Hippocampal neurogenesis in adult Old World primates

TLDR

Neurogenesis in the adult hippocampus is well established in rodents and has been reported in species such as tree shrews and marmosets, but has not yet been demonstrated in adult Old World primates. The study aimed to determine whether adult Old World primates generate new hippocampal neurons. Eleven adult Old World monkeys (ages 5–23) were injected with bromodeoxyuridine and the fate of labeled cells was examined at various survival times using neuronal and glial markers. New neurons were identified in the dentate gyrus of young‑adult and middle‑aged monkeys, with fewer astroglial cells, and evidence of neurogenesis, though less robust, was also seen in the oldest monkeys, confirming that adult Old World monkeys produce new hippocampal neurons and may serve as a primate model for studying neurogenesis.

Abstract

The production of new hippocampal neurons in adulthood has been well documented in rodents. Recent studies have extended these findings to other mammalian species, such as tree shrews and marmoset monkeys. However, hippocampal neurogenesis has not been demonstrated in adult Old World primates. To investigate this possibility, we injected 11 adult Old World monkeys of different ages (5–23 years) with the thymidine analog bromodeoxyuridine and examined the fate of the labeled cells at different survival times by using neuronal and glial markers. In the young-adult and middle-aged monkeys, we found a substantial number of cells that incorporated bromodeoxyuridine and exhibited morphological and biochemical characteristics of immature and mature neurons. New cells located in the dentate gyrus expressed a marker of immature granule neurons, Turned On After Division 64 kDa protein, as well as markers of mature granule neurons including neuron specific enolase, neuronal nuclei, and the calcium-binding protein calbindin. Fewer new cells expressed the astroglial marker glial fibrillary acidic protein. Evidence of neurogenesis was observed in the oldest monkeys (23 years) as well, but it appeared to be less robust. These results indicate that the adult brains of Old World monkeys produce new hippocampal neurons. Adult macaque monkeys may provide a useful primate model for studying the functional significance of adult neurogenesis.