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Effect of Dopamine D2 Receptor Antagonists on [18F]-FEOBV Binding

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journal contribution
posted on 17.02.2020, 17:05 by Anna Schildt, Erik F.J. de Vries, Antoon T.M. Willemsen, Bruno Lima Giacobbo, Rodrigo Moraga-Amaro, Jürgen W.A. Sijbesma, Aren van Waarde, Vesna Sossi, Rudi A.J.O. Dierckx, Janine Doorduin
The interaction of dopaminergic and cholinergic neurotransmission in, e.g., Parkinson’s disease has been well established. Here, D2 receptor antagonists were used to assess changes in [18F]-FEOBV binding to the vesicular acetylcholine transporter (VAChT) in rodents using positron emission tomography (PET). After pretreatment with either 10 mg/kg haloperidol, 1 mg/kg raclopride, or vehicle, 90 min dynamic PET scans were performed with arterial blood sampling. The net influx rate (Ki) was obtained from Patlak graphical analysis, using a metabolite-corrected plasma input function and dynamic PET data. [18F]-FEOBV concentration in whole-blood or plasma and the metabolite-corrected plasma input function were not significantly changed by the pretreatments (adjusted p > 0.07, Cohen’s d 0.28–1.89) while the area-under-the-curve (AUC) of the parent fraction of [18F]-FEOBV was significantly higher after haloperidol treatment (adjusted p = 0.022, Cohen’s d = 2.51) than in controls. Compared to controls, the AUC of [18F]-FEOBV, normalized for injected dose and body weight, was nonsignificantly increased in the striatum after haloperidol (adjusted p = 0.4, Cohen’s d = 1.77) and raclopride (adjusted p = 0.052, Cohen’s d = 1.49) treatment, respectively. No changes in the AUC of [18F]-FEOBV were found in the cerebellum (Cohen’s d 0.63–0.74). Raclopride treatment nonsignificantly increased Ki in the striatum 1.3-fold compared to control rats (adjusted p = 0.1, Cohen’s d = 1.1) while it reduced Ki in the cerebellum by 28% (adjusted p = 0.0004, Cohen’s d = 2.2) compared to control rats. Pretreatment with haloperidol led to a nonsignificant reduction in Ki in the striatum (10%, adjusted p = 1, Cohen’s d = 0.44) and a 40–50% lower Ki than controls in all other brain regions (adjusted p < 0.0005, Cohen’s d = 3.3–4.7). The changes in Ki induced by the selective D2 receptor antagonist raclopride can in part be quantified using [18F]-FEOBV PET imaging. Haloperidol, a nonselective D2/σ receptor antagonist, either paradoxically decreased cholinergic activity or blocked off-target [18F]-FEOBV binding to σ receptors. Hence, further studies evaluating the binding of [18F]-FEOBV to σ receptors using selective σ receptor ligands are necessary.

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