Biomedical subjects

S Frangou

Publications and source records attributed to S Frangou.

24 records · Page 2Linked to original sources

PubMed1997

Effect of haloperidol on nicotine-induced enhancement of vigilance in human subjects.

We posed the question whether the cognitive enhancement caused by nicotine in human subjects is mediated by dopamine (DA) release. This issue was addressed by testing performance in the Wesnes and Warburton vigilance task after s.c. nicotine with or without concomitant oral haloperidol. The subjects were moderate (10-14 cigarettes/day) smokers after overnight deprivation of smoking. After an initial practice session, each subject participated in four further sessions spread over 2 weeks, after: placebo/placebo, placebo/haloperidol (5 mg), placebo/nicotine (0.8 mg) or nicotine/haloperidol, double-blind with a balanced ordering of drug combinations. On each occasion, performance was measured on the vigilance task, a finger tapping test, and digit span forward and backward. Nicotine improved detection sensitivity on the vigilance task, and this effect was unchanged by haloperidol; the latter compound reduced forward digit span. Thus, the improved vigilance caused by nicotine does not appear to be mediated by DA systems.

Adolescent↗

PubMed1997

The Maudsley Family Study. 4. Normal planum temporale asymmetry in familial schizophrenia. A volumetric MRI study.

BACKGROUND: Loss or reversal of the normal asymmetry of the planum temporale (PT) has been reported in schicophrenia, and may be due to aberations in the gene(s) controlling the development of brain asymmetries. We tested this hypothesis in a sample of schizophrenics and their relatives from families multiply affected with the disorder. METHOD: We compared 32 schizophrenics and 55 of their non-schizophrenic first-degree relatives with 39 matched community controls. Volumetric measurements of the cortical volume beneath the PT were obtained using the Cavalieri method from three-dimensionally reconstructed magnetic resonance imaging images. RESULTS: PT volume asymmetry coefficients from patients and their relatives did not differ significantly from those of the controls. Gender-specific analysis did not revealany differences. CONCLUSIONS: Abnormalities in PT volume asymmetry are not present in familial schizophrenia, where genetic factors appear to predominate.

Adult↗

PubMed1996

Effects of nicotine and amphetamine on latent inhibition in human subjects.

Latent inhibition (LI) is a phenomenon in which repeated non-reinforced exposure to a stimulus retards subsequent conditioning to that stimulus; it reflects a process whereby irrelevant stimuli become ignored, and has been the subject of study concerning attentional abnormalities in schizophrenia. Low doses of the indirect dopamine (DA) agonists, amphetamine and nicotine, disrupt LI in the rat. These drugs are believed to disrupt LI via DA release in the nucleus accumbens; LI in amphetamine- and nicotine-treated rats is reinstated by administration of the DA antagonist haloperidol. In human subjects, low doses of amphetamine abolish LI, and more recently haloperidol has been shown to potentiate LI. The present study investigated the effects of nicotine on LI in human subjects, and also attempted to replicate the abolition of LI by amphetamine. Nicotine failed to affect LI when administered either subcutaneously or by cigarette smoking. LI was, however, abolished in a group of subjects given 5 mg amphetamine 90 min before testing. Supplementary analyses of the data pooled from all three experiments showed that, in contrast to an earlier report, LI was no weaker in smokers than in nonsmokers.

Adult↗

PubMed1996

Magnetic resonance spectroscopy in psychiatry: basic principles and applications.

In vivo magnetic resonance spectroscopy (MRS) is a safe and non-invasive tool which can be used to study aspects of brain chemistry and metabolism. Although a relatively recent technique in the field of psychiatric research, it has already been used in the study of anxiety and affective disorders, dementia, schizophrenia, and neurodevelopmental disorders. This review outlines the basic principles of MRS and summarises the research findings in psychiatric disorders. Although mostly preliminary, these findings highlight the capacity of MRS to detect subtle neurobiological abnormalities in mental disorders. They also suggest a future role for MRS in differential diagnosis and monitoring illness progression. Initial MRS studies have also focused on the metabolic effects of psychiatric treatments and could provide information about their relationship to clinical variables.

Brain Chemistry↗

PubMed1996

Imaging as a tool in exploring the neurodevelopment and genetics of schizophrenia.

Neuroimaging has enabled us to address questions about the timing and origin of brain abnormalities in schizophrenia. First episode and longitudinal computed tomography (CT) and magnetic resonance imaging (MRI) studies of schizophrenic patients have shown that the brain abnormalities are present at onset of psychosis and are non-progressive. Such findings support the idea that schizophrenia is a developmental rather than a degenerative condition. Furthermore, the presence of ventriculomegaly and diminished hemispheric asymmetry in familial schizophrenics and in those of their relatives who appear to be transmitting the disorder, implies involvement of the genes controlling neurodevelopment. However, genetic factors do not fully account for the development of schizophrenia; early environmental insults such as obstetric complications are also important and may interact with genetic predisposition. Brain development continues postnatally and profound maturational events also occur in adolescence and early adulthood. Magnetic resonance spectroscopy (MRS) studies allow the investigation of the developmental biochemistry of the living brain and are being used to explore the role of maturational brain events in determining the onset of psychosis.

Brain↗

PubMed1995

Computerized brain tissue classification of magnetic resonance images: a new approach to the problem of partial volume artifact.

Due to the finite spatial resolution of digital magnetic resonance images of the brain, and the complexity of anatomical interfaces between brain regions of different tissue type, it is inevitable that some voxels will represent a mixture of two or three different tissue types. Outright assignment of such "bipartial" or "tripartial" voxels to one class or another is more problematic and less reliable than assignment of "full-volume" voxels, wholly representative of a single tissue type. We have developed a computerized system for brain tissue classification of dual echo MR data, which uses a polychotomous logistic model for discriminant analysis, combined with a Bayes allocation rule incorporating differential prior probabilities, and spatial connectivity tests, to assign each voxel in the image to one of four possible classes: gray matter, white matter, cerebrospinal fluid, or unclassified. The system supports automated volumetric analysis of segmented images, has low operational overheads, and compares favorably with previous multivariate or "multispectral" approaches to brain MR image segmentation in terms of both validity (bootstrap misclassification rate = 3.3%) and interoperator reliability (intra-class correlation coefficients for all three tissue classes > 0.9). We argue that these improvements in performance stem from better methodological management of the related problems of non-Normality of MR signal intensity values and partial volume artifact.

Artifacts↗