Intranasal Insulin Decreases Autophagic and Apoptotic Death of Neurons in the Rat Hippocampal C1 Region and Frontal Cortex under Forebrain Ischemia-Reperfusion

The development of approaches to therapy of ischemic braininjuries requires a better insight into the mechanisms that regulateboth apoptotic and autophagic death of neurons. Under a strong ischemic(or other pathological) exposure, neurons can die from the activationof both apoptosis and autophagy. This study was aimed to assessthe contribution of autophagy and apoptosis activation to neuronalcell death in the hippocampal CA1 region and frontal cortex usingthe rat two-vessel occlusion/hypotension model of global forebrainischemia followed by long-term reperfusion, as well as to studythe ability of intranasal insulin to prevent autophagic and apoptotic deathof neurons. The inhibitors of autophagy (3-methyladenine), apoptosis(Ac-DEVD-CHO), or phosphate buffer (for control) were administeredto rats intracerebroventricularly before ischemia and reperfusion.To count viable neurons, Nissl staining of brain slices was performed. Duringischemia/reperfusion, the number of viable neurons in the hippocampalCA1 region decreased by 58.3 & PLUSMN; 1.5% of that in sham-operated rats(control taken as 100%). The administration of autophagy or apoptosisinhibitors increased the number of viable neurons in the hippocampalCA1 region from 58.3 & PLUSMN; 1.5 to 90.4 & PLUSMN; 2.2 (p <0.001) and 71.6 & PLUSMN; 1.8% (p <0.001) vs. control, respectively. Intranasal insulin administrationat a dose of 0.5 IU (before ischemia and at a daily basis for 7days during reperfusion) normalized the number of viable neuronsin the hippocampal CA1 region up to 100.2 & PLUSMN; 1.95% vs. control. Inthe frontal cortex, the viability of neurons also decreased underischemia/reperfusion, while the number of viable neurons increased afterthe administration of autophagy or apoptosis inhibitors, and evento a greater extent after intranasal insulin administration. Themain difference was a lower sensitivity of cortical vs. hippocampalneurons to ischemia/reperfusion. These data indicate that intranasalinsulin is able to decrease the death of brain neurons caused bythe activation of autophagy and apoptosis due to ischemia/reperfusion.