CB2 cannabinoid receptor agonist ameliorates novel object recognition but not spatial memory in transgenic APP/PS1 mice

The cannabinoid receptor 2 (CB2R) has been considered as a potential therapeutic target to ameliorate the neuroinflammation and cognitive impairments of Alzheimer's disease (AD). However, there has been little research on the diverse roles of CB2R in regulating different forms of cognitive abilities and underlying neuroinflammatory mechanisms. Thus, the focus of the present study was to investigate the effects of CB2R activation on cognitive abilities, activation and phenotype conversion of microglia, and dendrite complexity. Results showed that CB2R activation normalized the cortex-dependent novel object recognition memory deficit in a novel object recognition test (P < 0.05) and CB2R activation was ineffective for hippocampus-dependent spatial cognitive dysfunction in the Morris water maze test (P > 0.05). Moreover, activation of CB2R did not affect the formation of plaque in either the cortex or hippocampus (P > 0.05). Interestingly, in the cortex but not in the hippocampus of APP/PS1 mice, there was decreased immunofluorescence intensity of Iba1, M1 to M2 microglial phenotype conversion, and restored dendritic complexity after a long treatment period of CB2R agonist (All P < 0.05). Our results demonstrated that CB2R activation exerts a beneficial role in novel object recognition ability concomitant with region-specific regulation in microglia-mediated neuroinflammation and dendritic complexity in AD-model mice.