The aging brain: is function dependent on growth hormone/insulin-like growth factor-1 signaling?

The role of growth hormone (GH) and insulin-like growth factor-1 (IGF-1) in normal brain function is not well understood. Studies looking at cognition in humans with GH deficiency have produced controversial results. Experiments in which GH is administered to rodents have shown an apparent improvement in learning and memory. However, studies in which GH deficient or resistant mice were tested in learning and memory tasks reveal that these animals have normal cognitive performance and that their neural function does not deteriorate with age at the same rate as their normal siblings. Further research into this phenomenon revealed that these animals have elevated GH and IGF-1 expression in the hippocampus compared to normal animals. Additional studies with GH deficient and resistant mice suggested that these mutants experience a delay in age-related decline in locomotor activity and exploratory behavior. Data indicate that GH/IGF-1 deficiency and resistance do not impair neural function and instead may offer some degree of protection that results in delayed cognitive and motor aging.