The active component of the marijuana plant Cannabis sativa, Δ
produces numerous beneficial effects, including analgesia, appetite stimulation and nausea reduction,
in addition to its psychotropic effects. THC mimics the action of endogenous fatty acid derivatives,
referred to as endocannabinoids. The effects of THC and the endocannabinoids are mediated largely
by metabotropic receptors that are distributed throughout the nervous and peripheral organ systems.
There is great interest in endocannabinoids for their role in neuroplasticity as well as for therapeutic
use in numerous conditions, including pain, stroke, cancer, obesity, osteoporosis, fertility,
neurodegenerative diseases, multiple sclerosis, glaucoma and inflammatory diseases, among others.
However, there has been relatively far less research on this topic in the eye and retina compared with
the brain and other organ systems. The purpose of this review is to introduce the “cannabinergic”
field to the retinal community. All of the fundamental work on cannabinoids has been performed in
non-retinal preparations, necessitating extensive dependence on this literature for background.
Happily, the retinal cannabinoid system has much in common with other regions of the central
nervous system. For example, there is general agreement that cannabinoids suppress dopamine
release and presynaptically reduce transmitter release from cones and bipolar cells. How these effects
relate to light and dark adaptation, receptive field formation, temporal properties of ganglion cells
or visual perception are unknown. The presence of multiple endocannabinoids, degradative enzymes
with their bioactive metabolites, and receptors provides a broad spectrum of opportunities for basic
research and to identify targets for therapeutic application to retinal diseases.