RESPONSE OF EMBRYONIC RAT HIPPOCAMPAL-NEURONS IN CULTURE TO NEUROTROPHIN-3, BRAIN-DERIVED NEUROTROPHIC FACTOR AND BASIC FIBROBLAST GROWTH-FACTOR

Primary cultures of rat hippocampal cells have been used to evaluate t rophic effects of neurotrophin-3, brain-derived neurotrophic factor, n erve growth factor, and basic fibroblast growth factor. There was litt le survival in cultures prepared from embryonic day 17 embryos and gro wn in defined medium without growth factors. Addition of basic fibrobl ast growth factor produced a massive increase in the number of neurons present in the cultures seven days after plating. This action reflect ed proliferation of neuronal precursor cells rather than increased sur vival of initially plated neurons. Brain-derived neurotrophic factor w as ineffective under these conditions, whereas neurotrophin-3 produced a very small, but statistically significant increase in neuronal surv ival in the range of 20%. However, hippocampal neurons were responsive to brain-derived neurotrophic factor and neurotrophin-3 as demonstrat ed under culture conditions, resulting in survival in absence of the n eurotrophins. Acute administration of brain-derived neurotrophic facto r and neurotrophin-3 to hippocampal cultures grown at high density sti mulated the hydrolysis of phosphatidylinositol, a response earlier sho wn to be mediated by tyrosine receptor kinase neurotrophin receptors. Furthermore, when such cultures were grown in presence of neurotrophin -3 rates of glutamate and GABA uptake were increased. In contrast to t he findings obtained in cultures of embryonic day 17, cultures prepare d from embryonic day 14 or 15 animals were viable in absence of exogen ous growth factors. The specific neurotrophin receptor inhibitor, K-25 2b reduced survival in these cultures and this effect was partly overc ome by exogenous neurotrophin-3. Our findings suggest that hippocampal neuron survival at early embryonic stages may involve paracrine neuro trophin mechanisms, whereas the survival of hippocampal neurons of emb ryonic day 17 is not markedly enhanced by brain-derived neurotrophic f actor or neurotrophin-3. However, at this embryonic stage there is a f unctional response to both neurotrophins as made evident by the activa tion of tyrosine kinase receptor-linked signal transduction mechanisms and by the stimulation of transmitter-specific differentiation.