In the past several years a great deal of evidence has accumulated linking neuronal activation events to the regulation of gene expression. We have pursued an analysis of c-fos regulation in the nervous system to elucidate the molecular mechanisms involved in stimulus-transcription coupling. The c-fos gene can be viewed as an archetype of the set of cellular immediate-early genes encoding transcription factors. These genes are believed to function in coupling short-term signals elicited by extracellular to long-term changes in cellular phenotype by orchestrating alterations in target gene expression. Several animal seizure models have been used to demonstrate the activation of gene expression in specific populations of neurons. Using a transgenic mouse approach, based on a foslacZ fusion gene, we now demonstrate an association between c-fos expression and cell death in the nervous system. A delayed and protracted induction was observed following surgical lesion and in response to neurotoxin exposure. This system allows us to determine, for the first time, the DNA regulatory sequences that are responsible for the induction of gene expression in neurons in vivo. Furthermore, foslacZ transgenic mice provide a unique resource for identifying cell populations that respond to specific stimuli or that are susceptible to particular toxins.