Figure 7

Developmental profile of network activity in hippocampal and cortical cultures. (A) Representative phase-contrast images of cells dissociated from P1 rat hippocampi or cortices and grown on microelectrode arrays (MEAs) at a density of 150,000 cells/MEA. Recordings of spontaneous electrical activity were collected every 7 days beginning on DIV 7 and continuing through DIV 28. Active electrodes were defined as electrodes with an average of ≥; 5 spikes/min; inactive electrodes with < 5 spikes/min were excluded from analysis. Burst analysis was performed using Neuroexplorer (Version 3.2, NEX Technologies, Littleton, MA, USA), with a burst defined as a minimum of 4 spikes lasting 0.02 s with 0.1 s between bursts. Network activity as a function of DIV was measured as (B) number of active electrodes/well; (C) mean firing rate (MFR); and (D) mean bursting rate (MBR). Data were analyzed by two-way ANOVA. For each endpoint, a significant interaction between time and cell type was observed; therefore, post hoc mean contrast tests were performed to compare means within each cell type across time and means between cell types within each time point. *Means are significantly different between cell types within a time point (Sidak’s test, p < 0.05). All data are expressed as mean ± SD (12–24 wells across four 12-well MEA plates from two independent dissections). (E) Representative images of single wells within MEAs stained with Hoechst 33342 (blue) and propidium iodide (PI, pink) at the end of the recording period on 28 DIV. (F) Three random sites were imaged within each well to quantify the percentage of viable cells, which was determined using the following: [(# Hoechst-stained cells) – (# PI stained cells)]/(# Hoechst-stained cells) × 100. The difference in percent cell viability between 28 DIV hippocampal and cortical cultures were not significantly different.