Robert Sapolsky, whose work on stress I've talked about in a number of posts, is a polymath who maintains a number of quirky interests, one of which is describing a bizzare trick the protozoan Toxoplasma uses to reproduce itself, by infecting the brain of a mouse and altering its limbic system so that the poor mouse is sexually attracted to, rather than repelled by, the smell of cat urine (the protozoan requires the cat to sexually reproduce). The 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.And, since I'm mentioning Sapolsky, and haven't gotten around to passing on another interesting bit from him, here is his commentary on work by Gusquiere et al. showing that the beta male in a baboon troop can end up winning in the end. Here is the NYTimes review of the work.