Effect of Healthy Aging on the Cytoarchitecture of Layer V Pyramidal Neurons in the Motor Cortex of Rats: A Golgi Study

ABSTRACT In recent decades, the rate of aging has increased significantly worldwide. Since both cognitive and motor performance decline during aging, they are considered indicators of this stage of normal development. Successful, healthy aging—not associated with pathology—is accompanied by a decline in motor skills due to the underlying anatomical and functional organization of the motor cortex. Deep‐layer V neurons are thought to be the relay that translates afferent information to this cortical region and the organizers of the output of information that generates motor activity. Basal dendritic arborization was studied using the Sholl method, along with dendritic spine density and the amounts of distinct spine types in medial segments of primary dendrites in deep pyramidal neurons of layer V of the motor cortex of young (3–4 months) and aged (22–24 months), male Sprague–Dawley rats. Significant reductions in dendritic arborization and spine density were observed in the aged animals. Each spine type—thin, mushroom, stubby, and wide—existed in lower numbers than in the young animals. Results suggest both a reduction in the integrative capacity of synaptic stimuli by pyramidal cells and a downregulation in the processing of excitatory information. These findings could underlie the decline in the acquisition and maintenance of motor skills during healthy aging.