'Suicidal' rats may offer schizophrenia insights

[dr. what]

linky

Antipsychotic drugs can limit the behavioural abnormalities associated with a parasitic infection called toxoplasmosis in some rats – the condition causes them to become “suicidally” attracted to cats. The findings provide insight into a possible cause of schizophrenia, say the researchers behind the new study.

The results also hint that anti-psychotic medications such as haloperidol – used to control the symptoms of schizophrenia – could serve as much-needed treatments against the dormant stage of toxoplasmosis in humans, says Joanne Webster of Imperial College London, UK, and one of the study team. She adds, however, that “it’s still very much a black box as to how these drugs work” to fight the parasitic infection.

A latent toxoplasmosis infection might produce schizophrenia in humans, according to a theory by Fuller Torrey of the Stanley Medical Research Institute in Maryland, US, and a co-author on the study.

But other experts stress the possibility that genes or even marijuana abuse may predispose a person to this type of disorder. The idea that toxoplasmosis triggers schizophrenia remains “on the fringes”, according to Paul Corry, a spokesperson for the mental illness charity Rethink in London, UK.

Alan Brown of the New York State Psychiatric Institute notes that prenatal exposure to severe toxoplasmosis – often from a parasite found in cat faeces – can disrupt cognitive development in humans. And in a study published in 2005, he and his colleagues found that maternal exposure to the parasite may be a risk factor for schizophrenia.

But Brown adds that linking toxoplasmosis in adults to schizophrenia is still “a radical notion”.

Fatal attraction
Under normal circumstances, a rat steers clear of cats and their odours. But rats infected with the parasite Toxoplasma gondii develop a deadly attraction to the feline scent. This abnormal behaviour often leads them to the mouth of their predator, and allows the parasite to enter and complete its reproductive cycle in the cat.

It was no surprise, then, that in Webster’s recent experiment untreated infected rats chose to spend nearly three times as much time in laboratory containers holding woodchips treated with feline urine than their control counterparts. And the rats given anti-T. gondii drugs spent about 30% less time in the feline-scented area than the untreated infected rats.

But infected rodents given only haloperidol as a treatment similarly spent 28% less time around cat scent than their untreated but infected counterparts. All of the rats had been infected with the parasite in adulthood.

Webster suspects that the antipsychotic drug somehow suppresses replication of the parasite, stemming the development of the fatal feline attraction. She admits that the rodents’ abnormal behaviour is an imperfect model for human schizophrenia, but adds the observed changes in the rodents following haloperidol provides useful insights into the neurobiology of cognitive disorders.

She adds that more research is necessary to explore the possible link between toxoplasmosis and schizophrenia. And she stresses that the infection is common – affecting an estimated 50% of the UK population – so it could not trigger psychosis in all people carrying the parasite: “We don’t want to be scare-mongering.”

Journal reference: Proceedings of the Royal Society B (DOI: 10.1098/rspb.2005.3413)

[wolveraptor]

She adds, however, that “it’s still very much a black box as to how these drugs work” to fight the parasitic infection.

...do they just randomly throw chemicals into rats and see if they cure some delibitating disease? How could they have known to pick that drug if they didn't have a vague idea of what it was supposed to do?

By the way, I think it's a mistake to class these rats as "suicidal". The rats do not leap into the mouths of cats when infected by the parasite. They simply don't run when the smell of cat fills the air, and their brethren scamper. This makes it easier for the cat to catch the rat, so that the parasite can complete it's lifecycle. In other words, survival instincts are not completely surpressed.