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31 Pathological anxiety is thought to reflect a maladaptive state characterized by exaggerated 32 fear. Naturally occurring perturbations that reduce fear can be crucial in the search for new 33 treatments. The protozoan parasite Toxoplasma gondii invades rat brain and removes fear of 34 rats for cat odors, a change believed to be parasitic manipulation of host behavior aimed at 35 increasing parasite transmission. It is likely that mechanisms employed by Toxoplasma 36 gondii can be used as a heuristic tool to understand possible means of fear reduction in 37 clinical settings. Male Long-Evans rats were infected with Toxoplasma gondii and compared 38 with sham-infected animals 8 weeks post-infection. Amount of circulating plasma 39 corticosterone and dendritic arborization of basolateral amygdala principal neurons were 40 quantified. Previous studies have shown that corticosterone, acting within the basolateral 41 amygdala, enhances the fear response to environmental stimuli. Here we show that 42 Toxoplasma gondii infection causes a dendritic retraction in basolateral amygdala neurons. 43 Such dendritic retraction is accompanied by lower amount of circulating corticosterone both 44 at baseline and when induced by an aversive cat odor. The concerted effects of parasitism on 45 two pivotal physiological nodes of fear response provide an animal model relevant to stress 46 hormones interaction with amygdalar plasticity. 47