Abstract
Human cerebrospinal fluid (hCSF) has proven advantageous over conventional medium for culturing both rodent and human brain tissue. In addition, increased activity and synchrony, closer to the dynamic states exclusively recorded in vivo, were reported in rodent slices and cell cultures switching from artificial cerebrospinal fluid (aCSF) to hCSF. This indicates that hCSF possesses properties that are not matched by the aCSF, which is generally used for most electrophysiological recordings. To evaluate the possible significance of using hCSF as an electrophysiological recording medium, also for human brain tissue, we compared the network and single-cell firing properties of human brain slice cultures during perfusion with hCSF and aCSF. For measuring the overall activity from a majority of neurons within neocortical and hippocampal human slices, we used a microelectrode array (MEA) recording technique with 252 electrodes covering an area of 3.2 × 3.2 mm2. A second CMOS-based MEA with 4225 sensors on a 2 × 2 mm2 area was used for detailed mapping of action potential waveforms and cell identification. We found that hCSF increased the number of active electrodes and neurons and the firing rate of the neurons in the slices and induced an increase in the numbers of single channel and population bursts. Interestingly, not only an increase in the overall activity in the slices was observed, but a reconfiguration of the network could also be detected with specific activation and inactivation of subpopulations of neuronal ensembles. In conclusion, hCSF is an important component to consider for future human brain slice studies, especially for experiments designed to mimic parts of physiology and disease observed in vivo.
Highlights
The brain, with all its neurons, glial cells, and blood vessels, is cushioned and protected by a colorless fluid called cerebrospinal fluid (CSF)
To quantify the activity level of the 12 slices on the 256MEAs, we first extracted the number of active electrodes for each condition, showing 60.67 ± 18.15 electrodes active during artificial cerebrospinal fluid (aCSF), 95.42 ± 15.58 during Human cerebrospinal fluid (hCSF), and 59.08 ± 20.69 during washout, which was significantly different between the groups (p = 0.0062)
In Dunn’s multiple comparison test, we found that the increase in number of active electrodes between aCSF and hCSF (p = 0.0239) and the decrease in number of active electrodes between hCSF and washout (p = 0.0128) were both significantly different, while the number of active electrodes was not significantly different between aCSF and washout (p > 0.9999), altogether demonstrating reversibility of hCSFmediated activity increase (Figure 2A)
Summary
The brain, with all its neurons, glial cells, and blood vessels, is cushioned and protected by a colorless fluid called cerebrospinal fluid (CSF). When hCSF was compared to aCSF in experiments with rat slices, the spontaneous firing of action potentials increased in both hippocampal and cortical slices (Bjorefeldt et al, 2015). This activity seemed closer to the highly active states observed during recordings in vivo. Clear advantages utilizing hCSF as the culturing medium for human organotypic brain slices have previously been shown by our group (Schwarz et al, 2017, 2019) These cultures, acquired from resected human brain tissue, proved more viable and functionally intact over both short and long incubation times when using hCSF compared to conventional culturing medium (Schwarz et al, 2017). Both better understanding of the human physiology and disease mechanisms have been investigated with this ex vivo system (Wittner et al, 2001; Sandow et al, 2015; Dossi et al, 2018; Mansvelder et al, 2019)
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