NMDA receptor mediates dopamine release in the striatum of unanesthetized rats as measured by brain microdialysis

Evaluation of the potential role of glutamatergic, cholinergic, and nitrergic systems in the dopamine release induced by the pesticide glyphosate in rat striatum

Glyphosate (GLY) is a pesticide that severely alters nigrostriatal dopaminergic neurotransmission, inducing great increases in dopamine release from rat dorsal striatum. This GLY-induced striatal dopamine overflow occurs through mechanisms not yet fully understood, hence the interest in evaluating the role of other neurotransmitter systems in such effects. So, the main objective of this mechanistic study was to evaluate the possible mediation of the glutamatergic, cholinergic, and nitrergic systems in the GLY-induced in vivo dopamine release from rat dorsal striatum. The extracellular dopamine levels were measured by cerebral microdialysis and HPLC with electrochemical detection. Intrastriatal administration of GLY (5 mmol/L) significantly increased the dopamine release (1102%). Pretreatment with MK-801 (50 or 400 μmol/L), a non-competitive antagonist of NMDA receptors, significantly decreased the effect of GLY (by 70% and 74%, respectively), whereas AP-5 (400 μmol/L), a competitive antagonist of NMDA receptors, or CNQX (500 μmol/L), an AMPA/kainate receptor antagonist, had no significant effect. Administration of the nitric oxide synthase inhibitors, L-nitroarginine (L-NAME, 100 μmol/L) or 7-nitroindazole (7-NI, 100 μmol/L), also did not alter the effect of GLY on dopamine release. Finally, pretreatment of the animals with mecamylamine, an antagonist of nicotinic receptors, decreased the effect of GLY on dopamine release by 49%, whereas atropine, a muscarinic antagonist, had no significant effect. These results indicate that GLY-induced dopamine release largely depends on the activation of NMDA and nicotinic receptors in rat dorsal striatum. Future research is needed to determine the effects of this pesticide at environmentally relevant concentrations.

Role of voltage-dependent calcium channels on the striatal in vivo dopamine release induced by the organophosphorus pesticide glyphosate

In the present study, we investigated the role of voltage-sensitive calcium channels (VSCCs) on the striatal dopamine release induced by the pesticide glyphosate (GLY) using selective VSCC inhibitors. The dopamine levels were measured by in vivo cerebral microdialysis coupled to HPLC-ED. Nicardipine (L-type VSCC antagonist) or ω-conotoxin MVIIC (non-selective P/Q-type antagonist) had no effect on dopamine release induced by 5 mM GLY. In contrast, flunarizine (T-type antagonist) or ω-conotoxin GVIA (neuronal N-type antagonist) significantly reduced GLY-stimulated dopamine release. These results suggest that GLY-induced dopamine release depends on extracellular calcium and its influx through the T- and N-type VSCCs. These findings were corroborated by molecular docking, which allowed us to establish a correlation between the effect of GLY on blocked VSCC with the observed dopamine release. We propose new molecular targets of GLY in the dorsal striatum, which could have important implications for the assessment of pesticide risks in non-target organisms.

Intranigral Administration of β-Sitosterol-β-D-Glucoside Elicits Neurotoxic A1 Astrocyte Reactivity and Chronic Neuroinflammation in the Rat Substantia Nigra

Chronic consumption of β-sitosterol-β-D-glucoside (BSSG), a neurotoxin contained in cycad seeds, leads to Parkinson's disease in humans and rodents. Here, we explored whether a single intranigral administration of BSSG triggers neuroinflammation and neurotoxic A1 reactive astrocytes besides dopaminergic neurodegeneration. We injected 6 μg BSSG/1 μL DMSO or vehicle into the left substantia nigra and immunostained with antibodies against tyrosine hydroxylase (TH) together with markers of microglia (OX42), astrocytes (GFAP, S100β, C3), and leukocytes (CD45). We also measured nitric oxide (NO), lipid peroxidation (LPX), and proinflammatory cytokines (TNF-α, IL-1β, IL-6). The Evans blue assay was used to explore the blood-brain barrier (BBB) permeability. We found that BSSG activates NO production on days 15 and 30 and LPX on day 120. Throughout the study, high levels of TNF-α were present in BSSG-treated animals, whereas IL-1β was induced until day 60 and IL-6 until day 30. Immunoreactivity of activated microglia (899.0 ± 80.20%) and reactive astrocytes (651.50 ± 11.28%) progressively increased until day 30 and then decreased to remain 251.2 ± 48.8% (microglia) and 91.02 ± 39.8 (astrocytes) higher over controls on day 120. C3(+) cells were also GFAP and S100β immunoreactive, showing they were neurotoxic A1 reactive astrocytes. BBB remained permeable until day 15 when immune cell infiltration was maximum. TH immunoreactivity progressively declined, reaching 83.6 ± 1.8% reduction on day 120. Our data show that BSSG acute administration causes chronic neuroinflammation mediated by activated microglia, neurotoxic A1 reactive astrocytes, and infiltrated immune cells. The severe neuroinflammation might trigger Parkinson's disease in BSSG intoxication.

Glycine Signaling in the Framework of Dopamine-Glutamate Interaction and Postsynaptic Density. Implications for Treatment-Resistant Schizophrenia

Treatment-resistant schizophrenia (TRS) or suboptimal response to antipsychotics affects almost 30% of schizophrenia (SCZ) patients, and it is a relevant clinical issue with significant impact on the functional outcome and on the global burden of disease. Among putative novel treatments, glycine-centered therapeutics (i.e. sarcosine, glycine itself, D-Serine, and bitopertin) have been proposed, based on a strong preclinical rationale with, however, mixed clinical results. Therefore, a better appraisal of glycine interaction with the other major players of SCZ pathophysiology and specifically in the framework of dopamine - glutamate interactions is warranted. New methodological approaches at cutting edge of technology and drug discovery have been applied to study the role of glycine in glutamate signaling, both at presynaptic and post-synaptic level and have been instrumental for unveiling the role of glycine in dopamine-glutamate interaction. Glycine is a non-essential amino acid that plays a critical role in both inhibitory and excitatory neurotransmission. In caudal areas of central nervous system (CNS), such as spinal cord and brainstem, glycine acts as a powerful inhibitory neurotransmitter through binding to its receptor, i.e. the Glycine Receptor (GlyR). However, glycine also works as a co-agonist of the N-Methyl-D-Aspartate receptor (NMDAR) in excitatory glutamatergic neurotransmission. Glycine concentration in the synaptic cleft is finely tuned by glycine transporters, i.e. GlyT1 and GlyT2, that regulate the neurotransmitter's reuptake, with the first considered a highly potential target for psychosis therapy. Reciprocal regulation of dopamine and glycine in forebrain, glycine modulation of glutamate, glycine signaling interaction with postsynaptic density proteins at glutamatergic synapse, and human genetics of glycinergic pathways in SCZ are tackled in order to highlight the exploitation of this neurotransmitters and related molecules in SCZ and TRS.

Neurturin overexpression in dopaminergic neurons induces presynaptic and postsynaptic structural changes in rats with chronic 6-hydroxydopamine lesion

The structural effect of neurturin (NRTN) on the nigrostriatal dopaminergic system in animals remains unknown, although NRTN has been shown to be effective in Parkinson's disease animal models. Herein, we aimed to demonstrate that NRTN overexpression in dopaminergic neurons stimulates both neurite outgrowths in the nigrostriatal pathway and striatal dendritic spines in aging rats with chronic 6-hydroxydopamine (6-OHDA) lesion. At week 12 after lesion, pTracer-mNRTN-His or pGreenLantern-1 plasmids were intranigrally transfected using the NTS-polyplex nanoparticles system. We showed that the transgenic expression in dopaminergic neurons remained until the end of the study (12 weeks). Only animals expressing NRTN-His showed recovery of tyrosine hydroxylase (TH)+ cells (28 ± 2%), their neurites (32 ± 2%) and the neuron-specific cytoskeletal marker β-III-tubulin in the substantia nigra; striatal TH(+) fibers were also recovered (52 ± 3%), when compared to the healthy condition. Neurotensin receptor type 1 levels were also significantly recovered in the substantia nigra and striatum. Dopamine recovery was 70 ± 4% in the striatum and complete in the substantia nigra. The number of dendritic spines of striatal medium spiny neurons was also significantly increased, but the recovery was not complete. Drug-activated circling behavior decreased by 73 ± 2% (methamphetamine) and 89 ± 1% (apomorphine). Similar decrease was observed in the spontaneous motor behavior. Our results demonstrate that NRTN causes presynaptic and postsynaptic restoration of the nigrostriatal dopaminergic system after a 6-OHDA-induced chronic lesion. However, those improvements did not reach the healthy condition, suggesting that NRTN exerts lesser neurotrophic effects than other neurotrophic approaches.

Neurotensin-polyplex-mediated brain-derived neurotrophic factor gene delivery into nigral dopamine neurons prevents nigrostriatal degeneration in a rat model of early Parkinson's disease

Background

The neurotrophin Brain-Derived Neurotrophic Factor (BDNF) influences nigral dopaminergic neurons via autocrine and paracrine mechanisms. The reduction of BDNF expression in Parkinson’s disease substantia nigra (SN) might contribute to the death of dopaminergic neurons because inhibiting BDNF expression in the SN causes parkinsonism in the rat. This study aimed to demonstrate that increasing BDNF expression in dopaminergic neurons of rats with one week of 6-hydroxydopamine lesion recovers from parkinsonism. The plasmids phDAT-BDNF-flag and phDAT-EGFP, coding for enhanced green fluorescent protein, were transfected using neurotensin (NTS)-polyplex, which enables delivery of genes into the dopaminergic neurons via neurotensin-receptor type 1 (NTSR1) internalization.

Results

Two weeks after transfections, RT-PCR and immunofluorescence techniques showed that the residual dopaminergic neurons retain NTSR1 expression and susceptibility to be transfected by the NTS-polyplex. phDAT-BDNF-flag transfection did not increase dopaminergic neurons, but caused 7-fold increase in dopamine fibers within the SN and 5-fold increase in innervation and dopamine levels in the striatum. These neurotrophic effects were accompanied by a significant improvement in motor behavior.

Conclusions

NTS-polyplex-mediated BDNF overexpression in dopaminergic neurons has proven to be effective to remit hemiparkinsonism in the rat. This BDNF gene therapy might be helpful in the early stage of Parkinson’s disease.

NTS-Polyplex: a potential nanocarrier for neurotrophic therapy of Parkinson's disease

Nanomedicine has focused on targeted neurotrophic gene delivery to the brain as a strategy to stop and reverse neurodegeneration in Parkinson's disease. Because of improved transfection ability, synthetic nanocarriers have become candidates for neurotrophic therapy. Neurotensin (NTS)-polyplex is a "Trojan horse" synthetic nanocarrier system that enters dopaminergic neurons through NTS receptor internalization to deliver a genetic cargo. The success of preclinical studies with different neurotrophic genes supports the possibility of using NTS-polyplex in nanomedicine. In this review, we describe the mechanism of NTS-polyplex transfection. We discuss the concept that an effective neurotrophic therapy requires a simultaneous effect on the axon terminals and soma of the remaining dopaminergic neurons. We also discuss the future of this strategy for the treatment of Parkinson's disease.

FROM THE CLINICAL EDITOR

This review paper focuses on nanomedicine-based treatment of Parkinson's disease, a neurodegenerative condition with existing symptomatic but no curative treatment. Neurotensin-polyplex is a synthetic nanocarrier system that enables delivery of genetic cargo to dopaminergic neurons via NTS receptor internalization.

Manganese inhalation as a Parkinson disease model

The present study examines the effects of divalent and trivalent Manganese (Mn²⁺/Mn³⁺) mixture inhalation on mice to obtain a novel animal model of Parkinson disease (PD) inducing bilateral and progressive dopaminergic cell death, correlate those alterations with motor disturbances, and determine whether L-DOPA treatment improves the behavior, to ensure that the alterations are of dopaminergic origin. CD-1 male mice inhaled a mixture of Manganese chloride and Manganese acetate, one hour twice a week for five months. Before Mn exposure, animals were trained to perform motor function tests and were evaluated each week after the exposure. By the end of Mn exposure, 10 mice were orally treated with 7.5 mg/kg L-DOPA. After 5 months of Mn mixture inhalation, striatal dopamine content decreased 71%, the SNc showed important reduction in the number of TH-immunopositive neurons, mice developed akinesia, postural instability, and action tremor; these motor alterations were reverted with L-DOPA treatment. Our data provide evidence that Mn²⁺/Mn³⁺ mixture inhalation produces similar morphological, neurochemical, and behavioral alterations to those observed in PD providing a useful experimental model for the study of this neurodegenerative disease.

NMDA-mediated release of glutamate and GABA in the subthalamic nucleus is mediated by dopamine: an in vivo microdialysis study in rats

The present study investigated the effects of N-methyl-D-aspartic acid.H2O (NMDA) on the dopamine, glutamate and GABA release in the subthalamic nucleus (STN) by using in vivo microdialysis in rats. NMDA (100 micromol/L) perfused through the microdialysis probe evoked an increase in extracellular dopamine in the STN of the intact rat of about 170%. This coincided with significant increases in both extracellular glutamate (350%) and GABA (250%). The effect of NMDA perfusion on neurotransmitter release at the level of the STN was completely abolished by co-perfusion of the selective NMDA-receptor antagonist MK-801 (10 micromol/L), whereas subthalamic perfusion of MK-801 alone had no effect on extracellular neurotransmitter concentrations. Furthermore, NMDA induced increases in glutamate were abolished by both SCH23390 (8 micromol/L), a selective D1 antagonist, and remoxipride (4 micromol/L), a selective D2 antagonist. The NMDA induced increase in GABA was abolished by remoxipride but not by SCH23390. Perfusion of the STN with SCH23390 or remoxipride alone had no effect on extracellular neurotransmitter concentrations. The observed effects in intact animals depend on the nigral dopaminergic innervation, as dopamine denervation, by means of 6-hydroxydopamine lesioning of the substantia nigra, clearly abolished the effects of NMDA on neurotransmitter release at the level of the STN. Our work points to a complex interaction between dopamine, glutamate and GABA with a crucial role for dopamine at the level of the STN.

Functional and anatomical connection between the paraventricular nucleus of the thalamus and dopamine fibers of the nucleus accumbens

The shell of the nucleus accumbens (NacSh) receives a dense innervation from dopamine (DA) neurons in the ventral tegmental area (VTA) and from glutamate neurons in the paraventricular nucleus of the thalamus (PVT). The present study examined in urethane-anesthetized rats the effects of electrical stimulation of the PVT on DA levels in the NacSh as measured with amperometry and chronoamperometry. Stimulation of the PVT (40 Hz, 1.0 ms, 400 microA, 5 seconds) resulted in a brief increase in electrochemical currents detected in the NacSh. Inhibition of DA neurons in the VTA using lidocaine (4%, 500 nL) or intravenous apomorphine (0.15 mg/kg) decreased the resting voltammetric signal but had no effect on PVT-evoked responses. Blocking of ionotropic glutamate receptors in the NacSh with local administration of kynurenic acid attenuated the PVT-evoked responses. Anterograde tracing with biotinylated dextran amine demonstrated that PVT targets regions of very dense tyrosine hydroxylase fiber staining in the NacSh. Consistent with the projection pattern of the PVT to the NacSh, stimulation of the PVT evoked the largest oxidation current changes in the NacSh, whereas small or no changes were elicited in other areas of the striatum. This study suggests that glutamate release from PVT terminals can act on ionotropic glutamate receptors in the NacSh to induce DA efflux. Modulation of DA levels in the NacSh by the PVT may be linked to arousal-induced increases in DA tone and could be involved in the facilitation of specific behavioral patterns associated with arousal or stressful situations.

Substantia nigra compacta neurons that innervate the reticular thalamic nucleus in the rat also project to striatum or globus pallidus: Implications for abnormal motor behavior

The projections of the substantia nigra pars compacta (SNc) to the reticular thalamic nucleus (RTn) were assessed by measuring dopamine content and counting tyrosine hydroxylase positive (TH (+)) cells in rats with unilateral lesions induced by 6-hydroxydopamine (6-OHDA), and by using a fluorescent tract-tracing technique in rats without lesions. Injection of 6-OHDA in the RTn reduced dopamine content and the number of TH (+) cells in the SNc by about 50%. Branching of SNc was suggested by the finding that 6-OHDA deposited in the RTn significantly reduced dopamine in the striatum and globus pallidus. Moreover, injections of 6-OHDA into either the striatum or the globus pallidus significantly reduced dopamine content in the RTn. Fluorescent tracers injected into the RTn labeled TH (+) cells in the SNc. A high proportion of these TH (+) cells was double labeled when tracers were also injected into either the globus pallidus or striatum. Other experiments showed that systemic injection of apomorphine or methamphetamine induced turning behavior in rats with local deposits of 6-OHDA in either the RTn or the studied basal ganglia nuclei. The extensive dopaminergic branching suggests that the abnormal motor behavior of rats with 6-OHDA deposits in the RTn may be caused by dopaminergic denervation of more than one structure. The fact that lesion of a single dopaminergic neuron can reduce dopamine transmission in more than one structure is probably important in generating the manifestations of Parkinson's disease.

Neurotensin polyplex as an efficient carrier for delivering the human GDNF gene into nigral dopamine neurons of hemiparkinsonian rats

Recently we showed that the neurotensin polyplex is a nanoparticle carrier system that targets reporter genes in nigral dopamine neurons in vivo. Herein, we report its first practical application in experimental parkinsonism, which consisted of transfecting dopamine neurons with the gene coding for human glial cell line-derived neurotrophic factor (hGDNF). Hemiparkinsonism was induced in rats by a single dose of 6-hydroxydopamine (30 microg) into the ventrolateral part of the striatum. We showed that transfection of the hGDNF gene into the substantia nigra of rats 1 week after the neurotoxin injection produced biochemical, anatomical, and functional recovery from hemiparkinsonism. RT-PCR analysis showed mRNA expression of exogenous hGDNF in the transfected substantia nigra. Western blot analysis verified transgene expression by recognizing the flag epitope added at the C-terminus of the hGDNF polypeptide, which was found mainly in dopamine neurons by double immunofluorescence techniques. These data indicate that the neurotensin polyplex holds great promise for the neuroprotective therapy of Parkinson disease.

Dopamine-glutamate reciprocal modulation of release and motor responses in the rat caudate-putamen and nucleus accumbens of "intact" animals

Functional interactions between dopaminergic neurotransmission and glutamatergic neurotransmission are well known to play a crucial integrative role in the striatum, the major input structure of the basal ganglia now widely recognized to contribute to the control of motor activity and movements but also to the processing of cognitive and limbic functions. However, the nature of these interactions is still a matter of debate and controversy. This review (1) summarizes anatomical data on the distribution of dopaminergic and glutamatergic receptors in the striatum-accumbens complex, (2) focuses on the dopamine-glutamate interactions in the modulation of each other's release in the striatum-accumbens complex, and (3) examines the dopamine-glutamate interactions in the entire striatum involved in the control of locomotor activity. The effects of dopaminergic and glutamatergic receptor selective agonists and antagonists on dopamine and glutamate release as well on motor responses are analyzed in the entire striatum, by reviewing both in vitro and in vivo data. Regarding in vivo data, only findings from focal injections studies in the nucleus accumbens or the caudate-putamen of "intact" animals are reviewed. Altogether, the available data demonstrate that dopamine and glutamate do not uniformly interact to modulate each others' release and postsynaptic modulation of striatal output neurons. Depending on the receptor subtypes involved, interactions between dopaminergic and glutamatergic transmission vary as a multiple and complex combination of tonic, phasic, facilitatory, and inhibitory properties.

Inhibition of NMDA-induced striatal dopamine release and behavioral activation by the neuroactive steroid 3alpha-hydroxy-5beta-pregnan-20-one hemisuccinate

Our laboratory has previously shown that the synthetic neuroactive steroid 3alpha-hydroxy-5beta-pregnan-20-one hemisuccinate (3alpha5betaHS) is a negative modulator of NMDA receptors in vitro. Similarly, 3alpha5betaHS exhibits rapid sedative, analgesic, anticonvulsive, and neuroprotective effects in vivo. Here we report a study designed to investigate whether a negatively charged neuroactive steroid, 3alpha5betaHS, modulates the action of NMDA receptors in vivo. Our results indicate that peripherally administered 3alpha5betaHS enters the CNS and inhibits NMDA-mediated motor activity and dopamine release in the rat striatum. The increase in motor activity induced by intrastriatal microinjection of NMDA was blocked by the systemic administration of 3alpha5betaHS and the NMDA-induced increase in extracellular dopamine in the striatum was also attenuated by both systemically administered and intrastriatally administered (by in vivo microdialysis) 3alpha5betaHS. These data indicate that 3alpha5betaHS acts through striatal NMDA receptors in vivo. When taken together, these results suggest that neuroactive steroids may prove to be effective in the treatment of neurological and psychiatric disorders involving over-stimulation of NMDA receptors in the mesotelencephalic dopamine system.

Functional significance of nitric oxide in ionomycin-evoked [3H]GABA release from mouse cerebral cortical neurons

We investigated a role of nitric oxide (NO) on ionomycin-evoked [3H]GABA release using mouse cerebral cortical neurons. lonomycin dose-dependently released [3H]GABA up to 1 microM. The extent of the release by 0.1 microM ionomycin was in a range similar to that by 30 mM KCl. The ionomycin (0.1 microM)-evoked [3H]GABA release was dose-dependently inhibited by NO synthase inhibitors and hemoglobin, indicating that the ionomycin-evoked [3H]GABA release is mediated through NO formation. The inhibition of cGMP formation by 1H-[1,2,4] oxodizao [4,3-a] quinoxalin-1-one (ODQ), a selective inhibitor for NO-sensitive guanylate cyclase, showed no affects on the ionomycin-evoked [3H]GABA release. Tetrodotoxin and dibucaine significantly suppressed the ionomycin-evoked [3H]GABA release and ionomycin increased fluorescence intensity of bis-oxonol, suggesting the involvement of membrane depolarization in this release. The ionomycin-evoked [3H]GABA release was maximally reduced by about 50% by GABA uptake inhibitors. The concomitant presence of nifedipine and omega-agatoxin VIA (omega-ATX), inhibitors for L- and P/Q-type voltage-dependent calcium channels, respectively, caused the reduction in the ionomycin-evoked release by about 50%. The simultaneous addition of nifedipine, omega-ATX and nipecotic acid completely abolished the release. Although ionomycin released glutamate, (+)-5-methyl-1-,11-dihydro-5H-dibenzo-[a,d]cycloheptan-5,10-imine (MK-801) and 6,7-dinitroquinoxaline-2,3-dione (DNQX) showed no effects on the ionomycin-induced [3H]GABA release. Based on these results, it is concluded that NO formed by ionomycin plays a critical role in ionomycin-evoked [3H]GABA release from the neurons.

Calcitonin gene-related peptide-mediated increase in K(+)-induced [(3)H]-dopamine release from rat caudal striatal slices

The calcitonin-gene receptor peptide (alphaCGRP) receptor is present in high levels in the caudal striatum of the rat. Previous behavioural experiments have highlighted a possible correlation between alphaCGRP-mediated effects and the dopaminergic system. In this study, we examined the effect of alphaCGRP on K(+)-evoked [(3)H]-dopamine release in a slice preparation of the rat caudal striatum. The unstimulated release of [(3)H]-dopamine was not affected by alphaCGRP. However, alphaCGRP increased the release of [(3)H]-dopamine evoked by K(+) (30 mM) in a concentration-dependent manner. The stimulatory effect of alphaCGRP was blocked by the CGRP1 antagonist hCGRP(8-37) (without effect on its own). The stimulatory effect of 1 microM alphaCGRP was blocked by dizocilpine (MK-801), suggesting that excitatory transmission is involved in mediating the facilitated release. This study suggests that the peptide alphaCGRP, modulates dopamine release in the rat caudal striatum probably indirectly via glutamatergic transmission.

Involvement of intrinsic cholinergic and GABAergic innervation in the effect of NMDA on striatal dopamine efflux and metabolism as assessed by microdialysis studies in freely moving rats

Microdialysis perfusion was used to study the participation of striatal cholinergic and gamma-aminobutyric acid-ergic (GABAergic) neurotransmission in basal and N-methyl-D-aspartate (NMDA) receptor-modulated dopamine release and metabolism in the striatum of the freely moving rat. Reverse dialysis of atropine (1-50 microM) induced a concentration-related increase in dopamine efflux and decrease in 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) efflux. (+)-Bicuculline (10-100 microM) similarly increased dopamine efflux, but was without consistent effect on metabolite efflux. Reverse dialysis of NMDA (1 mM) evoked an approximately twofold increase in dopamine efflux and decreased DOPAC and HVA efflux to 30-40% of basal levels. The effect of NMDA on dopamine efflux was completely abolished by coadministration of tetrodotoxin (TTX; 1 microM) or atropine (10 microM), and markedly potentiated (approximately fourfold) by coadministration of (+)-bicuculline (50 microM). The NMDA-induced decrease in dopamine metabolite efflux was inhibited by coadministration of TTX or (+)-bicuculline, but was unaffected by atropine. Our data suggest that dopamine release in the striatum is subject to both cholinergic and GABAergic tonic inhibitory mechanisms mediated through muscarinic and GABAA receptors, respectively. Furthermore, NMDA-stimulated dopamine release also involves obligatory cholinergic facilitation and an inhibitory GABAergic component mediated through these respective receptors.

Opposite effects of calcium and magnesium on the central blood pressure regulation in the spontaneously hypertensive rats

The effects of intracerebroventricular administration of calcium or magnesium on the blood pressure regulation in the brain were investigated. The systolic blood pressure in spontaneously hypertensive rats (male, 13-week-old) was decreased by calcium chloride (100 microg/rat) and increased by magnesium chloride (20, 100 or 500 microg/rat). The depressor response induced by calcium was inhibited by magnesium chloride in a dose-dependent manner. Combining these results with those previously reported, it is suggested that magnesium inhibits the ability of calcium to reduce blood pressure through calmodulin- and dopamine-dependent functions in the brain.

Glutamate regulates the spontaneous and evoked release of dopamine in the rat striatum

Resting and evoked extracellular dopamine levels in the striatum of the anesthetized rat were measured by fast-scan cyclic voltammetry in conjunction with carbon fiber microelectrodes. Identification of the substance detected in vivo was achieved by inspection of background-subtracted voltammograms. Intrastriatal microinfusion of kynurenate, a broad-spectrum antagonist of ionotropic glutamate receptors, caused a decrease in the resting extracellular level of dopamine. The kynurenate-induced decrease was unaffected by systemic pretreatment with pargyline, an inhibitor of monoamine oxidase, but was significantly attenuated by systemic pretreatment with alpha-methyl-p-tyrosine, an inhibitor of tyrosine hydroxylase. Although glutamate by itself did not affect resting extracellular dopamine levels, glutamate did attenuate the kynurenate-induced decrease. Kynurenate decreased dopamine release in response to electrical stimulation of the medial forebrain bundle, an effect that was also attenuated by glutamate. These results suggest that both spontaneous and evoked dopamine release in the rat striatum are under the local tonic excitatory influence of glutamate. Interactions between central dopamine and glutamate systems that have been implicated in the etiologies of Parkinson's disease, schizophrenia, stress, and substance abuse. The precise nature of those interactions, however, remains a matter of some controversy.

Effect of magnesium on calcium-dependent brain function that prolongs ethanol-induced sleeping time in mice

The effect of intracerebroventricular (i.c.v.) administration of magnesium on calcium- and dopamine-dependent brain function was investigated behaviorally and biochemically. The duration of ethanol-induced sleeping time in mice was prolonged following i.c.v. administration of calcium chloride (10 micromol/kg) or dopamine (30nmol/mouse); however, it was not affected by magnesium chloride (10 or 40 micromol/kg). The ability of calcium to prolong ethanol-induced sleeping time was inhibited by the administration of magnesium chloride. The brain dopamine level in mice was significantly increased following i.c.v. administration of calcium chloride. Taking into consideration these results and those from previous studies, it is suggested that calcium enhances dopamine synthesis in the brain through a calmodulin-dependent system, and the increase in dopamine level prolongs ethanol-induced sleeping time. However, magnesium inhibits dopamine release. Therefore, magnesium may inhibit calcium-dependent brain function through dopaminergic neurons, and consequently reduce the effect of calcium on ethanol activity.

Inhibitory glutamatergic regulation of evoked dopamine release in striatum

Certain aspects of schizophrenia and Parkinson's disease suggest that glutamate might have an inhibitory effect on dopamine release. Several studies have reported that the excitatory actions of ionotropic glutamate agonists on extracellular dopamine levels in striatum are resistant to tetrodotoxin, which suggests that glutamate excites an impulse-independent mechanism of dopamine release. We tested the hypothesis that an inhibitory action of glutamate on dopamine terminals in the striatum specifically involves an impulse-dependent mechanism of dopamine release. We used voltammetry to monitor electrically-evoked dopamine release in striatal slices, which is completely tetrodotoxin- and Ca(2+)-sensitive and so provides a model of impulse-dependent dopamine release. Agonists of the ionotropic glutamate receptors significantly decreased the amplitude of the response, while antagonists significantly increased the amplitude of the response, by as much as approximately 60% in the case of kynurenic acid. These results support the hypothesis that ionotropic glutamate receptors can inhibit impulse-dependent dopamine release by a mechanism that acts locally within the striatum. This finding contrasts with previous reports that glutamate can excite impulse-independent dopamine release. This extends earlier findings that glutamate may both excite and inhibit subcortical dopamine systems by suggesting that the excitatory and inhibitory actions of striatal ionotropic glutamate receptors are specifically associated with impulse-independent and impulse-dependent dopamine release, respectively.

The rewarding properties of NMDA and MK-801 (dizocilpine) as indexed by the conditioned place preference paradigm

N-Methyl-D-aspartate (NMDA) ([R]-2-[Methylamino]succinic acid) is a specific excitatory amino acid. Two experiments were conducted to determine the rewarding properties of this compound using the conditioned place preference paradigm. In the first experiment, 40 male Sprague-Dawley rats received place preference conditioning for a 4 day period. The conditioned place preference apparatus consisted of two chambers with distinct visual and tactile cues, separated by a removable door. On days 2 and 4, rats were systemically administered NMDA (1.0, 15.0, and 30.0 mg/kg) paired with one chamber. On days 3 and 5, rats were systemically administered saline paired with the other chamber. Day 6 was the test day, and the rat was allowed free run of the entire apparatus in a drug-free state. Time spent in each side of the apparatus was computer recorded. NMDA produced a significant increase in the amount of time spent on the side previously paired with drug for 15.0 and 30.0, but not 1.0 mg/kg NMDA. In the second experiment, systemic administration of NMDA (30.0 mg/kg) paired with the noncompetitive NMDA receptor antagonist, MK-801 (0.5 mg/kg), resulted in neither place preference nor place aversion.

Lactic acid-induced increase of extracellular dopamine measured by microdialysis in rat striatum: evidence for glutamatergic and oxidative mechanisms

Striatal lactacidosis was induced by direct lactic acid perfusion to obtain a local pH as close as possible to that observed in ischemia. In a previous study we showed that such lactacidosis produces a diphasic increase in extracellular dopamine (DA). The present work investigated whether DA accumulation is related to a glutamatergic mechanism and/or production of reactive oxygen species (ROS) in the striatum. Concentrations of extracellular DA, glutamate and hydroxyl radicals ((.)OH) were measured in the presence or absence of an N-methyl-D-aspartate (NMDA) receptor blocker (dizocilpine, MK-801) or an antioxidant (Trolox). Measurements were performed using high-performance liquid chromatography (HPLC) with electrochemical and fluorimetric detection on samples obtained by an in vivo microdialysis perfusion technique and stored at -80 degrees C. The increase in lactic acid-induced DA was entirely suppressed by MK-801 and Trolox. Lactacidosis also induced an increase in extracellular glutamate and (.)OH concentrations at the same time as the first DA accumulation, as well as another (.)OH accumulation which preceded and accompanied the second DA concentration peak. Glutamate release was totally inhibited by MK-801 or Trolox. The first peak of (.)OH production was completely suppressed by MK-801 and Trolox, but the second one was only suppressed by Trolox. These data showed that the increase in DA induced by lactic acid was related to glutamatergic excitotoxicity and ROS production, suggested that the kinetic of events was different for the two DA accumulations.

Differential regulation of glutamate, aspartate and gamma-amino-butyrate release by N-methyl-D-aspartate receptors in rat striatum after partial and extensive lesions to the nigro-striatal dopamine pathway

The in vivo microdialysis methodology was used to assess the effect of N-methyl-D-aspartate (NMDA) receptor ligands on glutamate (GLU), aspartate (ASP) and gamma-aminobutyrate (GABA) extracellular levels in the striatum of anaesthetized rats, after damage to the dopamine (DA) nigrostriatal pathway by injections of different doses of 6-hydroxydopamine (6-OH-DA) seven days earlier. The 6-OH-DA treated rats were divided into two groups, corresponding to animals with 20-80% (partial) and 85-99% (extensive) striatal DA tissue depletion, respectively. In rats with partial DA depletion, the striatal extracellular ASP levels significantly increased after intrastriatal dialysis perfusion with MK-801 (100 microM), an antagonist of NMDA receptors. In addition, a change in the pattern of local NMDA (500 microM)- induced efflux of ASP was observed in the striatum of these rats. However, in these partially DA-depleted striata no changes were found in basal extracellular levels of GLU, ASP and GABA or in NMDA- and MK-801-mediated effluxes of GLU and GABA relative to striata from sham rats. In contrast, rats with extensive striatal DA depletion exhibited a significant increase in ASP and GABA extracellular striatal levels, after intrastriatal dialysis perfusion with NMDA. In addition, the MK-801-mediated stimulation of extracellular ASP levels was accentuated along with the appearance of a MK-801 mediated increase in extracellular striatal GLU. Finally, basal extracellular levels of ASP, but not of GLU and GABA, were found to increase in extensive DA-depleted striata when compared to sham and partially DA-depleted striata. Thus, a differential regulation of basal and NMDA receptor-mediated release of transmitter amino acids occur seven days after partial and extensive DA-depleted striatum by 6-OH-DA-induced lesions of the nigrostriatal DA pathway. These findings may have implications as regards the participation of NMDA receptors in the compensatory mechanisms associated with the progress of Parkinson's disease, as well as in the treatment of this neurological disorder.

Group I mGlu receptor modulation of dopamine release in the rat striatum in vivo

The present study investigated the ability of mGlu (metabotropic glutamate) receptor to modulate dopamine release in the striatum of freely moving rats assessed using the microdialysis technique. The group I and II mGlu receptor agonist (1S,3R)-ACPD (1-amino-cyclopentane-1,3-dicarboxylate; 1-3 mM) increased dopamine release (367% of basal levels) which was prevented by the non-selective mGlu receptor antagonist, (+)-MCPG (alpha-methyl-4-carboxyphenylglycine; 10 mM). The group I mGlu receptor agonist, DHPG (3,5-dihydroxyphenylglycine; 0.3-1 mM), also increased dopamine release (maximum increase 229%) which was also antagonised by (+)-MCPG (10 mM). In contrast, the group II mGlu receptor agonist, DCG-IV (2-(2,3-dicarboxycyclopropyl)glycine; 3-50 microM), induced a more modest increase in dopamine release (156% of basal levels). Combined administration of DHPG (1 mM) and DCG-IV (50 microM) maximally increased dopamine release by 252% of basal levels which was antagonised completely by (+)-MCPG (10 mM). Such findings indicate that group I (and possibly group II) mGlu receptors facilitate rat striatal dopamine release in vivo.

Reciprocal dopamine-glutamate modulation of release in the basal ganglia

Dopaminergic and glutamatergic transmissions have long been known to interact at multiple levels in the basal ganglia to modulate motor and cognitive functions. One important aspect of their interactions is represented by the reciprocal modulation of release. This topic has been the object of interest since the late 70's, particularly in the striatum and in midbrain dopaminergic areas (substantia nigra and ventral tegmental area). Analysis of glutamate-dopamine interactions in the control of each other's release is complicated by the fact that both glutamate and dopamine act on multiple receptor subtypes which can exert different effects. Therefore, glutamatergic modulation of dopamine release has been reviewed by analyzing the effects of glutamatergic selective receptor agonists and antagonists in the striatum (both motor and limbic portions) and in midbrain dopaminergic areas, as revealed by in vitro (slices, cell cultures, synaptosomes) and in vivo (push-pull, microdialysis and voltammetry techniques) experimental approaches. The same approach has been followed for dopaminergic modulation of glutamate release. The facilitatory nature of glutamate modulating both presynaptic and dendritic dopamine release has clearly emerged from in vitro studies. However, evidence is presented that, at least in the striatum and in the nucleus accumbens of awake rats, glutamate-mediated inhibitory effects may also occur. In vitro and in vivo experiments in the striatum and midbrain dopaminergic areas mainly depict dopamine as an inhibitory modulator of glutamate release. However, in vivo studies reporting dopamine D1 receptor mediated facilitatory effects are also considered. Therefore, the general notion that glutamate and dopamine act oppositely to regulate each other's release, is only partly supported by the available data. Conversely, the nature of the interaction between the two neurotransmitters seems to vary depending on the experimental approach, the brain area considered and the subtype of receptor involved.

Extracellular dopamine and catabolites in rat striatum during lactic acid perfusion as determined by in vivo microdialysis

Many experimental studies concerning hypoxia or ischemia have reported a decrease in intra/extracellular pH and massive dopamine (DA) release in the striatum. The present work investigated whether the increase in striatal extracellular DA is related to acidification or to lactate production. Striatal perfusion of lactic acid (pH 5.5) by microdialysis in conscious freely-moving rats induced an increase in extracellular concentrations of DA and catabolites, homovanillic acid (HVA) and 3,4-dihydroxyphenylacetic acid (DOPAC), as a probable result of acidification. Perfusion with sodium lactate (pH 7.4) failed to modify DA and catabolite release, whereas orthophosphoric acid produced the same effect as lactic acid. As lactic acidosis is known to induce a displacement of iron from its uptake sites, the possible role of this metal in response to acidosis was studied by perfusing ferrozine, an iron complexing agent, at the same time as lactic acid. The results showed that ferrous ions are involved in the process and suggested that oxygen free radicals play a role in the extracellular release of DA. Thus, lactic acid perfusion in rat striatum would appear to be a useful model for in vivo studies of the mechanisms responsible for increases in extracellular DA during hypoxia and ischemia.

Effect of N-methyl-D-aspartate and potassium on striatal monoamine metabolism in immature rat: an in vivo microdialysis study

Effects of N-methyl-D-aspartate (NMDA) and potassium on 5-day-old rat's brain were examined. We measured extracellular striatal monoamines such as dopamine (DA), 3,4 dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), and 5-hydroxyindole-3-acetic acid (5-HIAA) using intracerebral microdialysis. After 3 h stabilization, pups received varying concentrations of NMDA (1-3 mM) and potassium (200-800 mM) by intrastriatal perfusion for 32 minutes. Increasing the concentration of NMDA and potassium induced a dose related DA increase (p < 0.001), whereas DOPAC, HVA, and 5-HIAA decreased significantly. Five days later the same animals were sacrificed and the weight reduction of their cerebral hemispheres was measured. The weight of the drug perfused side was significantly reduced compared with that of the contralateral one. We examined next the relationship between the level of maximum DA and the relative hemisphere weight reduction. The DA peak was highly correlated with the hemisphere weight reduction (r = 0.70, n = 52, p < 0.001 in the NMDA group, r = 0.83, n = 30, p < 0.001 in the potassium group, respectively). These data show that each treatment alter striatal monoamine metabolism in immature rat brain and that the extracellular DA peak is a potential early indicator to estimate brain injury.

Failure to down regulate NMDA receptors in the striatum and nucleus accumbens associated with neuroleptic-induced dyskinesia

The syndrome of vacuous chewing movements (VCMs) in rats is similar in many respects to tardive dyskinesia (TD) in humans. Both syndromes are characterized by delayed onset of persistent orofacial dyskinesias in a sub-group of subjects chronically treated with neuroleptics. Using the rat model, we examined the role of NMDA receptor-mediated corticostriatal neurotransmission in the expression of VCMs. Rats were treated for 36 weeks with haloperidol decanoate or vehicle and then withdrawn for an additional 28 weeks. Chronic persistent VCMs were induced in one subgroup of treated animals (+VCM), but not in another group (-VCM). Rats from +VCM, -VCM groups and vehicle-treated controls were selected for post mortem studies (n = 12 to 14 per group). NMDA receptor levels were assessed using [3H]-MK-801 binding in sections from the mid-striatum and nucleus accumbens. Chronic haloperidol treatment produced a marked reduction of NMDA receptor binding levels throughout the striatum and nucleus accumbens. Post hoc comparisons demonstrated that -VCM rats had lower NMDA receptor binding levels than +VCM and vehicle-treated controls. Ventromedial striatum and nucleus accumbens core were the most affected areas. These findings suggest that down-regulation of striatal NMDA receptor binding levels may protect against the expression of neuroleptic-induced dyskinesia.

Regulation of striatal dopamine release by metabotropic glutamate receptors

In vivo microdialysis in conscious rats was used to assess the effect of metabotropic glutamate receptor stimulation on striatal dopamine release. Local application of the metabotropic glutamate agonist (+/-)-trans-1-aminocyclopentane-1,3-dicarboxylic acid (ACPD), via a microdialysis probe, produced a concentration-dependent response: infusion of 50 microM ACPD did not produce a significant effect on extracellular dopamine levels, while application of 100 microM or 500 microM ACPD increased dopamine release by approximately 50% or 100%, respectively. To examine the contribution of impulse flow and multisynaptic mechanisms to the ACPD-induced increase in dopamine release, 500 microM ACPD were coapplied with 2 microM tetrodotoxin (TTX). An increase in extracellular dopamine levels was observed after the application of 500 microM ACPD, despite the presence of TTX. To further study the actions of metabotropic glutamate receptor-stimulation on terminal release characteristics of dopamine, the effect of ACPD on 40 mM K+-stimulated dopamine release was investigated. It was found that application ofACPD reduces dopamine release in response to K+ stimulation. These data suggest that during basal conditions, metabotropic glutamate receptor activation facilitates striatal dopamine release, possibly through presynaptic, impulse-independent mechanisms. However, during conditions of hyperstimulation, activation of metabotropic receptors, in contrast to ionotropic receptors, reduces excess dopamine release.

Systemic morphine-induced Fos protein in the rat striatum and nucleus accumbens is regulated by mu opioid receptors in the substantia nigra and ventral tegmental area

To characterize how systemic morphine induces Fos protein in dorsomedial striatum and nucleus accumbens (NAc), we examined the role of receptors in striatum, substantia nigra (SN), and ventral tegmental area (VTA). Morphine injected into medial SN or into VTA of awake rats induced Fos in neurons in ipsilateral dorsomedial striatum and NAc. Morphine injected into lateral SN induced Fos in dorsolateral striatum and globus pallidus. The morphine infusions produced contralateral turning that was most prominent after lateral SN injections. Intranigral injections of [D-Ala2, N-Me-Phe4, Gly-ol5]-enkephalin (DAMGO), a mu opioid receptor agonist, and of bicuculline, a GABAA receptor antagonist, induced Fos in ipsilateral striatum. Fos induction in dorsomedial striatum produced by systemic administration of morphine was blocked by (1) SN and VTA injections of the mu1 opioid antagonist naloxonazine and (2) striatal injections of either MK 801, an NMDA glutamate receptor antagonist, or SCH 23390, a D1 dopamine receptor antagonist. Fos induction in dorsomedial striatum and NAc after systemic administration of morphine seems to be mediated by dopamine neurons in medial SN and VTA that project to medial striatum and NAc, respectively. Systemic morphine is proposed to act on mu opioid receptors located on GABAergic interneurons in medial SN and VTA. Inhibition of these GABA interneurons disinhibits medial SN and VTA dopamine neurons, producing dopamine release in medial striatum and NAc. This activates D1 dopamine receptors and coupled with the coactivation of NMDA receptors possibly from cortical glutamate input induces Fos in striatal and NAc neurons. The modulation of target gene expression by Fos could influence addictive behavioral responses to opiates.

Reciprocal interaction between glutamate and dopamine in the pars reticulata of the rat substantia nigra: a microdialysis study

We studied the interactions between glutamate and dopamine in the pars reticulata of the substantia nigra by using microdialysis in unanaesthetized rats. Increased extracellular levels of glutamate in the pars reticulata were obtained by microinjecting the muscarinic agonist carbachol into the ipsilateral subthalamic nucleus. The increase of glutamate levels was followed by increments in extracellular levels of dopamine and GABA. Increased levels of the three neurotransmitters were also observed during the administration of N-methyl-D-aspartate through the microdialysis probe. The increase in glutamate and GABA caused by N-methyl-D-aspartate was blocked by SCH 23390, a selective D1 antagonist. However, the D1 antagonist did not prevent the increase in dopamine levels. The selective D1 agonist SKF 38393, added to the microdialysis probe, increased the levels of the three neurotransmitters. However, after the lesion of the subthalamic nucleus with kainic acid, SKF 38393 increased only the level of GABA but not those of glutamate and dopamine. In addition, the lesion of the subthalamic nucleus produced a drastic (80%) fall in the extracellular levels of glutamate. These data suggest that glutamate, through N-methyl-d-aspartate receptors, stimulates the release of dopamine from dopaminergic dendrites present in the substantia nigra pars reticulata, and that dopamine in turn stimulates the release of glutamate and GABA. Both effects are mediated by D1 dopamine receptors present on subthalamonigral and striatonigral axon terminals, respectively.

Behavioural pharmacology of glutamate receptors in the basal ganglia

Glutamate receptors play a major role in the transmitter balance within the basal ganglia (BG). N-methyl-D-aspartate (NMDA) receptor stimulation within the striatum acts behaviourally depressant while intrastriatal as well as systemic administration of NMDA receptor-antagonists have rather stimulatory effects despite the different profiles of non-competitive-, competitive NMDA receptor- and glycine site-antagonists. In animal models of Parkinson's disease all these NMDA receptor antagonists counteract parkinsonian symptoms or act synergistically with L-3,4-dihydroxyphenylalanine (L-DOPA). The strong locomotion-inducing effect of the non-competitive NMDA receptor antagonists is partly, but not fully, mediated by a dopamine (DA) release in the nucleus accumbens. Manipulations at alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) receptors produce poor behavioural effects. These, however, are different or even opposed to NMDA receptor mediated effects. Local infusions of AMPA receptor-antagonists into the BG output nuclei have an anti-parkinsonian effect but systemic injections are ineffective. These drugs even counteract the anti-parkinsonian effect of DA agonists and of non-competitive NMDA receptor antagonists as well as the DA releasing effects of the latter drugs. Only few data on the role of metabotropic receptors exist but the different receptor subtypes with different regional distribution represent a promising target for pharmacological interventions.

Glutamatergic control over brain dopamine release in vivo and in vitro

Substantial evidence supports an important role for the excitatory neurotransmitter L-glutamate as a modulator of dopamine release in the central nervous system. All of the established glutamate receptor subtypes identified to date have been implicated in the regulation of dopamine release. It appears that glutamate can exert both facilitatory and inhibitory control over dopamine release and that this may be both phasic and tonic in nature. This regulatory role suggests that drugs acting at glutamate receptors may be potentially useful therapeutic agents in neurological disorders such as parkinsonism and schizophrenia.

Magnesium attenuates a striatal dopamine increase induced by anoxia in the neonatal rat brain: an in vivo microdialysis study

We evaluated the effects of magnesium on extracellular dopamine (DA) and its metabolites in the striatum of 5-d-old rats submitted to 16 min of anoxia using microdialysis and HPLC. Rat pups were divided into three groups and received either 1) intrastriatal perfusion (IS) of MgSO4, 2) intraperitoneal injection (IP) of MgSO4, and 3) NaCl and Ringer's solution, respectively in place of MgSO4. After stabilization, Mg2+, saline, and Ringer's solution were administered; then, 114 animals were exposed to 100% nitrogen for 16 min. Anoxia induced a DA surge, an acutely marked increase of DA, in both the control and the IP group. In contrast, the DA surge was significantly suppressed in the IS group (p < 0.01, analysis of variance). During anoxia, the plasma Mg2+ in the IP group, but not in the IS group, maintained a significantly higher level compared with the basal level. On the other hand, Mg2+ in the perfusates in the IS group, but not in the IP group, maintained a significantly high level during anoxia. Alterations induced by anoxia in other metabolites, 3,4-dihydroxyphenylacetic acid, homovanillic acid, norepinephrine, and 5-hydroxyindole-3-acetic acid, did not significantly differ among the three groups. We propose that elevated levels of Mg2+ in the striatum had inhibitory effects on the DA surge during anoxia.

Functional neuroanatomy of the nigrostriatal and striatonigral pathways as studied with dual probe microdialysis in the awake rat--II. Evidence for striatal N-methyl-D-aspartate receptor regulation of striatonigral GABAergic transmission and motor function

In the present study we used the dual probe approach to investigate striatal N-methyl-D-aspartate receptor regulation of GABA release from the substantia nigra pars reticulata of the awake, freely moving rat. One microdialysis probe of concentric design was implanted in the dorsolateral striatum and another in the ipsilateral substantia nigra pars reticulata. Perfusion with N-methyl-D-aspartate (100 microM) in the dorsolateral striatum decreased local dopamine release (-25%) and increased both glutamate (+40%) and GABA (+35%) release. Moreover, perfusion with N-methyl-D-aspartate (100 microM) in the dorsolateral striatum increased GABA release (+20%) in the substantia nigra pars reticulata. Perfusion with the lower (10 microM) N-methyl-D-aspartate concentration in the dorsolateral striatum did not affect striatal dopamine, glutamate and GABA release or nigral GABA release. Intrastriatal perfusion with the N-methyl-D-aspartate receptor antagonist dizocilpine maleate (10 microM), at a dose which by itself did not affect basal striatal or nigral neurotransmitter levels, prevented the effects of striatal perfusion with N-methyl-D-aspartate on both striatal and nigral neurotransmitter release. Intrastriatal dizocilpine maleate was also perfused concurrently with intranigral tetrodotoxin (10 microM) (see accompanying paper). Intrastriatal perfusion with dizocilpine maleate prevented the tetrodotoxin-induced rise in both striatal and nigral GABA levels and profoundly reduced the tetrodotoxin-induced contralateral turning. In addition, intrastriatal dizocilpine maleate delayed the increase in striatal glutamate release evoked by intranigral tetrodotoxin without affecting the associated decrease in striatal dopamine release. The present study demonstrates that N-methyl-D-aspartate receptors in the dorsolateral striatum regulate GABA release in the substantia nigra pars reticulata of the awake rat and provides evidence that this regulation plays a key role in motor function.

Nitric oxide-evoked [3H]taurine release is mediated by reversal of the Na(+)-dependent carrier-mediated taurine transport system

The pharmacological characteristics of [3H]taurine release evoked by nitric oxide (NO) were investigated using mouse cerebral cortical neurons in primary culture. N-Methyl-D-aspartate (NMDA) and S-nitroso-N-acetylpenicillamine (SNAP) dose-dependently increased [3H]taurine release from neurons. The NMDA-evoked release of [3H]taurine was reduced to the basal level by N omega-nitro-L-arginine, a NO synthase inhibitor, and MK-801, a noncompetitive antagonist for NMDA receptors. The NMDA- and SNAP-evoked releases of [3H]taurine were completely abolished by hemoglobin, indicating that these [3H]taurine releases were evoked by NO produced by NMDA receptor activation and liberated from SNAP. Withdrawal of Na+ from incubation buffer significantly inhibited the NMDA- and SNAP-induced [3H]taurine releases, whereas removal of Ca2+ produced no alteration in the SNAP-evoked [3H]taurine release. In addition, beta-alanine and guanidinoethane sulfonate, antitransporters of the carrier-mediated taurine transport system, reduced the NMDA- and SNAP-evoked releases of [3H]taurine in a dose-dependent manner. These results indicate that the NO-evoked [3H]taurine release from cerebral cortical neurons is mediated by a reversal of the Na(+)-dependent carrier-mediated taurine transport system.

Acute methamphetamine-induced zif/268, preprodynorphin, and preproenkephalin mRNA expression in rat striatum depends on activation of NMDA and kainate/AMPA receptors

This study tested the role of N-methyl-D-aspartate and kainate/AMPA receptors in mediating mRNA expression of the immediate early gene zif/268 and the opioid peptide genes preprodynorphin and preproenkephalin in rat forebrain following a single injection of methamphetamine. At 3 h after acute methamphetamine [4 mg/kg, intraperitoneally (IP)], quantitative in situ hybridization histochemistry revealed that zif/268 mRNA expression was increased in the dorsal striatum (caudoputamen) and in the sensory cortex. Preprodynorphin was increased in both dorsal and ventral striatum (nucleus accumbens) and preproenkephalin was increased in the dorsal striatum. Pretreatment with (+ or -)-3-(2-carboxypiperazin-4-yl)-propyl-1 -phosphonic acid (CPP) (10 mg/kg, IP), an N-methyl-D-aspartate receptor antagonist, blocked the methamphetamine-induced zif/268 mRNA expression in the striatum and in the region of sensory cortex representing the upper limb and nose. 6,7-Dinitro-quinoxaline-2,3-dione (DNQX) (100 mg/kg, IP), a kainate/AMPA receptor antagonist, did not reduce the ability of methamphetamine to induce zif/268 mRNA in striatal and cortical neurons. Furthermore, both antagonists caused a parallel blockade of methamphetamine-stimulated preprodynorphin mRNA expression in the dorsal and ventral striatum but did not significantly affect methamphetamine-stimulated preproenkephalin mRNA expression. CPP and DNQX reduced basal levels of zif/268 mRNA in cortical and striatal neurons but did not affect the constitutive expression of the two opioid mRNAs in the striatum. Neither antagonist had a significant effect on methamphetamine-induced hyperlocomotion and stereotypies. These results demonstrate that both N-methyl-D-aspartate and kainate/AMPA receptor-mediated glutamatergic transmission is linked to modulation of the methamphetamine-stimulated oploid peptide gene expression in rat forebrain. Furthermore, N-methyl-D-aspartate receptors participate in methamphetamine-stimulated zif/268 expression.

Concentration-dependent dual action of locally applied N-methyl-D-aspartate on extracellular dopamine in the rat prefrontal cortex in vivo

Using microdialysis, the glutamate agonist N-methyl-D-aspartate (NMDA) was perfused for 20 min through the medial prefrontal cortex of freely moving rats, and its effects on extracellular concentrations of dopamine (DA) were determined. NMDA (1 mM) increased DA to 170-1500%, depending on the intensity and duration of the clonic forelimb jerks and convulsions that were induced. NMDA (0.1 mM), however, decreased DA to 61%. Metabolites of DA were decreased after both concentrations of NMDA. The effects of both 0.1 mM and 1 mM NMDA were blocked by 0.5 mM of the competitive NMDA-antagonist D-AP-5. The NMDA-induced decrease in release and metabolism possibly results from an indirect action via an inhibitory local interneuron or polysynaptic circuit.

Cortical stimulation induces Fos expression in striatal neurons via NMDA glutamate and dopamine receptors

Cortical electrical stimulation has been shown to induce dense and widespread Fos expression throughout the ipsilateral and contralateral striatum. This raises interest for studying the mechanisms underlying the regulation of striatal neuron activity by cortical afferents, and for elucidating the interactions with other systems. However, the receptors mediating cortical-stimulation-induced expression of Fos in striatal neurons have not been identified. This was studied in the work reported here by stimulating the cortex after administration of glutamate or dopamine receptor antagonists, or after 6-hydroxydopamine (6-OHDA) lesion of the nigrostriatal dopaminergic system. Pretreatment with the non-competitive N-methyl-D-aspartate (NMDA) glutamate receptor antagonist MK-801 led to a marked reduction in the stimulation-induced density of Fos-immunoreactive nuclei in both the medial (about 80% reduction) and lateral (about 50-60% reduction) striatum. Preadministration of the D1-selective dopamine antagonist SCH-23390 alone or in combination with the D2-selective dopamine antagonist eticlopride led to a reduction in the stimulation-induced density of Fos-positive nuclei of about 60-65% in the lateral striatum, but no significant change in the medial region. The effects of 6-OHDA lesion were less pronounced, and the stimulation-induced density of Fos-immunoreactive nuclei decreased by only about 25% in the lateral region. These results indicate that both dopamine and NMDA glutamate receptors are involved in the induction of Fos by cortical stimulation, and support the hypothesis that cortex-dopamine interactions in the lateral striatum may be functionally different from those in the medial striatum.

N-methyl-D-aspartate stimulates dopamine release through nitric oxide formation in the nucleus accumbens of rats

Intracerebral microdialysis technique was utilized to study the effect of NG-nitro-L-arginine, a nitric oxide (NO) synthase inhibitor, on N-methyl-D-aspartate (NMDA)-induced dopamine overflow in the nucleus accumbens of unanesthetized, freely moving rats. Perfusion of 1 and 3 mM NMDA through the microdialysis probe dose-dependently increased the extracellular dopamine level in the nucleus accumbens. Coapplication of 0.5 mM D-(-)-2-amino-5-phosphonovaleric acid (D-AP5), a selective and competitive NMDA receptor antagonist, significantly reduced the dopamine overflow induced by 3 mM NMDA. Perfusion of 0.5 mM NG-nitro-L-arginine alone did not affect the basal dopamine level, whereas it suppressed the NMDA-evoked dopamine overflow in the nucleus accumbens when concurrently applied with 3 mM NMDA. These results suggest that NO mediates, at least in part, dopamine release resulting from NMDA receptor activation in the nucleus accumbens of rats.

Persistent increase in dopamine release following activation of metabotropic glutamate receptors in the rat nucleus accumbens

Intracerebral microdialysis technique was utilized to study the effect of the metabotropic glutamate receptor agonist, 1-aminocyclopentane-1,3-dicarboxylic acid (ACDP), on extracellular dopamine concentration in the nucleus accumbens of unanesthetized, freely moving rats. Perfusion of 1 mM (1S, 3R)-ACPD, a selective metabotropic glutamate receptor agonist, through the microdialysis probe caused a significant and persistent increase in extracellular dopamine level in the nucleus accumbens, which disappeared 2 h after perfusion of (1S, 3R)-ACPD was discontinued. On the other hand, a temporary increase in dopamine overflow was observed when 1 and 3 mM N-methyl-D-aspartate (NMDA), an ionotropic glutamate receptor agonist, was perfused into the nucleus accumbens. Application of 1 mM (1R, 3S)-ACPD, an inactive isomer, into the nucleus accumbens had no effect on the extracellular dopamine concentration. The metabotropic glutamate receptor antagonist, alpha-methyl-4-carboxyphenylglycine (MCPG) (5 mM) did not affect the basal dopamine level, but it attenuated the (1S, 3R)-ACPD-evoked dopamine overflow in the nucleus accumbens when applied concurrently with 1 mM (1S, 3R)-ACPD. These results suggest that a long-lasting dopamine overflow following activation of metabotropic glutamate receptors contrasts with a transient one in response to NMDA receptor activation in the nucleus accumbens.

Dynamic analysis of ethanol effects on NMDA-evoked dopamine overflow in rat striatum

This study was undertaken to dynamically examine the effects of ethanol on the striatal dopaminergic transmission, in terms of N-methyl-D-aspartate (NMDA)-evoked dopamine release and dopamine uptake. In the striatum of urethane-anesthetized Sprague-Dawley rats, extracellular dopamine was measured using in vivo electrochemical detection coupled with a nafion-coated carbon fiber working electrode. Micro-ejection of NMDA evoked a transient dopamine release from the dopamine-containing nerve terminals in striatum. Local application of ethanol by pressure ejection did not elicit significant changes in spontaneous dopamine release. However, with ethanol pretreatment, the time course of NMDA-induced dopamine release was markedly prolonged while the magnitude and the rate of clearance were significantly reduced. These effects were compared to those of nomifensine, a dopamine uptake blocker. Nominfensine pretreatment was found to augment the time course of NMDA-evoked dopamine release analogous to those by ethanol pretreatment. Furthermore, pretreatment with ethanol did not increase the time course parameters of dopamine signals if dopamine releases were induced by co-application of NMDA and nominfensine. These data suggest that in addition to the attenuation of NMDA-evoked dopamine release, ethanol inhibits dopamine uptake in a similar fashion to that observed with nomifensine in situ in the striatum. Indeed, ethanol altered the uptake of exogenous dopamine from the extracellular space of striatal cortex. The time course of dopamine signals was prolonged and the rate of clearance was reduced after ethanol treatment. Taken together, our data demonstrate that ethanol simultaneously inhibits NMDA-evoked dopamine release and dopamine uptake in the striatum, suggesting the importance of the interplay between release and uptake in ethanol effects on striatal dopaminergic transmission.

Role of nitric oxide in central synaptic transmission: effects on neurotransmitter release

Nitric oxide (NO), an unstable radical formed via oxidative deamination of L-arginine by NO synthase, has the activity to evoke release of several neurotransmitters including acetylcholine, catecholamines and neuroactive amino acids. N-methyl-D-aspartate (NMDA) receptor stimulation also causes neurotransmitter release through NO formation, which is supported by the data extracellular hemoglobin completely abolishes the stimulatory effect of NMDA on neurotransmitter release. In addition, NO formed by NMDA receptor activation exhibits its stimulatory action on neurotransmitter release extracellularly. A product formed by the reaction of NO and superoxide, peroxynitrite, is also considered to be partly involved in NO-evoked neurotransmitter release. The removal of Ca2+ or Na+ significantly reduces the release of GABA evoked by an NO generator, S-nitroso-N-acetylpenicillamine (SNAP), and simultaneous withdrawal of these ions completely abolishes the SNAP-induced release of GABA. Either in the presence or absence of Ca2+, GABA transport inhibitors such as nipecotic acid dose-dependently suppress the SNAP-induced GABA release in the presence of Na+. These results indicate that NO-evoked neurotransmitter release is mediated by two distinct release systems, a Ca2(+)-dependent system and the reverse process of a Na(+)-dependent carrier-mediated transport system.