Introduction: In humans, bruxism is defined as the grinding or clenching of the teeth. Pathological bruxism can cause damage to dental surfaces, joint pain and many other dentally related issues. Bruxism can be displayed while awake or during sleep. In humans, L-dopa can attenuate bruxism during sleep. To grind down continuously growing teeth, rats display a brux-like behavior while awake. L-dopa’s effect on brux-like motor patterns in rats have never been characterized. The influence of L-dopa on masticatory motor patterns has not been investigated in rats or humans. This pilot study used electromyography in three masticatory muscles to test the effects of acute L-dopa on brux-like motor patterns and mastication in rats.
Methods: Electromyography (EMGs) fine silver wire electrodes were surgically implanted into the anterior superficial masseter, anterior digastric, and posterior superficial masseter muscles of laboratory rats (Rattus norvegicus) (n=10). The fine silver wire electrodes were run sub-dermally to an electrode pedestal, which was secured to the skull via screws and dental cement. A preamplifier (X10) was attached to the headcap, and sent to a secondary amplifier (x100). This amplified signal was sent to an A/D converter, and digitally recorded with a personal computer. Rats received an IP injection of L-dopa (10mg/kg)/Benserazide (15mg/kg) or saline vehicle. We recorded brux-like EMG bursts for one hour after injection. After the initial hour of brux-like recording, the rats were given food and masticatory EMG bursts were recorded. After recording, at least one hundred onsets and offsets were collected for each behavior. This was done for every animal. For brux-like behavior, the number of episodes per hour, average episode duration, and total time displaying brux-like activity was obtained for each animal and compared using a Mann-Whitney U test. For brux-like and masticatory motor patterns, cycle period (onset-to-onset), burst duration (onset-to-offset), between burst (offset-onset), and cycles per second were recorded for every animal and compared using a Mann-Whitney U test. Phase values, which compare the timing of two muscles, was also obtained. Treatment groups were compared to assess L-dopa’s effects on brux-like and masticatory motor patterns.
Results: The number of brux-like episodes per hour in controls (μ=47.8, SD=18.7) was greater than the group that received the L-dopa treatment (μ=16, SD= 12.53); (U=2, p<0.05). Average episode duration and total time displaying brux-like activity per hour did not change (NS). Anterior superficial masseter cycle period, burst duration, between burst, and cycles per second were not different between treatments (NS). Anterior digastric cycle period, burst duration, and between burst were not different between treatments (NS). For the anterior digastric, the L-dopa treatment group had a higher rate of cycles per second (μ=7.271, SD=0.973) than the control group (μ=9.034, SD=1.422) (U=2, p=.05). We compared the phase relationships between the anterior superficial masseter and anterior digastric using a Watson-Williams F test and found the phase values to be similar (NS). Not enough posterior superficial masseter muscle traces were obtained for statistical test to be performed. The obtained results for the posterior superficial masseter muscle were characterized for future experiments.
Conclusion: Although L-dopa attenuates sleep bruxism in humans, it has not been used to assess brux-like motor patterns in rats. Rats display a conscious, brux-like motor pattern that is used to prevent tooth overgrowth. This study is the first to establish that brux-like motor patterns in the conscious rats are attenuated by acute doses of L-dopa. Brux-like motor patterns were attenuated with only a change to anterior digastric cycle period. L-dopa likely plays a role in initiating brux-like motor patterns, but it does not control rhythmogenesis. To our knowledge, mastication has not been examined in detail while under the influence of L-dopa in humans or rats, making this study the first to look at L-dopa’s effect on the motor pattern. The masticatory motor patterns remained unchanged between treatment groups (NS). Our study is the first to show that acute L-dopa exposure does not alter masticatory motor patterns. L-dopa does not have a strong influence over the masticatory CPG. This study established an animal model for use on future studies of brux-like behavior. The developed model can be applied in the future for drug interactions and basal ganglion studies.
|Advisor:||Welch, Dan B.|
|Commitee:||Essner, Richard, Kohn, Luci|
|School:||Southern Illinois University at Edwardsville|
|School Location:||United States -- Illinois|
|Source:||MAI 56/05M(E), Masters Abstracts International|
|Subjects:||Biology, Health sciences, Pharmacy sciences|
|Keywords:||Basal ganglia, Bruxism, Electromyography, L-dopa, Mastication, Phase analysis|
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