Epileptiform activity in mouse hippocampal slices induced by moderate changes in extracellular Mg(2+), Ca(2+), and K(+)

BACKGROUND: Rodent brain slices—particularly hippocampal slices—are widely used in experimental investigations of epileptiform activity. Oxygenated artificial cerebrospinal fluid (ACSF) is used to maintain slices in vitro. Physiological or standard ACSF containing 3–3.5 mM K(+), 1–2 mM Mg(2+), and 1–3 mM Ca(2+) generally does not induce population epileptiform activity, which can be induced by ACSF with high K(+) (8–10 mM), low Mg(2+), or low Ca(2+) alone or in combination. While low-Mg(2+) ACSF without intentionally added Mg salt but with contaminating Mg(2+) (≤ 50–80 µM) from other salts can induce robust epileptiform activity in slices, it is unclear whether such epileptiform activity can be achieved using ACSF with moderately decreased Mg(2+). To explore this issue, we examined the effects of moderately modified (m)ACSF with 0.8 mM Mg(2+), 1.3 mM Ca(2+), and 5.7 mM K(+) on induction of epileptiform discharges in mouse hippocampal slices. RESULTS: Hippocampal slices were prepared from young (21–28 days old), middle-aged (13–14 months old), and aged (24–26 months old) C57/BL6 mice. Conventional thin (0.4 mm) and thick (0.6 mm) slices were obtained using a vibratome and pretreated with mACSF at 35–36 °C for 1 h prior to recordings. During perfusion with mACSF at 35–36 °C, spontaneous or self-sustained epileptiform field potentials following high-frequency stimulation were frequently recorded in slices pretreated with mACSF but not in those without the pretreatment. Seizure-like ictal discharges were more common in thick slices than in thin slices. CONCLUSIONS: Prolonged exposure to mACSF by pretreatment and subsequent perfusion can induce epileptiform field potentials in mouse hippocampal slices. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12868-021-00650-3.