Protective effects of Salvia miltiorrhiza injection against learning and memory impairments in streptozotocin-induced diabetic rats

The aim of this study was to explore the protective effects of Salvia miltiorrhiza injection against learning and memory impairment in streptozotocin (STZ)-induced diabetic rats and the possible mechanism involved. Sprague Dawley male rats (n=30) were randomized into three groups: Diabetes, diabetes treated with S. miltiorrhiza injection and normal control. Diabetes was induced by an intraperitoneal injection of STZ (65 mg/kg). The S. miltiorrhiza injection-treated rats received an intraperitoneal injection of S. miltiorrhiza (5 ml/kg/day) while the rats of the other two groups were administered an intraperitoneal injection of the same volume of 0.9% saline for four weeks. After four weeks of treatment, the escape latency and search strategies in the rats were assessed by the Morris water maze test. The protein levels of mitogen-activated protein kinase phosphatase-1 (MKP-1) were also assessed by immunohistochemistry. Four weeks after the induction of diabetes, the body weight of the diabetic rats was significantly lower and the blood glucose concentration was significantly higher than that of the control rats. S. miltiorrhiza injection was observed to improve the blood glucose and learning ability (P<0.05). Compared with the control group, the expression of MKP-1 was significantly decreased in the hippocampal area of the diabetes group; S. miltiorrhiza injection-treated rats showed an increased expression compared with the diabetic rats, but the expression remained lower than that of the normal control group (P<0.05). In conclusion, S. miltiorrhiza injection can improve the learning and memory decline of diabetic rats. The changes in expression of MKP-1 under hyperglycemia may play a role in the protective effects of S. miltiorrhiza against dementia in diabetic rats.