MORPHOLOGY AND DISTRIBUTION OF ASTROCYTES IN THE MOLECULAR LAYER OF THE DENTATE GYRUS IN NZB BINJ, DREHER, AND C57BL/6J MICE/

Numerous ectopic granule cells are found in the molecular layer of the dentate gyrus in NZB/B1NJ and dreher mutant mice. These ectopic neuro ns occur either singly or in small clusters. In contrast, few ectopic granule cells are seen in the dentate molecular layer of C57BL/6J mice and dreher control littermates. In this investigation we have examine d the morphology, number, and distribution of molecular layer astrocyt es in NZB/B1NJ, dreher homozygotes, dreher littermate controls, and C5 7BL/6J mice to determine the effect of the presence of ectopic granule cells. In the molecular layer of C57BL/6J mice and dreher control lit termates, astrocytes have a typical stellate appearance with processes emanating in all directions. The arborization of astrocytes in areas devoid of ectopic granule cells in NZB/B1NJ mice and dreher homozygote s was similar to that in C57BL/6J mice and dreher control littermates. In contrast, the morphology of astrocytes in the immediate vicinity o f ectopic granule cells or ectopic clusters was distinctly non-stellat e. Furthermore, the somata and processes of these astrocytes occasiona lly appeared to make intimate contact with the ectopic granule cells. A quantitative analysis of the number and distribution of astrocytes i n NZB/BLNJ vs C57BL/6J mice and dreher vs. control littermates indicat ed that these parameters were not altered by the presence of the ectop ic neurons. We conclude that the trophic effects of ectopic neurons on glial cells can affect the growth and orientation of astrocytic proce sses without a concomitant effect on glial cell number. (C) 1994 Wiley -Liss, Inc.