Thursday, June 08, 2017

How farming made us all crazy

Let's make people crazy.
Blame it on your cat. Robbie Rae, a lecturer in genetics at Liverpool John Moores University, explains:
When we learned how to farm and select strains of crops that grew best in certain environments, we sometimes made a surplus that could be stored for the future. This brought wild mice and rats and with them cats and a hidden danger: the protozoan parasite, Toxoplasma gondii. 
This parasite can’t complete its lifecycle in humans, but we can be infected by it through coming into contact with cat faeces (or eating uncooked meat). The percentage of people estimated to be infected worldwide is between 30 and 40%. France has an infection level of a staggering 81%, Japan 7%, and the US 20%. 
T. gondii does strange things to rats and mice to make sure they come into contact with cats. They lose their inhibition of cats and cat urine. They become more exploratory and spend more time in daylight. But even stranger things happen when humans inadvertently come into contact with T. gondii. Men are more likely to be in car crashes due to riskier behaviour. They also are more aggressive and more jealous. 
Women, meanwhile, are more likely to commit suicide. It has even been suggested that T. gondii could potentially be involved in dementia, bipolar disorder, obsessive-compulsive disorder and autism. There is even evidence from more than 40 studies that people suffering from schizophrenia have elevated levels of IgG antibodies against T. gondii. 
So how does this tiny organism cause such extreme reactions? The full answer is still to be discovered but there are tantalising results that show it influences the levels of neurotransmitters such as dopamine. Cysts (bradyzoites) are found throughout the infected brain in clumps or individually in specific places such as the amygdala, which has been shown to control fear response in rats. 
Interestingly, an imbalance in dopamine levels is thought to be a characteristic of people that have schizophrenia. Analysis of the T. gondiigenome has discovered two genes that encode tyrosine hydroxylase, an enzyme that produces a precursor to making dopamine, called L-DOPA. And there is experimental evidence to support how this might go on to affect behaviour. Primarily, dopamine levels are high in infected mice and their T. gondii-related behaviour can be reduced if the antagonist of dopamine (haloperidol) is administered.
Bet you'll never think about the fear response in rats the same way again.

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