Manganese-induced atypical parkinsonism is associated with altered Basal Ganglia activity and changes in tissue levels of monoamines in the rat

Abstract

Manganese neurotoxicity is associated with motor and cognitive disturbances known as Manganism. However, the mechanisms underlying these deficits remain unknown. Here we investigated the effects of manganese intoxication on motor and non-motor parkinsonian-like deficits such as locomotor activity, motor coordination, anxiety and "depressive-like" behaviors. Then, we studied the impact of this intoxication on the neuronal activity, the globus pallidus (GP) and subthalamic nucleus (STN). At the end of experiments, post-mortem tissue level of the three monoamines (dopamine, norepinephrine and serotonin) has been determined. The experiments were carried out in adult Sprague-Dawley rats, daily treated with MnCl2 (10 mg/kg/, i.p.) for 5 weeks. We show that manganese progressively reduced locomotor activity as well as motor coordination in parallel with the manifestation of anxiety and "depressive-like" behaviors. Electrophysiological results show that, while majority of GP and STN neurons discharged regularly in controls, manganese increased the number of GP and STN neurons discharging irregularly and/or with bursts. Biochemical results show that manganese significantly decreased tissue levels of norepinephrine and serotonin with increased metabolism of dopamine in the striatum. Our data provide evidence that manganese intoxication is associated with impaired neurotransmission of monoaminergic systems, which is at the origin of changes in basal ganglia neuronal activity and the manifestation of motor and non-motor deficits similar to those observed in atypical Parkinsonism.

Figure 1. Experimental design and histological verifications.

(A) Schematic presentation of the experimental design with a time course of all the behavioral tests (EPM: elevated plus maze, FST: forced swim test, SPT: sucrose preference test) and electrophysiological recordings. The vertical arrows correspond to the days when the rats were submitted to the open field and rotarod tests. (B) Histological sections showing the location of the pontamine sky blue dots in the GP (left) and the STN (right). (C) Location of brain regions sampled for biochemistry studies. Circles delineate the rostral (top) and caudal (bottom) limits of the sampled regions of cortex and striatum used for HPLC.

Figure 2. Effect of manganese on body weight gain.

Values are the mean ± SEM. Data from Manganese-treated rats (n = 12) and controls (n = 11) were compared using the two way repeated measures ANOVA and Holm-Sidak post hoc. **p<0.01, ***p<0.001.

Figure 3. Manganese progressively reduced exploratory activity.

Exploratory activity histograms represent the number of horizontal (A), stereotypic (B), and vertical movements (C) recorded during the first session of 10 min in the “open field” actimeter before and during all period of treatment. Values are the mean ± SEM. Data from manganese-treated rats (n = 12) and controls (n = 11) were compared using the two way repeated measures ANOVA and Holm-Sidak post hoc. *p<0.05, **p<0.01.

Figure 4. Manganese progressively reduced locomotor activity.

Locomotor activity histograms represent the number of horizontal (A), stereotypic (B), and vertical movements (C) recorded during the second 10 min session in the “open field” actimeter before and during all the period of treatment. Values are the mean ± SEM. Data from manganese-treated rats (n = 12) and controls (n = 11) were compared using the two way repeated measures ANOVA and Holm-Sidak post hoc. *p<0.05, **p<0.01, ***p<0.001.

Figure 5. Manganese progressively reduced motor coordination.

Motor coordination histogram represents the time that rat stay on the bar of rotarod before and during all period of treatment. Values are the mean ± SEM. Data from manganese-treated rats (n = 5) and controls (n = 5) were compared using the two way repeated measures ANOVA and Holm-Sidak post hoc. **p<0.01, ***p<0.001.

Figure 6. Manganese induced anxiety, anhedonia and depressive like behaviors.

(A) Histograms showing the percentage of the number of entries into the open arms of elevated plus maze relative to the total number of entries into the four arms (left) and the percentage of time spent in the open arms relative to the total time spent in the four arms (right). (B) Histograms showing the immobility duration in the forced swim test and the percentage of sucrose consumption relative to the total consumption. Values are the mean ± SEM. Data from Manganese-treated rats (n = 5) and controls (n = 6) were compared using the Mann–Whitney test. *p<0.05, **p<0.01.

Figure 7. Manganese decreased the firing rate of GP neurons and increased the proportion of bursty and irregular neurons.

(ABC) Representative examples of spike trains recorded in the GP (a) with interspike interval histogram (b) and density histogram (c), showing a regular pattern in control rats (A) and irregular and bursty patterns in manganese (Mn)-treated animals (B and C respectively). (D) Firing rate histograms with values as the mean ± SEM. Firing rate data from manganese-treated rats and controls were compared using Student t-test. **p<0.01. (E) Firing pattern histograms showing the proportion of GP cells discharging regularly, irregularly or with bursts. Changes in the proportion of different firing patterns were analyzed using a chi square test. ***p<0.001 in comparison with controls.

Figure 8. Manganese decreased the firing rate of STN neurons and increased the proportion of irregular neurons.

(AB) Representative examples of spike trains recorded in the STN (a) with interspike interval histogram (b) and density histogram (c), showing a regular pattern in control rats (A) and irregular pattern in manganese (Mn)-treated animals (B). (C) Firing rate histograms with values as the mean ± SEM. Firing rate data from manganese-treated rats and controls were compared using Student t-test. (D) Firing pattern histograms showing the proportion of STN cells discharging regularly, irregularly or with bursts. Changes in the proportion of different firing patterns were analyzed using a chi square test. *p<0.05, ***p<0.001 in comparison with controls.