Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0030567 (Parkinson's disease)
 63,064 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The neurotransmitters dopamine (DA) and glutamate in the striatum play key roles in movement and cognition, and they are implicated in disorders of the basal ganglia such as Parkinson's disease. Excitatory synapses in striatum undergo a form of developmental plasticity characterized by a decrease in glutamate release probability. Here we demonstrate that this form of synaptic plasticity is DA and DA D2 receptor dependent. Analysis of spontaneous synaptic responses indicates that a presynaptic mechanism involving inhibition of neurotransmitter release underlies the developmental plasticity. We suggest that a major role of DA in the striatum is to initiate mechanisms that regulate the efficacy of excitatory striatal synapses, producing a decrease in glutamate release.
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PMID:Dopamine-dependent synaptic plasticity in striatum during in vivo development. 1115 26

The TaqIA D2 dopamine receptor (DRD2) minor (A1) allele was first associated with severe alcoholism a decade ago. Since then, studies both confirming and not confirmnning this finding were reported. However, a meta-analysis of a large number of Caucasian alcoholics (both more severe and less severe) and controls (both assessed and unassessed for substance use disorders) revealed a significantly higher frequency (p < 10(-6)) and prevalence (p < 10(-8)) of the DRD2 A1 allele in the alcoholics. Further analysis showed that the more severe alcoholics had a 3-fold higher prevalence of the DRD2 A1 allele than the assessed controls (p < 10(-10)), whereas no difference was found between the less severe alcoholics and the unassessed controls. DRD2 exonic or promoter mutations have not yet been associated with alcoholism, although two intronic variants at the TaqIB and intron 6 sites, which are in linkage disequilibrium with the TaqIA site, were associated with this disorder. Variants of the DRD2 gene have also been associated with cocaine, nicotine and opioid dependence, obesity and gambling. It is hypothesised that the DRD2 is a reinforcement or reward gene. Although less intensively studied than substance use disorders, the DRD2 gene has been implicated in Tourette's syndrome (TS), post-traumatic stress disorder (PTSD) and certain symptoms associated with affective disorders and schizophrenia. Further, DRD2 variants have been implicated in Parkinson's disease (PD) and in iatrogenically-induced movement disorders, as well as in certain migraineurs. Phenotypic differences have been associated with DRD2 variants. These include reduced D2 dopamine receptor numbers and diminished glucose metabolism in the brain of subjects who carry the DRD2 A1 allele. In addition, phenotypic differences have been found in neurocognitive and personality characteristics, and in treatment outcome of DRD2 variants. The involvement of the DRD2 gene in certain neuropsychiatric disorders opens up the potential of a targeted pharmacogenomic approach to the prevention and treatment of these disorders.
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PMID:The DRD2 gene in psychiatric and neurological disorders and its phenotypes. 1125 81

The dopamine system is known to be closely involved in brain neuronal dysfunction and in diseases such as Parkinson's disease, Tourette's syndrome, attention deficit hyperactive disorder, generation of pituitary tumors and schizophrenia. According to the classical dopamine hypothesis on the pathology of schizophrenia, conventional antipsychotics has D2 dopamine receptor antagonistic profiles. However, the use of typical antipsychotics has several limitations; that is, some patients do not respond to them, they can even worsen negative symptoms, and they can provoke unacceptable extrapyramidal and endocrine side effects. To produce effective antipsychotics with reduced side effects, partial agonists to D2 dopamine receptors (D2 receptors) have been developed. Despite the effectiveness of partial agonists for pre- and postsynaptic D2 receptors, administration of such drugs results in inconsistent clinical effects to ameliorate the symptoms of schizophrenia. Thus, strategies for obtaining ideal effective antipsychotics with reduced side effects are considered in this short review with respect to the intrinsic efficacies and affinities of the partial agonists, based on the partial agonist concept.
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PMID:Strategy for modulation of central dopamine transmission based on the partial agonist concept in schizophrenia therapy. 1156 10

While the pathophysiological changes induced by the loss of dopamine innervation in the basal ganglia by Parkinson's disease (PD) are well studied, little is known about functional changes in the neural circuitry of this area during normal aging. Here we report the first survey of age-associated changes in the basal ganglia of behaviorally characterized, awake rhesus monkeys, using pharmacological MRI to map responses to dopaminergic stimulation. Apomorphine, a mixed D(1)/D(2) dopamine receptor agonist, evoked little change in the substantia nigra (SN) of aged animals while significantly reducing activation in young adult monkeys. Compared to young animals, both apomorphine and d-amphetamine (which increases synaptic dopamine levels) significantly increased activation of the aged rhesus globus pallidus externa (GPe). In addition, the aged animals showed decreased activity in the putamen in response to d-amphetamine administration. Although the responses in the SN and putamen of the aged monkeys differed from those in animal models of PD, the apomorphine-evoked activation of their GPe corresponded with apomorphine-induced increases in neuronal activity seen in Parkinson's patients and animal models. Given the major role of the GPe in regulating motor behavior, the altered responses in the aged GPe may contribute significantly to the motor slowing and movement dysfunctions characterizing advanced age.
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PMID:Pharmacological MRI mapping of age-associated changes in basal ganglia circuitry of awake rhesus monkeys. 1169 47

Introduced on the market in 1989, pergolide, a D1/D2 dopamine receptor agonist, is still widely prescribed for the treatment of patients with early and advanced Parkinson's disease (PD). Initially, pergolide was introduced as an adjunct therapy to levodopa treatment in patients exhibiting fluctuating motor responses and dyskinesias. Results of recent randomized controlled clinical trials in de novo patients with PD show that pergolide is able to improve parkinsonian symptoms when used as monotherapy. Moreover, preliminary results of a long-term monotherapy study in early PD suggest that pergolide is as effective as levodopa, and that a significant delay in the time of the onset of levodopa-induced motor complications can be obtained. A number of randomized studies have shown that pergolide is more effective than bromocriptine as adjunct therapy to levodopa in patients with advanced PD; the greater benefit found with pergolide could be ascribed to its action on both D1 and D2 dopamine receptors. However, controlled comparative studies with new dopamine agonists, such as ropinirole, cabergoline, and pramipexole, have not been performed yet. Interestingly, few open studies in patients with complicated PD have shown that high doses of pergolide (> 6 mg/d) are able to improve motor fluctuations and dyskinesias through a dramatic reduction of levodopa dosage. The side-effect profile of pergolide is similar to that of other dopamine agonists, and complications such as sleep attack and serosal fibrosis have been rarely reported.
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PMID:Pergolide in the treatment of patients with early and advanced Parkinson's disease. 1185 89

Dual probe microdialysis was employed in conscious rats to investigate whether endogenous dopamine is involved in the stimulation of glutamate release in the substantia nigra pars reticulata following striatal NMDA receptor activation. Intrastriatal perfusion with NMDA (1 and 10 microm) facilitated nigral glutamate release (dizocilpine- and tetrodotoxin-sensitive). The D2 dopamine receptor antagonist raclopride increased spontaneous nigral glutamate release and caused a leftward shift in the NMDA sensitivity, lowering NMDA effective concentrations to submicromolar levels. Conversely, the D1 antagonist SCH23390 prevented the effect of NMDA (1 microm) and caused a rightward shift in the NMDA sensitivity. It was tested whether the antagonist effects were due to dopamine receptor blockade or increased tone on D1/D2 receptors. SCH23390 prevented the raclopride-induced enhancement of spontaneous but not NMDA-evoked glutamate release while raclopride left unchanged the SCH23390-induced inhibition. The physiopathological relevance of the dopaminergic modulation was strengthened by perfusing NMDA in the dopamine-depleted striatum of hemiparkinsonian rats. Nigral glutamate responsiveness to NMDA was enhanced as with raclopride. We conclude that endogenous striatal dopamine regulates both spontaneous and NMDA-induced nigral glutamate release via an opposite control mediated by D1 facilitatory and D2 inhibitory receptors. Alterations of this control may subserve the motor symptoms of Parkinson's disease.
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PMID:Striatal dopamine-NMDA receptor interactions in the modulation of glutamate release in the substantia nigra pars reticulata in vivo: opposite role for D1 and D2 receptors. 1239 May 25

The output of GABAergic medium-sized spiny neurons in the dorsal striatum is controlled in part by glutamatergic input from the neocortex and the thalamus, and dopaminergic input from ventral midbrain. We acutely isolated these neurons from juvenile (P14-24) rats to study the consequences of the interaction between glutamate and dopamine for neuronal excitability. Single-cell RT-PCR analysis was used to identify the expression patterns of dopamine receptors. D1 and D2 dopamine receptor mRNA was detected in 11/22 and 3/22 of isolated neurons, respectively. Receptor mRNA co-expression was detected in 1/22 cells tested. Whole-cell voltage clamp recording (V(h)=-70 mV) was combined with local or bath application of dopaminergic and glutamatergic agonists to explore dopamine receptor modulation of glutamatergic excitation. Glutamate-evoked inward currents (5 microM, Mg(2+)-free, 1 microM glycine) were attenuated by dopamine (5 microM) to 83.2+/-3.6% (n=31). NMDA-evoked (20 microM), APV-sensitive currents were attenuated by dopamine to 80.9+/-4.5% (n=24). NMDA-induced responses were also attenuated by the D1 receptor agonist SKF 38393 (1 microM; n=28), while the D2/3 receptor agonist quinpirole (10 microM) had no effect. The currents evoked by application of AMPA (5 microM) displayed a steady rundown. Application of dopamine abolished or significantly reduced the rundown in the cells tested (n=17). A similar effect was observed after the application of SKF 38393 (1 microM), while quinpirole (10 microM) had no significant effect. Our results provide direct evidence for modulation by dopamine of glutamatergic responses of striatal medium spiny neurons, and demonstrate that the effects of this neuromodulator are receptor subtype specific. Disruption of this modulatory effect is likely to contribute to movement disorders associated with Parkinson's disease.
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PMID:Receptor subtype-specific modulation by dopamine of glutamatergic responses in striatal medium spiny neurons. 1249 13

A2A adenosine receptors (A(2A)Rs) are expressed with the greatest abundance in the striatum and other nuclei of the basal ganglia. The segregated expression of A(2A)Rs on the GABAergic striatopallidal medium spiny neurons, where A(2A)R and D2 dopamine receptor mRNAs are colocalized, and the opposing functional interaction between adenosine and dopamine suggest that A(2A)Rs may be an important therapeutic target. To further explore the role of A(2A)Rs in the synaptic organization of the basal ganglia, the authors developed an antibody directed against the purified A(2A)R. Immunohistochemical studies in rat brain showed dense labeling of the neuropil in the striatum, nucleus accumbens, and olfactory tubercles with lighter labeling of terminals in the globus pallidus (GP), where A(2A)R transcript is not detected. Stimulation of A(2A)Rs on GP terminals may facilitate GABAergic signaling and contribute to the overactivation observed in Parkinson's disease (PD). Analysis at the ultrastructural level allowed a more detailed characterization of the mechanism(s) of A2A-mediated control of striatal output. In the striatum, terminals expressing A(2A)Rs accounted for 25% of the labeled elements. These presynaptic receptors may facilitate excitatory glutamatergic, inhibitory GABAergic, and possibly cholinergic striatal transmission. However, the majority of striatal A(2A)R immunoreactivity was found on postsynaptic elements, including dendrites of striatopallidal neurons, in which A(2A)R and GABA immunoreactivity is colocalized. Activation of these receptors may promote GABAergic signaling in striatopallidal output neurons and their local axon collaterals in the striatum. Many of the A2A-labeled dendrites were contacted by terminals forming asymmetric (excitatory) possibly glutamatergic synapses. Using the vesicular glutamate transporters (VGLUTs) as markers of glutamatergic terminals, the authors have found that VGLUT1-immunoreactive (ir) terminals make asymmetric contacts on A2A-ir spines and spine heads in the striatum, suggesting that regulation of striatal output by A(2A)R stimulation may involve facilitation of the cortical glutamatergic excitatory input to striatopallidal neurons. These ultrastructural findings suggest several pathways through which A2A receptor blockade may act to dampen the elevated striatopallidal GABAergic signaling that occurs in PD.
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PMID:Anatomy of adenosine A2A receptors in brain: morphological substrates for integration of striatal function. 1466 2

Dopamine acts in the striatum principally through the D1 and D2 dopamine receptor subtypes, which are segregated to the direct and indirect striatal projection neurons, respectively. As a consequence, degeneration of the dopamine input to the striatum results in opposing affects in these pathways. The resulting functional imbalance is thought to be responsible for the bradykinesia of Parkinson's disease, which may be temporarily normalized by dopamine replacement therapy. However, direct striatal projection neurons become irreversibly supersensitive to D1 dopamine receptor activation, despite the fact that there is an actual decrease in receptor number. Recent studies show that this D1 -supersensitive response results from a switch from the normal D1-mediated activation of protein-kinase A to an aberrant activation of ERK1/2/MAPkinase. This switch in D1-receptor-mediated regulation of protein kinase systems responsible for neuronal plasticity is suggested to underlie dyskinesia produced by L-DOPA treatment of Parkinson's disease.
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PMID:D1 dopamine receptor supersensitivity in the dopamine-depleted striatum animal model of Parkinson's disease. 1467 78

Dopamine neurotransmitter and its receptors play a critical role in the cell signaling process responsible for information transfer in neurons functioning in the nervous system. Development of improved therapeutics for such disorders as Parkinson's disease and schizophrenia would be significantly enhanced with the availability of the 3D structure for the dopamine receptors and of the binding site for dopamine and other agonists and antagonists. We report here the 3D structure of the long isoform of the human D2 dopamine receptor, predicted from primary sequence using first-principles theoretical and computational techniques (i.e., we did not use bioinformatic or experimental 3D structural information in predicting structures). The predicted 3D structure is validated by comparison of the predicted binding site and the relative binding affinities of dopamine, three known dopamine agonists (antiparkinsonian), and seven known antagonists (antipsychotic) in the D2 receptor to experimentally determined values. These structures correctly predict the critical residues for binding dopamine and several antagonists, identified by mutation studies, and give relative binding affinities that correlate well with experiments. The predicted binding site for dopamine and agonists is located between transmembrane (TM) helices 3, 4, 5, and 6, whereas the best antagonists bind to a site involving TM helices 2, 3, 4, 6, and 7 with minimal contacts to TM helix 5. We identify characteristic differences between the binding sites of agonists and antagonists.
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PMID:The predicted 3D structure of the human D2 dopamine receptor and the binding site and binding affinities for agonists and antagonists. 1499 1


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