Champalimaud Center for the Unknown, Champalimaud Neuroscience Programme, Av. Brasília, Doca de Pedrouços, 1400-038, Lisboa, Portugal.
University of Perugia, Department of Chemistry, Biology and Biotechnology, Building B, Via del Giochetto, 06122, Perugia, Italy.
Sci Rep. 2017 Oct 23;7(1):13822. doi: 10.1038/s41598-017-13229-y.
Toxoplasma gondii infects a broad range of hosts and can establish chronic infections with the formation of brain cysts. Infected animals show altered risk behaviour which has been suggested to increase capture probability of hosts, and thus enhance parasite transmission. It has been proposed that the ability of Toxoplasma cysts to secrete tyrosine hydroxylase could mediate these behavioural alterations. We tested the involvement of secreted tyrosine hydroxylase, coded by the parasite AaaH2 gene, in the development of alterations in mouse behaviour, by generating an AaaH2 deletion mutant parasite strain and testing its influence on behaviour. We found that both mice infected with wild type or AaaH2 mutant strains showed changes in risk behaviour. We confirmed these findings using factor analysis of the behaviour, which revealed that behavioural changes happened along a single dimension, and were observed in both infected groups. Furthermore, we developed a new behavioural paradigm in which animals are unpredictably trapped, and observed that both groups of infected animals perceive trapping but fail to adjust their behaviour to avoid further trapping. These results demonstrate that parasite-secreted AaaH2 TH is neither necessary for the generation of risky behaviour nor for the increased trappability observed during chronic Toxoplasma infection.
刚地弓形虫感染范围广泛，可以形成脑部囊包，从而建立慢性感染。受感染的动物表现出改变的风险行为，这被认为增加了宿主的捕获概率，从而增强了寄生虫的传播。有人提出，弓形虫囊包分泌酪氨酸羟化酶的能力可能介导了这些行为改变。我们通过生成 AaaH2 缺失突变寄生虫株并测试其对行为的影响，来检测寄生虫分泌的酪氨酸羟化酶（由寄生虫 AaaH2 基因编码）在小鼠行为改变中的作用。我们发现，感染野生型或 AaaH2 突变株的小鼠均表现出风险行为的改变。我们通过行为的因子分析证实了这些发现，该分析表明行为变化沿着单一维度发生，并且在两个感染组中都观察到了。此外，我们开发了一种新的行为范式，其中动物不可预测地被困住，并且观察到两组感染动物都感知到陷阱，但未能调整行为以避免进一步的陷阱。这些结果表明，寄生虫分泌的 AaaH2 TH 既不是产生冒险行为所必需的，也不是在慢性弓形虫感染期间观察到的增加的易捕获性所必需的。
