Stereoselective binding of 11C-raclopride in living human brain--a search for extrastriatal central D2-dopamine receptors by PET

The selective D2-dopamine receptor antagonist raclopride and its pharmacologically inactive (R)-enantiomer FLB472 were labelled with 11C and used in a study with positron emission tomography to examine the stereoselectivity of 11C-raclopride binding to central D2-dopamine receptors in three healthy men. After the injection of 11C-raclopride, there was a high accumulation of radioactivity in the dopamine-rich basal ganglia, whereas after the injection of 11C-FLB472 there was no such accumulation of radioactivity. Thus, the binding of 11C-raclopride is stereoselective. Distribution ratios [radioactivity in a brain region/"free" (not protein-bound) radioactivity in plasma] were calculated for the two enantiomers to study regional differences in the accumulation of radioactivity. The distribution ratios in white matter were similar for the two enantiomers. In the putamen, a three to four-fold higher distribution ratio was found for 11C-raclopride than for 11C-FLB472, reflecting the presence of specific binding of 11C-raclopride binding to D2-dopamine receptors in the basal ganglia. In the temporal and frontal cortices the distribution ratios were, however, only a few per cent higher for 11C-raclopride than for 11C-FLB472, indicating that if D2-dopamine receptors are present in the human neocortex, then their density is indeed very low.

PET scanning--a new tool in clinical psychopharmacology

Quantitative methods were developed for the determination of dopamine and benzodiazepine receptor characteristics in the living human brain by positron emission tomography (PET). As ligands, the 11C-labelled analogues of the selective antagonists of dopamine receptor subtypes, SCH 23390 and raclopride, and the benzodiazepine antagonist, Ro 15-1788, were used. Tracer amounts of the ligands were injected intravenously into healthy volunteers and schizophrenic patients. The distribution of ligand indicated high densities of D1 as well as D2 dopamine receptors in the basal ganglia. Binding of [11C]-SCH 23390 was also significant in the neocortex where it was shown to represent binding to D1 as well as to 5-HT2 serotonin receptors. High densities of specific benzodiazepine receptor binding were obtained in most neocortical brain areas and in the cerebellum. Using saturation procedures, Bmax and Kd values could be obtained for D2 and benzodiazepine receptors. A comparison of D2 receptor densities in drug-naive schizophrenic patients and healthy volunteers demonstrated similar receptor characteristics in the major basal ganglia in these groups of subjects. Different chemical classes of conventional and unconventional antipsychotic drugs produced a 65%-85% occupancy of D2 receptors when given in clinical doses to schizophrenic patients. High does of diazepam produced a marked occupancy of benzodiazepine receptors during the first hours after oral administration to healthy volunteers. These in vivo methods should be valuable tools for the further analysis of the effects of drug on neuroreceptors in the living brain of neuropsychiatric patients.

An acoustic-perceptual method for the quantitative evaluation of hypernasality

A computer implementation is proposed as a method for assessing the quality of an individual's speech from a perceptual and communicative point of view. The input to this procedure is a standardized set of speech samples (vowels and selected consonants) designed to permit an evaluation of the speaker's phonology. The output is a numerical specification of the functional adequacy of the target values of the phonetic segments under analysis. The computer program consists of three parts: a simulated auditory analyzer, the output of which is a spectral representation of each test item; an algorithm that computes a psychoacoustically based measure of distinctiveness or perceptual distance for each pair of test spectra, and a routine for comparing, in terms of this measure, the test items with the corresponding reference items drawn from a population of normal speakers or a recording made before patient intervention.