Assessment of cerebral dopamine D_{2/3}-receptors in patients with bilateral vestibular failure

BACKGROUND: Absence of peripheral vestibular input in bilateral vestibular failure (BVF) has been suggested to induce plastic reorganization in various brain regions. Among several neurotransmitters, dopamine is known to play a key role in corticostriatal-sensorimotor processing. However, the role of dopamine in vestibular plasticity is scantly documented. OBJECTIVE: Assessment of D2/3-receptors in patients with BVF. METHODS: D2/3-receptor-PET using [F]fallypride and MRI examinations were performed in 12 BVF-patients and 13 healthy controls. RESULTS: BVF-patients showed reduced D2/3-receptor availability (approximately 40%) in the temporo-parieto-occipital cortex bilaterally, including the multisensory vestibular cortex and visual motion-sensitive areas (MT/MST), as well as in the striatum and the right thalamus. Longer illness duration was associated with bilaterally lower D2/3-receptor availability in the middle/ superior temporal gyrus (GTm/s). D2/3-receptor availability in the right GTm/s and bilateral insula decreased with severity of symptoms. BVF-patients with oscillopsia showed reduced D2/3-receptor availability in the right MT/MST and midbrain tectum. CONCLUSIONS: Reduced D2/3-receptor availability in multisensory vestibular cortical network areas and basal ganglia may indicate a receptor down-regulation due to the lack of peripheral vestibular input. The more pronounced decline in D2/3-receptor availability in the multisensory vestibular cortex in patients with prolonged illness suggests the occurrence of progressive changes in dopamine transmission.