Recurrent subthreshold electrical activities of rat neocortical neurons progress during long-term culture

The properties of neocortical neurons during long-term culture on monolayers of astrocytes were examined using whole-cell recording and immunocytochemical techniques. The soma size of neocortical neurons became larger and most neurites reached neighboring neurons within 2 weeks. Recurrent subthreshold electrical activities mediated by synaptic activation were observed at 10 days of culture and became more frequent as the neurons grew. Their frequency reached to about 1 Hz at 4 weeks. While the total number of neurons decreased during culture, the ratio of gammaaminobutyric acid (GABA) positive to total (MAP2 positive) neurons increased. These results suggest that neurons grown on astrocytes become mature during cultivation, and that recurrent subthreshold electrical activities may be related to the development of GABAergic inputs.