Approaches to investigate adult oligodendrocyte progenitor cells (OPCs) by targeted cell ablation in the rodent central nervous system have been limited by methodological challenges resulting in only partial and transient OPC depletion. We have developed a novel pharmacogenetic model of conditional OPC ablation, resulting in the elimination of 99.7% of all OPCs throughout the brain. By combining recombinase-based transgenic and viral strategies for targeting of OPCs and ventricular-subventricular zone (V-SVZ)-derived neural precursor cells (NPCs), we found that new PDGFRα-expressing cells born in the V-SVZ repopulated the OPC-deficient brain starting 12 days after OPC ablation. Our data reveal that OPC depletion induces V-SVZ-derived NPCs to generate vast numbers of PDGFRα+/NG2+ cells with the capacity to migrate and proliferate extensively throughout the dorsal anterior forebrain. Further application of this novel approach to ablate OPCs will advance knowledge of the function of both OPCs and oligodendrogenic NPCs in health and disease.

ObjectiveTo present four patients seen over a five‐year period who developed severe protracted encephalitic illnesses but whose outcomes were favourable. Clinical featuresOf the four patients, aged 18, 22, 34 and 19, three presented with acute psychosis, and all had a prolonged clinical course requiring intensive care management. One patient had residual generalised seizures and the other three recovered fully. No infective or toxic agent could be identified but viral encephalitis was considered most likely. OutcomeDespite the protracted courses, the outcomes were favourable. This is in contrast to the generally poor outcomes in encephalitis caused by established infective agents such as herpes simplex type 1. ConclusionsWhen the aetiology and hence the natural history of the encephalitis is unknown, long‐term intensive support is appropriate.