Cannabis can help you see in the dark as the drug makes retina cells more sensitive to light, say researchers
Tests on stoned tadpoles gives scientific proof of claims fishermen can steer in the dark after smoking joints
CANNABIS could help people see in the dark - because it boosts the cells at the back of the eye that detect light.
The drug has an effect on ganglion cells in the retina which makes them more sensitive, a study reveals.
Scientists have previously found examples of cannabis users with enhanced night vision, but this is the first evidence of a cellular mechanism.
Some 25 years ago pharmacologist ME West found Jamaican fishermen who smoked cannabis or drank rum made with leaves and stems of the plant were able to steer their boats even on very dark nights.
Another research team found villagers in the Rif mountains of Morocco also had better night vision after using the drug.
One theory was that the drug relaxes eye muscles, allowing in more light - but experiments proved it in fact causes the pupils to constrict.
It was also thought the psychoactive chemical ingredients - called cannabinoids - may have an effect on the visual cortex area of the brain that controls sight.
Now the show the effect is more direct and cannabinoids actually boost the cells that detect light as it enters the eye.
Researchers from the US and Canada investigated the response of tadpoles of African clawed toads.
Because the tadpoles are transparent, the team was able to conduct experiments they could not carry out on humans or other animals.
The creatures also have a natural aversion to moving dark spots and will swim away from them.
Researchers gave them synthetic and natural cannabinoids and used special software to track their movements and test their avoidance responses.
In normal light their was no difference between the tadpoles that had the drug and sober tadpoles.
But in the dark, stoned tadpoles were significantly better at avoiding the dark spots than untreated ones.
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In a separate experiment, the scientists applied a synthetic cannabinoid to tadpole eye tissue in a petri dish.
Tiny electrodes measured how retinal ganglion cells responded to light. The drug made the cells more sensitive, increasing the rate at which they fired to both bright and dim light stimuli.
Closer investigation showed cannabinoids inhibit a protein called NKCC1, reducing the concentration of chloride ions inside retinal ganglion cells and making them more excitable and more sensitive to light.
It is hoped the findings could pave the way for treatments for human diseases such as retinitis pigmentosa and glaucoma, which cause blindness by killing off cells in the retina.
In theory cannabis could slow down degenerative eye diseases and improve patients' vision.
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