The effects of short- and long-term cocaine exposure on the expression of the nuclear transcription factor genes, c-fos and zif/268, as well as the opioid peptides, preprodynorphin (PPD) and preproenkephalin (PPE), in various regions of rat brain were evaluated by injecting i.p. saline or 10, 20, or 30 mg/kg cocaine HCl once daily for 1 or 10 days. In situ hybridization histochemistry was performed using 40mer oligonucleotides coding for c-fos and zif/268, or 48mers coding for PPD and PPE, followed by quantitative image analysis. Behavioral ratings demonstrated that on day 1 cocaine-induced activity increased in a dose-dependent manner. Statistical analysis revealed that repeated administration of cocaine for 10 days resulted in an augmentation of the behavioral response elicited by acute exposure to cocaine. Image analysis of film autoradiograms demonstrated that 1 h after a single injection of cocaine, the expression of c-fos and zif/268, but not PPD or PPE in the dorsal striatum and cortex, was enhanced in a dose-dependent manner as compared to that in saline controls. In contrast, administration of 30, but not 10 or 20, mg/kg cocaine for 10 days increased the expression of PPD but not PPE, mRNA and downregulated that of c-fos and zif/268 as compared to acute cocaine. These data indicate that repeated, high dose cocaine administration induces an increased PPD but not PPE genomic response and that the expression of c-fos and zif/268 is dissociable from that of PPD.