GDNF and early-onset autosomal dominant Alzheimer disease: The examples supporting this possibility include aged rats exhibiting better cognitive function with the overexpression of GDNF in astrocytes [99], improved cognitive functions seen in an animal model of TLE with the administration of IGF-1 [56], better memory function observed in a model of Alzheimer's disease with FGF-2 gene transfer into the hippocampus, [100], and NSC grafts improving cognitive function in an animal model of Alzheimer's disease through BDNF upregulation [101].