Effect of curcumin on brain insulin receptors and memory functions in STZ (ICV) induced dementia model of rat

Curcumin, the principal curcuminoid of turmeric, exhibits beneficial role in several neurodegenerative disorders such as dementia of Alzheimer type. Recent evidences suggest the involvement of brain insulin receptors (IRs) in the pathophysiology of dementia disorders. Therefore, the present study was undertaken to investigate the effect of curcumin on memory functions, brain IRs, acetylcholinesterase (AChE) activity and oxidative stress in intracerebroventricular (ICV) administered streptozotocin (STZ) induced dementia in rats. Rats were injected with STZ (3 mg/kg, ICV) bilaterally twice, on day 1 and 3 and curcumin (200 mg/kg, po) was administered in pre- and post-treatment schedules. STZ (ICV) treated group had shown memory deficit as indicated by no significant decrease in latency time in Morris water maze test and significant decrease in IR protein level in both hippocampus and cerebral cortex. Pre- and post-treatment of curcumin in STZ (ICV) treated rats significantly restored the memory deficit and IR protein level in both the regions. Furthermore, STZ (ICV) resulted into enhanced AChE activity in hippocampus and cerebral cortex which was normalized by curcumin pre- and post-treatment. An increase in MDA level and decrease in GSH level were obtained in both hippocampus and cerebral cortex in STZ treated group, indicating state of oxidative stress, which was also attenuated by pre- and post-treatment of curcumin. The results suggest that besides the anticholinesterase and antioxidant activity, effect on brain IR may also be an important factor for protective effect of curcumin against STZ induced dementia model.