Maze learning and motor activity deficits in adult mice induced by iron exposure during a critical postnatal period

Newborn mice were administered Fe2+ (iron succinate: 7.5 mg/kg, b.wt) on ei ther Days 3-5, 10-12 or 19-21, or vehicle (saline) at the same times, postn atally. Spontaneous motor behaviour and radial arm maze learning were teste d at the age of 3 months. It was found that mice treated with Fe2+ during p ostnatal Days 10-12 were markedly hypokinetic during the 1st 20-min test pe riod and hyperkinetic during the 3rd and final 20-min test period. These mi ce showed an almost complete lack of habituation of spontaneous motor activ ity parameters to the test chambers. In the radial arm maze, the Days 10-12 treatment group evidenced significantly both more errors in arm choices an d longer latencies to acquire all eight pellets; these mice showed also a s evere trial-to-trial retention deficit as indexed by retention quotients. T hese behavioural deficits were observed also in animals treated with Fe2+ d uring postnatal Days 3-5, but the effects were less pronounced, indicating the higher susceptibility of the brain for Fe2+-induced damage during Days 10-12 postpartum. Treatment with Fe2+ on Days 19-21 did not induce behaviou ral alterations in comparison with its respective control (vehicle) group. Analysis of total brain iron content indicated significantly more iron (mu g/g) accumulation in the basal ganglia, but not frontal cortex, of mice fro m the Days 3-5 and 10-12 Fe2+ (7.5 mg/kg) treatment groups. The contributio n of iron overload during the immediate postnatal to later functional defic its seems to implicate symptoms of Parkinsonism but the kinetics of iron up take to the brain and its regional distribution at this critical period of development awaits elucidation. (C) 2000 Elsevier Science B.V. All rights r eserved.