Voltage-gated CaV2.1 Ca2+ channels play a crucial role in regulating neurotransmitter release, thus contributing to processes such as learning and memory. Despite their recognised importance in neural function, there is limited information on their potential involvement in neurodegenerative conditions such as Alzheimer's disease (AD). Aims: to explore the impact of amyloid-β (Aβ) pathology on the nanoscale compartmentalization of CaV2.1-GABAB in the hippocampus.Methods: We used histoblot and SDS-digested freeze-fracture replica labelling (SDS-FRL) techniques in the CA1 field of the hippocampus.Results: Histoblots showed that the density of CaV2.1 channel was significantly reduced in the hippocampus of APP/PS1 mice in a laminar-dependent manner in 12-months-old APP/PS1 mice. At the ultrastructural level, CaV2.1 was enriched in the active zone of the axon terminals and was present at a very low density over the surface of dendritic tree of the CA1 pyramidal cells. In APP/PS1 mice, the density of CaV2.1 in the active zone was significantly reduced in the strata radiatum and lacunosum-moleculare, while it remained unaltered in the stratum oriens. Double SDS-FRL showed a co-clustering of CaV2.1 channel and GABAB1 receptor in nanodomains (~ 40-50 nm) in wild type mice, while in APP/PS1 mice this nanoarchitecture was absent.Conclusions: these findings suggest that the Aβ pathology-induced reduction in CaV2.1 channel density and CaV2.1-GABAB1 co-clustering may play a role in the synaptic transmission alterations shown in the AD hippocampus.Grant PID2021-125875OB-I00 funded by MCIN/AEI/ 10.13039/501100011033 and “ERDF A way of making Europe”, and Junta de Comunidades de Castilla-La Mancha (SBPLY/21/180501/000064)