Combining In Situ Hybridization with Retrograde Tracing and Immunohistochemistry for Phenotypic Characterization of Individual Neurons

In situ hybridization, using radioactive and nonradioactive probes, is at present, a widespread technique that has been developed and improved over the past 15 yr, and has become an extremely powerful tool for the study of cellular interactions through gene expression and gene regulation. Progress in sensitivity, the wide range of available markers, and the development of image analysis systems for quantification, especially at the cellular level, have made this approach particularly useful for the investigation of the cellular interactions and regulations of many heterocellular systems, especially the central nervous system (1 –4 ).