We previously reported that trait aggression, proposed as an endophenotype for suicidal behavior, is positively associated with Toxoplasma gondii (T. gondii) seropositivity in females, but not in males. Additionally, older males seropositive for T. gondii 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 T. gondii positives through the intrinsic production of dopamine by the microorganism. Therefore, we investigated associations between trait aggression and interactions between T. gondii 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 T. gondii -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 T. gondii-positive males, but not in T. gondii-negative males. These findings point toward a gender-specific reciprocal moderation by Phe:Tyr ratio and T. gondii seropositivity of their associations with aggression scores, and lead to experimental interventions geared to manipulating levels of dopamine precursors in selected T. gondii positive individuals with increased propensity for aggression.

中文翻译：

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弓形虫血清阳性和血苯丙氨酸 - 酪氨酸比率与性状攻击性相关的相互调节

我们之前报道过，作为自杀行为的内表型提出的攻击性特征与弓形虫(刚地弓形虫) 血清阳性在女性中，但在男性中没有。此外，年龄较大的男性血清阳性刚地弓形虫在包括自我攻击在内的特质攻击方面得分较低。特质攻击可能受到多巴胺能信号的影响，多巴胺能信号已知受性别和年龄的调节，并可能在刚地弓形虫通过微生物自身产生的多巴胺产生阳性反应。因此，我们研究了特质攻击性与相互作用之间的关联。刚地弓形虫酶联免疫吸附试验 (ELISA) IgG 滴度测定血清阳性和高效液相色谱法 (HPLC-) 测量了 1000 名精神健康样本中多巴胺前体苯丙氨酸 (Phe)、酪氨酸 (Tyr) 的血液水平及其比例参与者。攻击性特征使用测量攻击因素的问卷 (FAF) 进行评估，该问卷是德国版的 Buss-Durkee 敌意问卷。我们发现 1) 特征攻击性得分的下降刚地弓形虫 -阳性老年男性仅出现在 Phe:Tyr 比率低的个体中，并且 2) Phe:Tyr 比率与总攻击性和选定的攻击性子量表之间存在正相关关系刚地弓形虫-阳性男性，但不是刚地弓形虫- 阴性男性。这些发现表明 Phe:Tyr 比率和刚地弓形虫它们与攻击性分数相关的血清学阳性，并导致实验性干预措施旨在操纵选定的多巴胺前体水平刚地弓形虫积极的个体，攻击倾向增加。