Micro-RNAs constitute a family of small noncoding ribonucleic acids that are 
posttranscriptional regulators of messenger RNA activity. Although micro-RNAs 
are known to be dynamically regulated during neural development, the role of 
micro-RNAs in brain aging and neurodegeneration is not known. This study 
examined micro-RNA abundance in the hippocampal region of fetal, adult and 
Alzheimer's disease brain. The data indicate that micro-RNAs encoding miR-9, 
miR-124a, miR-125b, miR-128, miR-132 and miR-219 are abundantly represented in 
fetal hippocampus, are differentially regulated in aged brain, and an alteration 
in specific micro-RNA complexity occurs in Alzheimer hippocampus. These data are 
consistent with the idea that altered micro-RNA-mediated processing of messenger 
RNA populations may contribute to atypical mRNA abundance and neural dysfunction 
in Alzheimer's disease brain.