UMLS:C0036341 - FACTA Search

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Query: UMLS:C0036341 (schizophrenia)
60,220 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Dopamine is the neurotransmitter most often implicated in the pathogenesis of schizophrenia. However, glutamatergic antagonists can cause psychotic symptoms in otherwise normal humans, and exacerbate these symptoms in schizophrenics. These findings have led to a model of dopamine-glutamate interactions in limbic cortex and striatum as a potential substrate for symptom production in schizophrenia. From this model, we might expect that cortical and striatal expression of non-NMDA ionotropic glutamate receptors would be differentially regulated by antipsychotic treatment. To begin to address this question, we examined the regulation of mRNA levels of the AMPA (gluR1-gluR4), low affinity kainate (gluR5-gluR7), and high affinity kainate (KA1-KA2) receptor subunits by clozapine (20 mg/kg/day) and haloperidol (2 mg/kg/day) treatment for 2 weeks. Both clozapine and haloperidol caused region-specific alterations in the mRNA levels of these subunits, but there was no differential regulation in the cortex vs. the striatum. Haloperidol caused a decrease in gluR2 and gluR4 mRNA levels in both cortex and striatum and an increase in KA2 mRNA levels in the striatum only. However, clozapine treatment caused an increase in gluR7 mRNA expression, and a decrease in gluR3 mRNA expression, in both cortex and striatum while causing an increase in KA2 mRNA levels, and a decrease in gluR4 mRNA levels, in the striatum only. These dissimilarities may represent an interesting mechanism for some of the differential therapeutic or toxic effects of clozapine and haloperidol, and also may be relevant to our understanding of dopamine-glutamate interactions in schizophrenia.
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PMID:Clozapine and haloperidol differentially affect AMPA and kainate receptor subunit mRNA levels in rat cortex and striatum. 922 32

Alcoholism is one of a group of common psychiatric diseases which are well-defined clinically and strongly influenced genetically, but which are likely to be highly heterogeneous in causation, genetically and otherwise. Dopamine is a key neurotransmitter in drug-mediated reinforcement. Based on association studies with the Taq1A downstream marker, the D2 dopamine receptor has been proposed to be the "Reward Deficiency Syndrome Gene." Ser311Cys, a naturally occurring variant which largely inactivates transduction after D2 receptor activation, was abundant (0.16) in a Southwestern American Indian population we studied. Therefore, we were able to provide a critical test of the D2 hypothesis of vulnerability to alcoholism by evaluating Ser311Cys and also the intron-2 STR and Taq1A markers at this locus in a total of 459 subjects, including 373 sib pairs, from large families. The result is that neither alcoholism, substance use disorders nor schizophrenia show a relationship to Ser311Cys genotype, even when the 15 Cys311/Cys311 homozygous individuals are compared to others. Furthermore, sib pair analysis incorporating information across all three sib pair categories: concordant affected, discordant and concordant unaffected revealed no effect of DRD2 genotype or haplotype on alcoholism or substance use disorder.
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PMID:Linkage and association of a functional DRD2 variant [Ser311Cys] and DRD2 markers to alcoholism, substance abuse and schizophrenia in Southwestern American Indians. 1049 Jul 20

Existing pathophysiological models of schizophrenia are limited in their ability to account for all the clinical dimensions of the disorder. The purpose of this article is to describe a comprehensive hypothesis of the pathophysiology of schizophrenia and specifically how a deficit in neural regulation of developmental origin can lead to a pathologic form of neuroplasticity, i.e., neurochemical sensitization, which causes the onset and psychotic symptoms of the illness. We propose that the symptoms of schizophrenia may be caused by deficits in neural regulation resulting in a pathologic condition of neurochemical sensitization analogous to the preclinical model of pharmacologically-induced behavioral sensitization. This condition, if sustained, can lead to potential neurotoxic effects which produce structural neuronal alterations and persistent morbidity. Several lines of indirect and direct clinical evidence are consistent with this hypothesis. These include the ability of stimulant and psychotomimetic drugs to induce psychosis in normal subjects, the development of apparent sensitization to psychosis-inducing effects of stimulants in chronic stimulant abusers and the increased susceptibility of patients with schizophrenia to the psychotogenic effects of Dopamine (DA) agonists. This hypothesis integrates and extends the work of other investigators and is consistent with specific aspects of the longitudinal course of schizophrenia. The association of longer duration and more episodes of psychosis, with poor treatment response and outcome, are also consistent with this model. Form this hypothesis, specific predictions about the illness course, treatment interventions, and pathophysiologic features of schizophrenia can be derived and tested through clinical investigation.
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PMID:Neurochemical sensitization in the pathophysiology of schizophrenia: deficits and dysfunction in neuronal regulation and plasticity. 932 46

It has been suggested by Arinami et al. (1994) that there is a positive relationship between schizophrenia and the Cys311 polymorphism of the Dopamine receptor D2 (DRD2) gene. However, some recent reports do not support this relationship. The differing results could be due to two causes, [1] There may be a regional difference in the proportion of schizophrenia due to the Cys311 or [2] the control groups in the recent studies might have included young schizophrenics. Accordingly, an analysis of the age of schizophrenic patients in the Fukuoka region was undertaken. The Cys311 allele frequencies for the control group was 0.040 and for the schizophrenic group was 0.057, which were not statistically different. Although this data did not corroborate the above mentioned positive relationship, it was found that the allele frequency was higher statistically than in any previous report for both the schizophrenic and control groups. These findings indicate that the frequency of the Cys311 is biased geographically and that this must considered when investigating the occurrences of genetic variants and diseases.
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PMID:Ser-311-Cys polymorphism of the dopamine D2 receptor gene and schizophrenia--an analysis of schizophrenic patients in Fukuoka. 933 51

The ventral striatum is included in brain circuits which connect brain areas classically ascribed to the motor or to the limbic system. In fact, the ventral striatum is involved in the connection between motivationally relevant stimuli and adaptive behaviours. Dopamine neurotransmission in the ventral striatum is essential for the increase in motor activity produced by motivational, salient, stimuli, such as food or novelty or by the administration of psychostimulants. Adenosine plays a role opposite to dopamine in the striatum and adenosine agonists produce similar behavioural effects as dopamine antagonists. On the other hand, adenosine antagonists, like caffeine, produce similar effects to increased dopaminergic neurotransmission in the striatum. Specific antagonistic interactions between specific subtypes of adenosine and dopapaine receptors in the basal ganglia play an essential role in the behavioural effects of adenosine agonists and antagonists. In particular, a strong antagonistic interaction between adenosine A2A and dopamine D2 receptors seems to take place in the striopallidal GABAergic neurons which originate in the ventral striatum. Therefore, adenosine A(ZA) agonists provide a potential new treatment for schizophrenia, since the dopamine D2 receptors of the ventral striopallidal neurons appear to be involved in the antipsychotic effects of neuroleptics. In fact, in animal models, the adenosine A2A agonist CGS 21680 has a profile of antipsychotic with a low liability to induce extrapyramidal side effects.
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PMID:Adenosine-dopamine interactions in the ventral striatum. Implications for the treatment of schizophrenia. 934 76

Dopamine receptor antagonists, particularly haloperidol, have been the most effective medications in currently available double-blind placebo-controlled studies for treating the disruptive behaviors often associated with pervasive developmental disorder (PDD). The rationale for trying risperidone in this population includes its dopamine-blocking activity; its seemingly lower incidence of tardive dyskinesia when compared to standard neuroleptics; the possibility that risperidone may ameliorate the social withdrawal of PDD, as it does the negative symptoms in schizophrenia; and substantial effects on serotonergic neurotransmission, which has been shown to be dysregulated in some patients with PDD. This study was an open-label pilot trial of risperidone in 6 subjects (aged 7-14 years, mean = 10.7) who met DSM-III-R criteria for a PDD diagnosis. The mean optimal dose was 2.7 mg daily (range 1-6). Mean duration of risperidone administration was 5.2 months (range 1-8). Despite the small sample size, risperidone treatment appeared to be associated with significant improvements in ratings of angry affect (p = 0.04) and lability of affect (p = 0.03) and with a trend (p = 0.10) toward a reduction of mean hyperactivity scores. Clinical Global Improvement scale ratings were statistically significant (p < 0.001). Increased sociability was reported in 3 subjects by their parents and family following the study. Three patients continued on risperidone for over 2 years, and none showed any loss of its apparent therapeutic effects. Weight gain was observed in 5 of 6 patients, with a median increase of 5.4 kg (12 lbs) in 7 weeks. Other side effects included transient sedation, increased salivation, and stereotypies. One child showed a worsening of pre-existing tic and phobic symptoms after 5 months of successful monotherapy. No loss of therapeutic effect was noted in the 3 subjects who remained on risperidone for over 2 years, but 1 patient developed hepatotoxicity and another developed withdrawal dyskinesia, similar to her prior experience with haloperidol. Overall, 5 of the 6 patients derived significant clinical benefits from risperidone. Pharmacologic alternatives for treating behavioral symptoms in PDD are need, and risperidone may be a promising possibility.
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PMID:Risperidone in children and adolescents with pervasive developmental disorder: pilot trial and follow-up. 946 34

Recent advances in molecular neurobiology led to a new understanding on mammalian brain dopaminergic system which plays a major role in the regulation of motor, cognitive, emotional, neuroendocrine functions as well as in the pathogenesis of several pathological conditions, including neurodegenerative diseases, affective disorders, schizophrenia, drug addiction etc. Functional, biochemical and pharmacological heterogeneity of dopamine receptors, which were divided into D1-like (D1 and D5 subtypes) and D2-like (D2, D3 and D4) families of receptors has been postulated. The article reviews the recent advances including author's own results concerning the structure and function of main dopaminergic brain system, i.e. nigrostriatal and mesolimbic. The problem of autoreceptor regulation of dopaminergic neurotransmission, particularly, the processes of dopamine synthesis, release and metabolism has been specially discussed. An involvement of D2 and D3 dopamine autoreceptors in the control of these processes and differences in the mode of action of typical and atypical neuroleptics demonstrating various affinities to D2 and D3 dopamine receptors are analysed in detail. Dopamine and its metabolites have been determined on freely moving rats using brain microdialysis and high performance liquid chromatography. It is hypothesized that dopamine D3 autoreceptor is preferentially involved in the regulation of dopamine release while D2 one is responsible for the control of dopamine synthesis and metabolism in rat basal ganglia in vivo.
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PMID:[Brain dopamine receptors: structure, functional role, and modulation by psychotropic substances]. 950 73

The locomotor stimulation induced by the N-methyl-D-aspartate (NMDA) receptor antagonist MK-801 (dizocilpine) in mice was regarded as a model of at least some aspects of schizophrenia. The serotonin synthesis inhibitor dl-p-chlorophenylalanine (PCPA) was used to evaluate the involvement of endogenous serotonin in (a) the induction of MK-801-induced hyperlocomotion in NMRI mice, and (b) the inhibition of MK-801-induced hyperlocomotion by each of five monoaminergic antagonists (M100907, clozapine, olanzapine, raclopride, SCH23390). Further, brain monoaminergic biochemistry was characterised in rats and mice after various drug treatments. PCPA pretreatment did not significantly reduce MK-801-induced hyperlocomotion in any of the experiments performed; however in a meta-analysis of six experiments, the locomotion displayed by MK-801-treated animals was diminished 17% by PCPA pretreatment. The selective 5-HT2A receptor antagonist M100907 exerted a dose-dependent inhibition of MK-801-induced hyperlocomotion. This effect was abolished in mice pretreated with PCPA, but could be restored in a dose-dependent manner by restitution of endogenous 5-HT by means of 5-hydroxytryptophan (5-HTP). On the other hand, the inhibition of MK-801-induced hyperlocomotion exerted by the selective dopamine D-2 receptor antagonist raclopride or the dopamine D-1 receptor antagonist SCH23390 was unaffected by PCPA pretreatment. The antipsychotics clozapine and olanzapine displayed a split profile. Hence, the inhibitory effect on MK-801-induced hyperlocomotion exerted by low doses of these compounds was diminished after PCPA pretreatment, while inhibition exerted by higher doses was unaffected by PCPA. These results suggest that (1) MK-801-induced hyperlocomotion is accompanied by an activation of, but is not fully dependent upon, brain serotonergic systems. (2) In the hypoglutamatergic state induced by MK-801, endogenous serotonin exerts a stimulatory effect on locomotion through an action at 5-HT2A receptors, an effect that is almost completely counterbalanced by a concomitant inhibitory impact on locomotion, mediated through stimulation of serotonin receptors other than 5-HT2A receptors. M100907, by blocking 5-HT2A receptors, unveils the inhibitory effect exerted on locomotion by these other serotonin receptors. (3) Dopamine D-2 receptor antagonistic properties of antipsychotic compounds, when they come into play, override 5-HT2A receptor antagonism. Possible implications for the treatment of schizophrenia with 5-HT2A receptor antagonists are discussed. It is hypothesized that treatment response to such agents is dependent on increased serotonergic tone.
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PMID:Rodent data and general hypothesis: antipsychotic action exerted through 5-Ht2A receptor antagonism is dependent on increased serotonergic tone. 972 Sep 68

Reports of a reduction in the risk of developing Parkinson's disease and Alzheimer's disease in tobacco smokers, together with the loss of high-affinity nicotine binding in these diseases, suggest that consequences of nicotinic cholinergic transmission may be neuroprotective. Changes in brain dopaminergic parameters and nicotinic receptors in response to tobacco smoking have been assessed in this study of autopsy samples from normal elderly individuals with known smoking histories and apolipoprotein E genotype. The ratio of homovanillic acid to dopamine, an index of dopamine turnover, was reduced in elderly smokers compared with age matched non-smokers (P<0.05) in both the caudate and putamen. Dopamine levels were significantly elevated in the caudate of smokers compared with non-smokers (P<0.05). However there was no significant change in the numbers of dopamine (D1, D2 and D3) receptors or the dopamine transporter in the striatum, or for dopamine D1 and D2 receptors in the hippocampus in smokers compared with non-smokers or ex-smokers. The density of high-affinity nicotine binding was higher in smokers than non-smokers in the hippocampus, entorhinal cortex and cerebellum (elevated by 51-221%) and to a lesser extent in the striatum (25-55%). The density of high-affinity nicotine binding in ex-smokers was similar to that of the non-smokers in all the areas investigated. The differences in high-affinity nicotine binding between smokers and the non- and ex-smokers could not be explained by variation in apolipoprotein E genotype. There were no differences in alpha-bungarotoxin binding, measured in hippocampus and cerebellum, between any of the groups. These findings suggest that chronic cigarette smoking is associated with a reduction of the firing of nigrostriatal dopaminergic neurons in the absence of changes in the numbers of dopamine receptors and the dopamine transporter. Reduced dopamine turnover associated with increased numbers of high-affinity nicotine receptors is consistent with attenuated efficacy of these receptors in smokers. A decrease in striatal dopamine turnover may be a mechanism of neuroprotection in tobacco smokers that could delay basal ganglia pathology. The current findings are also important in the interpretation of measurements of nicotinic receptors and dopaminergic parameters in psychiatric conditions such as schizophrenia, in which there is a high prevalence of cigarette smoking.
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PMID:Dopamine and nicotinic receptor binding and the levels of dopamine and homovanillic acid in human brain related to tobacco use. 972 42

Dopamine D2-like receptors (D2, D3, and D4) are major targets for action of typical and atypical neuroleptics, commonly used in the treatment of schizophrenia. To understand their individual functional contribution, subtype-selective anti-peptide antibodies were raised against D2, D3, and D4 receptor proteins. The antibodies were shown to be specific on immunoblots of rat brain membranes and immunoprecipitated the solubilized native dopamine receptors in an antibody concentration-dependent manner. In addition, they also bind selectively to the respective recombinant D2, D3, and D4 receptor membrane proteins from cDNA transfected cells. Immunolocalization studies show that the D2-like receptor proteins had differential regional and cellular distribution in the cerebral cortex, hippocampus, basal ganglia, cerebellum, and midbrain, thus providing anatomical substrate for area-specific regulation of the dopamine neurotransmission. In cortical neurons, D4 receptor protein was found in both pyramidal and nonpyramidal cells, whereas D2 and D3 seem to be mostly associated with nonpyramidal interneurons. In rat hippocampus, the expression pattern of D2-like receptors (D4>D3>D2) mirrored that obtained with immunoprecipitation studies. D2 and D4 receptor immunolabeling was observed in the thalamic reticular nucleus, which was negative for the D3 subtype. Species differences were also observed; for example, the D4 subtype receptor is the most highly expressed protein in the rat cortex, whereas it is significantly less in human cortex. Differential patterns of D2, D3, and D4 receptor expression in rat and human brain should shed light on the therapeutic actions of neuroleptic drugs and may lead to the development of more specifically targeted antipsychotic drugs.
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PMID:Differential regional and cellular distribution of dopamine D2-like receptors: an immunocytochemical study of subtype-specific antibodies in rat and human brain. 985 4

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