Discovery of a new role for cannabinoids in vision - Compounds found in marijuana could improve night vision.
Scientists used a variety of methods to test the reaction of tadpoles to visual stimuli while exposed to high levels of exogenous or endogenous cannabinoids. Exogenous cannabinoids are artificially introduced drugs, while endogenous cannabinoids are naturally found in the body.
Contrary to expectations, the activation of cannabinoid signaling in tadpoles has actually increased the activity of retinal ganglion cells (RGCs), which transmit information from the eye to the brain regarding the detection of the light. According to the findings of previous studies, cannabinoids generally have the effect of reducing, not increasing, neurotransmission.
"You first look skeptical when you look at something that contradicts popular ideas. However, we have tried the experiment many times, using various techniques, and it has always resulted in the same result, "says Ed Ruthazer, professor of neurology and neurosurgery at the Montreal Neurological Institute. McGill University, and lead author of the article. "From then on, we had to determine what was happening. The first reaction is to ignore our observations. But the effect was so strong that we knew it was something important. "
The researchers found that a class of cannabinoid receptors, CB1Rs, play a role in suppressing chloride transport in CRGs. When the receptors are activated, the chloride levels decrease, which causes the hyperpolarization of the cell and makes it capable of discharging at higher frequencies when stimulated.
In tadpoles, this meant that they could discern lighter objects in low light, more than when they had not been exposed to increased cannabinoid levels. The team used software developed with Paul Wiseman, a professor of physics and chemistry at McGill, to detect changes in behavior among tadpoles.
It is too early to say that cannabinoids have the same effect on the human eye, but there is empirical evidence in the scientific literature that cannabis ingestion has improved the night vision of Jamaican and Moroccan fishers.
The most interesting fact, according to Professor Ruthazer, is to have discovered a hitherto unknown role for cannabinoids in cell signaling in the brain. Theusage thérapeutique cannabinoids is becoming more accepted by the medical community, which requires more than ever to understand accurately and comprehensively the role of these chemicals in the brain.
"Our work provides an interesting potential mechanism for cannabinoid regulation of neuronal firing. It will of course be important to confirm that similar mechanisms also play a role in mammalian eyes. Although more technically difficult, a similar study should be carried out in the mouse retina or even in cell cultures of the human retina, "adds Professor Ruthazer.
The full article on the study appeared in eLife the August 8 2016. The work was financially supported by the Canadian Institutes of Health Research, the Quebec Research Fund - Health, Epilepsy Canada, and a grant from the FONCER Neuroengineering Training Program of the Natural Sciences and Engineering Research Council.
source: http://www.theneuro.ca/ & https://elifesciences.org