Decrease in Adult Neurogenesis and Neuroinflammation Are Involved in Spatial Memory Impairment in the Streptozotocin-Induced Model of Sporadic Alzheimer's Disease in Rats.

Early impairments in cerebral glucose metabolism and insulin signaling pathways may participate in the pathogenesis of the sporadic form of Alzheimer's disease (sAD). Intracerebroventricular (ICV) injections of low doses of streptozotocin (STZ) are used to mimic sAD and study these alterations in rodents. Streptozotocin causes impairments in insulin signaling and has been reported to trigger several alterations in the brain, such as oxidative stress, neuroinflammation, and dysfunctions in adult neurogenesis, which may be involved in cognitive decline and are features of human AD. The aim of the present study was to assess the influence of neuroinflammation on the process of adult neurogenesis and consequent cognitive deficits in the STZ-ICV model of sAD in Wistar rats. Streptozotocin caused an acute and persistent neuroinflammatory response, reflected by reactive microgliosis and astrogliosis in periventricular areas and the dorsal hippocampus, accompanied by a marked reduction of the proliferation of neural stem cells in the dentate gyrus of the hippocampus and subventricular zone. Streptozotocin also reduced the survival, differentiation, and maturation of newborn neurons, resulting in impairments in short-term and long-term spatial memory. These results support the hypothesis that neuroinflammation has a detrimental effect on neurogenesis, and both neuroinflammation and impairments in neurogenesis contribute to cognitive deficits in the STZ-ICV model of sAD.

Effects of curcumin on short-term spatial and recognition memory, adult neurogenesis and neuroinflammation in a streptozotocin-induced rat model of dementia of Alzheimer's type.

Curcumin is a natural polyphenol with evidence of antioxidant, anti-inflammatory and neuroprotective properties. Recent evidence also suggests that curcumin increases cognitive performance in animal models of dementia, and this effect would be related to its capacity to enhance adult neurogenesis. The aim of this study was to test the hypothesis that curcumin treatment would be able to preserve cognition by increasing neurogenesis and decreasing neuroinflammation in the model of dementia of Alzheimer's type induced by an intracerebroventricular injection of streptozotocin (ICV-STZ) in Wistar rats. The animals were injected with ICV-STZ or vehicle and curcumin treatments (25, 50 and 100mg/kg, gavage) were performed for 30days. Four weeks after surgery, STZ-lesioned animals exhibited impairments in short-term spatial memory (Object Location Test (OLT) and Y maze) and short-term recognition memory (Object Recognition Test - ORT), decreased cell proliferation and immature neurons (Ki-67- and doublecortin-positive cells, respectively) in the subventricular zone (SVZ) and dentate gyrus (DG) of hippocampus, and increased immunoreactivity for the glial markers GFAP and Iba-1 (neuroinflammation). Curcumin treatment in the doses of 50 and 100mg/kg prevented the deficits in recognition memory in the ORT, but not in spatial memory in the OLT and Y maze. Curcumin treatment exerted only slight improvements in neuroinflammation, resulting in no improvements in hippocampal and subventricular neurogenesis. These results suggest a positive effect of curcumin in object recognition memory which was not related to hippocampal neurogenesis.