In mammalian systems, the heme oxygenase (HO) isozymes HO-1 (HSP32) and HO-2 oxidatively cleave the heme molecule to produce bile pigments and carbon monoxide. Although HO-1 is inducible by various chemicals in systemic organs and cell culture systems, this communication reports for the first time the induction of this stress protein and its transcript by a chemical in the brain. In addition, this study demonstrates expression of HO-1 in select populations of cells in the brain in response to GSH depletion. Specifically, treatment of adult rats with diethyl maleate (DEM; 4.7 mmol/kg) caused a pronounced decrease in brain GSH content within 1 h. GSH levels remained significantly depressed for at least 24 h postinjection. Northern blot analysis of brain poly(A)+ mRNA following DEM treatment revealed on the average a sixfold increase in the 1.8-kb HO-1 mRNA level compared with that of controls; concomitant with this change was a decrease in GSH levels. Total brain HO activity was not significantly altered along with the increase in HO-1 mRNA level. The increase in transcription of HO-1 was a direct response to GSH depletion, as judged by the observation that treatment of neonatal rats with L-buthionine-(S,R)-sulfoximine (BSO) (3 mmol/kg, twice daily, for 2 days), a selective inhibitor of GSH synthesis, caused a marked depression in total brain GSH level and a concomitant increase in brain 1.8-kb HO-1 mRNA content. The magnitude of the increase was up to approximately 11.5-fold that of the control level, as evidenced by northern blot analysis.(ABSTRACT TRUNCATED AT 250 WORDS)