INSULIN-LIKE GROWTH-FACTOR I-IMMUNOREACTIVE PEPTIDE IN ADULT HUMAN CEREBELLAR PURKINJE-CELLS - COLOCALIZATION WITH LOW-AFFINITY NERVE GROWTH-FACTOR RECEPTOR

It has been proposed that Insulin-like growth factor I is involved in the development, growth and maintenance of the central nervous system possibly interacting with other trophic factors. High levels of insulin-like growth factor I have been detected in the cerebellum during development and adulthood suggesting a specific role for insulin-like growth factor I in this brain area. While there is ever increasing data regarding the cell types containing endogenous insulin-like growth factor I in the rat brain, no information on the human brain is yet available. In the present study we sought to analyse the precise location of insulin-like growth factor I peptide in the adult human cerebellum using a specific antiserum against recombinant human insulin-like growth factor I. After immunocytochemistry, numerous Purkinje cells exhibited intense positive staining occupying the cell soma, dendrites and dendritic spines as well as axons. Occasionally, immunoreactive Purkinje cell axons were arciform and exhibited bulbous dilatations along their proximal length. Putative recurrent collaterals of Purkinje cell axons were also insulin-like growth factor I reactive. Double-staining immunocytochemistry in the same sections consistently showed, as expected, co-expression of insulin-like growth factor I and calbindin, although a few calbindin containing Purkinje cells lacked insulin-like growth factor I immunostaining suggesting there are insulin-like growth factor I positive Purkinje cell subsets in the human cerebellum. In addition, co-expression of insulin-like growth factor I and low-affinity nerve growth factor receptor-immunoreactive protein was found in a subpopulation of insulin-like growth factor I positive Purkinje cells. The results of this study prove the presence of insulin-like growth factor I. immunoreactivity in a Purkinje cell subpopulation of the adult human cerebellum suggesting that insulin-like growth factor I may participate in paracrine or autocrine regulatory systems in the adult human brain.