Morphological alterations in the occipital cortex of aged rats with impaired memory: a Golgi-Cox study

This study investigated a possible link between morphological alterations of pyramidal neurons in layer V of the occipital cortex and the degree of spatial memory impairment in aged rats. Measurements of cortical thickness, density of dendritic branching, and spine counts were carried out in young adult (5 months old) and aged (26 months old) Long-Evans female rats on Golgi-Cox silver-stained material. Using the water-maze task, well- and poorly performing rats were distinguished statistically on the basis of their reference-memory scores. When subsequently compared with young rats or to aged rats with good performances, the well-performing rats had a reduced cortical thickness and exhibited weaker high-order branching of basal dendrites on their pyramidal neurons. When dendritic spines were counted on a 50-microm-long straight portion of a basal dendrite, no difference was observed between young and aged rats. Our results suggest that structural alterations affecting pyramidal neurons in the occipital cortex of aged rats may contribute to spatial memory impairment. Indeed, in a subpopulation of well-performing aged rats, these structural alterations were less marked than in the population of bad performers.