Neurons depend for survival on local neurotrophic factors which act in an autocrine/paracrine manner. However, the effect of paracrine signaling of brain microvascular endothelial cells (BMECs) under pathological conditions on neuron survival is not fully understood. In this study we cultured rat BMECs and cortical neurons. BMECs were cultured in oxygen-glucose-deprived (OGD) conditions to mimic cerebral ischemia in vitro. The conditioned media of normal BMECs or OGD-injured BMECs were used to culture normal or injured neurons. Neuron activity, free Ca(2+) concentration, NMDA receptor status, mitochondrial membrane potential and cytochrome C release level were determined. The results showed: mitochondrial activity of injured neurons was significantly increased and lactate dehydrogenase (LDH) leakage was decreased (P<0.05) by grown in conditioned medium of normal BMECs. Inversely, mitochondrial activity of normal or injured neurons was decreased and LDH leakage was significantly increased (P<0.05) by grown in conditioned medium of injured BMECs. The changes in free Ca(2+) concentration, NMDA receptor status, mitochondrial membrane potential and cytochrome C release level were consistent with the changes in neuronal activity. These findings suggest that the conditioned medium of normal BMECs has a neuroprotective effect. However, this protective effect was lost after BMECs injury; in fact, the conditioned medium became neurotoxic. Therefore, it appears that early recovery of BMECs might be helpful for neuron survival.