Based on insulin resistance hypothesis of sporadic Alzheimer's (sAD) origin, intracerebroventricular injection of streptozotocin at the doses of 1-3 mg/kg have introduced as a suitable method to induce animal model of sAD (ICV-STZ model). However, these doses could not reflect the potential effects of environmental or internal factors on the exacerbation of Alzheimer's behavioral symptoms, since these doses are not able to imitate the early stages of Alzheimer's disease, and the cognitive impairment induced by these doses is not gradual. On the other hand, quantitative studies have not thoroughly examined the behavioral effect of lower doses of streptozotocin. In this study, using Y-maze, morris water maze (MWM) and novel object recognition test (NORT), the effect of icv injection of 0.5 mg/Kg dose of streptozotocin was investigated on the function of working, spatial and novel object recognition memory of animal 1, 2.5, 3.5, and 6 months after injection in rat. The memory of the new object was initially disrupted 2.5 months after the injection, and this impairment was aggravated over the time. Morever, as compared with control animals, impairments in the function of working and spatial memory was observed in icv-STZ treated animals from 3.5 months onwad and the signs of memory impairments intensified Over the time. Considering the shortcomings of the current ICV-STZ model of sAD, it seems that injection of this dose is a more appropriate model to examine the effects of various environmental or intrinsic factors on the aggravation or improvement of cognitive Alzheimer's symptoms. More investigations are needed to prove the results of this study.

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