Circulating insulin-like growth factor (IGF)-1 Regulates Hippocampal IGF-1 Levels and Brain Gene Expression During Adolescence

This study, using a growth hormone (GH)-deficient dwarf animal model and peripheral GH replacement, investigated the effects of circulating IGF-1 during adolescence on IGF-1 levels in the brain. Our results demonstrated that hippocampal IGF-1 protein concentrations during adolescence are highly regulated by circulating IGF-1, which were reduced by GH deficiency and restored by systematic GH replacement. In contrast, IGF-1 levels in the CSF were decreased by GH deficiency but not restored by GH replacement. Furthermore, analysis of gene expression using microarrays and RT-PCR indicated that circulating IGF-1 levels did not modify the transcription of IGF-1 or its receptor in the hippocampus but did regulate genes that are involved in microvascular structure and function, brain development, and synaptic plasticity, which potentially support brain structures involved in cognitive function during this important developmental period.