Immunohistochemical localization of insulin-like growth factor binding protein-5 in the developing rat nervous system.

The insulin-like growth factors (IGF-I and IGF-II) are peptides with both growth-promoting and insulin-like metabolic effects. The IGFs interact with and are modulated by a group of six IGF-binding proteins (IGFBP-1 through IGFBP-6). Previous studies have characterized IGFBP-5 and IGF-I gene expression in the developing nervous system. In the current study, cellular and tissue-specific distribution of IGFBP-5 protein was examined in the developing rodent nervous system using immunohistochemistry. Beginning with embryonic stage E12, IGFBP-5 immunoreactivity was observed in peripheral nerves. This pattern persisted through adulthood and was detected within Schwann cells and axons after postnatal day 16 (P16). IGFBP-5 immunoreactivity first appeared in the CNS at P16. Purkinje cells of the cerebellum were immunostained at P16, P32 and in the adult. IGFBP-5 immunoreactivity was also detected in several brain stem nuclei and their corresponding tracts as well as neuroglia. Nerve tracts and glia in the postnatal spinal cord were also immunopositive, however, spinal cord neurons were not stained. The current results, coupled with the known profile of IGF-I expression during nervous system development demonstrates the colocalization of IGF-I and IGFBP-5 in PNS, cerebellum, and brain stem.