Low-magnesium medium induces epileptiform activity in mouse olfactory bulb slices

Area of Science:

• Neuroscience
• Electrophysiology
• Epilepsy Research

Background:

• Magnesium-free medium enhances glutamate receptor function but can induce seizure-like activity.
• The rodent olfactory bulb (OB) slice is a common model for studying odor processing.
• Ictogenic (seizure-inducing) conditions are sometimes used in OB slice preparations.

Purpose of the Study:

• To investigate low magnesium (Mg2+)-induced epileptiform discharges in mouse OB slices.
• To characterize the nature and mechanisms of these seizure-like events (SLEs).
• To evaluate the OB slice as a model for studying seizure mechanisms, particularly slow direct current (DC) shifts.

Main Methods:

• Extracellular and whole-cell electrophysiological recordings in mouse OB slices.
• Induction of epileptiform activity using low-Mg2+ medium.
• Pharmacological manipulation to assess the role of N-methyl-D-aspartate (NMDA) and α-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) receptors and sodium currents.

Main Results:

• Low-Mg2+ induced two distinct activities: delta-frequency oscillations and minute-long SLEs.
• SLEs involved sustained depolarization of output neurons and were dependent on NMDA receptors and sodium currents.
• AMPA receptors facilitated SLEs, which initiated in the glomerular layer and propagated slowly.

Conclusions:

• Low-Mg2+ medium should be used cautiously in OB slices due to induced seizure-like activity.
• The observed SLEs resemble clinically relevant slow DC shifts in seizures.
• The OB slice offers a valuable in vitro model for studying isolated epileptiform DC shifts in acute seizures.