Auditory cortical neurons in vitro: initial pharmacological studies.

Dissociated embryonic tissue from murine auditory cortex formed spontaneously active monolayer networks in culture that were maintained for up to 113 days in vitro (div). As a first step in determining whether neurons retain histiotypic properties, we subjected a set of 10 cultures to a sequence of 4 synaptically active substances. The test sequence consisted of 50 microM bicuculline, 10 microM strychnine, 5 microM NMDA, and 20 microM GABA. Recordings were made for 5-30 min under each condition followed by complete medium changes. Six to 14 channels with the best signal-to-noise ratios were selected for analysis that consisted of continual chart recordings of integrated burst data and further analysis of short data segments after digitizing and processing. All networks showed spontaneous activity, but had greatly varying native activity ranging from organized, quasi-periodic bursting on all channels to more complex spatio-temporal patterns with less coordination among channels. Bicuculline triggered oscillatory activity, simplified bursting, increased burst amplitude, and enhanced burst regularity among electrodes. Strychnine also changed the burst activity to a simpler pattern and enhanced the burst amplitude, indicating presence of glycine receptors in cortical tissue. Application of NMDA increased burst frequencies, but reduced burst regularity and coordination among channels. 20 microM of GABA inhibited all bursting activity in the networks. These results suggest that monolayer networks cultured on multi-electrode arrays retain some basic histiotypic pharmacological responses and may provide useful platforms for the study of network dynamics in the auditory cortex.