THE EFFECTS OF LOW-LEVEL LEAD-EXPOSURE IN DEVELOPING RATS - CHANGES IN CIRCADIAN LOCOMOTOR-ACTIVITY AND HIPPOCAMPAL NORADRENALINE TURNOVER

The circadian spontaneous locomotor activity of rats exposed to 0.1 mg Pb/kg, orally from 3 days-4 and 6 wk of age was similar to that of controls. Hyperactivity during initial hours of recording was observed in rats that were treated with Pb until 8 wk of age. When treatment was discontinued for 2 wk, previously Pb-exposed rats had a tendency to be hypoactive. The elevated locomotor activity in 8 wk-old Pb-treated rats was not accompanied by any significant changes of noradrenaline [norepinephrine] levels in the cerebral cortex or hippocampus. Alterations in noradrenaline content of the hippocampus were observed in rats that had been treated with Pb for 4 and 6 wk. The turnover rate of noradrenaline in the hippocampus was also significantly reduced following treatment for 6 wk. Regional distribution of Pb in the brains of Pb-exposed rats showed a large accumulation of the metal in the hippocampus. The alterations of the noradrenergic function in the hippocampus may have been associated with the preferential storage of Pb in this region.