Role of oral sensory and serotonergic neurons in dopamine-induced tongue movement in rat

Background: Oral dyskinesia is a condition in which oral organs exhibit involuntary movements. The aim of this study was to determine the contribution of oral sensation to the control of oral dyskinesia using an animal model that exhibits vacuous tongue movements after systemic administration of dopamine (DA) agonists. Methods: Adult male Sprague-Dawley rats were used in all experiments. Tongue movement was elicited in a freely moving rat model by systemic administration of a mixture of the D1 receptor agonist SKF38393 and the D2 receptor agonist quinpirole. The number of tongue protrusions was calculated from electrical myographic data obtained from the genioglossal muscle. Extracellular concentrations of DA and serotonin (5-HT) in the nucleus accumbens were determined using in vivo microdialysis. To investigate the effects of oral sensation on vacuous tongue movement, deafferentation of the palatal mucosa was performed, and the above experiments were repeated. Results: The hyperactivity of tongue protrusion induced by administration of SKF38393 and quinpirole was significantly inhibited by palatal deafferentation. Palatal deafferentation also significantly reduced the increase in extracellular 5-HT concentration in the nucleus accumbens produced by administration of DA agonists. Conclusions: These results support the important contribution of oral sensation to vacuous tongue protrusion in a rat model of oral dyskinesia.