Fig. 6. ³H-PIB binding experiments with mixtures of AD and ND cortical homogenates.

To detect the potential presence of a diffusible element in AD1 cortical tissue that inhibits PIB binding in vitro, we incubated 1.0nM ³H-PIB with 1:1 mixtures of cortical homogenates from a typical PIB-sensitive AD case (AD2) and the PIB-refractory case AD1. We did not identify an inhibitory or synergistic effect on PIB binding in either the temporal or occipital cortical homogenates. Rather, the quantity of PIB binding to mixed homogenates was approximately the sum of total PIB binding to each individual homogenate. Similar results were seen when 1.0nM ³H-PIB was incubated with mixtures of temporal and occipital cortical homogenate from AD2 and a nondemented control case (ND2) that alone exhibited negligible high-affinity PIB binding.