Circadian-related Dynamics of the Endocannabinoid System in Male Mouse Brain

Abstract Endocannabinoids (eCBs) and related lipids play crucial roles in brain function, including the regulation of circadian rhythms and sleep. To comprehensively map these molecules, we employed liquid chromatography high-resolution tandem mass spectrometry (LC/HRMS/MS) to quantify 78 lipids across 14 families in seven brain areas of male mice at four time points throughout the day (every six hours), and during sleep initiation. We found that most eCBs from the fatty acids (FAs) family, particularly arachidonic acid (AA), were highly abundant in the mouse brain in all brain areas and during the circadian rhythm. High eCBs abundance was shown in deeper brain areas, while temporal differences using the Cosinor analysis revealed 26 eCBs behaving in a circadian rhythm response, with linolenic acid (LnA) being the only lipid to show rhythmicity across all brain areas. Sleep initiation (ZT1) was associated with increased N-acylphosphatidylethanolamine phospholipase D (NAPE-PLD) activity and N-acylethanolamide (NAE) levels in the cortex and hippocampus, while wake extension (WEx) altered 2-monoacylglycerol (2-MAG) metabolism and increased cannabinoid receptor 1 (CB1) expression. These findings provide a detailed lipidomic map of eCBs and related lipids in the male mouse brain, highlighting their area-specific distribution, circadian regulation, and involvement in sleep/wake transitions. Given the link between sleep disruption and neurodegeneration, future studies should investigate whether the observed eCB dysregulation contributes to sleep disturbances in these conditions, and if targeting these pathways offers novel therapeutic strategies. Significant Statement This comprehensive study provides a high-dimensional map of eCBs and related lipids in the male mouse brain, revealing intricate spatial and temporal dynamics highlighting the role of these lipids in regulating fundamental physiological processes such as circadian rhythm and sleep.