Expression of heme oxygenase in the oxygen-sensing regions of the rostral ventrolateral medulla

Recently, unique regions in the rostral ventrolateral medulla (RVLM) have b een found to be oxygen sensitive. However, the mechanism of sensing oxygen in these RVLM regions is unknown. Because heme oxygenase (HO) has been show n to be involved in the hypoxic responses of the carotid body and pulmonary artery, the aim of this study was to determine whether HO is present in th e RVLM and whether expression of HO is altered by chronic hypoxia. Adult ra ts were exposed to hypoxia (10% O-2) or normoxia (21% O-2) for 10 days, and the mRNA for HO-1 and HO-2 was examined in the RVLM by using RT-PCR. Expre ssion of HO-2 mRNA was seen in the RVLM of both control and hypoxic samples , whereas expression of HO-1 mRNA was only seen in the RVLM of hypoxic samp les. HO-2 was immunocytochemically localized in brain sections (40 mum) to the C1 region and pre-Botzinger complex of the RVLM. Together, these result s indicate that HO-2 is present in the RVLM under control conditions and th at HO-1 is induced in the RVLM during chronic hypoxia, consistent with a po tential role for HO in the oxygen-sensing function of these cardiorespirato ry RVLM regions.