LOCALIZATION OF INSULIN-LIKE GROWTH-FACTOR-I (IGF-I) IMMUNOREACTIVITYIN THE OLIVOCEREBELLAR SYSTEM OF DEVELOPING AND ADULT-RATS

The molecular mechanisms which underlie the development of the olivoce rebellar topography are not fully understood. Insulin-like growth fact or-I (IGF-I) is a growth factor known to play important roles in neura l development and it has been identified within the cerebellum and the inferior olive. To assess the contribution of IGF-I to the developmen t of climbing fibre topography, the distribution of IGF-I-Like immunor eactivity (IGF-I TR) was identified in the cerebellar cortex and infer ior olive of rats 0, 3, 5, 7, 10, 15, 21, 28 and 90 days old. In the c erebellar cortex, IGF-I IR was localised solely to Purkinje cells and its distribution was spatially and temporally regulated in a manner wh ich coincides with climbing fibre development. At birth, weak IGF-T IR was detected in a few Purkinje cells in the ventral vermis. More Purk inje cells became positive until at postnatal day 7 (P7) all Purkinje cells displayed IGF-I IR. Subsequently, a subpopulation of Purkinje ce lls lost their reactivity for IGF-I to leave IGF-I-positive cells orga nised into sagittal bands by P15. IGE-I IR was also seen in all subdiv isions of the inferior olive between birth and P10 in a distribution w hich paralleled the maturation of the inferior olive. The Purkinje cel l and inferior olivary IGF-I IR parallels climbing fibre development a nd thus the results of this study support the hypothesis that TGF-I is involved in the development of climbing fibre topography.