Chronic suppression of monoacylglycerol lipase restores adult neurogenesis in the septal but not the temporal DG in Ts65Dn mouse model of Down syndrome

Down syndrome (DS) is a genetic disorder characterized by cognitive impairment and varying degrees of changes in emotion-related behaviors. A deficiency in adult hippocampal neurogenesis is among the cellular mechanisms implicated in both abnormalities. Previously, we observed that chronic inhibition of monoacylglycerol lipase (MAGL) with the selective inhibitor JZL184 increased brain levels of the endocannabinoid 2-arachidonoylglycerol (2-AG), improved hippocampal synaptic plasticity and long-term memory, but did not affect anxiety-related thigmotactic behavior in Ts65Dn mice, a genetic model of DS. In this study, we tested the hypothesis that these effects of JZL184 might be associated with changes in adult hippocampal neurogenesis. Ts65Dn mice and their normosomic (2 N) littermates were injected daily for 3 weeks with JZL184 or vehicle, and bromodeoxyuridine (BrdU) was co-administered during the chronic phase of the treatment. BrdU-immunopositive cells were quantified in the septal, medial, and temporal segments of the dentate gyrus (DG). It was observed that both the total number and the density of BrdU-positive cells were significantly reduced in Ts65Dn mice compared to their 2 N littermate controls. Strikingly, JZL184 treatment effects exhibited a profound septo-temporal bias: the BrdU-immunopositive cell density was restored to near control levels in the septal DG (a region presumably linked to cognitive function), but it was largely unaffected in the temporal DG (presumably associated with emotion-related behaviors). These results suggest that chronic MAGL inhibition may provide a targeted region-specific therapeutic strategy for cognitive impairment in Down syndrome, potentially independent of its effects on emotional behavior.