NEUROTROPHIN-4 5 PROMOTES SURVIVAL AND DIFFERENTIATION OF RAT STRIATAL NEURONS DEVELOPING IN CULTURE/

Cultures of dissociated striatal neurons from fetal rats were prepared , and were grown in the presence of neurotrophin-4/5 (NT-4/5) as well as the other known neurotrophins, nerve growth factor (NGF), brain-der ived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3). We found th at acute administration of NT-4/5 to 7-day-old cultures stimulates the hydrolysis of phosphatidylinositol, an event involved in neurotrophin signal transduction. Growth of striatal cultures in the presence of N T-4/5 resulted in increased cell survival, as indicated by elevations in cell number, protein content, and a measure of mitochondrial enzyme activity (MTT assay). NT-4/5 increased GABA uptake and staining inten sity in these cultures, as indicated by GABA immunocytochemistry, indi cating a trophic action on GABAergic neurons, the predominant neuron t ype in the striatum. To further identify responsive cell populations w e analysed for calretinin, a calcium-binding protein known to colocali ze with GABA in a number of neuronal cells. In cultures prepared from rats of embryonic day 15, NT-4/5 strongly increased the number of calr etinin-positive cells as well as calretinin levels, as determined by W estern blot analysis. When the cultures were prepared from embryonic d ay 18 rats, NT-4/5 very strongly increased the morphological different iation of calretinin-positive cells, whereas the increase in cell numb er was less prominent. All effects produced by NT-4/5 were mimicked by BDNF with similar potency. NT-3 was less effective than NT-4/5 and BD NF, and its effects were limited to cultures prepared from embryonic d ay 15 rats, suggesting a role in the regulation of cell survival at ea rly developmental stages. NGF did not affect any of the measured param eters. Our findings identify NT-4/5 as potent neurotrophic factor for striatal neurons, able to promote their survival and differentiation.