The Journal of Neurophysiology Vol. 81 No. 1 January 1999, pp. 399-403
Copyright ©1999 The American Physiological Society

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A Relative Energy Failure Is Associated With Low-Mg²⁺ But Not With 4-Aminopyridine Induced Seizure-Like Events in Entorhinal Cortex

S. Schuchmann¹, K. Buchheim², H. Meierkord², and U. Heinemann¹

¹ Institut für Neurophysiologie and ² Neurologische Klinik und Poliklinik, Universitätsklinikum Charité, Humboldt-Universität Berlin, D-10117 Berlin, Germany

Schuchmann, S., K. Buchheim, H. Meierkord, and U. Heinemann. A relative energy failure is associated with low-Mg²⁺ but not with 4-aminopyridine induced seizure-like events in entorhinal cortex. J. Neurophysiol. 81: 399-403, 1999. During seizure-like events (SLEs), intracellular Ca²⁺ concentration ([Ca²⁺]_i) increases causing depolarization of the mitochondrial membrane and subsequent intramitochondrial accumulation of Ca²⁺. Mitochondrial depolarization results in an interruption of oxidative phosphorylation and increase in reactive oxygen species. Calcium activates enzymes of the citrate cycle. A characteristic feature of the low-Mg²⁺-induced SLEs is that they are transformed to a late activity refractory to anticonvulsant drugs, which may be regarded as a model system of difficult to treat status epilepticus. In contrast, 4-aminopyridine (4-AP)-induced activity rarely evolves to such late activity. The autofluorescence of NAD(P)H was used to monitor changes in cellular energy metabolism in the entorhinal cortex in two in vitro models of focal epilepsy. During repetitive 4-AP-induced SLEs there was a short decrease followed by a long-lasting overshoot of the NAD(P)H signal. This sequence remained unaltered during recurring SLEs. In contrast, during recurrent low-Mg²⁺-induced SLEs, the brief initial NADH signal reduction was unchanged but the following overshoot of NADH displayed a continuous decrease. This indicates a relative energy failure, which may contribute to the transformation to late activity in the low-Mg²⁺ model.

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