Auditory cortical neurons in vitro: cell culture and multichannel extracellular recording

Self organization, pattern generation, and pattern processing in local cortical circuits are difficult to study in vivo. The complexities of cortical circuits require simplified systems for study. We have developed a simplified model of auditory cortical neurons growing as monolayer networks in culture. Neurons dissociated from auditory cortex of 14-day mouse embryos were grown on photoetched microelectrode array containing 64 transparent indium-tin oxide electrodes. Cultures were maintained in incubators for up to 113 days. Neurons developed processes and made synaptic connections. All cultures were spontaneously active and exhibited complex temporal burst patterns. In a data set of 12 cultures, the number of active channels varied from culture to culture and ranged from 6-17. Signal/noise ratios ranged from 3:1 to a maximum of 16:1. No significant correlations were found between age of the culture and number of active channels, or signal/noise ratios. Spontaneous firing patterns recorded from various channels showed complex bursting patterns in all cultures. Within a culture, coordinated synchronous bursting were found among some channels, and independent bursting on others. Preliminary histological analysis of cultures using the Loots-modified Bodian stain showed neurons with axonal and dendritic profiles growing extensively on top of the glial carpet. Neuronal processes crossing the electrodes singly or in small groups were also observed. Pyramidal and non-pyramidal cells could be identified. In a pool of 2,093 neurons in a 49-day-old culture, the average size of the somata was found to be 16 microns, with a mode of 12 microns.