The main active compound found in the marijuana plant, tetrahydrocannabinol, is responsible for its psychotropic effects but also for its numerous beneficial actions such as appetite stimulation, nausea reduction, analgesia, and muscle spasm suppressor. Although cannabis consumption leads to some visual disturbances, the exact role of the endocannabinoid system (ECS) in normal vision is still unknown. Many studies have looked into the localization of this complex system (receptors, ligands, and enzymes) throughout the various components of the visual system of different animal models in order to obtain clues about its role. In fact, the retina, optic nerve, dorsal lateral geniculate nucleus, and visual cortices all express parts of the ECS. Manipulating this system pharmacologically or genetically has also an impact on visual function. In this book chapter, we provide the current understanding of how the ECS is involved in the functioning of the visual system and special emphasis is put on data obtained in monkeys, representing the most relevant animal model for visual neuroscience research. The mechanisms that control endocannabinoid (eCB) release and activation of cannabinoid receptors are discussed. We also propose a model highlighting the mechanisms involved in the regulation of photopic and scotopic vision taking advantage of the spatial specificity of the eCB signaling system and its physiological activation conditions.
Part of the book: Primates