Examinations of Bilateral Epileptiform Activities in Hippocampal Slices Obtained From Young Mice

Abstract

Bilateral interconnections through the hippocampal commissure play important roles in synchronizing or spreading hippocampal seizure activities. Intact hippocampi or bilateral hippocampal slices have been isolated from neonatal or immature rats (6–7 or 12–21 days old, respectively) and the mechanisms underlying the bilateral synchrony of hippocampal epileptiform activities have been investigated. However, the feasibility of examining bilateral epileptiform activities of more developed hippocampal circuitry in vitro remains to be explored. For this, we prepared bilateral hippocampal slices from C57 black mice, a strain commonly used in neuroscience and for genetic/molecular modifications. Young mice (21–24-day-old) were used in most experiments. A 600-μm-thick slice was obtained from each mouse by horizontal vibratome sectioning. Bilateral dorsal hippocampal and connecting dorsal hippocampal commissure (DHC) tissues were preserved in the slice and extrahippocampal tissues were removed. Slices were recorded in a submerged chamber mainly at a room temperature (21–22°C). Bilateral CA3 areas were monitored by extracellular recordings, and unilateral electrical stimulation was used to elicit CA3 synaptic field potentials. The unilateral stimulation could elicit population spikes in the contralateral CA3 area. These contralateral spikes were attenuated by inhibiting synaptic transmission with cobalt-containing medium and were abolished when a cut was made at the DHC. Self-sustained and bilaterally correlated epileptiform potentials were observed following application of 4-aminopyradine and became independent after the DHC cut. Bilateral hippocampal activities were detectable in some slices of adult mice and/or at 35–36°C, but with smaller amplitudes and variable waveforms compared to those observed from slices of young mice and at the room temperature. Together, these observations suggested that examining bilateral epileptiform activities in hippocampal slices of young mice is feasible. The weaknesses and limitations of this preparation and our experimentation are discussed.

Axonopathy and altered synaptic development in early hippocampal epileptogenesis of Dravet syndrome

“…AAV-PHP.eB hSyn-gCamp7f was injected in the lateral ventricle of newborn mice. Consistent with the literature (Liu et al 2020), ex vivo spontaneous network activity was most robust and reproducible in CA3 in our in vitro preparation. Recordings revealed a reduction of overall calcium-peak frequencies (0.26 ± 0.004 Hz, n = 271 vs. 0.24 Hz ± 0.002 Hz, n = 983, p = 0.00213) while the neuronal bursting activity was increased with significantly longer calcium-peak durations (3.08 ± 0.055 s, n = 271 vs. 4.12 ± 0.036 s, n = 983, p < 0.0001), larger peak area under the curve (AUC) (1.742 ± 0.465, n = 255 vs 4.10 ± 0.357, n = 926, p < 0.0001) and peak amplitudes (0.1917 ± 0.009 ΔF/F 0 , n = 271 vs. 0.23 ± 0.0.008 ΔF/F 0 , n = 983, p < 0.0001) as well as a higher maximal cross-correlation between pairs of neurons within brain slices of Scn1a +/A1783V mice (0.05 ± 0.001, n = 5828 vs. 0.06 ± 0.0004, n = 56989, p < 0.0001), altogether indicating network hyperexcitability in CA3 (Supplementary Figure 4).…”

AsHC 360 Exposure Influence on Epileptiform Discharges in Hippocampus of Infantile Male Rats In Vitro

“…Moreover, epileptiform events having a constant discharge time of 300-2000 ms were defined as PIDs (pre-ictal discharges). Additionally, epileptiform events with continuous discharge times more than 2000 ms were identified as IDs (ictal discharges) [53]. In this study, we also adopted a minimum frequency of activity criterion to exclude events characterized by low-frequency spiking that are not indicative of genuine epileptiform activity.…”