Aims: 

To follow-up development of manganese-induced functional changes of the central nervous system by repeatedly recording cortical electrical activity and open-field (OF) motility of rats wearing chronic cortical electrodes.

Methods: 

Four male Wistar rats were equipped with two pairs (one over each hemisphere) of epidurally placed chronic electrodes, and a "crown" enabling leading-off of electrocorticogram (ECoG). After healing, one 60-min recording session per week was held for 10 weeks. The rat was put in an OF box to detect movement by infrared light gates while its crown was cable-connected to the recording setup. After the 2^nd week, the rats had 7.5 mg/l MnCl₂ in the drinking water. From the OF records, ambulation distance and time spent with ambulation, local activity and immobility was obtained. From the ECoG, power spectrum and total power was calculated.

Results: 

In the first 4 weeks of Mn exposure, the rats' ambulation distance substantially decreased, and the time spent in immobility and length of immobile periods increased. Later on, these changes showed little progression. In a 5^th, untreated control rat, mobility decrease (due primarily to aging) started only from the 5^th week. Motility decrease during one 60-min session (habituation) was also stronger in the exposed rats. The total power of ECoG in treated rats increased in the first 4 weeks (mainly between ca. 5 and 35 Hz) compared to the control. The spectrum peak at 7–8 Hz was replaced by a broader range of increased activity, apparently in periods dominated by immobility.

Conclusions: 

1) Combination of repeated ECoG and OF recording is suitable for following-up development of Mn-induced neurotoxicity. 2) The functional alterations depend on the time and/or summed dose of Mn exposure, but not linearly. 3) Total power and spectrum of ECoG and the level of motility are apparently correlated.