Amyloid-β injection in rat amygdala alters tau protein but not mRNA expression

Previously we demonstrated local and distant changes in tau protein imnnunoreactivity reminiscent of those seen in Alzheimer's disease (AD) following a unilateral injection of amyloid-beta (A beta)(25-35) into the rat amygdala. To explore the relevance of these findings to AD, we compared the effects of A beta(1-42) to those of A beta(25-35). Injections of both A beta(1-42) and A beta(25-35) into rat amygdala resulted in increased tau-2 immunolabeling in neurons. To determine whether these alterations were due to changes in the expression of tau, we measured tau protein expression by Western blotting and tau mRNA isoform expression by the reverse transcription-polymerase chain reaction in the amygdala, hippocampus, and cerebellum following a unilateral injection of A beta(25-35)-treated (59-69 kDa) compared to the vehicle-treated (67-72 kDa) animals 8 days following treatment. There were no changes in tau mRNA expression in any brain region examined. In this model, just as in AD, there is an increase in tau protein levels without a change in tau mRNA expression, suggesting that A beta peptides may influence tau protein stability in both the rat and the human brain. (C) 2000 Academic Press.