Leptin receptor signaling is required for normal hippocampal spine formation in vivo. Hippocampal slices were prepared from P28 to P32 wild-type (WT) or db/db mutant mice. CA1 and CA3 neurons were filled with lucifer yellow to visualize spine density. Representative images (A) and average spine and filopodia densities (B) of WT and db/db mice are shown. Data were analyzed using Student t tests (±SEM; *, P < .05; **, P < .01).