Effects of cerebral ischemia on neuronal hemoglobin

This study examined whether neuronal hemoglobin (Hb) is present in rats. It then examined whether cerebral ischemia or ischemic preconditioning (IPC) affects neuronal Hb levels in vivo and in vitro. In vivo, male Sprague-Dawley rats were subjected to either 15 mins of transient middle cerebral artery occlusion (MCAO) with 24 h of reperfusion, an IPC stimulus, or 24 h of permanent MCAO (pMCAO), or IPC followed 3 days later by 24 h of pMCAO. In vitro, primary cultured neurons were exposed to 2 h of oxygen-glucose deprivation (OGD) with 22 h of reoxygenation. Results showed that Hb is widely expressed in rat cerebral neurons but not astrocytes. Hemoglobin expression was significantly upregulated in the ipsilateral caudate and the cortical core of the middle cerebral artery territory after IPC. Hemoglobin levels also increased more in the penumbral cortex and the contralateral hemisphere 24 h after pMCAO, but expressions in the ipsilateral caudate and the cortical core area were decreased. Ischemic preconditioning modified pMCAO-induced brain Hb changes. Neuronal Hb levels in vitro were increased by 2 h of OGD and 22 h of reoxygenation. These results indicate that Hb is synthesized in neurons and can be upregulated by ischemia.