Figure 3.

Insulin and Aβ proteolysis in primary neurons of WT control and GK rats. Primary neurons from two GK and two WT postnatal day 0 litters (each litter containing seven to eight pups) were incubated with 40 pmol/L of radiolabeled substrate, and degradation was quantified by the TCA assay. Bars represent the mean degradation for the 6-hour time points. A: ¹²⁵I-insulin degradation by neurons 17 to 19 days in vitro. Bars represent means ± SEM of seven to eight determinations (160,000 and 80,000 cells/cm² cultures from each litter in two independent assays) after normalization to the mean WT percent degradation for each culture density, allowing combination of the two data sets. *, P = 0.005. B: ¹²⁵I-Aβ_1-40 degradation and inhibition by insulin by neurons 9 to 11 and 19 to 21 days in vitro. Degradation assays were performed in the presence and absence of 10 μmol/L insulin in the medium. Bars represent means ± SEM of 9 to 10 determinations (160,000 and 80,000 cells/cm² cultures from each litter in two to three independent assays) after normalization to the mean WT percent degradation for each culture density, allowing combination of the data sets; **, P < 0.001for difference between WT and GK degradation).