Differing expression of insulin-like growth factor I in the developing and in the adult rat cerebellum.

Insulin-like growth factor I (IGF-I; somatomedin C) is a trophic peptide of importance for the development of several tissues and organs. In the present study we have mapped the cellular distribution and dynamic changes of IGF-I immunoreactivity in the rat cerebellum from its postnatal development to maturity. In vitro hybridization of IGF-I mRNA was used to demonstrate that the IGF-I immunoreactive material was synthesized in the cerebellum during a limited time period of cerebellar differentiation. IGF-I immunoreactivity was absent in primordial nerve cells but was present in neuroglial cells during the first two days after birth and then rapidly increased in intensity in the latter during the next few days. Proliferative nerve cells in the external granular layer did not express IGF-I immunoreactivity, while migrating and differentiating nerve cells as well as neuroglial cells showed intense labelling. Starting about 2 weeks postnatally, the IGF-I immunoreactivity declined, first in the neuroglial cells and eventually in the nerve cells. No IGF-I immunoreactivity could be demonstrated in the normal adult cerebellum. Colchicine pretreatment did, however, enable demonstration of IGF-I immunoreactivity in adult cerebellar nerve cells but not in neuroglial cells. In vitro hybridization revealed IGF-I mRNA in the developing cerebellum but only at very low levels in the adult cerebellum. It is concluded that IGF-I is likely to be a factor of importance for the development and maturation of nerve cells and neuroglial cells in the brain.(ABSTRACT TRUNCATED AT 250 WORDS)

Immunohistochemical localization of insulin-like growth factor I in the adult rat.

Rabbit antisera against native human insulin-like growth factor I (IGF-I; somatomedin C) or a synthetic tetradecapeptide, representing the carboxyterminal amino acids 57-70 of human IGF-I, were used to map immunohistochemically the distribution of IGF-I immunoreactive material in adult rats. Both antisera were specific for IGF-I, as characterized by immunoabsorption, immunoblotting and radioimmunoassay. There was no cross-reactivity to IGF-II, relaxin or pro-insulin; substances having a high degree of structural homology with IGF-I. High IGF-I immunoreactivity was observed in spermatocytes of the testis; in oocytes, granulosa and theca interna cells of the ovary during early stages of follicle development; in some lymphocytes and in reticular cells of lymphoid and hematopoietic organs; in salivary gland duct cells; in the adrenal medulla, the parathyroid gland and the Langerhans' islets. Chondrocytes in the epiphyseal and rib growth plates and at articular surfaces showed strong IGF-I immunoreactivity. Brown but not white fat cells were stained. Nerve cells in the peripheral and autonomic nervous system showed faint to intense IGF-I immunoreactivity. In contrast, neurons and neuroglial cells in the central nervous system were generally negative; motor neurons being an exception. Erythropoietic, thrombocytopoietic and myeloic cells in the bone marrow showed IGF-I immunoreactivity, but only at defined developmental stages. Hepatocytes showed faint IGF-I immunoreactivity, but became more intensely stained after pretreatment with colchicine. The present results suggest that IGF-I is synthetized by cells in several tissues and organs in the adult rat. There was an apparent association between the localization of IGF-I and cell differentiation.(ABSTRACT TRUNCATED AT 250 WORDS)