Turning conventional wisdom on its head, researchers have found that cannabinoids, the active agent in marijuana, may improve low-light vision of vertebrates by sensitising retinal cells.
The experiment was conducted in tadpoles and it is too early to say if cannabinoids have the same effect on human vision, but there is anecdotal evidence in scientific literature of cannabis ingestion improving night vision of Moroccan fishermen, the study pointed out.
"Our work provides an exciting potential mechanism for cannabinoid regulation of neuronal firing, but it will obviously be important to confirm that similar mechanisms are also at play in the eyes of mammals," said the paper's senior author Ed Ruthazer, Professor at Montreal Neurological Institute of McGill University in Canada.
The researchers used a variety of methods to test how tadpoles react to visual stimuli when they have been exposed to increased levels of exogenous or endogenous cannabinoids.
They found that, contrary to what they expected, activating cannabinoid signaling in tadpoles actually increased the activity in their retinal ganglion cells (RGCs), which are responsible for transmitting information about light detection from the eye to the brain.
Previous studies found that cannabinoids typically work to reduce neurotransmission, not increase it.
"Initially you distrust yourself when you see something that goes against widely held ideas, but we tried the experiment so many times, using diverse techniques, and it was a consistent result," Ruthazer said.
What the researchers found is that one class of cannabinoid receptor, known as CB1R, plays a role in the suppression of chloride transport into the retinal cells.
When the receptor is activated, chloride levels are reduced, which hyperpolarises the cell, making it able to fire at higher frequencies when stimulated.
For the tadpoles, this meant they were able to detect dimmer objects in low light than when they had not been exposed to increased levels of cannabinoids.
The findings were published in the journal eLife.