02/05/2026
In November 2024, researchers published the study "Alterations of Endocannabinoid Signaling and Microglia Reactivity in the Retinas of AD-like Mice Precede the Onset of Hippocampal β-Amyloid Plaques" in the Journal of Neurochemistry. The study explored how the retina, often called a "window to the brain," could reveal early signs of Alzheimer’s disease (AD).
The team examined endocannabinoid system (ECS) changes and microglial activity—immune cells of the nervous system—in a mouse AD model before significant brain changes, like β-amyloid plaques, developed. They focused on how these processes could contribute to neuroinflammation and oxidative stress, which are hallmark early events in Alzheimer’s pathology.
To conduct this research, the scientists used a genetically modified mouse model known as Tg2576, mimicking some aspects of Alzheimer’s disease. They focused on 12-month-old mice, a stage when β-amyloid plaques have not yet formed in the brain. Using advanced lab techniques, they analyzed the retinas of these mice for signs of inflammation, changes in ECS components, and oxidative stress markers.
Their work revealed increased numbers of microglia, indicating early retinal inflammation and elevated oxidative stress but no significant neuronal degeneration or retinal thinning.
The study found key alterations in the ECS, particularly in the levels of 2-arachidonoylglycerol (2-AG), an important signaling molecule. The researchers discovered a significant decrease in 2-AG levels in the retinas of AD-like mice, accompanied by an increase in the enzyme MAGL, which breaks down 2-AG. This imbalance, combined with increased levels of the CB2 receptor (linked to inflammation), suggests the ECS is dysregulated in AD.
Interestingly, these changes occurred in the retina before β-amyloid plaques appeared in the brain, reinforcing that the retina reflects early Alzheimer ’s-related changes.
The study also highlighted the role of microglia, immune cells in the retina that can influence inflammation and neuronal health. In AD-like mice, microglia numbers were significantly higher compared to healthy mice, suggesting these cells are reacting to early signs of damage or stress. Despite this, there were no significant changes in glutamate levels—a neurotransmitter often linked to cell damage—indicating that retinal neurons might still function normally at this stage.
These findings support the potential use of the retina as a non-invasive tool to detect AD before brain damage becomes severe. By identifying ECS dysregulation and inflammation as early markers, the study opens the door for exploring new therapies targeting these pathways to slow or prevent AD progression.
-Mike Robinson, founder Global Cannabinoid Research Center, The Researcher OG