-infected mice exhibited impaired spatial working memory. No differences in parasite antibody titres were seen between PRU- and ME49-infected mice. The present data suggest the effect of T. gondii infection on mouse behaviour is parasite strain-dependent.

The effects of toxoplasma infection on rodent behavior are dependent on dose of the stimulus.

Parasite Toxoplasma gondii blocks the innate aversion of rats for cat urine, putatively increasing the likelihood of a cat predating a rat. This is thought to reflect an adaptive behavioral manipulation, because toxoplasma can reproduce only in cat intestines. While it will be adaptive for the parasite to cause an absolute behavioral change, fitness costs associated with the manipulation itself suggest that the change is optimized and not maximized. We investigate these conflicting suggestions in the present report. Furthermore, exposure to cat odor causes long-lasting acquisition of learnt fear in the rodents. If toxoplasma manipulates emotional valence of cat odor rather than just sensory response, infection should affect learning driven by the aversive properties of the odor. As a second aim of the present study, we investigate this assertion. We demonstrate that behavioral changes in rodents induced by toxoplasma infection do not represent absolute all-or-none effects. Rather, these effects follow a non-monotonous function dependent on strength of stimulus, roughly resembling an inverted-U curve. Furthermore, infection affects conditioning to cat odor in a manner dependent upon strength of unconditioned stimulus employed. Non-monotonous relationship between behavioral manipulation and strength of cat odor agrees with the suggestion that a dynamic balance exists between benefit obtained and costs incurred by the parasite during the manipulation. This report also demonstrates that toxoplasma affects emotional valence of the cat odor as indicated by altered learned fear induced by cat odor.

[Effect of chronic Toxoplasma infection on the spatial learning and memory capability in mice].

OBJECTIVE: To investigate the effect of chronic infection of Toxoplasma gondii on the spatial learning and memory capability in mice. METHODS: Toxoplasma tachyzoites (RH strain) were reanimated at 37 degrees C after 15 days' storage at -20 degrees C, and injected intraperitoneally to mice of the experimental group each with 7.7 x 10(5). Normal saline was given to the control group, 0.5 ml per mouse. Two months later, all mice were tested in the Morris Water Maze. Smears of the mice brain homogenate and pathological sections were examined. RESULTS: (1) The density of cysts in the brain homogenate was 15/HP, and there was no evident pathological change in the hippocampus and adjacent areas of mice in the brain in the experimental mice. (2) Latency to platform, cumulative distance to the platform, total distance traveled in both experimental and control groups decreased significantly with the increase of training days (P < 0.01). The latency and cumulative distance in experimental group were significantly longer than that of the control group (P < 0.01). (3) The searching strategy of mice in the experimental group was significantly different from that of the control group. CONCLUSION: Toxoplasma tachyzoites can induce chronic infection in mice and the infection can damage at some extent the spatial learning and memory capability of mice.

A decade of discoveries in veterinary protozoology changes our concept of "subclinical" toxoplasmosis.

One of the most compelling topics to emerge from the last decade of veterinary protozoology is disease caused by a zoonotic pathogen, Toxoplasma gondii, in otherwise healthy people. These findings may catch the health professions by surprise, because veterinary and medical courses and textbooks typically emphasize that T. gondii infections are subclinical, unless acquired in utero or the patient has a serious immunosuppressive condition. Nevertheless, numerous reports in the last decade associate toxoplasmosis with lymphadenopathy, fever, weakness and debilitation, ophthalmitis, and severe multisystemic infections in people who do not have immunosuppressive conditions. Toxoplasmosis in rodents causes altered behavior, and similar mental aberrations are coming to light in humans; recent studies associate T. gondii infection with personality shifts and increased likelihood of reduced intelligence or schizophrenia. These conditions reduce the quality of life of individuals, and may exact a significant economic burden upon society. Of course, toxoplasmosis continues to cause serious conditions in AIDS patients and congenitally infected people, as well as abortions and encephalitis in domestic and wild animals. Environmental contamination is heavy enough to extend into marine wildlife. It is time for the health professions to amend teaching curricula regarding T. gondii. Veterinary parasitologists should lead the way in developing methods to reduce the prevalence of T. gondii in food animals. Public health policies should prohibit the practice of allowing pet cats to roam. Organizations and individuals that feed feral cats are unwittingly contributing to the dissemination of T. gondii, by sustaining artificially dense populations of a definitive host of this protozoal parasite.

The effect of Toxoplasma gondii and other parasites on activity levels in wild and hybrid Rattus norvegicus.

Using both correlational and experimental evidence, the relationship between parasite load and host activity was assessed in brown rats, Rattus norvegicus. Two hypotheses were tested--(1) that parasites with indirect life-cycles, involving transmission between a prey and its predator, will alter the activity of the intermediate host so as to increase its susceptibility to predation by the definitive host and (2) that activity levels in parasitized rats would be increased rather than decreased. Four groups of rats (n = 140) were examined. One group (n = 50) were wild brown rats trapped from 3 UK farmsteads, with naturally occurring parasites. The others were purpose-bred wild/laboratory hybrid rats with experimentally induced parasitic infections of either (n = 15) adult-acquired or (n = 15) congenitally-acquired Toxoplasma gondii (an indirect life-cycle parasite), or (n = 15) Syphacia muris (a direct life-cycle parasite). Uninfected hybrid rats ( n = 45), matched for sex, age and weight, served as controls. Rats were housed individually in outdoor cages, and their activities were recorded on video-tapes for 6 non-consecutive 10 h nights. Exercise wheels were also available for the hybrid rats. Out of 6 parasite species detected in the wild rats, T. gondii was the only one which required predation by a definitive host to complete its life-cycle, and was also the only parasite to be associated with higher activity levels in infected than uninfected rats. Hybrid rats infected with T. gondii were also more active than those uninfected, whereas there were no differences in activity levels between S. muris infected and uninfected rats. This study shows that the indirect life-cycle parasite T. gondii can influence the activity of its intermediate host the rat. I suggest that this may facilitate its transmission to the cat definitive host.

Effect of Toxoplasma gondii upon neophobic behaviour in wild brown rats, Rattus norvegicus.

The effect of Toxoplasma gondii on neophobic behaviour (the avoidance of novel stimuli) was assessed in four groups of wild rats with naturally occurring Toxoplasma infection. Two groups were placed in individual cages and tested in a series of experiments which examined the effect of Toxoplasma on the rat's reaction to 3 food-related novel stimuli (odour, food-container, food). A trappability study was performed on the other two groups to test whether Toxoplasma had an effect on probability of capture. The results show that low neophobia was significantly associated with positive Toxoplasma titres in 3 out of 4 groups. We suggest that differences between infected and uninfected wild rats arise from pathological changes caused by Toxoplasma cysts in the brains of infected rats. Such behavioural changes may be selectively advantageous for the parasite as they may render Toxoplasma-infected rats more susceptible to predation by domestic cats (the definitive host of Toxoplasma) and, as a side-effect, more susceptible to trapping and poisoning during post control programmes.