Tadpoles, night vision, and cannabis.

In Brain Science, Senses and Perception by Brainy Days Ahead

Researchers at the Montreal Neurological Institute probe decades of mysterious reports of an association in fishermen between smoking cannabis (marijuana) and extraordinary night vision. Instead of observing pot-smoking fishermen, they looked to tadpoles of the African clawed toad, Xenopus laevis, which are transparent and therefore amenable to observation. Tadpoles have a natural tendency to avoid dark moving dots. In the dark, tadpoles given the cannabinoid avoided significantly more dots than untreated ones, which only responded to the dots as if by chance. The researchers then used microelectrodes to measure how retinal ganglion cells, whose fibers form the optic nerve, respond to light. The ganglion cells became more sensitive, increasing the rate at which they fired to both bright and dim light stimuli. The sensitivity was due to inhibition of a protein called NKCC1, a co-transporter protein that normally shuttles sodium, potassium, and chloride ions into and out of cells. The concentrations of these ions determine the electrical properties of nerve cells. Bottom line, the experiments showed that cannabinoids reduced the concentration of chloride ions inside the retinal ganglion cells, making them more excitable and more sensitive to light.