ANOMALOUS BINDING OF RADIOLABELED OLIGONUCLEOTIDE PROBES TO PLAQUES AND TANGLES IN ALZHEIMER-DISEASE HIPPOCAMPUS

Several reports indicate that Alzheimer disease (AD) brain contains el evated levels of heat shock 70 proteins. To determine the cellular loc alization of the heat shock 70 mRNAs, specific oligonucleotide probes were in situ hybridized to AD and control brains. When oligonucleotide s were in situ hybridized to brain sections with no AD neuropathology, hybridization was cell-specific and prior ribonuclease (RNase) treatm ent of adjacent sections resulted in no hybridization signal. However, in situ hybridization to AD hippocampus resulted in heavy grain depos ition over senile plaques and neurofibrillary tangles. Despite alterin g a number of experimental variables, we observed a similar pattern of grain deposition with most of the oligonucleotides tested, including one oligonucleotide specific for glutamic acid decarboxylase mRNA. In situ hybridization with either an RNA probe for glutamic acid decarbox ylase or an oligonucleotide probe specific for 18S rRNA did not show t his pattern of grain deposition. In control studies a sense hsc70 olig onucleotide showed no grain deposition in either cerebellum or hippoca mpus. Sections from AD hippocampus pretreated with RNase prior to in s itu hybridization demonstrated enhanced grain deposition with the majo rity of probes tested. Anomalous in situ hybridization to AD hippocamp us was usually eliminated by removing formamide from the posthybridiza tion washes, although post-RNase sticking often remained intense. Thes e findings indicate that artifactual probe binding to senile plaques a nd neurofibrillary tangles may complicate the analysis of in situ hybr idization studies using oligonucleotide probes to determine mRNA distr ibution in AD brain.