The protective effect of Azadirachta excelsa leaves extract and quercetin treatment on the learning and memory impairments in relation with insulin and amylin levels in the brain of streptozotocin-induced diabetic rats

Abstract

Azadirachta excelsa increases the secretion of plasma insulin with subsequent reduction of fasting blood glucose. However, its protective effect towards brain amylin and insulin levels as well as the memory and learning functions remain elusive. Thus, this study aimed to ascertain the effect of A. excelsa and quercetin consumptions on the brain amylin and insulin concentrations as well as memory and learning abilities of the streptozotocin (STZ)-induced diabetic rats. Diabetic condition was induced in the male Sprague Dawley rats by the intraperitoneal injection of 60 mg/kg body weight (bwt) STZ. The experimental animals were divided into normal control (saline), diabetic control (saline), Metformin-treated diabetic (1000 mg/kg bwt) (positive control), A. excelsa-treated diabetic (250 mg/kg bwt) and Quercetin-treated diabetic (40 mg/kg bwt) rats. All treatments were administered orally by oral gavage once daily throughout the 8 weeks of the treatment period. Amylin and insulin concentrations were determined by using the commercial rat amylin and insulin immunoassay kits, while learning and memory consolidation parameters were conducted using Morris Water Maze (MWM) paradigm. Treatment with A. excelsa had significantly (p < 0.05) improved the concentration of both brain amylin and insulin. In MWM test, the administration of A. excelsa and quercetin significantly (p < 0.05) attenuated the learning and memory impairments in STZ-induced diabetic rats. These analytical results provide evidence that A. excelsa can improve learning and memory impairments due to diabetes by increasing the amylin and insulin levels. These also suggest that, quercetin might only improve the learning and memory impairment, but not be the one that contributed to the improvement in the brain amylin and insulin concentrations. Keywords: Azadirachta excelsa, Streptozotocin-induced diabetes, Morris Water Maze, Cognitive impairment, Amylin, Insulin