Differences in pyramidal cell structure and function in V1 and PFC of young and aging monkeys
Amatrudo, Joseph Michael
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Functional specialization of neocortical regions is influenced strongly by input source, which varies widely. For instance, the primary visual cortex (V1) receives visual input primarily from the lateral geniculate nucleus and functions to process sensory signals, while the prefrontal cortex (PFC) receives input primarily from higher-order association cortices and is involved in higher cognitive function. This difference in inputs and function, has led previous studies to investigate structural differences in corticocortical layer III pyramidal cells from V1 and PFC in the rhesus monkey using cell-filling techniques; these studies reported significantly greater basal dendritic complexity and spine number in cells of PFC. This dissertation confirms and greatly expands these findings, by measuring electrophysiological and morphological properties of layer II/III pyramidal cells from both V1 and PFC via whole-cell patch-clamp recordings in in vitro slices prepared from rhesus monkey cortex and complete 3D neuronal reconstructions. Cells from V1 fire a greater number of action potentials in response to a given stimulus, and demonstrate significantly less dendritic complexity and fewer dendritic spines. Computational modeling of representative V1 and PFC cells demonstrates that while cellular morphology strongly influences functional properties, it does not fully account for the observed functional differences. Next, the effects of normal aging were assessed on layer II/III pyramidal cells of both V1 and PFC. While pyramidal cells of both areas demonstrate morphological alterations with aging, only cells found in PFC demonstrate significantly increased excitability with age. In addition, the current underlying the slow afterhyperpolarization (sIAHP) significantly increases in amplitude with age in layer II/III pyramidal cells of PFC, while it is unchanged in cells of V1. Based on these findings, it is apparent that structural and functional properties of layer II/III pyramidal cells of V1 and PFC differ significantly in young animals. Furthermore, normal aging has a strong impact on the functional properties of pyramidal cells of monkey PFC, but not V1. These differences likely reflect the functional specialization of these regions. The PFC underlies cognition; therefore, the corticocortical pyramidal cells found within PFC are more complex and susceptible to age effects than those found in V1.
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