Subchronic metformin pretreatment enhances novel object recognition memory task in forebrain ischemia: behavioural, molecular, and electrophysiological studies

Metformin exerts its effect via AMP-activated protein kinase (AMPK), which is a key sensor for energy homeostasis that regulates different intracellular pathways. Metformin attenuates oxidative stress and cognitive impairment. In our experiment, rats were divided into 8 groups; some were pretreated with metformin (Met, 200 mg/kg) and (or) the AMPK inhibitor Compound C (CC) for 14 days. On day 14, rats underwent transient forebrain global ischemia. Data indicated that pretreatment of ischemic rats with metformin reduced working memory deficits in a novel object recognition test compared to group with ischemia-reperfusion (I-R) (P < 0.01). Pretreatment of the I-R animals with metformin increased phosphorylated cyclic-AMP response element-binding protein (pCREB) and c-fos levels compared to the I-R group (P < 0.001 for both). The level of CREB and c-fos was significantly lower in ischemic rats pretreated with Met + CC compared to the Met + I-R group. Field excitatory postsynaptic potential (fEPSP) amplitude and slope was significantly lower in the I-R group compared to the sham operation group (P < 0.001). Data showed that fEPSP amplitude and slope was significantly higher in the Met + I-R group compared to the I-R group (P < 0.001). Treatment of ischemic animals with Met + CC increased fEPSP amplitude and slope compared to the Met + I-R group (P < 0.01). We unravelled new aspects of the protective role of AMPK activation by metformin, further emphasizing the potency of metformin pretreatment against cerebral ischemia.