Using Tg12099(+/−) rats, which do not display overt signs of tauopathy yet express the MAPT*P301S transgene, we unilaterally injected tau fibrils (1 mg/mL) or PBS (vehicle) into the hippocampus and overlying cortex of 2-month-old Tg12099(+/−) rats (Fig. 8a). The gene discussed is MAPT; the disease is tauopathy.