EFFECTS OF AGE ON THE DENSITY OF PERINEURONAL NETS AND PARVALBUMIN-EXPRESSING INTERNEURONS IN THE RETROSPLENIAL CORTEX OF BEHAVIORALLY CHARACTERIZED MACAQUES

Abstract

Aging takes a toll on all aspects of one’s body, including the brain. Deficits in cognitive function, which are associated with normal brain aging, have been seen in both human and macaque models. While several brain aging models are used, Macaca mulattas are useful in that they do not develop neurodegenerative diseases like humans do while also having many anatomical similarities to humans, allowing for better understanding of the normal brain aging process. In previous literature, it has been suggested that extracellular buffering structures, known as perineuronal nets, play a role in the aging brain, specifically with regards to neuronal protection and plasticity. In order to better understand the effect that these perineuronal nets have on brain aging, the density of these nets, along with the density of the parvalbumin interneurons that the nets preferentially surround, was recorded. To further unpack the impact of these nets on cognition, their density was compared to performance on three common behavioral tasks that test object recognition memory, reward-associated recognition memory, and spatial short-term memory. We observed a greater proportion of parvalbumin (PV) neurons that expressed perineuronal nets (PNNs) in adult monkeys compared to aged monkeys. There were, however, no age differences seen in the density of perineuronal nets, or parvalbumin interneurons within the retrosplenial cortex. With regard to the behavioral data, better object recognition performance was significantly associated with a higher proportion of parvalbumin-expressing interneurons surrounded by perineuronal nets. No significant effects were observed in the other behavioral tasks.