Modulation of synapsin I gene expression in rat cortical neurons by extracellular matrix.

1. Neuronal differentiation depends on crosstalk between genetic program and environmental cues. In this study we tried to dissect this complex interplay by culturing neurons from fetal rat brain cortices in a chemically defined, neuron-specific, medium and on different substrata, either artificial (poly-D-lysine) or natural. 2. Among the extracellular matrix compounds used in this study, two (collagen I and fibronectin) allowed only a weak attachment of cortical neurons to the substratum, while the others (collagen IV, laminin, and basal lamina from Engelbreth-Holm-Swarm sarcoma) allowed both firm attachment and moderate to extensive neurite outgrowth from neuronal cell bodies. 3. By using synapsin I gene expression as a parameter of neuronal differentiation, we found that neurite outgrowth and neuronal differentiation are not linearly linked. Synapsin I gene expression, in fact, was maximal in neurons cultured on laminin, while the fastest neuritic outgrowth was recorded in cultures on poly-D-lysine. 4. The data presented in this paper are consistent with the hypothesis that the extracellular matrix plays an active role in modulating the differentiative program of neurons.