Long-term decreased cannabinoid type-1 receptor activity restores specific neurological phenotypes in the Ts65Dn mouse model of Down syndrome

Intellectual disability is the most prevalent and limiting hallmark of Down syndrome (DS), without any pharmacological treatment available. Neurodegeneration and neuroinflammation are relevant neurological features of DS reaching to early development of Alzheimers disease. Preclinical evidence suggests that the endocannabinoid system, an important neuromodulator on cognition and neuroinflammation, could act as beneficial target in DS. Indeed, cannabinoid type-1 receptor (CB1R) activity was enhanced in the hippocampus of young-adult trisomic Ts65Dn mice, a well-characterized surrogate model of DS. In previous studies, inhibition of CB1R, was able to restore key neurological deficits in this mouse model. To determine the possible clinical relevance of this target, it is mandatory to evaluate the long-term consequences of attenuated CB1R activity and to minimize the possible side-effects associated to this mechanism. We found that CB1R expression was significantly enhanced in the hippocampus brains of aged DS subjects. Similarly, middle-aged trisomic mice showed enhanced CB1R expression. Long-term oral administration of a low dose of the CB1R specific antagonist rimonabant was administered to male and female Ts65Dn trisomic and wild-type mice from the time of weaning to 10 months, an age when signs of neurodegeneration have been described in the model. CB1R inhibition resulted in significant cognitive improvement in novel object-recognition memory in trisomic male and female mice, reaching a similar performance to that of wild-type littermates. Interestingly, this long-term rimonabant treatment modify locomotor activity, anxiety-like behavior, body weight or survival rates. Brain analysis at 10 months of age revealed noradrenergic and cholinergic neurodegeneration signs in trisomic mice that were not modified by the treatment, although the alterations in hippocampal microglia morphology shown by vehicle-treated trisomic mice was normalized in trisomic mice exposed to rimonabant. Altogether, our results demonstrate a sustained pro-cognitive effect of CB1R inhibition at doses that do not produce major side effects that could be associated to an anti-inflammatory action, suggesting a potential interest in this target of to preserve cognitive functionality in DS.