Amphetamine challenge decreases yohimbine binding to α2 adrenoceptors in Landrace pig brain.
BACKGROUND
The noradrenaline (NA) system is implicated in neurodegenerative and psychiatric disorders; however, our understanding is impaired by the lack of well-validated radioligands to assess NA function and release. Yohimbine, an α2 adrenoceptor antagonist, has recently been developed as a carbon-11 [11C]-labeled radioligand for positron emission tomography (PET) imaging studies.


OBJECTIVE
Here we explore the hypothesis that yohimbine can be used as an in vivo tracer of NA receptor binding and release during amphetamine challenges in Landrace pigs.


METHODS
Pigs underwent baseline PET scans with [11C]yohimbine and were then challenged with 10 mg/kg d-amphetamine 20 min prior to a second [11C]yohimbine scan. Using the Logan analysis model, volumes of distribution were calculated from fits of the kinetic data 25-90 min post-yohimbine injection.


RESULTS
Amphetamine decreased [11C]yohimbine volume of distribution in the brain regions under investigation, including the thalamus, caudate nucleus, and cortical regions.


CONCLUSIONS
These data suggest that the binding of [11C]yohimbine to α2 adrenoceptors may be displaceable by increases in synaptic concentrations of the endogenous ligand, NA, and possibly dopamine, suggesting the possibility that [11C]yohimbine may be used as a surrogate marker of NA release in vivo.
Department of Nuclear Medicine and PET Center, Aarhus University Hospital, Norrebrogade 44, Building 10G, Aarhus C 8000, Denmark.
Anne M
AM
Landau
Doris J
DJ
Doudet
Steen
S
Jakobsen
D058669:Adrenergic alpha-2 Receptor Antagonists / Q000378:metabolism* / Q000493:pharmacokinetics; D000661:Amphetamine / Q000494:pharmacology*; D000818:Animals; D001921:Brain / Q000000981:diagnostic imaging / Q000378:metabolism; D002250:Carbon Radioisotopes; D005260:Female; D009638:Norepinephrine / Q000378:metabolism; D049268:Positron-Emission Tomography / Q000379:methods; D019275:Radiopharmaceuticals / Q000378:metabolism / Q000493:pharmacokinetics; D018341:Receptors, Adrenergic, alpha-2 / Q000378:metabolism*; D013552:Swine; D014018:Tissue Distribution; D015016:Yohimbine / Q000378:metabolism* / Q000493:pharmacokinetics
D058669:Adrenergic alpha-2 Receptor Antagonists; D002250:Carbon Radioisotopes; D019275:Radiopharmaceuticals; D018341:Receptors, Adrenergic, alpha-2; D015016:Yohimbine; D000661:Amphetamine; D009638:Norepinephrine