Adult Neurogenesis Occurs in Primate Sensorimotor Cortex following Cervical Dorsal Rhizotomy

Adult neurogenesis remains controversial in the cerebral cortex. We have previously shown in monkeys and rats that reactive neurogenesis occurs in the spinal dorsal horn 6-8 weeks after a cervical dorsal rhizotomy. Here, in three monkeys with the same lesion, we asked whether it also occurs coincidentally in the corresponding primary somatosensory and motor cortex, where significant topographic and neuronal reorganization is known to occur. Monkeys (male Macaca fascicularis) were given 5-bromo-2-deoxyuridine (BrdU) injections 2-3 weeks after the rhizotomy, and were perfused 4-6 weeks later. Cells colabeled for BrdU and five different neuronal markers were observed within the primary somatosensory and motor cortex, and their distributions were compared bilaterally. Cells colabeled with BrdU and the astrocytic marker glial fibrillary acidic protein (GFAP) were also quantified for comparison. A significant number of BrdU/NeuN- and BrdU/calbindin-colabeled cells were observed in topographically reorganized cortex. Small numbers of BrdU/GFAP-colabeled cells were also consistently observed bilaterally, but these cells were never colabeled with any of the neuronal markers. Of the cells colabeled with BrdU and a neuronal marker, at least half had an inhibitory phenotype. However, excitatory pyramidal neurons were also identified with classic pyramidal morphology. Cortical neurogenesis was not observed in other cortical regions. It was also not observed in the primary sensorimotor, prefrontal, or posterior parietal cortex in an additional control monkey (male Macaca fascicularis) that had no surgical intervention. Our findings provide evidence for reactive endogenous cortical neurogenesis after a dorsal rhizotomy, which may play a role in functional recovery.