Abstract
Background: Linear association between diabetes mellitus (DM) and cognitive decline is documented in various epidemiological studies.

Aims and Objectives: The objectives of the study were to evaluate the effect of hydroalcoholic extract of Costus speciosus leaves (CSL) on cognitive deficits induced by type 2 DM models.

Materials and Methods: Wistar rats were used for the study. We had seven groups of six rats each. Type 2 diabetes was induced in thirty six Wistar rats and the other six rats were kept as normal control. For induction, first, one dose of nicotinamide 110 mg/kg was injected, after 15 min streptozotocin (STZ) 50 mg/kg was injected intraperitoneally. Seven days after induction, from the dorsal vein of the tail, blood sample was collected and fasting blood glucose (FBG) levels were estimated. Rats with FBG > 200 mg/dl were randomly assigned to six groups of six rat each – Diabetic control (DC) – Negative control, Glibenclamide group – standard control, piracetam group, glibenclamide + piracetam group, CSL 200 mg, CSL 400 mg. Baseline values for learning and memory were recorded on day 1 before starting the treatment. With Hebb-William maze, Time taken to reach reward chamber (TRC), with Shuttle box avoidance test, Step through latency (STL) and with Elevated plus maze, Transfer latency (TL) were recorded. The means of five sessions were recorded for each rat. FBG and cognitive parameters such as TRC, STL, and TL were recorded on day 30 of treatment for all the groups. Data were analyzed using one way ANOVA and post hoc Tukey test.

Results: CSL 200 and CSL 400 groups showed decrease in FBG level in comparison to the DC which was significant (P < 0.001). CSL 200 group showed decrease in TRC, STL, and TL in comparison to DC which was significant (P < 0.001, P < 0.001, and P < 0.003, respectively). There was significant decrease in TRC and STL in comparison to DC (P < 0.001) in CSL 400 group. CSL 400 group also showed decrease in STL compared to glibenclamide, piracetam and CSL 200 group which was statistically significant.

Conclusion: Hydro-alcoholic extract of CSL showed antihyperglycemic and dose dependent cognitive improvement in models of type 2 diabetes.

Key words: Type 2 Diabetes; Costus speciosus Leaves; Cognitive Deficits; Hebb William Maze; Elevated Plus Maze