Dopamine D1 receptor inhibition of NMDA receptor currents mediated by tyrosine kinase-dependent receptor trafficking in neonatal rat striatum

The selective dopamine D1 receptor agonist SKF81297 modulates NMDA receptor currents independently of D1 receptors

Dopamine D₁ receptor (D₁R) agonists are frequently used to study the role of D₁Rs in neurotransmission and behaviour. They have been repeatedly shown to modulate glutamatergic NMDAR currents in the prefrontal cortex (PFC), giving rise to the idea that D₁R activation tunes glutamatergic networks by regulating NMDAR activity. We report that the widely used D₁R agonist SKF81297 potentiates NMDAR currents in a dose-dependent manner, independently of D₁R activation in mPFC slices, cortical neuron cultures and NMDAR-expressing recombinant HEK293 cells. SKF81297 potentiated NMDAR currents through both GluN2A and GluN2B subtypes in the absence of D₁R expression, while inhibiting NMDAR currents through GluN2C and GluN2D subtypes. In contrast, the D₁R ligands SKF38393, dopamine and SCH23390 inhibited GluN2A- and GluN2B-containing NMDAR currents. SKF81297 also inhibited GluN2A- and GluN2B-containing NMDAR currents at higher concentrations and when glutamate/glycine levels were high, exhibiting bidirectional modulation. To our knowledge, these findings are the first report of a D₁R-independent positive modulatory effect of a D₁R ligand on NMDA receptors. Importantly, our results further emphasize the possibility of off-target effects of many D₁R ligands, which has significant implications for interpreting the large body of research relying on these compounds to examine dopamine functions.

Blockade of spinal dopamine D1/D2 receptor suppresses activation of NMDA receptor through Gαq and Src kinase to attenuate chronic bone cancer pain

Introduction

Spinal N-methyl-D-aspartate receptor (NMDAR) is vital in chronic pain, while NMDAR antagonists have severe side effects. NMDAR has been reported to be controlled by G protein coupled receptors (GPCRs), which might present new therapeutic targets to attenuate chronic pain. Dopamine receptors which belong to GPCRs have been reported could modulate the NMDA-mediated currents, while their exact effects on NMDAR in chronic bone cancer pain have not been elucidated.

Objectives

This study was aim to explore the effects and mechanisms of dopamine D1 receptor (D1DR) and D2 receptor (D2DR) on NMDAR in chronic bone cancer pain.

Methods

A model for bone cancer pain was established using intra-tibia bone cavity tumor cell implantation (TCI) of Walker 256 in rats. The nociception was assessed by Von Frey assay. A range of techniques including the fluorescent imaging plate reader, western blotting, and immunofluorescence were used to detect cell signaling pathways. Primary cultures of spinal neurons were used for in vitro evaluation.

Results

Both D1DR and D2DR antagonists decreased NMDA-induced upregulation of Ca²⁺ oscillations in primary culture spinal neurons. Additionally, D1DR/D2DR antagonists inhibited spinal Calcitonin Gene-Related Peptide (CGRP) and c-Fos expression and alleviated bone cancer pain induced by TCI which could both be reversed by NMDA. And D1DR/D2DR antagonists decreased p-NR1, p-NR2B, and Gαq protein, p-Src expression. Both Gαq protein and Src inhibitors attenuated TCI-induced bone cancer pain, which also be reversed by NMDA. The Gαq protein inhibitor decreased p-Src expression. In addition, D1DR/D2DR antagonists, Src, and Gαq inhibitors inhibited spinal mitogen-activated protein kinase (MAPK) expression in TCI rats, which could be reversed by NMDA.

Conclusions

Spinal D1DR/D2DR inhibition eliminated NMDAR-mediated spinal neuron activation through Src kinase in a Gαq-protein-dependent manner to attenuate TCI-induced bone cancer pain, which might present a new therapeutic strategy for bone cancer pain.

Synaptic Potentiation at Basal and Apical Dendrites of Hippocampal Pyramidal Neurons Involves Activation of a Distinct Set of Extracellular and Intracellular Molecular Cues

In the central nervous system, several forms of experience-dependent plasticity, learning and memory require the activity-dependent control of synaptic efficacy. Despite substantial progress in describing synaptic plasticity, mechanisms related to heterogeneity of synaptic functions at local circuits remain elusive. Here we studied the functional and molecular aspects of hippocampal circuit plasticity by analyzing excitatory synapses at basal and apical dendrites of mouse hippocampal pyramidal cells (CA1 region) in acute brain slices. In the past decade, activity of metalloproteinases (MMPs) has been implicated as a widespread and critical factor in plasticity mechanisms at various projections in the CNS. However, in the present study we discovered that in striking contrast to apical dendrites, synapses located within basal dendrites undergo MMP-independent synaptic potentiation. We demonstrate that synapse-specific molecular pathway allowing MMPs to rapidly upregulate function of NMDARs in stratum radiatum involved protease activated receptor 1 and intracellular kinases and GTPases activity. In contrast, MMP-independent scaling of synaptic strength in stratum oriens involved dopamine D1/D5 receptors and Src kinases. Results of this study reveal that 2 neighboring synaptic systems differ significantly in extracellular and intracellular cascades that control synaptic gain and provide long-searched transduction pathways relevant for MMP-dependent synaptic plasticity.

Molecular basis of dopamine replacement therapy and its side effects in Parkinson's disease

There is currently no cure for Parkinson's disease. The symptomatic therapeutic strategy essentially relies on dopamine replacement whose efficacy was demonstrated more than 50 years ago following the introduction of the dopamine precursor, levodopa. The spectacular antiparkinsonian effect of levodopa is, however, balanced by major limitations including the occurrence of motor complications related to its particular pharmacokinetic and pharmacodynamic properties. Other therapeutic strategies have thus been developed to overcome these problems such as the use of dopamine receptor agonists, dopamine metabolism inhibitors and non-dopaminergic drugs. Here we review the pharmacology and molecular mechanisms of dopamine replacement therapy in Parkinson's disease, both at the presynaptic and postsynaptic levels. The perspectives in terms of novel drug development and prediction of drug response for a more personalised medicine will be discussed.

Basal Ganglia Neuromodulation Over Multiple Temporal and Structural Scales-Simulations of Direct Pathway MSNs Investigate the Fast Onset of Dopaminergic Effects and Predict the Role of Kv4.2

The basal ganglia are involved in the motivational and habitual control of motor and cognitive behaviors. Striatum, the largest basal ganglia input stage, integrates cortical and thalamic inputs in functionally segregated cortico-basal ganglia-thalamic loops, and in addition the basal ganglia output nuclei control targets in the brainstem. Striatal function depends on the balance between the direct pathway medium spiny neurons (D1-MSNs) that express D1 dopamine receptors and the indirect pathway MSNs that express D2 dopamine receptors. The striatal microstructure is also divided into striosomes and matrix compartments, based on the differential expression of several proteins. Dopaminergic afferents from the midbrain and local cholinergic interneurons play crucial roles for basal ganglia function, and striatal signaling via the striosomes in turn regulates the midbrain dopaminergic system directly and via the lateral habenula. Consequently, abnormal functions of the basal ganglia neuromodulatory system underlie many neurological and psychiatric disorders. Neuromodulation acts on multiple structural levels, ranging from the subcellular level to behavior, both in health and disease. For example, neuromodulation affects membrane excitability and controls synaptic plasticity and thus learning in the basal ganglia. However, it is not clear on what time scales these different effects are implemented. Phosphorylation of ion channels and the resulting membrane effects are typically studied over minutes while it has been shown that neuromodulation can affect behavior within a few hundred milliseconds. So how do these seemingly contradictory effects fit together? Here we first briefly review neuromodulation of the basal ganglia, with a focus on dopamine. We furthermore use biophysically detailed multi-compartmental models to integrate experimental data regarding dopaminergic effects on individual membrane conductances with the aim to explain the resulting cellular level dopaminergic effects. In particular we predict dopaminergic effects on Kv4.2 in D1-MSNs. Finally, we also explore dynamical aspects of the onset of neuromodulation effects in multi-scale computational models combining biochemical signaling cascades and multi-compartmental neuron models.

Combination of behaviorally sub-effective doses of glutamate NMDA and dopamine D1 receptor antagonists impairs executive function

Impairment of executive function is a core feature of schizophrenia. Preclinical studies indicate that injections of either N-methyl d-aspartate (NMDA) or dopamine D₁ receptor blockers impair executive function. Despite the prevailing notion based on postmortem findings in schizophrenia that cortical areas have marked suppression of glutamate and dopamine, recent in vivo imaging studies suggest that abnormalities of these neurotransmitters in living patients may be quite subtle. Thus, we hypothesized that modest impairments in both glutamate and dopamine function can act synergistically to cause executive dysfunction. In the present study, we investigated the effect of combined administration of "behaviorally sub-effective" doses of NMDA and dopamine D₁ receptor antagonists on executive function. An operant conditioning-based set-shifting task was used to assess behavioral flexibility in rats that were systemically injected with NMDA and dopamine D₁ receptor antagonists individually or in combination prior to task performance. Separate injections of the NMDA receptor antagonist, MK-801, and the dopamine D₁ receptor antagonist, SCH 23390, at low doses did not impair set-shifting; however, the combined administration of these same behaviorally sub-effective doses of the antagonists significantly impaired the performance during set-shifting without affecting learning, retrieval of the memory of the initial rule, latency of responses or the number of omissions. The combined treatment also produced an increased number of perseverative errors. Our results indicate that NMDA and D₁ receptor blockade act synergistically to cause behavioral inflexibility, and as such, subtle abnormalities in glutamatergic and dopaminergic systems may act cooperatively to cause deficits in executive function.

Effects of dopamine D1 receptor blockade on the ERG b- and d-waves during blockade of ionotropic GABA receptors

Background

Some data indicate that the dopaminergic and GABAergic systems interact in the vertebrate retina, but the type of interactions is not well understood.

Methods

In this study we investigated the effect of dopamine D₁ receptor blockade by 75 μM SCH 23390 on the electroretinographic ON (b-wave) and OFF (d-wave) responses in intact frog eyecup preparations and in eyecups where the ionotropic GABA receptors were blocked by 50 μM picrotoxin. Student’s t-test, One-way repeated measures ANOVA with Bonferroni post-hoc test and Two-way ANOVA were used for statistical evaluation of the data.

Results

We found that SCH 23390 alone significantly enhanced the amplitude of the b- and d-waves without altering their latency. The effect developed rapidly and was fully expressed within 8-11 min after the blocker application. Picrotoxin alone also markedly enhanced the amplitude of the ERG ON and OFF responses and increased their latency significantly. The effect was fully expressed within 25-27 min after picrotoxin application and remained very stable in the next 20 min. The effects of SCH 23390 and picrotoxin are similar to that reported in our previous studies. When SCH 23390 was applied on the background of the fully developed picrotoxin effect, it diminished the amplitude of the b- and d-waves in comparison to the corresponding values obtained during application of picrotoxin alone.

Conclusion

Our results demonstrate that the enhancing effect of D₁ receptor blockade on the amplitude of the ERG b- and d-waves is not evident during the ionotropic GABA receptor blockade, indicating an interaction between these neurotransmitter systems in the frog retina. We propose that the inhibitory effect of endogenous dopamine mediated by D₁ receptors on the ERG ON and OFF responses in the frog retina may be due to the dopamine-evoked GABA release.

Electronic supplementary material

The online version of this article (doi:10.1186/s40662-016-0064-4) contains supplementary material, which is available to authorized users.

Dopamine increases NMDA-stimulated calcium flux in striatopallidal neurons through a matrix metalloproteinase-dependent mechanism

Dopamine (DA) is a potent neuromodulator known to influence glutamatergic transmission in striatal medium spiny neurons (MSNs). It acts on D1- and D2-like DA receptors that are expressed on two distinct subpopulations. MSNs projecting to the substantia nigra express D1 receptors (D1Rs), while those projecting to the lateral globus pallidus express D2 receptors (D2Rs). D1R signalling in particular can increase excitatory transmission through varied protein kinase A-dependent, cell-autonomous pathways. Mechanisms by which D1R signalling could increase excitatory transmission in D2R-bearing MSNs have been relatively less explored. Herein, the possibility is considered that D1R agonists increase levels of soluble factors that subsequently influence N-methyl-D-aspartate (NMDA)-stimulated calcium flux in D2R neurons. This study focuses on matrix metalloproteinases (MMPs) and MMP-generated integrin binding ligands, important soluble effectors of glutamatergic transmission that may be elevated in the setting of excess DA. It was observed that DA and a D1R agonist, SKF81297, increase MMP activity in extracts from striatal slices, as determined by cleavage of the substrate β-dystroglycan. Using mice engineered to express the calcium indicator GCaMP3 in striatopallidal D2R-bearing neurons, it was also observed that SKF81297 pretreatment of slices (60 min) potentiates NMDA-stimulated calcium increases in this subpopulation. Effects are diminished by pretreatment with an antagonist of MMP activity or an inhibitor of integrin-dependent signalling. Together, results suggest that DA signalling can increase excitatory transmission in D2R neurons through an MMP-dependent mechanism. Future studies may be warranted to determine whether D1R-stimulated MMP-dependent processes contribute to behaviours in which increased activity in striatopallidal MSNs plays a role.

Allosteric modulation of GluN2C/GluN2D-containing NMDA receptors bidirectionally modulates dopamine release: implication for Parkinson's disease

BACKGROUND AND PURPOSE

Allosteric modulators of ionotropic receptors and GPCRs might constitute valuable therapeutic tools for intervention in several diseases, including Parkinson's disease (PD). However, the possibility that some of these compounds could alter neurotransmission in health and disease has not been thoroughly examined. Hence, we determined whether CIQ, a positive allosteric modulator of NMDA receptors that contain the GluN2C or GluN2D subunits, modulates dopamine release in the striatum of control mice and of a mouse model of presymptomatic Parkinsonism.

EXPERIMENTAL APPROACH

We used amperometry to measure, in mouse brain slices containing the dorsal striatum, dopamine release evoked by stimulations that mimicked tonic (single pulses) or phasic (trains) activity. We used control mice and mice with a partial, 6-hydroxydopamine-induced, degeneration of dopaminergic neurons in the substantia nigra.

KEY RESULTS

In control mice, CIQ inhibited tonic dopamine release and induced an initial inhibition followed by a long-lasting increase in phasic release. Pirenzepine, a muscarinic receptor antagonist, blocked the depression of release induced by CIQ, but not the long-lasting potentiation. CIQ also increased action potential firing in striatal cholinergic interneurons. In the partially dopamine-depleted striatum, CIQ induced an inhibition followed by a potentiation of both tonic and phasic release, but did not significantly increase the firing of cholinergic interneurons.

CONCLUSIONS AND IMPLICATIONS

CIQ has bidirectional, activity- and ACh-dependent, modulatory effects on dopamine release in the striatum. This study suggests a potentially valuable means to enhance dopamine release in presymptomatic Parkinsonism.

Dopamine preferentially inhibits NMDA receptor-mediated EPSCs by acting on presynaptic D1 receptors in nucleus accumbens during postnatal development

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.

Cocaine-induced changes in NMDA receptor signaling

Addictive states are often thought to rely on lasting modification of signaling at relevant synapses. A long-standing theory posits that activity at N-methyl-D-aspartate receptors (NMDARs) is a critical component of long-term synaptic plasticity in many brain areas. Indeed, NMDAR signaling has been found to play a role in the etiology of addictive states, in particular, following cocaine exposure. However, no consensus is apparent with respect to the specific effects of cocaine exposure on NMDARs. Part of the difficulty lies in the fact that NMDARs interact extensively with multiple membrane proteins and intracellular signaling cascades. This allows for highly heterogeneous patterns of NMDAR regulation by cocaine in distinct brain regions and at distinct synapses. The picture is further complicated by findings that cocaine effects on NMDARs are sensitive to the behavioral history of cocaine exposure such as the mode of cocaine administration. This review provides a summary of evidence for cocaine-induced changes in NMDAR expression, cocaine-induced alterations in NMDAR function, and cocaine effects on NMDAR control of intracellular signaling cascades.

Extrasynaptic targeting of NMDA receptors following D1 dopamine receptor activation and cocaine self-administration

We previously showed that after repeated exposure to cocaine, D1-like dopamine receptor (D1DR) stimulation reverses plastic changes of AMPA receptor-mediated signaling in the nucleus accumbens shell. However, there is little information on the impact of cocaine self-administration on D1-NMDA receptor interactions in this brain region. Here, using whole-cell patch-clamp recordings, we assessed whether cocaine self-administration alters the effects of D1DR stimulation on synaptic and extrasynaptic NMDA receptors (NMDARs). In slices from cocaine-naive rats, pretreatment with a D1DR agonist decreased synaptic NMDAR-mediated currents and increased the contribution of extrasynaptic NMDARs. In contrast, neither cocaine self-administration alone nor cocaine experience followed by D1DR stimulation had an effect on synaptic or extrasynaptic NMDAR signaling. Activation of extrasynaptic NMDARs relies on the availability of extracellular glutamate, which is regulated primarily by glutamate transporters. In cocaine-experienced animals, relative to cocaine-naive rats, administration of a glutamate reuptake blocker, DL-threo-β-benzyloxyaspartic acid, revealed increased extrasynaptic NMDAR activity and stronger baseline activity of glutamate uptake transporters. In cocaine-naive rats, the D1DR-mediated increase in extrasynaptic NMDAR signaling was independent of the activity of glutamate reuptake transporters. Together, these results indicate that cocaine experience blunts the influence of D1DRs on synaptic and extrasynaptic NMDAR signaling. Additionally, prior cocaine self-administration limits activation of the extrasynaptic NMDAR pool by increasing glutamate reuptake. These findings outline a pattern of adaptive interactions between D1DRs and NMDARs in the nucleus accumbens shell and demonstrate upregulation of extrasynaptic NMDAR signaling as a novel consequence of cocaine self-administration.

Role of G-proteins in the effects of leptin on pedunculopontine nucleus neurons

The pedunculopontine nucleus (PPN), the cholinergic arm of the reticular activating system, regulates waking and rapid eye movement sleep. Here, we demonstrate immunohistochemical labeling of the leptin receptor signaling isoform in PPN neurons, and investigated the effects of G-protein modulation and the leptin triple antagonist (TA) on the action of leptin in the PPN. Whole-cell patch clamp recordings were performed in rat brainstem slices from 9 to 17 day old pups. Previous results showed that leptin caused a partial blockade of sodium (I(Na)) and h-current (I(H)) in PPN neurons. TA (100 nM) reduced the blockade of I(Na) (~ 50% reduction) and I(H) (~ 93% reduction) caused by leptin. Intracellular guanosine 5'-[β-thio]diphosphate trilithium salt (a G-protein inhibitor) significantly reduced the effect of leptin on I(Na) (~ 60% reduction) but not on I(H) (~ 25% reduction). Intracellular GTPγS (a G-protein activator) reduced the effect of leptin on both I(Na) (~ 80% reduction) and I(H) (~ 90% reduction). These results suggest that the effects of leptin on the intrinsic properties of PPN neurons are leptin receptor- and G-protein dependent. We also found that leptin enhanced NMDA receptor-mediated responses in single neurons and in the PPN population as a whole, an effect blocked by TA. These experiments further strengthen the association between leptin dysregulation and sleep disturbances. Beck et al. investigated the effects of leptin on the intrinsic properties of neurons from the pedunculopontine nucleus (PPN). Leptin reduced the amplitude of voltage-gated sodium (I(Na)) and hyperpolarization-activated cyclic nucleotide-gated HCN (I(H)) channels. These effects were antagonized by a leptin receptor (OB-R) antagonist and by the G-protein antagonist GDPβ.

Dopaminergic modulation of synaptic transmission in cortex and striatum

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.

Inflammation-induced shift in spinal GABA(A) signaling is associated with a tyrosine kinase-dependent increase in GABA(A) current density in nociceptive afferents

To account for benzodiazepine-induced spinal analgesia observed in association with an inflammation-induced shift in the influence of the GABA(A) receptor antagonist gabazine on nociceptive threshold, the present study was designed to determine whether persistent inflammation is associated with the upregulation of high-affinity GABA(A) receptors in primary afferents. The cell bodies of afferents innervating the glabrous skin of the rat hind paw were retrogradely labeled, acutely dissociated, and studied before and after the induction of persistent inflammation. A time-dependent increase in GABA(A) current density was observed that was more than twofold by 72 h after the initiation of inflammation. This increase in current density included both high- and low-affinity currents and was restricted to neurons in which GABA increased intracellular Ca(2+). No increases in GABA(A) receptor subunit mRNA or protein were detected in whole ganglia. In contrast, the increased current density was completely reversed by 20-min preincubation with the tyrosine kinase inhibitor genistein and partially reversed with the Src kinase inhibitor PP2. Genistein reversal was partially blocked by the dynamin inhibitor peptide P4. Changes in nociceptive threshold following spinal administration of genistein and muscimol to inflamed rats indicated that the pronociceptive actions of muscimol observed in the presence of inflammation were reversed by genistein. These results suggest that persistent changes in relative levels of tyrosine kinase activity following inflammation provide not only a sensitive way to dynamically regulate spinal nociceptive signaling but a viable target for the development of novel therapeutic interventions for the treatment of inflammatory pain.

Dopamine D(1) receptor-mediated enhancement of NMDA receptor trafficking requires rapid PKC-dependent synaptic insertion in the prefrontal neurons

Understanding the interaction between dopamine and glutamate, particularly the interaction of dopamine and NMDA receptors, may enable a more rational approach to the treatment of schizophrenia, drug addiction, and other psychiatric disorders. We show that, in prefrontal cortical neurons, dopamine D(1)-induced enhancement of NMDA receptor function depends on rapid insertion of new NMDA receptor 2B subunits on the synaptic surface. Protein kinase A (PKA) inhibitor, but not protein kinase C (PKC) inhibitor, completely blocked dopamine D(1) agonist SKF-81297-induced increase of the total expression of NMDA receptors. Furthermore, SKF-81297 failed to alter the surface expression and synaptic insertion of NMDA receptors in the presence of PKA inhibitor, phospholipase C inhibitor, PKC inhibitor, or Src family kinase inhibitor. Our data suggest that D(1)-mediated enhancement of NMDA current depends on the NMDA receptor trafficking through rapid synaptic insertion and both PKA and PKC signaling pathways play important roles in the regulatory process. Although both PKA and PKC mediate the D(1)-induced enhancement of NMDA receptors, the phospholipase C-PKC-Src pathway is only required for surface expression and new synaptic insertion of NMDA receptors.

Activation of glycogen synthase kinase-3 beta is required for hyperdopamine and D2 receptor-mediated inhibition of synaptic NMDA receptor function in the rat prefrontal cortex

The interactions between dopamine and glutamate systems play an essential role in normal brain functions and neuropsychiatric disorders. The mechanism of NMDA receptor regulation through high concentrations of dopamine, however, remains unclear. Here, we show the signaling pathways involved in hyperdopaminergic regulation of NMDA receptor functions in the prefrontal cortex by incubating cortical slices with high concentration of dopamine or administering dopamine reuptake inhibitor 1-(2-[bis-(4-fluorophenyl)methoxy]ethyl)- 4-(3-phenylpropyl)piperazine (GBR12909) in vivo. We found that, under both conditions, the synaptic NMDA receptor-mediated currents were significantly attenuated by excessive dopamine stimulation through activation of D(2) receptors. Furthermore, high dose of dopamine failed to affect NMDA receptor-mediated currents after blockade of NR2B subunits but triggered a dynamin-dependent endocytosis of NMDA receptors. The high-dose dopamine/D(2) receptor-mediated suppression of NMDA receptors was involved in the increase of glycogen synthase kinase-3beta (GSK-3beta) activity, which in turn phosphorylates beta-catenin and disrupts beta-catenin-NR2B interaction, but was dependent on neither Gq11 nor PLC (phospholipase C). Moreover, the hyperdopamine induced by GBR12909 significantly decreased the expression of both surface and intracellular NR2B proteins, as well as NR2B mRNA levels, suggesting an inhibition of protein synthesis. These effects were, however, completely reversed by administration of either GSK-3beta inhibitor or D(2) receptor antagonist. These results therefore suggest that GSK-3beta is required for the hyperdopamine/D(2) receptor-mediated inhibition of NMDA receptors in the prefrontal neurons and these actions may underlie D(2) receptor-mediated psychostimulant effects and hyperdopamine-dependent behaviors in the brain.