Alteration of the CNS pathway to the hippocampus in a mouse model of Niemann–Pick, type C disease

► Neurons in CA2&3 regions of the hippocampus decreased dramatically in the NPC−/− mouse. ► Pseudorabies virus positive cell number in CNS hippocampal pathway significantly decreased. ► Changes in the CNS hippocampal pathway may contribute to symptoms of Niemann–Pick disease, type C. Niemann–Pick type C disease (NPC) is an autosomal recessive disorder that results in premature death due to progressive neurodegeneration including dementia. To understand neuronal pathways connecting to the hippocampus, retrograde transneuronal labeling method with Bartha strain of pseudorabies virus (PRV) was employed in 40 NPC+/+, NPC+/− and NPC−/− mice. Immunohistochemistry using polyclonal antibody against PRV and streological counting were used. The number of neurons and synapse in CA2&3 regions of the hippocampus decreased dramatically in the NPC−/− mouse compared to the NPC+/+ or +/− mouse. The number of PRV positive cell was significantly decreased in several regions including the entorhinal and piriform cortex in the NPC−/− mouse. More severely, lateral septal dorsal nucleus, dorsal entorhinal cortex and medial geniculate body showed no positive labeling in the NPC−/− mouse. However, the hippocampus, medial septal and supramammilary nuclei showed increased immunoreactivity in the NPC−/− mouse. Our data suggest that the synaptic loss and discontinuity of the CNS hippocampal pathway may contribute to understanding the mechanism of symptoms and functional disabilities such as memory and learning disturbance in NPC patients.