IGF1 GENE DISRUPTION RESULTS IN REDUCED BRAIN SIZE, CNS HYPOMYELINATION, AND LOSS OF HIPPOCAMPAL GRANULE AND STRIATAL PARVALBUMIN-CONTAINING NEURONS

Homozygous Igf1(-/-) mice at 2 months of age had reduced brain weights , with reductions evenly affecting all major brain areas. The gross mo rphology of the CNS was normal, but the size of white matter structure s in brain and spinal cord was strongly reduced, owing to decreased nu mbers of axons and oligodendrocytes. Myelinated axons were more strong ly reduced in number than unmyelinated axons. The volume of the dentat e gyrus granule cell layer was reduced in excess of the decrease in br ain weight. Among populations of calcium-binding protein-containing ne urons, there was a selective reduction in the number of striatal parva lbumin-containing cells. Numbers of mesencephalic dopaminergic neurons , striatal and basal forebrain cholinergic neurons, and spinal cord mo toneurons were unaffected. Cerebellar morphology was unaltered. Our fi ndings suggest cell type- and region-specific functions for IGF-I and emphasize prominent roles in axon growth and maturation in CNS myelina tion.