Magnesium Effects on Nonsynaptic Epileptiform Activity in Leech Retzius Neurons

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.

Effect of low potassium concentration on cadmium induced epileptiform activity of leech retzius neurons

“…Praktično su samo započeta ispitivanja na RNP Hirudo medicinalis [6]. Na našem modelu RNP Haemopis sanguisuga rađeno je ispitivanje efekta Ni 2 [7], ali nije rađeno ispitivanje efekta Cd 2+ . Zato smo preduzeli seriju ogleda sa Cd 2+ da bi smo utvrdili da li joni ovog prelaznog metala mogu izazvati epileptiformnu aktivnost na našem modelu.…”

“…Ni 2+ i Co 2+ [7], sada smo poredili učinke Cd 2+ sa učincima Ni 2+ i Co 2+ . Cd 2+ dovodi do nastanka repetitivne aktivnosti u mnogo nižoj koncentraciji (100µmol/l) nego Ni 2+ i Co 2+ koji su bili primenjivani u koncentraciji od 3 mmol/l.…”

“…platoa produžene depolarizacije tokom kojih se javljaju salve akcionih potencijala [5,7]. Ovi platoi imaju sve karakteristike PDS koji predstavljaju ćelijsku osnovu epilepsije.…”

“…Karakteristike i dinamika Cd 2+ izazvanih PDS slični su karakteristikama epileptiformne aktivnosti izazvane Ni2+ u koncentraciji od 3 mmol/l na istom modelu [7]. Razlog zbog koga Cd 2+ nije takođe primenjen u dozi od 3 mmol/l je taj što je pokazano da u većim dozama Cd 2+ može ispoljiti svoje efekte na druge jonske kanale.…”

Paroxysmal Depolarization Shift in Leech Retzius Nerve Cells Revisited

“…The paroxysmal depolarization shift (PDS) is a hallmark of epileptiform activities at cellular level [1][2][3]. PDS or bursting is characterized by the firing of rapid series of several action potentials with very short (less than ~5ms interspike interval) on the top of the depolarizing membrane envelope [1][2][3][4].…”