Apolipoprotein E (apoE), a lipid transporting protein, has been shown to play a vital role in nerve repair and remodeling. Since the olfactory system is in a continuous state of remodeling, the present study tested the hypothesis that apoE is required for normal functioning of the olfactory system. Olfactory function of the wild type (WT) and apoE deficient (apoE KO) mice was assessed by using three standard olfactory tests: 1) the buried food pellet (BFP) test; 2) the odor choice (OC) test; and 3) the odor cued taste avoidance (OCTA) test. The visible food pellet test (VFP) was not used to assess olfactory function, but to rule out lack of motivation to find a buried pellet. ApoE KO mice performed poorly in all the tests as compared to WT mice, except the visible pellet test, in which the apoE KO mice performed better than wild type. ApoE KO mice had significantly longer latency to find the buried pellet than WT mice in the BFP test. In the OC experiment, apoE KO mice were unable to differentiate water from an odorant solution. Furthermore, in the OCTA test, the apoE KO mice were significantly less effective than WT mice at avoiding water containing an odorant and tastant. These data demonstrate that apoE deficiency in apoE KO mice leads to a deficit in olfactory function, suggesting an important role for apoE in the olfactory system
