Immunostaining of insulin receptor β is not rescued in β2m^−/−TAP^−/− neurons by treatment with either soluble β₂m or insulin. A, WT and β2m^−/−TAP^−/− hippocampal neurons (19 DIV) treated with insulin, then fixed and stained for IRβ. Insulin application does not rescue the loss of C19 staining in β2m^−/−TAP^−/− neurons. Scale bar, 50 μm. B, Live WT and β2m^−/−TAP^−/− mouse hippocampal slices incubated with vehicle or soluble insulin, then fixed and stained with IRβ antibodies (C19). Bath application of insulin (bottom) does not rescue the loss of C19 staining in β2m^−/−TAP^−/− neurons. Scale bar, 20 μm. C, WT and β2m^−/−TAP^−/− hippocampal neurons (19 DIV) treated with soluble β₂m, then fixed and immunostained for IRβ. Bath application of β₂m does not rescue the loss of C19 staining in β2m^−/−TAP^−/− neurons. Scale bar, 50 μm.