CELL-ADHESION MOLECULE EXPRESSION IN THE REGENERATING RAT FACIAL NUCLEUS

Transection of the rat facial nerve leads to an intrinsic microglial r eaction in the facial nucleus. In the present study, we have examined immunocytochemically the expression of cell adhesion molecules during this process. Resting microglia constitutively expressed the LFA-1alph a and beta chain (CD11a and CD18) in the white matter, rather than in the intact, control facial nucleus. From 24 h after facial nerve trans ection onward, activated microglia showed an increased expression of L FA-1alpha and beta. The immunoreactivity reached its peak around day 7 following axotomy, i.e. at a time when activated microglia are found in a close perineuronal position. In contrast, the expression of the p rincipal ligand of LFA-1, i.e. ICAM-1, remained unchanged following ax otomy, the immunoreactivity being constitutively found on cerebral blo od vessels. Increased LFA-1 expression thus appears to be a general ma rker for microglial activation and might further be involved in the re arrangement of the microglial cytoskeleton upon activation of this cel l.