To test for involvement of fractalkine and eNOS deficiency in AD-induced collateral rarefaction, we crossed B6.2xTg mice (since 3xTg mice are on a mixed B6-129Sv background) with B6.CX3CR1−/− mice and also with B6.eNOS transgenic mice (the latter have a twofold increase in NO production [32]). This evidence concerns the gene CX3CR1 and Alzheimer disease.