Implication of the myo-inositol pathway in behavioural alterations of infected threespine sticklebacks

Threespine sticklebacks Gasterosteus aculeatus infected with the tapeworm Schistocephalus solidus display impairments in their anti-predator responses. They also have increased expression of the gene encoding the IMPase 1 enzyme in their brains, which is part of a key step in myo-inositol synthesis. IMPase 1 and myo-inositol levels are the targets of lithium treatment in patients with bipolar disorder. Although promising candidates, we do not know if IMPase 1 and myo-inositol are directly implicated in the changes in risky behaviours measured in Schistocephalus-infected fish. Understanding the molecular mechanisms directly or indirectly involved in these behavioural alterations is crucial to understand the evolution of host-parasite interactions. Here, we increased myo-inositol levels of uninfected fish and inhibited IMPase 1 activity in infected fish to test the prediction that it would decrease and increase their anti-predator behaviour respectively. We found that uninfected fish with increased myo-inositol levels (by injecting exogenous myo-inositol or by inducing endogenous production using an osmotic challenge) did not decrease their anti-predator responses. However, infected fish treated with lithium chloride had some of their anti-predator behaviours restored, but not all. They spent less time swimming close to the surface, showed lowered activity, had a higher latency to feed in a novel environment and spent more time frozen after a predator attack. Our results suggest that the target of lithium treatment is implicated in the risky behaviours of infected fish and supports the idea that the parasite-associated alteration in behaviour has a multifactorial nature. Read the free Plain Language Summary for this article on the Journal blog.

Automated summary

Threespine sticklebacks infected with the tapeworm Schistocephalus solidus display impairments in their anti-predator responses and have increased expression of the IMPase 1 gene. The study found that altering myo-inositol levels and inhibiting IMPase 1 activity had effects on the anti-predator behaviors of infected fish, suggesting a potential role for lithium treatment in parasite-induced behavioral changes.