Objective     To investigate change of myelin proteolipid protein (PLP) expression

myelin structures

central conductive function and the relationship among them in aged rats.      Methods     Eighteen rats aging 18-24 months and 18 at 6-7 months were subjected. Immunohistochemistry was applied to detect the expressive changes of PLP. LEICA QWIN image analytical system was used to show integrated optical density (IOD) of PLP immunostaining. Transmission electron microscopy (TEM) was used to observe the ultrastructural changes of white matter in rats

such as myelin sheath and axon. The conductive latency of perforant pathway was recorded by electrophysiological methods to evaluate central conductive function of forebrain regions in rats.      Results     Immunohistochemistry showed PLP was positive expressed in the striatum

callosum

anterior commissure

subcortex regions in 2 groups. But the PLP expression was significantly decreased in aged group than in young group (P0.01). There were obvious differences in the ultrastructure of white matter. Aged rats had enlarged axons with megamitochondria in them and increased gaps among axon and myelin

separated compact layer

even confused

destructed in myelin sheath. The central conductive latency was increased significantly in aged group than young group (P0.01).      Conclusion     Aged rats have decreased PLP expression

which might be relevant to the morphological and structural changes of myelin sheath

and have certain relation with the decline of conductive function during brain aging.