Opiate regulation of the nuclear proto-oncogene c-fos was studied in the locus coeruleus (LC) and other regions of rat brain by immunoblotting, northern blotting, and in situ hybridization procedures. Precipitation of opiate withdrawal in rats, which is known to increase LC firing rates 4-fold, led to a two- to three-fold increase in levels of mRNA and protein for c-fos in the LC 1-2 h after initiation of withdrawal. In contrast, levels of c-fos expression were decreased in LC from rats treated acutely or chronically with morphine but not experiencing withdrawal, conditions under which LC firing rates are depressed. Similar regulation of c-fos expression during opiate withdrawal was found in the amygdala, ventral tegmentum, nucleus accumbens, neostriatum, and cerebral cortex, but not in a number of other brain regions studied, which included the hippocampus, dorsal raphe, periaqueductal gray, and paragigantocellularis. In the LC and some other brain regions, induction of c-fos during opiate withdrawal was associated with a parallel induction of c-jun, another nuclear proto-oncogene, which, like c-fos, is expressed rapidly in brain in response to certain extracellular stimuli. The results demonstrate a novel use of c-fos in neuropharmacology, namely to map neuronal pathways and neuronal cell types activated in response to acute and chronic opiate administration and during opiate withdrawal, as well as in response to other psychotropic drug treatments.