(A) Light microscopy reveals dense RGS14 labeling of pyramidal cell bodies in CA2. By contrast, there is virtually no labeling in CA3. CA1 displays a lighter RGS14 labeling than CA2, which is preferentially localized in the neuropil. (B and C) Electron micrographs of RGS14-positive terminals (Ter) forming asymmetric axo-dendritic (B) or axo-spinous (C) synapses in CA1. In each micrograph, RGS14-immunoreactive axon terminals (Ter), spines (Sp) and dendrites (Den) are indicated, while u.Ter, u.Sp, and u.Den mark unlabeled corresponding elements. The red arrowheads point at asymmetric synapses that involve RGS14-containing terminals, which likely originate from CA2-CA1 axonal projections. (D) Post-synaptic RGS14 labeling in CA1 dendrites and spines.