Effect of magnesium deficiency on nonspecific excitability level (NEL) and audiogenic seizure susceptibility.

Magnesium deficiency in weanling rats caused an increase in NEL and in audiogenic seizure susceptibility. These behavioral effects were apparent after eight days of magnesium restriction and could be reversed by dietary rehabilitation. Serum magnesium declined rapidly from 1.87 +/- 0.10 mEq/L to 0.91 +/- 0.24 mEq/L in two days. Cerebrospinal fluid (CSF) magnesium decreased gradually from 1.86 mEq/L, becoming significantly lower (1.44 +/- 0.23 mEq/L) after eight days. When deficient rats were injected IP with MgCl2, raising the serum magnesium concentration to 6.6 mEq/L, NEL decreased to normal while audiogenic seizure susceptibility remained. Both NEL and audiogenic seizure susceptibility in rats reflect central nervous system magnesium concentration, except when serum magnesium concentration is very high. Very high serum magnesium concentration lowers NEL but does not reduce audiogenic seizure susceptibility if CSF magnesium is low.