Abstract
Cat odors induce rapid, innate and stereotyped defensive behaviors in rats at first exposure, a presumed response to the evolutionary pressures of predation. Bizarrely, rats infected with the brain parasite Toxoplasma gondii approach the cat odors they typically avoid. Since the protozoan Toxoplasma requires the cat to sexually reproduce, this change in host behavior is thought to be a remarkable example of a parasite manipulating a mammalian host for its own benefit. Toxoplasma does not influence host response to non-feline predator odor nor does it alter behavior on olfactory, social, fear or anxiety tests, arguing for specific manipulation in the processing of cat odor. We report that Toxoplasma infection alters neural activity in limbic brain areas necessary for innate defensive behavior in response to cat odor. Moreover, Toxoplasma increases activity in nearby limbic regions of sexual attraction when the rat is exposed to cat urine, compelling evidence that Toxoplasma overwhelms the innate fear response by causing, in its stead, a type of sexual attraction to the normally aversive cat odor.
Highlights
A fascinating phenomenon in behavioral biology is the ability of parasites to manipulate host behavior for their own benefit
Given the precipitous evolutionary pressures of both reproduction and predation, these pathways run as direct projections from the olfactory bulb to the limbic system and generate rapid and stereotyped behavioral output
The limbic ‘defensive’ and ‘reproductive’ pathways run in parallel through the medial amygdala and hypothalamus in close anatomical proximity
Summary
A fascinating phenomenon in behavioral biology is the ability of parasites to manipulate host behavior for their own benefit. Toxoplasma requires the cat intestine to reproduce sexually, is shed in cat feces, and must make its way from the ground to another cat host [4] Toxoplasma manages this in part by infecting ground-dwelling rats who, remarkably, begin selectively preferring areas with cat urine [5,6,7]. Infected rats retain normal defensive behavior to non-feline predator odor and normal performance on memory, anxiety, fear and social tasks [6,8]. This specific preference for cat odor is likely an adaptive manipulation by Toxoplasma, increasing infected rat predation rates and facilitating Toxoplasma transmission to the cat
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