APP and Alzheimer disease: In vivo studies have demonstrated that GLP-1R, GLP-1R/GIPR, or GLP-1R/GIPR/glucagon receptor agonists enhanced the hippocampal (Park et al., 2021) or neocortical (Ohtake et al., 2014) BDNF expression in WT mice, while restoring BDNF levels in the hippocampus of APP/PS1 mice (Tai et al., 2018), 3 × Tg and 5xFAD AD animal models (Park et al., 2021) as well as the SNpc and striatum of MPTP-treated rodents (Ji et al., 2016; Lv et al., 2021).