In situ hybridization--visualization and quantitation of genetic expression in mammalian brain.

In situ hybridization techniques have been developed that quantitate the relative levels of specific mRNAs in individual cell types of a heterogeneous tissue, the mammalian brain. Here, we discuss those special procedures and precautions necessary for hybridizing radiolabeled probes to developing and adult brain mRNAs. The probes discussed include double-stranded recombinant DNA, as well as single-stranded DNA, RNA, and polyuridylate. We detail the procedure for determining the relative numbers of hybrids formed and computing the ratio of specific mRNAs to total polyadenylated mRNA and discuss the importance of this ratio for comparison of relative levels of specific mRNAs within and among cell types in an individual brain or between brains.