Journal of Neuroscience, Vol 11, 1381-1389, Copyright © 1991 by Society for Neuroscience
Non-steady-state measurement of in vivo radioligand binding with positron emission tomography: specificity analysis and comparison with in vitro binding
JS Perlmutter, SM Moerlein, DR Hwang and RD Todd
Department of Neurology and Neurological Surgery, Washington University School of Medicine, St. Louis, Missouri 63110.
We previously have developed a non-steady-state method for in vivo
measurement of radioligand-receptor binding in brain using positron
emission tomography (PET) and 18F-spiperone (18F-SP). This method has
proven to be highly sensitive to the detection of decreases in the apparent
number of available specific binding sites. The purposes of this
investigation are to demonstrate the specificity of this PET assay and
compare findings to in vitro binding assays. Three to six studies were
performed in each of five male baboons. Each animal was pretreated with
either ketanserin [serotonergic (S2)], eticlopride [dopaminergic (D2)], or
unlabeled SP to compete with 18F-SP for specific binding sites. Sequential
PET scans and arterial-blood samples were collected for 3 hr after
intravenous injection of 18F-SP. Data were analyzed with a
three-compartment model that considered the accumulation of radiolabeled
metabolites in arterial blood. Five baboons were killed, and
radioligand-receptor binding in vitro was measured by homogenate
techniques. There was no detectable in vitro or in vivo specific binding of
SP in cerebellum. The specific binding of SP in striatal tissue in vitro
was approximately 74% to D2 sites and 26% to S2 sites, whereas ketanserin
displaced all specific binding in frontal cortex. In close agreement,
specific binding measured in vivo with PET revealed that 68% of apparent
striatal binding could be blocked by pretreatment with eticlopride, and 34%
by ketanserin. The small apparent difference between receptor binding in
vitro and in vivo may result from the relatively poor resolution of
PET.(ABSTRACT TRUNCATED AT 250 WORDS)