Figure 4.

The N-methyl--aspartate receptor (NMDAR) is required for the neuroprotective effect of tissue-type plasminogen activator (tPA). (A) Mean cell survival in wild-type (Wt) neurons treated with tPA 5 nmol/L or plasmin 10 nmol/L, either alone or in combination with the NMDAR antagonist MK-801 10 μ, followed 5 minutes later by exposure to 55 minutes of oxygen–glucose deprivation (OGD) conditions; n=12 for each observation. ^*P<0.01 versus cells cotreated with tPA and MK-801. ^**P<0.01 versus cells cotreated with plasmin and MK-801. (B) Mean cell survival in Wt and tPA^−/− neurons exposed to 5 minutes of OGD (hypoxic preconditioning, HP), followed 5 minutes later by incubation under OGD conditions for 55 minutes. A subgroup of tPA^−/− cells was treated with tPA 5 nmol/L or plasmin 10 nmol/L either alone or in combination with MK-801 10 μmol/L; n=10 for each observation. Data represent mean±s.d. ^*P<0.01 versus cells cotreated with MK-801. ^§P<0.01 versus tPA^−/− neurons preconditioned either in absence of tPA or with a combination of tPA and MK-801. ^P<0.01 versus preconditioned and non-preconditioned tPA^−/− neurons and versus tPA^−/− neurons cotreated with plasmin and MK-801 during the preconditioning phase. HP denotes the moment when cells were treated with tPA or plasmin alone or in combination with MK-801. Indicates the moment when cells were exposed to sublethal hypoxia. (C) Mean percentage decrease in the volume of the ischemic lesion in Wt mice either left untreated or injected with MK-801 1 μg/kg intraperitoneally, followed by ischemic preconditioning and transient occlusion of the middle cerebral artery (tMCAO) 1 hour later; n=10; ^*P<0.01 versus mice preconditioned without MK-801. (D) Mean cell survival in Wt neurons incubated with tPA 1 or 5 nmol/L, followed 5 minutes later by exposure to kainic acid (KA) 250 μmol/L; n=10; P<0.01 versus neurons exposed to KA without preconditioning with tPA. IPC, ischemic preconditioning.