Effect of acute administration of certain heavy metals and their combinations on the spontaneous and evoked cortical activity in rats.

The aim of this study was to see the effect of acutely administered inorganic lead, mercury, manganese, and their combinations, on the electrical activity in the somatosensory system of rats. Male Wistar rats were anaesthetised with urethane, the head was fixed in a stereotaxic frame and the left hemisphere was exposed. Weak electric shocks to the whiskers and the tail served as stimuli. Spontaneous and stimulus-evoked activity was recorded from the primary projection area of the whiskers and the tail. After an hour of control recording, one of the following was given to the rat i.p.: 1000mg/kg Pb(2+), 7mg/kg Hg(2+), 50mg/kg Mn(2+), 500mg/kg Pb(2+)+25mg/kg Mn(2+), or 500mg/kg Pb(2+)+3.5mg/kg Hg(2+). Lead caused a massive increase in the cortical response amplitude, starting immediately after administration and developing in the next 40-50min. Latency showed a minimal increase. The spontaneous activity was moderately shifted to lower frequencies. The effect of Hg(2+) on the response amplitude and on the ECoG was similar but stronger than that of Pb(2+). The effect of Mn(2+) on the evoked activity was marked but less strong than with Pb(2+). The ECoG shift was moderate. With Hg(2+) and Mn(2+), the response amplitude showed first a decrease than an increase. The effect of the Pb(2+)+Mn(2+) combination on the activities was not additive but the correlation between the alteration of the ECoG and the evoked potential was stronger than with any of the metals alone. With Pb(2+)+Hg(2+), the effect of Pb(2+) dominated on the evoked and that of Hg(2+) on the spontaneous activity. In the peripheral nerve, action potential amplitude and conduction velocity were decreased. These alterations of the spontaneous and stimulus-evoked cortical activity probably reflected a specific action of the heavy metals on the nervous activity.