Abstract
Background/Aim: The dorsal striatum is a brain area integrating information for movement output. The local field potentials (LFPs) reflect the neuronal activity that can be used for monitoring brain activities and controlling movement. Materials and Methods: Rhythmic low gamma power activity (30.1-45 Hz) in the dorsal striatum was monitored according to voluntary motor movement in rotarod and bar tests in 0.5 mg/kg haloperidol-induced mice. Results: Haloperidol can effectively induce movement impairment indicated by decreased low gamma LFP with the lessened rotarod test’s latency fall, and the enhanced bar test’s descending latency. L-DOPA was used for the induction of a dopamine-dependent signal. The results showed that 25 mg/kg of L-DOPA could reverse the effect of haloperidol by enhancing low gamma oscillation concomitantly with the improvement in behavioral movement as fast as 60 min after administration, suggesting that dopamine signaling increases low gamma frequency of LFP in correlation with the improved mice movement. This work supports quantitative LFP assessment as a monitoring tool to track drug action on the nervous system. Conclusion: In animal models of motor impairment, oral dopaminergic treatment can be effective in restoring motor dysfunction by stimulating low gamma power activity in the dorsal striatum.
Parkinson’s disease (PD) results from dopaminergic neuron degeneration (1, 2). As a result of decreased dopaminergic activities in the striatum, subthalamic nucleus (STN)-mediated activation increases, and globus pallidus external segment (GPe)-mediated inhibition decreases, affecting globus pallidus internal segment (GPi) – substantia nigra pars reticulata (SNpr) inhibition and thalamus inhibition, resulting in reduced activation of the cortex (3). Haloperidol is an antagonist of dopamine D2 receptors, which produces catalepsy and extra-pyramidal Parkinson’s symptoms (4, 5). Haloperidol can cause chronic movement disorders, whose pathophysiology is linked to oxidative stress and neurotoxicity (6, 7).
Localized field potential oscillations (LFPs) reflect brain functions including attention, perception, movement planning and initiation, and memory (8, 9). There is an excessive synchronization between cortical beta rhythms and spike discharges in the basal ganglia in Parkinson-like rodent models (10, 11). Known as “broadband gamma”, the gamma frequency range between 50 and 200 Hz may be an indicator of underlying asynchronous spikes (12, 13). Parkinson’s disease is associated with an increase in broadband gamma activity in the primary motor cortex (14). There is also evidence linking altered LFPs in the dorsal striatum with Parkinson’s disease (15-17). This study used haloperidol-induced mice to evaluate low gamma activity every 30 min before and after L-3,4-Dihydroxyphenylalanine (L-DOPA) administration. By examining the motor movement, we can examine whether LFP patterns are distributed in relation to movement initiation, and locomotory activity.
Materials and Methods
Mice. The experiment was performed on adult male Swiss albino mice weighing 35-40 g at the start of the investigation. During this experiment, animals were fed ad libitum and maintained in a standard controlled environment. PSU’s Animals Ethical Committee approved the protocols for the care and use of the experimental animals in this study [project license number: 2562-01-072]. The surgical procedures were described previously (18). Intracranial electrode implantation was performed in the unipolar dorsal striatum (+0.5 mm posterior to bregma, +2.0 mm lateral to the midline, +3.0 mm ventral below the dura) of animals.
Treatment scheme. The experimental studies included three groups of animals and are summarized in Figure 1. For the control group, 0.1 M hydrochloric acid pH 5.5-6 was injected intraperitoneally 30 min before oral administration of saline. In the HAL group, 0.5 mg/kg haloperidol was administered intraperitoneally followed by saline administration orally. In the L-DOPA group, 25 mg/kg of L-DOPA was gavaged after intraperitoneal injection of 0.5 mg/kg haloperidol. As a result, the experiments were divided into three phases: 30 min baseline, 30 min haloperidol injection, and 180 min evaluation phase. At the end of each phase, locomotor activity was measured for 5 min with an open field chamber (akinesia), rotarod coordination (motor coordination), and catalepsy (bradykinesia and rigidity). Video of animal exploration was transferred to the computer for movement analysis by the open-source toolbox OptiMouse (19). Rotarod test was performed at a speed of 4 to 40 rounds per min. For each mouse, latency to fall was calculated as the average of three falls (20). The latent period for which animals could stay at the horizontal bar placed 5 cm above the ground was used to determine the rigidity of the catalepsy muscles.
Treatment scheme. Animals were divided in 3 groups: control, HAL and L-DOPA groups.
Local field potential acquisition and analysis. The dorsal striatum was also monitored for low gamma power activity (30.1-45 Hz). PowerLab 16/35 systems (AD Instruments, Sydney, Australia) were used to collect, amplify, and digitize local field potential signals. Hanning window cosine (window size=0.976 s, overlaps=0.488 s) and the Fast Fourier Transform (FFT) algorithm were conducted for frequency analysis through LabChart software.
Statistical analyses. The effect of treatments on low gamma power and locomotion scores was determined by one-way ANOVA. Multiple comparisons were performed using Tukey’s post hoc test to determine significance. Differences were considered significantly at p-value<0.05.
Results
Rotarod test. The latent period on rotarod was decreased from 260.7 s in baseline to 43.3 s and remained during the evaluation phase in the HAL group. Similarly, the latent period in the L-DOPA group was reduced from 261.5 s to 62.2 s after haloperidol injection (Figure 2A). The effect of treatments on rotarod coordination was statistically determined during the injection phase. The mean latent period on the rotarod among the three groups was significantly different, F(2,18)=63.08, p<0.0001. Multiple comparison revealed significantly decreased latent period on the rotarod for HAL and L-DOPA animal groups in comparison to control group (p<0.0001) (Figure 2B). There was an increase in the latent period in the L-DOPA group during the evaluation phase. Therefore, the influence of treatments was also statistically analyzed during the evaluation phase. The mean latency on the rotarod was significantly different between the three groups during this phase, F(2,18)=51.53, p<0.0001. The L-DOPA animal group showed a significantly increased latent period on the rotarod in comparison to the HAL group (p=0.0105) (Figure 2C).
Effects of haloperidol-induced locomotor impairment and levodopa pretreatment in behavioral tests. Latency period on rotarod displayed in 30 min time interval (A). The average latent period on rotarod was determined in the injection phase (B) and evaluation phase (C). Latency period on the bar showed in 30 min time interval (D). The average latent period on the bar was determined in the injection phase (E) and evaluation phase (F). Data represent mean±S.E.M. Tukey’s Post hoc test was significant at *p<0.05, **p<0.01, ***p<0.001 and ****p<0.0001.
Bar test. In the HAL group, the latent period on the bar increased from 4.5 s at baseline to 94.7 s during injection phase (Figure 2D). The effect was prolonged throughout the entire evaluation session. Animals in the L-DOPA group showed a similar pattern of increased latency on the bar from 0 to 165.5 s. The influence of treatments on the bar test was statistically analyzed during the injection phase. There were significant differences in the mean latent period between the three groups [F(2,18)=7.338, p=0.0055]. Multiple comparison revealed the latent period on the bar increased significantly in the L-DOPA animal group (p<0.0001) in comparison to the control group (Figure 2E). There was a decrease in the latent period in the L-DOPA group. Therefore, the influence of treatments was statistically analyzed during the evaluation phase. The mean latency on the bar among the three groups during this phase was significantly different; F(2,18)=32.72, p<0.0001. The L-DOPA group showed a significantly decreased latent period on the bar in comparison to the HAL group (p=0.0105) (Figure 2F).
Locomotor activity. In an open field chamber, the locomotor movement was tracked and analyzed in the speed parameter for 5 min each time. The speed was not different among groups (Figure 3).
Effects of haloperidol-induced locomotor impairment and levodopa pretreatment in the speed of movement. Five min in an open field chamber at 30 min time intervals were analyzed.
Local field potential analysis. The acute impact of haloperidol i.p. injection in percent total power of low gamma activities was determined in a time series (Figure 4A). The distribution of low gamma following haloperidol injection was reduced in the HAL and L-DOPA groups (Figure 4B). The percentage power of low gamma was suppressed in the average of 180 min of the recording session in the HAL group. The mean percent total power of low gamma activity between the three groups was significantly different during the injection phase [F(2,18)=56.63, p<0.0001]. Multiple comparison revealed that low gamma activity decreased significantly in the HAL and L-DOPA animal groups (p<0.0001) (Figure 4C). There was an increase in low gamma activity in the L-DOPA group. The mean percent power of low gamma activity during the evaluation phase was significantly different; F(2,18)=22.55, p<0.001. The L-DOPA group showed a significantly increased low gamma brain oscillation in comparison to the HAL group (p=0.0002) (Figure 4D).
Effects of treatments in local field potential monitoring. Dorsal striatum low gamma activity in the three groups is visualized (A). Raw signals range from 1 to 100 Hz in the upper chart, while low gamma activity range from 30.1-45 Hz in the lower chart. The average low gamma activity was monitored (B). The percent total power of low gamma oscillation was determined in the injection phase (C) and evaluation phase (D). Data represent mean±S.E.M. Tukey’s Post hoc test was significant at ***p<0.001 and ****p<0.0001.
Discussion
Rhythmic gamma activity is observed in local field potential, and oscillations in the striatum are correlated with voluntary movement, reward, and decision-making in healthy individuals (21, 22). Based on quantitative analyses of local field potentials, low gamma activity within the striatum is produced by neurons during movement (23). Disorders of the dopamine and motor systems, such as Parkinson’s and Huntington, result in abnormal network activity within the striatum (24-26). Pathological gamma oscillations interrelated with impaired dopamine release indicated synaptic loss and reduced dynamic range of unitary glutamatergic synaptic transmission in the striatum of a Huntington mouse model (27). Since low gamma activity in the dorsal striatum correlates with dopamine release in the striatal pathway, mice treated with saline showed a normal dopamine concentration in the striatum of about 4.5 mg/g. As haloperidol was administered at 0.5 mg/kg, striatal dopamine concentrations gradually decreased to 3.7 M/mg tissue. When the dopamine precursor levodopa was administered to animals, it reversed the effect of monoamine depletion on dopamine levels and motor activity (28). In summary, these findings suggest that dopamine increases synchronized neuronal oscillations at low gamma frequencies in the dorsal striatum, promoting efficient physical and functional movement. Movement could be generated even if these oscillations synchronize across the dorsal striatum by drugs or deep brain stimulation.
Acknowledgements
This work was supported by grants from the Graduate School and the Division of health and applied science, Faculty of Science, Prince of Songkla University, Hatyai, Songkhla, Thailand.
Footnotes
Authors’ Contributions
A study design was developed by CR, NS and EK. This manuscript was authored by NS. The surgical procedures were monitored by DC. Final approval of the manuscript was obtained from all Authors after critical revision.
Conflicts of Interest
All Authors declare that they have no conflicts of interest in relation to this study.
- Received October 31, 2022.
- Revision received November 10, 2022.
- Accepted November 14, 2022.
- Copyright © 2023, International Institute of Anticancer Research (Dr. George J. Delinasios), All rights reserved
This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY-NC-ND) 4.0 international license (https://creativecommons.org/licenses/by-nc-nd/4.0).
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