Synaptic potentiation induced by a protein factor in cultured cerebral neurons

1. We reported in a previous paper that long-lasting enhancement of spontan eous excitatory post synaptic currents (SEPSCs) in cultured chick cerebral neurons was induced by exposure to a conditioned medium (CM) prepared by Mg 2+-free treatment of neurons. This suggested that the CM contained a diffus ible factor(s) for the potentiation. 2. In this paper, the factor(s) was shown to be a protein(s) by heat and tr ypsin treatment of the CM. 3. The factor induced the potentiation within 5 min, but it was not require d for maintenance of increased SEPSCs. 4. The factors in CM induced the potentiation without protein synthesis. 5. Protein synthesis at least in postsynaptic neurons, was indispensable to induce the potentiation by the Mg2+-free condition.