Diabetic neuropathies in brain are induced by deficiency of BDNF.

Diabetes is known to be one of the risk factors for dementia; however, neuropathic changes in the brain of patients with the disease have not been completely revealed. So in the present study, we investigated the brain function of rats with diabetes induced by streptozotocin (STZ), one of the most commonly used animal models for diabetes. In the diabetic rats, immediately working memory performance was impaired in the Y-maze task and neuronal cytoskeleton proteins such as calbindin, synaptophysin, and syntaxin were reduced. Furthermore, morphological observation by Golgi staining showed a decrease in the number of basal dendrites and abnormality of spine structure. Next, we measured the content of brain-derived neurotrophic factor (BDNF) in the diabetic brain, because BDNF is one of the essential proteins for the maintenance of neuronal functions including synapse function and neuronal transmissions. In the diabetic brains, both protein and mRNA levels of BDNF were severely reduced. These results suggest that, in diabetes, synapse dysfunction is, at least in part, caused by a failure of BDNF synthesis in the brain.