The application of in situ hybridization for the detection of neuropeptide mRNA has made a very significant contribution to the understanding of fundamental mechanisms of gene expression in neural tissues. First, as a powerful tool for analyzing the pattern of spatial and temporal expression of neuropeptide genes, in situ hybridization has provided useful insights into the functional implications of mRNA distribution and localized neuropeptide synthesis. In addition, in situ hybridization allows the localization of different forms of alternatively spliced transcripts from a single neuropeptide gene to be determined with very high sensitivity and resolution, essentially at the single cell level. This feature is significant, because alternative pre-mRNA splicing has proven to be an almost ubiquitous mechanism for posttranscriptional regulation and information amplification in the nervous system.