Circling behavior depending on striopallidal and vestibular functions

Unilateral electrolytic lesions of the pallidum in rats produced circling behavior towards the lesioned side, whereas similar lesions of the fasciculus tegmenti dorsolateralis--including the crossed descending striopallidal and ascending vestibular pathways--evoked circling towards the intact side. Intraperitoneal injections of dopamine agonists, apomorphine or methamphetamine, enhanced the circling in these animals. Unilateral lesions of different parts of the vestibular nuclei per se caused a comparable circling but in opposite directions: Lesions of the superior and lateral vestibular nuclei caused circling towards the intact side, whereas lesions of the inferior and medial vestibular nuclei caused circling towards the lesioned side. In the animals with vestibular lesions, only apomorphine induced tight circling, but methamphetamine did not potentiate circling behavior. Chemical analyses of biogenic amines suggest that unilateral interruptions of the ascending vestibular pathway increase turnover of dopamine metabolism in the striatum on the lesioned side. The findings in the present study suggest that the vestibular function is involved in striopallidal function for circling behavior by modulatingdopamine receptor activity in the striatum.