Double fluorescent staining for EPOR (red) and NeuN (green) to detect the number of neurons expressing EPOR after TBI. No EPOR-positive neurons were detected in the cortex (a, b, and c) of EPOR-null sham mice. Some neurons expressed EPOR in the wild-type mice (d, e, and f). TBI significantly increased the number of neurons expressing EPOR in the cortex (g), CA3 (h), and CA1 (i) regions in the wild-type mice. EPO treatment increased the number of EPOR-positive neurons in the injured cortex (j), CA3 (k), and CA1 (l) of wild-type mice (scale bars = 50 μm in a–l). (m) The number of EPOR-positive neurons. Data represent mean ± SD (n = 6 for wild-sham mice; n = 8 for wild-saline and wild-EPO mice; n = 6 for null-sham mice; n = 10 for null-saline and null-EPO mice; EPO, erythropoietin; EPOR, EPO receptor; SD, standard deviation).