Effects of Ba 2+ and Cd 2+ on convulsive electroshock sensitivity and 45Ca distribution in brain subcellular fractions in mice

Abstract

Barium increases the convulsive corneal electroshock sensitivity of mice tested 0.5 hr after Ba 2+ administration (6.6 and 20 mg/kg, ip) but decreases sensitivity of mice tested 24 hr after Ba 2+ (2, 6.6, and 20 mg/kg, ip). Twenty-four hours after Cd 2+ injection (0.34, 1.1, and 3.4 mg/kg, ip) the percentage of mice convulsing after electroshock was decreased, but 0.5 hr after Cd 2+ was given no alteration of electroshock sensitivity was seen. Doses of Ba 2+ and Cd 2+ which alter electroshock threshold were used to determine effects of these ions on 45Ca distribution in subcellular fractions of whole mouse brain. Distribution of Ba and Cd in brain subcellular fractions was also determined. Elevated 45Ca in synaptosomes 0.5 hr after Ba 2+ injection may reflect the ability of Ba 2+ to cause membrane depolarization and influx of calcium, and these effects may be associated with increased electroshock sensitivity. Increased 45Ca in brain synaptosomes was correlated with elevated electroconvulsive shock threshold 24 hr after Cd 2+ administration. Excess Ca 2+ in cortical neurons may explain the decreased responsiveness of mice to electroconvulsive shock 24 hr after Cd 2+ treatment. Accumulation of Ba 2+ in neurons in the CNS also appears to increase electroconvulsive shock threshold.