Insulin-like growth factor 1-receptor (IGF-1R) in developing and adult human dorsal root ganglia

Insulin-like growth factors (IGFs) promote neurite outgrowth in cultured sensory neurons that binding to IGF type 1 receptor (IGF-1R) and seem to be involved in the pathogenesis of some metabolic and toxic peripheral neuropathies coursing with altered sensitivity. However, the distribution of IGF-1R in the human sensory peripheral nervous system is unknown. In this study, we used light immunohistochemistry to analyse the occurrence and localization of IGF-1R in developing (6 to 22 weeks of estimated gestational age, e.g.a.) and adult (age range 25-41 years) human dorsal root ganglia (DRG). In human embryos (6-8 weeks e.g.a.) and young foetuses (9 weeks e.g.a.), most neurons (84%, 92%, and 83%, respectively) displayed IGF-1R immunoreactivity (IR). In older foetuses (12 and 22 weeks e.g.a.), the number of immunoreactive neurons decreased progressively (78 and 68%, respectively) reaching values similar to those observed in adults (64%). The subpopulation of adult primary sensory neurons showing IGF-1R IR covered the entire size range, but the neurons were mainly small. Furthermore, in adults all satellite glial cells and Schwann cells were immunoreactive. The present results suggest a role for IGF-1R in the differentiation and maturation of primary sensory neurons, and in the maintenance of a subset of them in adulthood, as well as in the control of peripheral glial cells (Schwann and satellite glial cells). These findings might serve as a basis for future studies in pathologic DRG, in which IGF-1R or its ligands may be involved.