Expression of CD95L and CD95 is also found in the brain at embryonic and early postnatal stages in regions with detectable levels of apoptosis. CD95 expression was detected in the cerebrum, cerebellum and hippocampus (Park et al., 1998). CD95L was also found constitutively expressed in neuroglial cells in the embryonic brain (Shin et al., 2002). The lpr and gld mice have a functionally deficient CD95 receptor and ligand, respectively (Cohen and Eisenberg, 1992). Examination of the neuronal density in the hippocampus of these mice revealed no differences compared to wild-type (wt) animals. Thus, apoptosis in the developing brain does not seem to be controlled by the CD95/CD95L system. Similarly, NSCs express CD95 on their surface, as assessed by fluorescence-activated cell sorter (FACS) analysis. Further, stimulation of CD95 with different doses of ligand and for different periods of time did not induce death of NSCs (Ceccatelli et al., 2004; own unpublished data). We are currently working on the elucidation of the function and downstream signalling of CD95 in NSCs and developing neurons.