Effect of AAV9-CamKII-NPC1 treatment in the CA3 hippocampus and layer V neocortex of Npc1-/- mice. (A–R) Immunohistochemical imaging of mouse Npc1 or human NPC1 protein (red) in the hippocampus and Layer V neocortex, co-stained with NeuN (green) and filipin (blue). (A–F) Endogenous Npc1 expression in the Npc1+/+ mouse, with NeuN stain removed in (B,D,F) to better show the neuronal Npc1 or NPC1 expression and magnified images of Layer V neocortex (C,D) and CA3 hippocampus (E,F). (G–L) Endogenous expression of Npc1 or NPC1 protein in the Npc1-/- mouse, with NeuN stain removed in (H,J,L) to better show the lack of Npc1 or NPC1 and high level of intracellular filipin inclusions, with magnified images of Layer V neocortex (I,J) and CA3 hippocampus (K,L). (M-R) NPC1 expression in the Npc1-/- mice injected with AAV9-CamKII-NPC1. NeuN stain removed in (N,P,R) to better show the presence of NPC1 in some neurons and the reduced level of intracellular filipin inclusions, with magnified images of Layer V neocortex (O,P), and CA3 hippocampus (Q,R). Quantification of filipin and Npc1 or NPC1 mean pixel intensity of the neuronal cell body in Layer V neocortical neurons (S, T) and CA3 hippocampal neurons (U, V), data expressed as mean ± S.E.M. A.U. = arbitrary units. * P < 0.05, **P < 0.01, ****P < 0.0001, one-way ANOVA with Tukey’s post-test.