This protective role has, however, not remained unchallenged (Herms et al., 1995) and was, for example, not detected when the influence of PrP on LTP was investigated in hippocampal slices dissected from intercrosses of Prnp knockout mice and an AD mouse model, which itself exhibits an LTP defect (Calella et al., 2010). Here, PRNP is linked to Alzheimer disease.