Recovery of vestibulogastrointestinal symptoms during vestibular compensation after unilateral labyrinthectomy in rats.

Background: The loss of unilateral vestibular function causes vestibulogastrointestinal symptoms that include nausea and vomiting. However, the temporal changes occurring on vestibular compensation are unclear. Thus, the temporal changes and the role of the cerebellum in the recovery of vestibulogastrointestinal symptoms after unilateral labyrinthectomy (UL) were investigated in this study.

Methods: Vestibulogastrointestinal symptoms were evaluated for intestinal transit and geometric center, whereas vestibulo-ocular symptoms were represented by spontaneous nystagmus. Expression of the c-Fos protein was observed in the vestibular nuclei. These were measured at 30 minutes and at 2, 6, and 24 hours after UL in rats.

Results: Intestinal transit was 66.3% +/- 7.6% in the control animals but significantly decreased to 40.7% +/- 7.8%, 46.3% +/- 6.3%, and 48.6% +/- 10.8% at 30 minutes (p < 0.01), 2 hours (p < 0.01), and 6 hours (p < 0.05) after UL, respectively. The intestinal transit showed a recovery to control levels 24 hours after UL. The geometric center was 5.6 +/- 0.4 in control animals but significantly decreased to 2.1 +/- 0.4, 2.9 +/- 0.3, and 4.0 +/- 0.3 at 30 minutes, 2 hours, and 6 hours after UL, respectively (p < 0.01). Recovery of the geometric center to control levels, 24 hours after UL, was reported. Uvulonodullectomy significantly decreased the intestinal transit and geometric center for 24 hours after surgery (p < 0.01). Moreover, UL in uvulonodullectomized animals significantly decreased the intestinal transit and geometric center for 24 hours after surgery (p < 0.01). Pretreatment of the UL animals with MK-801 significantly increased the geometric center 30 minutes after surgery (p < 0.01). Unilateral labyrinthectomy produced spontaneous nystagmus, 28.9 +/- 1.5, 23.3 +/- 1.4, 17.5 +/- 1.5, and 9.2 +/- 0.9 beats per 10 seconds at 30 minutes and at 2, 6, and 24 hours after UL, respectively. Expression of the c-Fos protein was significantly increased in the medial vestibular nuclei and inferior vestibular nuclei at 1, 2, and 6 hours after UL, and the expression was significantly decreased in animals that were pretreated with MK-801 (p < 0.01).

Conclusion: These results suggest that the recovery of vestibulogastrointestinal symptoms is faster than that of vestibulo-ocular symptoms and that the cerebellum and glutamate have an important role to play in the recovery of symptoms after UL.