Abstract

The effects of Mg 2+ on Ni 2+-induced epileptiform bursting activity and input membrane resistance during this activity of leech Retzius neurons were examined using intracellular recordings. To induce epileptiform activity, 3 mmol/l NiCl 2 was added into superfusing Ringer (Ri) saline. To test for dose-dependence of the effects of Mg 2+ on the induced epileptiform activity, MgCl 2 was added in concentrations from 1 mmol/l to 20 mmol/l Mg 2+ to the Ni 2+-containing Ri saline. Input membrane resistance (IMR) was measured in standard Ri, Ni 2+ Ri and 20 mmol/l Mg 2+ Ni 2+ Ri saline. Superfusion with Ni 2+ Ri induced epileptiform bursting activity characterized by generation of paroxysmal depolarization shifts (PDSs). Parameters of epileptiform activity including PDS frequency, PDS duration, PDS amplitude and the number of spikes/PDS were measured. Magnesium suppressed Ni 2+-induced epileptiform activity, significantly reducing values of all parameters observed in a concentration-dependent manner. The highest concentration applied of 20 mmol/l Mg 2+ completely eliminated epileptiform activity. To test for the effect of Mg 2+ on membrane conductance during bursting, IMR was measured. Magnesium significantly increased IMR during bursting suppression.

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