17β-Oestradiol Protects Primary-Cultured Rat Cortical Neurons from Ketamine-Induced Apoptosis by Activating PI3K/Akt/Bcl-2 Signalling

Numerous studies in rodents have indicated that exposure to ketamine during the period when synaptogenesis is highly active induces neurodegeneration. Thus, there is a growing need to develop strategies to prevent ketamine-induced brain injury in the developing brain. Oestradiol is a neuroactive steroid that prevents neuronal cell death in different experimental models by activating cell survival signals and inhibiting apoptotic signals. The main goal of this study was to investigate the neuroprotective effects of 17-oestradiol against ketamine-induced apoptotic neurodegeneration in primary-cultured cortical neurons. The data revealed that 17-oestradiol (0.1M) in combination with ketamine (100M) increased cell viability in the MTT assay and reduced the number of apoptotic cells detected by TUNEL and Hoechst 33258 staining. To elucidate a possible mechanism by which 17-oestradiol exerts its neuroprotective effect, we investigated the PI3K pathway using an inhibitor of PI3K, LY294002. The protective effects of 17-oestradiol were abrogated by LY294002. Furthermore, we found that 17-oestradiol not only induced phosphorylation of the PI3K substrate Akt, but also increased the expression of Bcl-2, which down-regulated ketamine-induced caspase-3 activity and inhibited neuronal apoptosis. These data demonstrate that 17-oestradiol exerts a neuroprotective effect against ketamine-induced neuronal apoptosis by activating the PI3K/Akt/Bcl-2 signalling pathway. Therefore, 17-oestradiol appears to be a promising agent in preventing or reversing ketamine's toxic effects on neurons at an early developmental stage.