This concurs with studies showing that IgG seropositivity reflects exposure, but not chronic infection (Dubey and Frenkel, 1998; Jones and Dubey, 2012). In addition, we examined evidence for microglial response to the parasite across the time course. Our findings demonstrate that while cysts are randomly distributed throughout the forebrain, individual variation in cyst localization, beginning 3 weeks post-infection, can explain individual variation in the effects of on behavior. Additionally, not all infected rats develop cysts in the forebrain, and attenuation of predator odor aversion and changes in anxiety-related behavior are linked with cyst presence in specific forebrain areas. Finally, the immune response to cysts is striking. These data provide the foundation for testing hypotheses about proximate Fulvestrant S enantiomer mechanisms by which alters behavior in specific brain regions, including consequences of establishment of a homeostasis between and the host immune response. 1. Introduction can persist LRP2 chronically in the brain with a remarkably high host survival rate (Montoya and Liesenfeld, 2004). While chronic infection is considered non-pathogenic in immunocompetent human hosts, evidence suggests that engages in manipulation of host biology and behavior (Flegr, 2013; Kaushik infection, one of the most prominent being a disruption of predator odor avoidance behavior (Berdoy on predator odor avoidance behavior are particularly relevant as has an indirect life cycle with transmission occurring though multiple hosts (including rodents), but with sexual reproduction occurring solely in feline predators. Evolutionary pressures in the context of this reproductive restriction may have led to the emergence of parasite-induced biological and Fulvestrant S enantiomer behavioral changes that increase the rates of feline predation of infected rodents, and therefore the reproductive success of the parasite. Such changes appear to include Fulvestrant S enantiomer (but are perhaps not limited to) a disruption of predator odor avoidance behavior. Mechanisms by which alters host behavior are not well understood. Distributed throughout functional neural circuits in the brain, cysts and the host immune response to these cysts represent likely candidates for the underlying causes of behavioral changes. Cyst distributions in mice have been reported to include neural circuits known to regulate fear- or anxiety-related behavior (Berenreiterova cyst presence and location (Afonso infection (Dubey and Frenkel, 1998; Innes, 1997). While immune response has been demonstrated around cysts in chronically infected mice (Kim and Boothroyd, 2005), less is known about the neuroimmune response to cysts in rats over time. Studies in rats have suggested that subtle tropisms in cyst distribution for the amygdala (Vyas manipulation of specific host behaviors is dependent on the location of cysts within the brain and that cyst distribution and behavioral changes are time-dependent functions post-infection. We infected male Long-Evans rats and examined neural distribution of cysts and evidence for microglial activation weekly across a 6 week time course in conjunction with behavioral testing in a predator odor approach-avoidance task, elevated plus maze, and open field arena. Our findings demonstrate that not all on behavior. 2. Methods 2.1 Toxoplasma gondii preparation A Prugniaud type II strain of genetically modified to constitutively express green fluorescent protein (GFP) under GRA2 promoter and firefly luciferase under tubulin promoter (provided by J. Boothroyd Laboratory), was maintained as tachyzoites by passage through human foreskin fibroblast monolayers. Infected fibroblasts were washed with phosphate buffered saline (PBS), resuspended in PBS and syringe-lysed to release tachyzoites. Tachyzoites were counted by haemocytometer for infection dosage. 2.2 Subjects and T. gondii-infection Male Long-Evans rats (10 weeks at start of experiment; Charles River Laboratories) were housed in groups of 3 by treatment and handled weekly for weight monitoring after infection and 2 minutes daily for one week prior to the start of behavioral testing. Health status was monitored throughout the experiment. Rats were randomly assigned to 1 1 of 6 time course treatment groups (1, 2, 3, 4, 5, and 6 weeks post-infection [wpi]; n=18; N=108). For each treatment, 18 rats were each injected with 10 million tachyzoites (intraperitoneally; i.p.) in approximately 0.5 mL sterile PBS on a single day in the appropriate week prior to brain and blood (tissue) collection. An uninfected control group (n=18) was mock-infected with sterile PBS (i.p.) 4 weeks prior to tissue collection. All procedures related to animal maintenance and experimentation were approved by the Stanford University Administrative Panel for Laboratory Animal Care and conformed to the U.S. National Institutes of Health Guide for the Care and Use of Laboratory Animals. All efforts were made to minimize the number of rats used and their suffering. 2.3 Experimental design Starting 9 days prior to tissue collection, rats were tested, one trial each,.