Receptor subtype-specific modulation by dopamine of glutamatergic responses in striatal medium spiny neurons
ABSTRACT 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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ABSTRACT: Among the many neuromodulators used by the mammalian brain to regulate circuit function and plasticity, dopamine (DA) stands out as one of the most behaviorally powerful. Perturbations of DA signaling are implicated in the pathogenesis or exploited in the treatment of many neuropsychiatric diseases, including Parkinson's disease (PD), addiction, schizophrenia, obsessive compulsive disorder, and Tourette's syndrome. Although the precise mechanisms employed by DA to exert its control over behavior are not fully understood, DA is known to regulate many electrical and biochemical aspects of neuronal function including excitability, synaptic transmission, integration and plasticity, protein trafficking, and gene transcription. In this Review, we discuss the actions of DA on ionic and synaptic signaling in neurons of the prefrontal cortex and striatum, brain areas in which dopaminergic dysfunction is thought to be central to disease.Neuron 10/2012; 76(1):33-50. DOI:10.1016/j.neuron.2012.09.023 · 15.98 Impact Factor
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ABSTRACT: Nucleus accumbens (nAcb), a major site of action of drugs of abuse and dopamine (DA) signalling in MSNs (medium spiny neurons), is critically involved in mediating behavioural responses of drug addiction. Most studies have evaluated the effects of DA on MSN firing properties but thus far, the effects of DA on a cellular circuit involving glutamatergic afferents to the nAcb have remained rather elusive. In this study we attempted to characterize the effects of dopamine (DA) on evoked glutamatergic excitatory postsynaptic currents (EPSCs) in nAcb medium spiny (MS) neurons in 1 to 21 day-old rat pups. The EPSCs evoked by local nAcb stimuli displayed both AMPA/KA and NMDA receptor-mediated components. The addition of DA to the superfusing medium produced a marked decrease of both components of the EPSCs that did not change during the postnatal period studied. Pharmacologically isolated AMPA/KA receptor-mediated response was inhibited on average by 40% whereas the isolated NMDA receptor-mediated EPSC was decreased by 90%. The effect of DA on evoked EPSCs were mimicked by the D1-like receptor agonist SKF 38393 and antagonized by the D1-like receptor antagonist SCH 23390 whereas D2-like receptor agonist or antagonist respectively failed to mimic or to block the action of DA. DA did not change the membrane input conductance of MS neurons or the characteristics of EPSCs produced by the local administration of glutamate in the presence of tetrodotoxin. In contrast, DA altered the paired-pulse ratio of evoked EPSCs. The present results show that the activation D1-like dopaminergic receptors modulate glutamatergic neurotransmission by preferentially inhibiting NMDA receptor-mediated EPSC through presynaptic mechanisms.PLoS ONE 05/2014; 9(5):e86970. DOI:10.1371/journal.pone.0086970 · 3.53 Impact Factor
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ABSTRACT: This work compares the effects on brain stimulation reward (BSR) when combining D2 dopamine receptor and AMPA glutamate receptor manipulations in the sublenticular central extended amygdala (SLEAc) and the nucleus accumbens shell (NAc shell). Thirty-seven male Long Evans rats received medial forebrain bundle (MFB) stimulation electrodes and bilateral injection guide cannulae aimed at either the SLEAc or the NAc shell. The rate-frequency paradigm was used to assess drug-induced changes in stimulation reward effectiveness and in response rate following 0.5μl infusions of 0.50μg of 1,2,3,4-tetrahydro-6-nitro-2,3-dioxo-benzo[f]quinoxaline-7-sulfonamide (NBQX) (AMPA receptor antagonist), 10.0μg of quinpirole (D2 receptor agonist), 0.25μg of AMPA (AMPA receptor agonist), 3.0μg of eticlopride (D2 receptor antagonist), 0.50μg of NBQX with 10.0μg of quinpirole, and 0.25μg of AMPA with 3.0μg of eticlopride. The drugs were injected both ipsi- and contralateral to the stimulation site. AMPA blockade and D2 stimulation synergized to reduce BSR's reward efficacy when directed at the SLEAc contralateral to the stimulation site whereas changes in reward efficacy were primarily D2-dependent following injections into the ipsilateral SLEAc. When injected into the NAc shell the drugs had only one significant effect on the frequency required to maintain half-maximal responding: injections of NBQX with quinpirole ipsilateral to the stimulation site increased required frequency significantly more than did injections of saline. Contrary to expectations, stimulating AMPA receptors with and without co-blockade of D2 receptors also decreased the stimulation's reward efficacy, although these effects may reflect general behavioral disruption more than effects on reward per se. These results indicate a role for the SLEAc in BSR and also suggest that SLEAc neurons ipsi- and contralateral to the stimulated MFB play their roles in BSR through different mechanisms.Neuroscience 08/2012; 224:1-14. DOI:10.1016/j.neuroscience.2012.08.019 · 3.33 Impact Factor