Simultaneous detection of two messenger RNAs in the central nervous system: a simple two-step in situ hybridization procedure using a combination of radioactive and non-radioactive probes

We present here a method enabling the simultaneous detection of two messenger RNAs in tissue sections by use of a two-step in situ hybridization procedure. Tissue sections were hybridized with a radioactive probe and coated with emulsion. The emulsion was processed for development, fixed, and a second hybridization was performed through the emulsion with a biotinylated probe subsequently revealed with streptavidin-alkaline phosphatase. This procedure allows the detection of two mRNAs without loss of signal, removal of the emulsion, or spurious reaction. The simultaneous detection of oxytocin and vasopressin mRNAs in the hypothalamus, and of dopamine receptor and neuropeptide mRNAs in the striatum, demonstrated the efficiency of the procedure. Such a two-step procedure provides a simple and flexible way to make possible comparative analysis of the localization of two mRNAs within the same tissue section.