Synaptic potentiation induced by a protein factor in cultured cerebral neurons.

1. We reported in a previous paper that long-lasting enhancement of spontaneous 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 diffusible factor(s) for the potentiation. 2. In this paper, the factor(s) was shown to be a protein(s) by heat and trypsin treatment of the CM. 3. The factor induced the potentiation within 5 min, but it was not required 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 Mg(2+)-free condition.