Altered electrophysiological characteristics of developing rat cortical neurones after chronic methylmercury chloride treatment

Abstract

The effect of methylmercury chloride on the excitability of developing cortical neurons was tested. Methylmercury was administered in the drinking water to pregnant rats during gestation and suckling period and the offspring were investigated. The electrical characteristics of the neuronal membranes as well as the synaptic responses evoked by electrical stimulation of the corpus callosum were measured in brain slices. Slices prepared from the somatosensory cortex of 4-week-old rats were analyzed using sharp electrode intracellular microelectrophysiological recording technique. Long-lasting treatment with low doses of methylmercury chloride caused a slight decrease in the membrane potential and in the amplitude of spikes together with an enhanced excitability. Some of the treated animals were grown up without any further methylmercury application, and their offspring (second generation) were also studied electrophysiologically. These untreated offspring had normal neuronal characteristics. The altered membrane characteristics detected in the 4-week-old MeHg treated animals might be the consequence of the abnormal developmental processes taking place in the presence of MeHg which may alter the normal neuronal excitability. Besides this, the acute toxic effect of Hg2+, which was present in the brain at the time of investigations, has to be taken into consideration.