GRM1 and cystic fibrosis: Proper formation of parallel fiber (PF) to PC synapses is a prerequisite for the late phase of CF elimination (Hashimoto, Yoshida, et al. 2009), and the neural activity along the mossy fiber‐granule cell‐PF circuit is considered to activate mGluR1 at PC dendrites (Nakayama et al. 2024).