Assessment of extrastriatal dopamine D2-receptors in patients with bilateral vestibular failure

Objectives Chronic absence of bilateral peripheral vestibular input in bilateral vestibular failure (BVF) induces plastic cortical reorganization, especially in the visual and vestibular cortex. Dopamine is known to be involved in corticostriatal synaptic plasticity processes, but it is unclear whether it is involved in vestibular neurotransmission of humans. We aimed to analyse the striatal and extrastriatal dopamine D2-receptor (D2R) availability in patients with BVF using the high affinity D2-ligand [18F]fallypride.

Methods 12 BVF-patients and 13 age- and sex-matched healthy controls (HC) were included. Parametric voxel-wise binding potentials (BPND) to the D2R were estimated using Logan’s graphical analysis. Parametric BPND images were coregistered on individual MRI and normalised to the ICBM-template. Statistical analysis was performed using SPM8. Findings were compared with corresponding analyses in the age-matched HC group.

Results Patients with BVF presented with significantly decreased D2R availability bilaterally in the temporo-parieto-occipital cortex, including the motion sensitive areas (MT/MST), the inferior parietal lobule (IPL), the insula including the parieto-insular vestibular cortex (PIVC) and the cingulate cortex. In addition, decreased D2R availability was found in the striatum and thalamus. Shorter duration of illness (<2 y) was associated with higher D2R availability in the right IPL and the right middle temporal gyrus when compared to long disease duration (>2 y).

Conclusions The dopaminergic system seems to be involved in plastic cortical reorganization of the multisensory vestibular cortical network. Lower D2R availability in the multisensory vestibular cortical areas in BVF-patients can be interpreted as a down-regulation of D2R due to the lack of peripheral vestibular input. Furthermore, the availability of D2R in important vestibular cortical areas might be influenced by the duration of illness