title: Comparison of spike parameters from optically identified GABAergic and glutamatergic neurons in sparse cortical cultures.
abstract: Primary neuronal cultures share many typical features with the in vivo situation, including similarities in distinct electrical activity patterns and synaptic network interactions. Here, we use multi-electrode array (MEA) recordings from spontaneously active cultures of wildtype and glutamic acid decarboxylase 67 (GAD67)-green fluorescent protein (GFP) transgenic mice to evaluate which spike parameters differ between GABAergic interneurons and principal, putatively glutamatergic neurons. To analyze this question we combine MEA recordings with optical imaging in sparse cortical cultures to assign individual spikes to visually-identified single neurons. In our culture system, excitatory and inhibitory neurons are present at a similar ratio as described in vivo, and spike waveform characteristics and firing patterns are fully developed after 2 weeks in vitro. Spike amplitude, but not other spike waveform parameters, correlated with the distance between the recording electrode and the location of the assigned neuron's soma. Cluster analysis of spike waveform properties revealed no particular cell population that may be assigned to putative inhibitory or excitatory neurons. Moreover, experiments in primary cultures from transgenic GAD67-GFP mice, which allow optical identification of GABAergic interneurons and thus unambiguous assignment of extracellular signals, did not reveal any significant difference in spike timing and spike waveform parameters between inhibitory and excitatory neurons. Despite of our detailed characterization of spike waveform and temporal spiking properties we could not identify an unequivocal electrical parameter to discriminate between individual excitatory and inhibitory neurons in vitro. Our data suggest that under in vitro conditions cellular classifications of single neurons on the basis of their extracellular firing properties should be treated with caution.
authors: Institute of Physiology, University Medical Center of the Johannes Gutenberg University Mainz, Germany.
authors: Keiko
authors: K
authors: Weir
authors: Institute of Physiology, University Medical Center of the Johannes Gutenberg University Mainz, Germany.
authors: Oriane
authors: O
authors: Blanquie
authors: Institute of Physiology, University Medical Center of the Johannes Gutenberg University Mainz, Germany.
authors: Werner
authors: W
authors: Kilb
authors: Institute of Physiology, University Medical Center of the Johannes Gutenberg University Mainz, Germany.
authors: Heiko J
authors: HJ
authors: Luhmann
authors: Institute of Physiology, University Medical Center of the Johannes Gutenberg University Mainz, Germany.
authors: Anne
authors: A
authors: Sinning
keywords: imaging; interneurons; multi-electrode array; network activity; neuronal culture; spike waveform
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