INTRANASAL INSULIN DECREASES AUTOPHAGIC AND APOPTOTIC DEATH OF NEURONS IN THE RAT HIPPOCAMPAL C1 REGION AND FRONTAL CORTEX UNDER FOREBRAIN ISCHEMIA–REPERFUSION

Abstract

The development of approaches to therapy of ischemic brain injuries requires a better insight into the mechanisms that regulate both apoptotic and autophagic death of neurons. Under a strong ischemic (or other pathological) exposure, neurons can die from the activation of both apoptosis and autophagy. This work was aimed to assess the contribution of autophagy and apoptosis activation to neuronal cell death in the hippocampal CA1 region and frontal cortex using the rat two-vessel occlusion/hypotension model of global forebrain ischemia with subsequent long-term reperfusion, as well as to study the ability of intranasal insulin to prevent autophagic and apoptotic death of neurons. The inhibitors of autophagy (3-methyladenine), apoptosis (Ac-DEVD-CHO), or phosphate buffer (for control) were administered to rats intracerebroventricularly before ischemia and reperfusion. To count viable neurons, brain sections were stained with a Nissl stain. During ischemia–reperfusion, the number of viable neurons in the hippocampal CA1 region decreased by 58.3 ± 1.5% of their count in sham-operated rats (control taken as 100%). The administration of autophagy or apoptosis inhibitors increased the number of viable neurons in the hippocampal CA1 region from 58.3 ± 1.5% to 90.4 ± 2.2% (p 0.001) and 71.6 ± 1.8% (p 0.001) vs. control, respectively. Intranasal insulin administration at a dose of 0.5 IU (before ischemia and at a daily basis for 7 days during reperfusion) normalized the number of viable neurons in the hippocampal CA1 region up to 100.2 ± 1.95% vs. control. In the frontal cortex, the viability of neurons also decreased under ischemia–reperfusion, while the number of viable neurons increased after the administration of autophagy or apoptosis inhibitors, and even to a greater extent after intranasal insulin administration. The main difference was a lower sensitivity of cortical vs. hippocampal neurons to ischemia–reperfusion. These data indicate that intranasal insulin is able to decrease the death of brain neurons caused by the activation of autophagy and apoptosis due to ischemia–reperfusion.