Dopamine D(2/3) receptor occupancy of apomorphine in the nonhuman primate brain--a comparative PET study with [11C]raclopride and [11C]MNPA.
Synapse
; 63(5): 378-89, 2009 May.
Article
en En
| MEDLINE
| ID: mdl-19173265
Binding studies in vitro have demonstrated that the dopamine D2 receptor may exist in two affinity states for agonists. The high affinity state is thought to represent the functional state of the receptor and proportions might alter during disease. In vitro studies further indicate that agonists induce measurable D(2) receptor occupancy at clinically relevant concentrations but only when measured at the high affinity state. Recently developed PET-radioligands, such as [11C]MNPA, have now made it possible to directly study agonist binding in vivo. The aim of this study was to compare the inhibition by apomorphine of agonist and antagonist radioligand binding to D(2/3) receptors in vivo. A total of 36 PET measurements were performed with the D(2/3) antagonist [11C]raclopride or the D(2/3) agonist [11C]MNPA in two cynomolgus monkeys. On each study day, a baseline measurement was followed by two consecutive pretreatment studies with rising doses of apomorphine (0.01, 0.05, 0.15, 0.5, 1.0, and 3.0 mg/kg). Binding potential (BP(ND)) values were calculated for the striatum with cerebellum as reference region. Apomorphine inhibited [11C]raclopride and [11C]MNPA binding in a dose-dependent manner and to a similar extent. ID(50) and K(i) values were 0.26 mg/kg and 29 ng/ml for [11C]raclopride and 0.50 mg/kg and 31 ng/ml for [11C]MNPA. The present observations do not support the existence of two affinity states in vivo. It might thus be speculated that all D(2/3) receptors are in the high affinity state at in vivo conditions.
Texto completo:
1
Colección:
01-internacional
Base de datos:
MEDLINE
Asunto principal:
Encéfalo
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Apomorfina
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Receptores de Dopamina D2
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Racloprida
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Tomografía de Emisión de Positrones
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Receptores de Dopamina D3
Límite:
Animals
Idioma:
En
Revista:
Synapse
Asunto de la revista:
NEUROLOGIA
Año:
2009
Tipo del documento:
Article
País de afiliación:
Suecia
Pais de publicación:
Estados Unidos