Reciprocal moderation by Toxoplasma gondii seropositivity and blood phenylalanine – tyrosine ratio of their associations with trait aggression

Abstract

<jats:title>Abstract</jats:title><jats:p>We previously reported that trait aggression, proposed as an endophenotype for suicidal behavior, is positively associated with <jats:italic>Toxoplasma gondii</jats:italic> (<jats:italic>T. gondii</jats:italic>) seropositivity in females, but not in males. Additionally, older males seropositive for <jats:italic>T. gondii</jats:italic> had lower scores on measures of trait aggression, including self-aggression. Trait aggression may be influenced by dopaminergic signaling, which is known to be moderated by gender and age, and potentially enhanced in <jats:italic>T. gondii</jats:italic> positives through the intrinsic production of dopamine by the microorganism. Therefore, we investigated associations between trait aggression and interactions between <jats:italic>T. gondii</jats:italic> enzyme-linked immunoabsorbant assay (ELISA) IgG titer-determined seropositivity and high-performance liquid chromatography- (HPLC-) measured blood levels of dopamine precursors phenylalanine (Phe), tyrosine (Tyr), and their ratio in a sample of 1000 psychiatrically healthy participants. Aggressive traits were assessed using the questionnaire for measuring factors of aggression (FAF), the German version of the Buss-Durkee hostility questionnaire. We found that 1) the decrease in trait aggression scores in <jats:italic>T. gondii</jats:italic><jats:italic>-</jats:italic>positive older males was only present in individuals with a low Phe:Tyr ratio, and 2) that there was a positive correlation between Phe:Tyr ratio and total aggression and selected subscales of aggression in <jats:italic>T. gondii</jats:italic>-positive males, but not in <jats:italic>T. gondii</jats:italic>-negative males. These findings point toward a gender-specific reciprocal moderation by Phe:Tyr ratio and <jats:italic>T. gondii </jats:italic>seropositivity of their associations with aggression scores, and lead to experimental interventions geared to manipulating levels of dopamine precursors in selected <jats:italic>T. gondii</jats:italic> positive individuals with increased propensity for aggression.</jats:p>

302. Sleep Onset Insomnia, Daytime Sleepiness and Sleep Duration in Relationship to Toxoplasma gondii IgG Seropositivity and Serointensity

“…The above-mentioned gender-related differences were particularly evident in those with high phenylalanine:tyrosine ratio [79]. There are previous reports of an increased score of trait aggression in infected women compared to uninfected women, being also moderated by the phenylalanine:tyrosine ratio [78,80], and of a significantly lower score in self-control and higher vigilance in infected men vs. noninfected men [81]. Reproductive implications of T. gondii seropositivity have also been reported in rodents, with T. gondii-infected male rats being preferentially chosen as mates over the non-infected males by non-infected female rats, potentially due to changes in testosterone levels [82].…”

Toxoplasma gondii IgG associations with sleepwake problems, sleep duration and timing

“…A high phenylalanine:tyrosine ratio, resulting from inhibition of phenylalanine hydroxylase [67,68], can be the consequence of Th1 activation, one of the central immune mechanisms responsible for containing T. gondii infection in immunocompetent hosts [69]. We recently reported how associations between T. gondii and aggression [70] or impulsivity [71], known to be in part modulated by dopaminergic pathways, interact with plasma peripheral levels of phenylalanine:tyrosine ratios. Independent of dopaminergic mechanisms, as any microbial organism, T. gondii can promote sleep through the induction of the immune system.…”

Sleep onset insomnia, daytime sleepiness and sleep duration in relationship toToxoplasma gondiiIgG seropositivity and serointensity

“…The above-mentioned gender-related differences were particularly evident in those with high phenylalanine:tyrosine ratio [79]. There are previous reports of an increased score of trait aggression in infected women compared to uninfected women, being also moderated by the phenylalanine:tyrosine ratio [78, 80], and of a significantly lower score in self-control and higher vigilance in infected men vs. non-infected men [81]. Reproductive implications of T. gondii seropositivity have also been reported in rodents, with T. gondii- infected male rats being preferentially chosen as mates over the non-infected males by non-infected female rats, potentially due to changes in testosterone levels [82].…”