Structural synaptic remodeling in the perirhinal cortex of adult and old rats following object-recognition visual training.

The ultrastructural features of layer 11 synapses in the perirhinal cortex of adult (4- to 6-month-old) and old (25- to 27-month-old) rats exposed to a six-session object recognition visual training were investigated by morphometric methods. The comparative analysis showed a higher synaptic numeric density, a lower synaptic average area, and a lower percentage of megasynapses (S > 0.5 mu m(2)) in old trained rats versus controls, and a higher percentage of small (S < 0.15 mu m(2)) junctions in adult trained rats versus controls. The more marked synaptic remodeling underlying memory consolidation in the perirhinal cortex of old rats might reflect a pre-existing lower dynamic status.