Membranous bodies in the cerebral cortex of aging rats: an electron microscope study.

Large complex membranous bodies are described in the cerebral cortex of adult rats. Although these bodies are not very prevalent, they appear with increasing frequency as the age of the animal increases from 12 to 28 months. The membranous bodies are composed of varying amounts of membranes, cytoplasm and empty vacuoles, and they occur within dendrites which must expand to accomodate them. Some of these bodies measure 9 mu X 13 mu although the median size is about 6 mu in diameter. The membranes which make up the bulk of the complex bodies are assembled into sheets. These sheets are composed of 4 to as many as 100 layers and form undulating circular profiles within dendrites. The individual trilaminar membranes are about 60 A thick and exhibit a distinct tendency to pair within the sheets they form. The source of this great volume of membranes is not known since one finds neither a visible continuity with membranous organelles nor early stages in the formation of these membranous bodies.