Le système endocannabinoïde dans la rétine du singe : expression, localisation et fonctions

Cannabis produces a range of psychological and physiological effects on the human body. Cannabinoids are the chemical compounds found in cannabis that activate an endogenous system, termed the endocannabinoid (eCB) system. Reports made in the 1970s have noted that cannabis consumption affects vision. It is therefore suggested that the eCB system is present in the visual system, particularly in the retina. This thesis aims at characterizing the expression, localization, and role of the eCB system in the vervet monkey retina. This animal model has a similar visual system as humans. Using immunohistochemistry methods presented in the article of Annexe I, we have established an experimental protocol to answer our goal. In the first series of four articles, we have characterized the expression and localization of the cannabinoid receptor 1 (CB1R), cannabinoid receptor 2 (CB2R), and the putative cannabinoid receptor GPR55. In Article 1, we have demonstrated that CB1R and a key enzyme of this system, FAAH (fatty acid amide hydrolase), are expressed in the central and peripheral retina, but heavily present in the fovea, the retinal region responsible for high acuity vision. In Article 2, we have localized CB2R in the glial Müller cells and hypothesized a possible mechanism of action of CB2R involving potassium buffering. In Article 3, we found that GPR55 is exclusively expressed in rods and have proposed its role through the modulation of calcium and sodium channels in rods. Given that these three receptors are segregated in the vervet monkey retina, we suggested that they might have distinct roles in retinal physiology. In Article 4, we reported a comparative analysis of the expression of the eCB system components in the retina of rodents, tree shrews (small mammals considered as early primates), and monkeys. This paper provides evidence that the eCB system is differently expressed in the retina of these mammals and suggests a distinctive role of eCBs in visual processing. In the subsequent series of three articles, we confirmed their suggested roles in the retina by using electroretinography (ERG) and intravitreal injections of agonist and antagonist of these receptors. We concluded that they indeed play important roles in the retina. In Article 5, we developed a standard protocol for ERG testing in our animal model and have published an ERG atlas with normalized amplitudes and latency values similar to that of humans, following the guidelines of the International Society for Clinical Electrophysiology of Vision. In Article 6, we showed that blockade of CB1R or CB2R with specific antagonists modifies the ERG, both in photopic and scotopic conditions, which confirms the implication of these receptors in normal retinal function. Finally, in Article 7 (expression of GPR55 in rods only), we confirmed the suggest role of GPR55 in rods by showing that activation or blockade of GPR55 with a specific agonist (lysophosphatidylglucoside) or antagonist (CID16020046) increases or decreases the amplitude of the scotopic ERG waveforms. Taken together, these articles demonstrate that CB1R, CB2R, and GPR55 are differentially expressed in the vervet monkey retina and have distinct roles. This work has also clinical relevance in the way that we have discovered new pharmacological targets that can be used for treatment of many retinal diseases.

Keyphrases: Singes, Retina, Cannabinoid receptor, Immunohistochemistry, Monkey, Tree shrews, Rodents, Electroretinogram