Why smokers are paranoid

Paranoia is one of the most unpleasant "side effects" of marijuana. It's also a key experience shared by marijuana smokers and people with schizophrenia. But exactly how does smoking a joint cause the feeling that dark forces are conspiring to do you wrong?
New research in rats may help explain the source of this distress. The study, led by Steven Laviolette at the University of Western Ontario in Canada, involved training rats to fear the scent of either almond or peppermint. The scents were delivered to rats in a cage either with black-and-white striped walls or with black polka dots on a gray background. (The rats were not pre-tested for their taste in interior design.) One scent was accompanied by an electric shock to the rodents' feet, while the other scent was not.
At the same time, researchers experimented with the activity of the CB1 receptors in a certain region of the rats' brains. These cannabinoid receptors are activated by the main psychoactive component of marijuana, THC. In some rats, the scientists blocked CB1-receptor activity; in others, they used a marijuana-like drug to enhance it.
When scientists blocked the CB1 receptors in a region called the basolateral amygdala — which is involved in the processing of fear and emotion — the rats that got strong electric shocks did not learn to fear the associated scent or the cage in which they received it. After getting shocked, they were just as happy as unaffected rats to explore the cage and smell the scent.
When rats were given a drug that enhanced cannabinoid-receptor activity, however, even receiving a minor shock was enough to cause them to freeze with fear when they were later exposed to the cage and its related scent. Without the marijuana-like drug, small shocks did not have the same effect.

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