Brain dopamine D-1 receptors in twins discordant for schizophrenia
ABSTRACT It has been suggested that deficits in higher-order cognitive functions serve as intermediate phenotypic indicators of genetic vulnerability to schizophrenia. The dopamine hypothesis of schizophrenia postulates that insufficiency of dopamine transmission in the prefrontal cortex contributes to the cognitive deficits observed in patients with the disease, and there is robust empirical evidence for a central role of prefrontal cortex dopamine D(1) receptors in working memory functions.
The authors examined the genetic and nongenetic effects on D(1) receptor binding in schizophrenia by studying monozygotic and dizygotic twin pairs discordant for schizophrenia as well as healthy comparison twins using positron emission tomography (PET) and the D(1) receptor antagonist ligand [(11)C]SCH 23390. Performance on neuropsychological tests sensitive to frontal lobe functioning was evaluated.
High D(1) receptor density in the medial prefrontal cortex, superior temporal gyrus, and heteromodal association cortex (angular gyrus) was associated with increasing genetic risk for schizophrenia (comparison twins < unaffected dizygotic co-twins < unaffected monozygotic co-twins). Medicated schizophrenia patients demonstrated a widespread reduction in D(1) receptor binding when compared with the unaffected co-twin, and higher doses of antipsychotics were associated with lower D(1) receptor binding in the frontotemporal regions.
This study demonstrated an association between genetic risk for schizophrenia and alterations in cortical D(1) receptor binding, an observation that has implications for future studies of the molecular genetics of schizophrenia. In addition, the data indicate a widespread reduction of D(1) receptor binding in medicated schizophrenia patients, supporting a link between antipsychotic drug action and dopamine D(1) receptor down-regulation.
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ABSTRACT: Abstract To evaluate the contribution of individual synaptic constituents, all available in vivo imaging studies on schizophrenic patients were subjected to a retrospective analysis. For the pool of drug-naïve, drug-free, and acutely medicated patients, major findings were increases in neostriatal dopamine (DA) synthesis and release and decreases in neostriatal DA transporters and D1 receptors, neostriatal, thalamic, frontal, and parietal D2 receptors, mesencephalic/pontine and temporal 5-HT1A receptors, frontal and temporal HT2A and μ-amino butyric acid (GABA)A receptors. Based on the findings on drug-naïve and drug-free patients, it may be hypothesized that schizophrenia initially is characterized by an impaired mechanism of D2 autoreceptor and heteroreceptor sensitization leading to sensitization instead of desensitization in response to increased levels of neostriatal DA. Neuroleptic medication blocks neostriatal D2 autoreceptor and heteroreceptors, reducing neostriatal DA and disinhibiting DA action mediated by D2 heteroreceptor binding sites. Ultimately, this may result in a restitution of GABA function, leading to a recovery of inhibitory input to the target regions of the descending corticothalamostriatal efferents. Furthermore, a blockade of inhibitory and excitatory neocortical 5-HT function may be inferred, which is likely to reduce (excitatory) DAergic input to the mesolimbic target regions of corticothalamostriatal projections.Reviews in the neurosciences 02/2014; 25(1):25-96. DOI:10.1515/revneuro-2013-0063 · 3.31 Impact Factor
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ABSTRACT: Introduction: Antipsychotic drugs date back to the 1950s and chlorpromazine. Soon after, it was established that blockade of dopamine and, in particular, the D2 receptor was central to this effect. Dopamine continues to represent a critical line of investigation, although much of the work now focuses on its potential in other symptom domains. Areas covered: A search was carried out for investigational drugs using the key words 'dopamine', 'schizophrenia' and 'Phase III' in an American clinical trial registry (clinicaltrials.gov), published articles using the National Library of Medicine's PubMed database, and supplemented results with a manual search of cross-references and conference abstracts. Drugs were excluded that were already FDA approved. Expert opinion: There remains interest, albeit diminished, in developing better antipsychotic compounds. The greatest enthusiasm currently centres on dopamine's role in negative and cognitive symptom domains. With theories conceptualising hypodopaminergic activity as underlying these deficits, considerable effort is focused on drug strategies that will enhance dopamine activity. Finally, a small body of research is investigating dopaminergic compounds vis-à-vis side-effect treatments. In domains beyond psychosis, however, dopamine arguably is not seen as so central, reflected in considerable research following other lines of investigation.Expert Opinion on Pharmacotherapy 12/2013; DOI:10.1517/14656566.2014.873790 · 2.86 Impact Factor
Gastroenterology 01/2011; 140(5). DOI:10.1016/S0016-5085(11)60835-4 · 12.82 Impact Factor