Synaptic localization of striatal NMDA, quisqualate and kainate receptors

Cortical ionotropic glutamate receptor antagonism protects against methamphetamine-induced striatal neurotoxicity

Binge administration of the psychostimulant drug, methamphetamine (mAMPH), produces long-lasting structural and functional abnormalities in the striatum. mAMPH binges produce nonexocytotic release of dopamine (DA), and mAMPH-induced activation of excitatory afferent inputs to cortex and striatum is evidenced by elevated extracellular glutamate (GLU) in both regions. The mAMPH-induced increases in DA and GLU neurotransmission are thought to combine to injure striatal DA nerve terminals of mAMPH-exposed brains. Systemic pretreatment with either competitive or noncompetitive N-methyl-D-aspartic acid (NMDA) antagonists protects against mAMPH-induced striatal DA terminal damage, but the locus of these antagonists' effects has not been determined. Here, we applied either the NMDA receptor antagonist, (dl)-amino-5-phosphonovaleric acid (AP5), or the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor antagonist, dinitroquinoxaline-2,3-dione (DNQX), directly to the dura mater over frontoparietal cortex to assess their effects on mAMPH-induced cortical and striatal immediate-early gene (c-fos) expression. In a separate experiment we applied AP5 or DNQX epidurally in the same cortical location of rats during a binge regimen of mAMPH and assessed mAMPH-induced striatal dopamine transporter (DAT) depletions 1 week later. Our results indicate that both ionotropic glutamate receptor antagonists reduced the mAMPH-induced Fos expression in cerebral cortex regions near the site of epidural application and reduced Fos immunoreactivity in striatal regions innervated by the affected cortical regions. Also, epidural application of the same concentration of either antagonist during a binge mAMPH regimen blunted the mAMPH-induced striatal DAT depletions with a topography similar to its effects on Fos expression. These findings demonstrate that mAMPH-induced dopaminergic injury depends upon cortical NMDA and AMPA receptor activation and suggest the involvement of the corticostriatal projections in mAMPH neurotoxicity.

Striatal dopamine and glutamate receptors modulate methamphetamine-induced cortical Fos expression

Methamphetamine (mAMPH) is a psychostimulant drug that increases extracellular levels of monoamines throughout the brain. It has previously been observed that a single injection of mAMPH increases immediate early gene (IEG) expression in both the striatum and cerebral cortex. Moreover, this effect is modulated by dopamine and glutamate receptors since systemic administration of dopamine or glutamate antagonists has been found to alter mAMPH-induced striatal and cortical IEG expression. However, because dopamine and glutamate receptors are found in extra-striatal as well as striatal brain regions, studies employing systemic injection of dopamine or glutamate antagonists fail to localize the effects of mAMPH-induced activation. In the present experiments, the roles of striatal dopamine and glutamate receptors in mAMPH-induced gene expression in the striatum and cerebral cortex were examined. The nuclear expression of Fos, the protein product of the IEG c-fos, was quantified in both the striatum and the cortex of animals receiving intrastriatal dopamine or glutamate antagonist administration. Intrastriatal infusion of dopamine (D1 or D2) or glutamate [N-methyl-D-aspartic acid (NMDA) or alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)] antagonists affected not only mAMPH-induced striatal, but also cortical, Fos expression. Overall, the effects of the antagonists occurred dose-dependently, in both the infused and non-infused hemispheres, with greater influences occurring in the infused hemisphere. Finally, unilateral intrastriatal infusion of dopamine or glutamate antagonists changed the behavior of the rats from characteristic mAMPH-induced stereotypy to rotation ipsilateral to the infusion. These results demonstrate that mAMPH's actions on striatal dopamine and glutamate receptors modulate the widespread cortical activation induced by mAMPH. It is hypothesized that dopamine release from nigrostriatal terminals modulates activity within striatal efferent pathways, thereby disinhibiting thalamo-cortical circuits. By extension, these results suggest processes through which repeated exposure to mAMPH might influence cortical function in mAMPH abusers.

Effects of ethanol and 3,4-methylenedioxymethamphetamine (MDMA) alone or in combination on spontaneous and evoked overflow of dopamine, serotonin and acetylcholine in striatal slices of the rat brain

Ethanol (EtOH) potentiates the locomotor effects of 3,4-methylenedioxymetamphetamine (MDMA) in rats. This potentiation might involve pharmacokinetic and/or pharmacodynamic mechanisms. We explored whether the latter could be local. Using a slice superfusion approach, we assessed the effects of MDMA (0.3, 3microm) and/or EtOH (2mm) on the spontaneous outflow and electrically evoked release of serotonin (5-HT), dopamine (DA) and acetylcholine (ACh) in the striatum, and for comparison, on 5-HT release in hippocampal and neocortical tissue. MDMA and less effectively EtOH, augmented the outflow of 5-HT in all regions. The electrically evoked 5-HT release was increased by MDMA at 3microm in striatal slices only. With nomifensine throughout, EtOH significantly potentiated the 0.3microm MDMA-induced outflow of 5-HT, but only in striatal slices. EtOH or MDMA also enhanced the spontaneous outflow of DA, but MDMA reduced the electrically evoked DA release. With fluvoxamine throughout superfusion, EtOH potentiated the effect of MDMA on the spontaneous outflow of DA. Finally, 3microm MDMA diminished the electrically evoked release of ACh, an effect involving several receptors (D2, 5-HT2, NMDA, nicotinic, NK1), with some interactions with EtOH. Among other results, we show for the first time a local synergistic interaction of EtOH and MDMA on the spontaneous outflow of striatal DA and 5-HT, which could be relevant to the EtOH-induced potentiation of hyperlocomotion in MDMA-treated rats. These data do not preclude the contribution of other pharmacodynamic and/or pharmacokinetic mechanisms in vivo but support the hypothesis that EtOH may affect the abuse liability of MDMA.

Hippocampal modulation of locomotor activity induced by focal activation of postsynaptic dopamine receptors in the core of the nucleus accumbens

The locomotor effects of intra-NAcc injection of dopamine receptor agonists following discrete lesion or inhibition of the DH or the VH have been poorly investigated using only the indirect dopamine receptor agonist amphetamine. In the present study, we investigated how lidocaine in the DH or the VH modulated hyperlocomotion induced by focal injection into the NAcc core of the selective D1-like receptor agonist, SKF 38393, or coinjection of SKF 38393, and the selective D2-like receptor agonist, LY 171555; the latter pharmacological condition being required for the full expression of the postsynaptic effects of D2-like receptor agonists, and recognized to produce a locomotor response mainly mediated by D2-like postsynaptic receptors. Rats were given the D1-like receptor agonist SKF 38393 alone or in combination with the D2-like receptor agonist LY 171555 into the NAcc core, and lidocaine into the DH or the VH. Then, locomotor activity was recorded. Focal injection into the NAcc core of SKF 38393 alone or in combination with LY 171555 resulted in an increase of locomotor activity. Administration of lidocaine into the DH further potentiated the increase in locomotor activity induced by activation of D1-like receptors or co-activation of D1-like and D2-like receptors in the NAcc core. Administration of lidocaine into the VH also potentiated the increase in locomotor activity induced by D1-like receptor activation, but decreased that produced by co-activation of D1-like and D2-like receptors in the NAcc core. Taken together, these results suggest that under lidocaine-free conditions the DH may exert a tonic inhibitory modulation on hyperlocomotion mediated by D1-like and D2-like postsynaptic receptors in the NAcc core, while the VH may exert a tonic inhibitory on hyperlocomotion mediated by D1-like receptors and a tonic facilitatory control on hyperlocomotion mediated by D2-like postsynaptic receptors.

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.

Cortical glutamatergic markers in schizophrenia

Post-mortem studies have yet to produce consistent findings on cortical glutamatergic markers in schizophrenia; therefore, it is not possible to fully understand the role of abnormal glutamatergic function in the pathology of the disorder. To better understand the changes in cortical glutamatergic markers in schizophrenia, we measured the binding of radioligands to the ionotropic glutamate receptors (N-methyl D-aspartate, [3H]CGP39653, [3H]MK-801), amino-3-hydroxy-5-methyl-4-isoxazole ([3H]AMPA), kainate ([3H]kainate), and the high-affinity glutamate uptake site ([3H]aspartate) using in situ radioligand binding with autoradiography and levels of mRNA for kainate receptors using in situ hybridization in the dorsolateral prefrontal cortex from 20 subjects with schizophrenia and 20 controls matched for age and sex. Levels of [3H]kainate binding were significantly decreased in cortical laminae I-II (p = 0.01), III-IV (p < 0.05), and V-VI (p < 0.01) from subjects with schizophrenia. By contrast, levels of [3H]MK-801, [3H]AMPA, [3H]aspartate, or [3H]CGP39653 binding did not differ between the diagnostic cohorts. Levels of mRNA for the GluR5 subunit were decreased overall (p < 0.05), with no changes in levels of mRNA for GluR6, GluR7, KA1, or KA2 in tissue from subjects with schizophrenia. These data indicate that the decreased number of kainate receptors in the dorsolateral prefrontal cortex in schizophrenia may result, in part, from reduced expression of the GluR5 receptor subunits.

Striatal glutamate release evoked in vivo by NMDA is dependent upon ongoing neuronal activity in the substantia nigra, endogenous striatal substance P and dopamine

The aim of the present microdialysis study was to investigate whether the increase in striatal glutamate levels induced by intrastriatal perfusion with NMDA was dependent on the activation of extrastriatal loops and/or endogenous striatal substance P and dopamine. The NMDA-evoked striatal glutamate release was mediated by selective activation of the NMDA receptor-channel complex and action potential propagation, as it was prevented by local perfusion with dizocilpine and tetrodotoxin, respectively. Tetrodotoxin and bicuculline, perfused distally in the substantia nigra reticulata, prevented the NMDA-evoked striatal glutamate release, suggesting its dependence on ongoing neuronal activity and GABA(A) receptor activation, respectively, in the substantia nigra. The NMDA-evoked glutamate release was also dependent on striatal substance P and dopamine, as it was antagonized by intrastriatal perfusion with selective NK(1) (SR140333), D(1)-like (SCH23390) and D(2)-like (raclopride) receptor antagonists, as well as by striatal dopamine depletion. Furthermore, impairment of dopaminergic transmission unmasked a glutamatergic stimulation by submicromolar NMDA concentrations. We conclude that in vivo the NMDA-evoked striatal glutamate release is mediated by activation of striatofugal GABAergic neurons and requires activation of striatal NK(1) and dopamine receptors. Endogenous striatal dopamine inhibits or potentiates the NMDA action depending on the strength of the excitatory stimulus (i.e. the NMDA concentration).

Modulation of the locomotor responses induced by D1-like and D2-like dopamine receptor agonists and D-amphetamine by NMDA and non-NMDA glutamate receptor agonists and antagonists in the core of the rat nucleus accumbens

Dopamine and glutamate interactions in the nucleus accumbens (NAcc) play a crucial role in both the development of a motor response suitable for the environment and in the mechanisms underlying the motor-activating properties of psychostimulant drugs such as amphetamine. We investigated the effects of the infusion in the NAcc of NMDA and non-NMDA receptor agonists and antagonists on the locomotor responses induced by the selective D(1)-like receptor agonist SKF 38393, the selective D(2)-like receptor agonist quinpirole, alone or in combination, and D-amphetamine. Infusion of either the NMDA receptor agonist NMDA, the NMDA receptor antagonist D-AP5, the non-NMDA receptor antagonist CNQX, or the non-NMDA receptor agonist AMPA resulted in an increase in basal motor activity. Conversely, all of these ionotropic glutamate (iGlu) receptor ligands reduced the increase in locomotor activity induced by focal infusion of D-amphetamine. Interactions with dopamine receptor activation were not so clear: (i). infusion of NMDA and D-AP5 respectively enhanced and reduced the increase in locomotor activity induced by the infusion of the D(1)-like receptor agonist of SKF 38393, while AMPA or CNQX decreased it; (ii). infusion of NMDA, D-AP5, and CNQX reduced the increase in locomotor activity induced by co-injection of SKF 38393+quinpirole--a pharmacological condition thought to activate both D(1)-like and D(2)-like presynaptic and postsynaptic receptors, while infusion of AMPA potentiated it; (iii). infusion of either NMDA, D-AP5 or CNQX, but not of AMPA, potentiated the decrease in motor activity induced by the D(2)-like receptor agonist quinpirole, a compound believed to act only at presynaptic D(2)-like receptors when injected by itself. Our results show that NMDA receptors have an agonist action with D(1)-like receptors and an antagonist action with D(2)-like receptors, while non-NMDA receptors have the opposite action. This is discussed from a anatamo-functional point of view.

Decreased hippocampal NMDA, but not kainate or AMPA receptors in bipolar disorder

OBJECTIVES

The purpose of this study was to determine whether there are changes in the density of ionotropic glutamate receptors in the hippocampus of subjects with bipolar disorder.

METHODS

Using in situ radioligand binding with semiquantitative autoradiography, we measured the density of [3H]MK-801, [3H]CGP39653, [3H]AMPA and [3H]kainate binding in hippocampi, obtained postmortem, from eight subjects with type 1 bipolar disorder and 8 age- and sex-matched controls.

RESULTS

In subjects with bipolar disorder there were significant decreases in the density of [3H]MK-801 binding in the Cornu Ammonis (CA) 3 (mean +/- SEM; 108.8 +/- 12.2 versus 166.2 +/- 18.0 fmol/mg ETE, p < 0.005) as well as the pyramidal (102.8 +/- 9.2 versus 136.6 +/- 11.2 fmol/mg ETE, p < 0.05) and polymorphic (21.73 +/- 6.5 versus 53.26 +/- 11.6 fmol/mg ETE, p < 0.05) layers of the subiculum. In addition, two-way analysis of variance (ANOVA) revealed a decrease in the density of [3H]CGP39653 binding across the hippocampal formation in bipolar subjects, which did not reach significance in any subregion. There were no changes in the densities of [3H]AMPA or [3H]kainate binding in these subjects.

CONCLUSIONS

[3H]CGP39653 and [3H]MK-801 bind to the glutamate binding site and open ion channel of the n-methyl-d-aspartate (NMDA) receptor, respectively. Therefore, these data suggest that there is a decrease in the number of open ion channels associated with no significant change in the apparent density of NMDA receptors in regions of the hippocampus from subjects with bipolar disorder.

A change in the density of [(3)H]flumazenil, but not [(3)H]muscimol binding, in Brodmann's Area 9 from subjects with bipolar disorder

BACKGROUND

This study examines the hypothesis that there are changes in cortical serotonergic, GABAergic and glutamatergic systems in bipolar disorder and schizophrenia.

METHODS

In situ radioligand binding and autoradiography were used to measure neurochemical markers in Brodmann's Area (BA) 9 from control subjects and subjects with bipolar disorder or schizophrenia (n=8 per group).

RESULTS

Compared to tissue from schizophrenic (mean+/-S.E.M, 385+/-44 fmol/mg ETE) and control (383+/-44 fmol/mg ETE) subjects, there was an increase in the density of [(3)H]flumazenil binding to the benzodiazepine binding site on the GABA(A) receptor in subjects with bipolar disorder (451+/-17 fmol/mg ETE; P<0.05). There was no difference in the density of [(3)H]muscimol binding to the GABA(A) receptor or in the density of the serotonin(1A) receptor, serotonin(2A) receptor, ionotropic glutamate receptors or the serotonin transporter between the three cohorts. There was an age-related decrease in NMDA receptor density in control subjects that was absent in schizophrenia and bipolar disorder. An age-related increase in [(3)H]flumazenil binding in schizophrenia was absent in control and bipolar disorder subjects.

LIMITATIONS

This study involved a relatively small number of individuals.

CONCLUSIONS

An increase in the gamma2-receptor sub-unit in the GABA(A) receptor has been shown to increase benzodiazepine but not [(3)H]muscimol binding, this is the mismatch in binding we have shown in BA 9 from subjects with bipolar disorder. Thus, a change in the assembly of receptor subunits into GABA(A) receptors may be involved in the neuropathology of bipolar disorder. There may also be differences in age-related changes in cortical receptor density between bipolar disorder and schizophrenia.

Differential expression of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate receptor subunits by calretinin-immunoreactive neurons in the human striatum

We recently reported the existence of medium and large intemeurons immunoreactive for the calcium-binding protein calretinin in the human striatum. We also showed a selective sparing of all medium, but not all large, calretinin-immunoreactive striatal neurons in Huntington's disease striatum. Because glutamate receptor-mediated excitotoxicity has been implicated in the massive loss of striatal projection neurons that characterizes Huntington's disease, we have applied a double-antigen localization procedure to post mortem tissue from eight normal human subjects to determine the expression of the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate glutamate receptor subunits 1/2/4 by the calretinin-immunoreactive interneurons. The two types of calretinin-immunoreactive neurons were found to display various patterns of glutamate receptor subunit expression and a specific regionalization was also noted in the expression of these glutamate receptor subunits. Approximately half of the large calretinin-immunoreactive neurons displayed immunoreactivity for glutamate receptor subunits 1 and 2, and about the same proportion of medium calretinin-immunoreactive neurons expressed glutamate receptor subunits 1 and 4. These double-labeled neurons were rather uniformly distributed in the caudate nucleus and putamen. In contrast, as much as 70.1% of the large calretinin-immunoreactive neurons displayed glutamate receptor subunit 4 immunoreactivity in the postcommissural portion of the putamen, an area that corresponds to the sensorimotor striatal territory. For their part, the medium calretinin-immunoreactive neurons were markedly enriched with glutamate receptor subunit 2, 76% of them being double labeled in the caudate nucleus, which corresponds to the striatal associative territory, compared with 85.5% in the postcommissural putamen. Receptor subunit composition plays a key role in determining the functional properties of glutamate receptors, including their permeability to calcium and susceptibility to excitotoxic insults. Thus, the differential expression of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate glutamate receptor subunits reported here may help to explain the selective sparing of certain types of calretinin-immunoreactive striatal interneurons in Huntington's disease, although other factors, such as post-transcriptional editing, are also likely to be involved.

NMDA receptor antagonists inhibit apomorphine-induced climbing behavior not only in intact mice but also in reserpine-treated mice

The present study showed that the noncompetitive N-methyl-D-aspartate (NMDA) receptor antagonists, MK-801 {(+)-5-methyl-10,11-dihydroxy-5H-dibenzo-[a,d]-cyclohepten-5,10-im ine hydrogen maleate}, ketamine, dextrorphan and dextromethorphan attenuated apomorphine-induced climbing behavior in reserpine-treated mice. In addition, the competitive NMDA receptor antagonists, D(-)-2-amino-5-phosphonopentanoic acid (AP-5) and D(-)-3-(2-carboxypipera-zine-4-yl)-propyl-1-phosphonic acid (CPP), also inhibited the apomorphine-induced climbing behavior in reserpine-treated mice as well as in intact mice. Previous work in our laboratory had shown that the noncompetitive NMDA receptor antagonists, MK-801, ketamine, dextrorphan and dextromethorphan cause a pronounced inhibition of apomorphine-induced cage climbing behavior in intact mice, suggesting the involvement of NMDA receptors in the glutamatergic modulation of dopaminergic function at the postsynaptic dopamine (DA) receptors. Therefore, the present results strongly support our previous conclusion that the NMDA receptors play important roles in the glutamatergic modulation of dopaminergic function at the postsynaptic DA receptors.

Glutamate-dopamine interactions mediate the effects of psychostimulant drugs

The striatum, a major central nervous system structure modulating movement, is enriched with glutamatergic and dopaminergic innervation. By altering activities of both glutamatergic and dopaminergic transmissions the psychostimulants, amphetamine and cocaine, induce behavioral changes in experimental animals. Activation of the two systems is also essential in the mediation of drug-stimulated gene expression in striatal neurons, which is considered to be an important component of the neuroplasticity underlying long-term profiles of stimulant use. Interactions between the two systems occur at multiple levels that determine the final outcome of drug stimulation. Emerging studies on the detailed transsynaptic and intracellular mechanisms of glutamatedopamine interactions in response to stimulant exposure are providing cellular and molecular insight into the pathophysiology of stimulant abuse.

Vagally-regulated gastric motor activity: evidence for kainate and NMDA receptor mediation

Blockade of GABA(A) receptors in the dorsal vagal complex produces marked gastric motor excitation. This effect is abolished by a prior microinjection of a non-selective excitatory amino acid receptor antagonist. Here we present functional evidence for kainate and NMDA receptor-mediated gastric excitation in the dorsal vagal complex. Microinjections into the dorsal vagal complex were performed in alpha-chloralose-anesthetized rats using multi-barrelled glass micropipettes while recording intragastric pressure and motility. Kainic acid (30 and 100 pmol in 30 nl) and NMDA (100 and 300 pmol) produced dose-related increases in intragastric pressure and motility. The gastric responses to kainate (30 pmol) and NMDA were selectively abolished by prior microinjection 6,7-dinitroquinoxaline-2,3-dione (600 pmol, 60 nl) and DL-2-amino-5-phosphanopentanoic acid (2 nmol), respectively. Atropine (1 mg/kg, i.v.) pretreatment blocked kainate-, NMDA- and L-glutamate-induced gastric excitation. Thus, both kainate- and NMDA-receptors in the dorsal vagal complex can independently cause vagally-mediated gastric motor excitation.

Regional localization of dopamine and ionotropic glutamate receptor subtypes in striatolimbic brain regions

Localization of dopamine (D(1)-, D(2)-like, and D(4)) and ionotropic glutamate (NMDA, AMPA, and KA) receptor subtypes within the striatolimbic forebrain remains incomplete, but basic to understanding the functional organization of this important brain region. We found that frontal cortical ablation supported colocalization of D(4) and NMDA receptors on corticostriatal afferents to caudate-putamen and nucleus accumbens in rat forebrain. Local injection of kainic acid into caudate-putamen, nucleus accumbens, or hippocampus produced massive local postsynaptic losses of D(1)- and D(2)-like, as well as NMDA, AMPA, and KA receptors, and kainic acid ablation of hippocampal-striatal projections indicated the selective expression of presynaptic NMDA and KA autoreceptors. Degeneration of nigrostriatal dopamine projections with 6-hydroxydopamine showed that all three glutamatergic subtypes exist as heteroceptors on nigrostriatal dopaminergic terminals. Our findings suggest common interactions between excitatory glutamatergic and inhibitory dopaminergic receptors in rat forebrain. Further localization of these receptor subtypes in striatolimbic forebrain should help to clarify their contributions to the pathophysiology of neuropsychiatric disorders and their treatment.

Intra-striatal phencyclidine inhibits N-methyl-D-aspartic acid-stimulated increase in glutamate levels of freely moving rats

1. The authors investigated the effect of local phencyclidine (phenylcyclohexylpiperidine, PCP) on extracellular levels of glutamate and gamma-amino butyric acid (GABA) in rat striatum using in vivo microdialysis. 2. Intrastriatal infusion of PCP (1 mM) via a microdialysis probe did not alter the basal extracellular levels of either glutamate or GABA. Addition of N-methyl-D-aspartic acid (NMDA; 0.2, 0.5 and 1 mM) to the perfusion medium resulted in a dose-dependent increase in extracellular levels of glutamate. 3. Intrastriatal infusion of tetrodotoxin (0.1, 1, 10 microM), a highly selective blocker of voltage-dependent sodium channels, significantly attenuated the NMDA-stimulated release of glutamate, suggesting that NMDA-evoked release of glutamate originated from the neuronal pool and that the increase of striatal glutamate level was regulated indirectly via NMDA receptors. 4. The NMDA-induced release of glutamate was reduced significantly by pretreatment with local PCP (1 mM). Dizocilpine (MK801; 0.2 mM), a non-competitive NMDA antagonist, completely inhibited the NMDA-stimulated release of glutamate. 5. These results suggest that, in the striatum, PCP inhibits corticostriatal glutamatergic neurotransmission by inhibiting the release of glutamate probably via postsynaptic NMDA receptors.

The release of amino acids from rat neostriatum and substantia nigra in vivo: a dual microdialysis probe analysis

It has previously been demonstrated, in dual probe microdialysis studies, that stimulation of the neostriatum with kainic acid causes the release of GABA both locally within the neostriatum and distally in the substantia nigra, observations that are consistent with the known anatomy of the basal ganglia. The object of the present study was to further examine the characteristics of GABA release and to determine whether taurine, which has been proposed to be present in striatonigral neurons, has similar characteristics of release, and to examine the release of excitatory amino acids under the same conditions. To this end, dual probe microdialysis studies were carried out on freely-moving rats. The application of kainic acid to neostriatum enhanced the release of GABA, taurine, aspartate and glutamate locally in the neostriatum and distally in the substantia nigra. The distal release of each amino acid in the substantia nigra was sensitive to the administration of 6,7-dinitroquinoxaline-2,3-dione and tetrodotoxin to the neostriatum. Similarly the local release of GABA, aspartate and glutamate but not taurine was sensitive to the intrastriatal application of 6,7-dinitroquinoxaline-2,3-dione or tetrodotoxin. It is concluded that the release of taurine from the substantia nigra has similar characteristics to that of GABA and may be released from the terminals of striatonigral neurons following the stimulation of their cell bodies in the neostriatum. The release of taurine in the neostriatum however, is likely to be mediated mainly by different mechanisms and not related to neuronal activity. The release of excitatory amino acids is likely to involve indirect effects in the neostriatum and polysynaptic pathways in the substantia nigra.

Localization of ionotropic glutamate receptors in caudate-putamen and nucleus accumbens septi of rat brain: comparison of NMDA, AMPA, and kainate receptors

Changes in binding of selective radioligands at NMDA ([3H]MK-801), AMPA ([3H]CNQX), and kainate ([3H]kainic acid) glutamate (GLU) ionotropic receptors in rat caudate-putamen (CPu) and nucleus accumbens (NAc) were examined by quantitative autoradiography following: 1) unilateral surgical ablation of frontal cerebral cortex to remove descending corticostriatal GLU projections, 2) unilateral injection of kainic acid (KA) into CPu or NAc to degenerate local intrinsic neurons, or 3) unilateral injections of 6-hydroxydopamine (6-OH-DA) into substantia nigra to degenerate ascending nigrostriatal dopamine (DA) projections. Cortical ablation significantly decreased NMDA receptor binding in ipsilateral medial CPu (20%), and NAc (16%), similar to previously reported losses of DA D4 receptors. KA lesions produced large losses of NMDA receptor labeling in CPu and NAc (both by 52%), AMPA (41% and 45%, respectively), and kainate receptors (40% and 45%, respectively) that were similar to the loss of D2 receptors in CPu and NAc after KA injections. Nigral 6-OH-DA lesions yielded smaller but significant losses in NMDA (17%), AMPA (12%), and kainate (11%) receptor binding in CPu. The results indicate that most NMDA, AMPA, and kainate receptors in rat CPu and NAc occur on intrinsic postsynaptic neurons. Also, some NMDA, but not AMPA or kainate, receptors are also found on corticostriatal projections in association with D4 receptors; these may, respectively, represent excitatory presynaptic NMDA autoreceptors and inhibitory D4 heteroceptors that regulate GLU release from corticostriatal axons in medial CPu and NAc. Conversely, the loss of all three GLU receptor subtypes after lesioning DA neurons supports their role as excitatory heteroceptors promoting DA release from nigrostriatal neurons.

Expression of NMDA receptor-1 (NR1) and huntingtin in striatal neurons which colocalize somatostatin, neuropeptide Y, and NADPH diaphorase: a double-label histochemical and immunohistochemical study

The subset of striatal neurons which colocalize SS/NPY/NADPH-d are selectively resistant to neurodegeneration in Huntington's Disease (HD) and to excitotoxic cell death induced experimentally with NMDA receptor (NMDAR) agonists. Here we have analyzed the expression of immunoreactive NMDAR-1 (NR1) subunit (as an index of NMDAR protein) and of huntingtin (the normal product of the HD gene) in primary cultures of rat striatum to see if differential expression of the two antigens in the subset of SS/NPY/NADPH-d and other striatal neurons can explain their selective resistance or vulnerability. Double-label histochemical and immunocytochemical studies were carried out using conventional and confocal laser scanning microscopy to characterize the cellular and subcellular expression of NR1 and SS, or NPY or bNOS, together with NADPH-d histochemistry. The percentages of cultured striatal neurons that were positive for NADPH-d, SS, NPY, bNOS, and NRI were, respectively, 3.8, 8.4, 10.2, 5.1, and 80%. The majority of striatal NADPH-d neurons coexpressed SS and NPY; 17% of SS-producing neurons were strongly positive for NR1; the remaining cells (approximately 80%) exhibited only weak NR1 expression. Comparable data were obtained for NPY-positive neurons, 15% of which colocalized NR1 strongly and 70-80% weakly. By double-label immunofluorescence, huntingtin was nonselectively expressed in virtually all striatal neurons including SS/NPY/NADPH-d neurons. These results show that the majority of striatal SS/NPY/NADPH-d neurons express NR1. The relative abundance of NR1 in SS/NPY/NADPH-d neurons, however, varies between a small subset of neurons that are receptor rich and the remainder that express low levels only and may determine susceptibility to NMDAR-mediated neurotoxicity. Huntingtin is nonselectively expressed in virtually all striatal neurons and does not appear to be a determinant of the selective resistance of normal striatal SS/NPY/NADPH-d neurons to NMDA toxicity.

Spatial distribution of kainate receptor subunit mRNA in the mouse basal ganglia and ventral mesencephalon

In an attempt to gain knowledge of the possible functions of kainate receptors, we have used in situ hybridization to examine the regional and cellular expression patterns of glutamate receptor subunits GluR5-7, KA1 and KA2 in the adult mouse basal ganglia, known to play a pivotal role in the translation of motivation into actions. Kainate receptor subunits were found to be differentially expressed in the circuitry forming the basal ganglia. They differ from each other in expression levels and their spatial localization. GluR6 appeared as the key subunit for the descending gamma-aminobutyric acid (GABA)ergic-glutamatergic pathways, with highest message levels in the caudate putamen, globus pallidus and subthalamic nucleus as well as in the nucleus accumbens and olfactory tubercle. GluR7 exhibited highest expression in the ascending nigrostriatal and mesolimbic dopaminergic neurons. GluR5 had a restricted distribution pattern, with high expression in the ventral pallidum, the islands of Calleja and pars compacta of the substantia nigra. KA2 was usually coexpressed with GluR6, although with a generally lower level of expression. Finally, KA1 mRNA was barely detectable in these neuronal circuits. These data suggest that kainate receptors in general may be involved in the functions associated with the basal ganglia, with a key role in the control of the central dopaminergic transmission. Thus, they might be implicated in the neurodegenerative and psychic disorders associated with an impairment of the basal ganglia.

Progressive augmentation of striatal and accumbal preprotachykinin mRNA levels by chronic treatment with methamphetamine and effect of concurrent administration of the N-methyl-D-aspartate receptor antagonist MK-801

We have assessed the time course of repeated administration of methamphetamine (METH; 4 mg/kg) and withdrawal on the levels of preprotachykinin (PPT) and preproenkephalin (PPE) mRNA abundance in the caudate-putamen (CPu) and nucleus accumbens (NAc) of the rat brain by in situ hybridization histochemistry. Neostriatal PPT mRNA levels rose gradually between days 1 and 6 of treatment, with the greatest elevation observed at day 6. After 6 days of daily injections twice per day, PPT mRNA increases in dorsomedial (172%) and ventromedial (196%) aspects of the CPu were significantly higher than in dorsolateral (147%) and ventrolateral (135%) subdivisions. Similarly, PPT mRNA levels were increased in the anterior CPu (163%) and NAc (121%). Concurrent administration of METH and the NMDA receptor antagonist MK-801 attenuated METH-induced increases of PPT mRNA in all aspects of the CPu at day 6 of treatment and completely prevented the increase in the NAc. Moreover, animals treated with METH for 6 days and then withdrawn for 15 days displayed PPT mRNA levels in striatum and accumbens that were statistically indistinguishable from those of controls. Adjacent sections from the same brains were used to assess PPE mRNA levels. PPE mRNA levels were transiently elevated in dorsal and ventral aspects of the CPu at day 1 and decayed to control levels at days 3 and 6. The results demonstrate that progressive treatment with methamphetamine causes stepwise elevation of preprotachykinin mRNA levels in the neostriatum. Moreover, the increase of neuropeptide mRNA shows selectivity, since PPE mRNA levels did not display progressive accumulation of message. The effects of progressive METH treatment on neostriatal PPT mRNA expression decay when the drug is withdrawn, suggesting that this neuropeptidergic system may not represent a neuroadaptation sustaining enduring sensitization to amphetamines, but may play a role in the progressive augmentation of locomotor activity elicited by this class of drug.

In vitro autoradiography of ionotropic glutamate receptors in hippocampus and striatum of aged Long-Evans rats: relationship to spatial learning

Using in vitro autoradiography, we investigated [3H] alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate, [3H]kainate and [3H]N-methyl-D-aspartate binding in two forebrain regions, the hippocampus and striatum, of young (four months of age) and aged (24-25 months of age) Long-Evans rats that had previously been tested for spatial learning ability in the Morris water maze. Although there was substantial preservation of binding in the aged rats, reductions in binding were present in the aged rats that were specific to ligand and anatomical region. In the hippocampus of aged rats, [3H] alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate binding in CA1 and [3H]kainate binding in CA3 were reduced. In contrast, N-methyl-D-aspartate binding was not significantly different between age groups. There was evidence of sprouting in the dentate gyrus molecular layer of aged rats, indicated by changes in the topography of [3H]kainate binding. Binding density was analysed with respect to patch/matrix compartmentalization in the striatum. The most striking result was a large decrease in N-methyl-D-aspartate binding in aged rats that was not limited to any dorsal/ventral or patch/matrix area of the striatum. Additionally, [3H]kainate binding in striatal matrix was modestly reduced in aged rats. Of these age effects, only N-methyl-D-aspartate binding in the striatum and [3H]kainate binding in the CA3 region of the hippocampus were correlated with spatial learning, with lower binding in the aged rats associated with better spatial learning ability. Age-related alterations in ionotropic glutamate receptors differ with respect to the receptor subtype and anatomical region examined. The age effects were not necessarily indicative of cognitive decline, as only two age-related binding changes were correlated with spatial learning. Interestingly, in these instances, lower binding in the aged rats was associated with preserved spatial learning, suggesting a compensatory reduction in receptor binding in a subpopulation of aged rats.

Changes in [3H]AMPA and [3H]kainate binding in rat caudate-putamen and nucleus accumbens after 6-hydroxydopamine lesions of the medial forebrain bundle: an autoradiographic study

The binding parameters of [3H] alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) and [3H]kainate binding were examined in caudate-putamen and nucleus accumbens of rat striatum after unilateral lesions of the right medial forebrain bundle (MFB) using in vitro receptor autoradiography. Lesioning of the dopaminergic fibres in the MFB with 6-hydroxydopamine (6-OHDA) resulted, after one or four weeks, in a significant decrease in the levels of [3H]GBR 12935 (1-[2-diphenylmethoxy)-ethyl]-4-(3-phenylpropyl) piperazine) in ipsilateral caudate-putamen and nucleus accumbens (62 and 43%, respectively). A comparison of the dissociation constants (Kd) of [3H]AMPA and [3H]kainate binding in caudate-putamen and nucleus accumbens between control and MFB-lesioned side did not indicate any significant change. However, the maximum number of [3H]AMPA and [3H]kainate binding sites (Bmax) were significantly decreased in caudate-putamen and nucleus accumbens of the MFB-lesioned side of the brain. This decrease was between 17 and 26%. Our results suggested that at least one-fourth to one-fifth of AMPA and kainate receptors in rat caudate-putamen and nucleus accumbens are localized on the presynaptic endings of dopamine fibres that follow the MFB. A role of non-NMDA glutamate receptors in the presynaptic regulation of dopamine release in rat striatum is therefore supported.

Unilateral frontal cortex ablation producing neglect causes time-dependent changes in striatal glutamate receptors

This study's goal is to identify adaptations involving striatal glutamate (GLU) or dopamine (DA) receptors that may contribute to recovery of function following cortical injury. Unilateral aspiration of the medial agranular region of frontal cortex (AGm) in rats produces neglect of contralateral stimuli. Pharmacological and immunocytochemical studies suggest that glutamatergic and dopaminergic processes within striatum may contribute to spontaneous recovery from this neglect. This study examined by autoradiography radioligand binding to striatal GLU and DA receptor subfamilies in AGm-ablated rats surviving 5 days (unrecovered) or 3 or more weeks (recovered) postsurgery. Density of radioligand binding was quantified in striatal subregions by computerized image analysis. Compared to striatal binding densities in the intact hemisphere, [3H]kainate binding and [3H]GLU binding to NMDA receptors were decreased in the lesioned hemisphere of unrecovered AGm-ablated rats, but normalized (for kainate) or increased (for NMDA) in the lesioned hemisphere of recovered rats. Ablation of AGm did not affect [3H]AMPA binding or the binding of [3H]SCH23390, [3H]spiperone, or [3H]mazindol to dopaminergic D1 or D2 receptor subfamilies, or to DA uptake sites, respectively. The results suggest that a small percentage of NMDA and kainate receptors are located on corticostriatal axon terminals, and that over time an upregulation of striatal NMDA and/or kainate receptors may offset the loss of cortical glutamatergic input caused by cortical injury. These time-dependent alterations in GLU receptors may contribute to the recovery of function and normalizations of immediate early gene expression seen weeks after AGm ablation. Upregulation of striatal dopamine receptors was not evident, and thus is unlikely to mediate recovery from neglect produced by cortical injury.

Acute treatment with the N-methyl-D-aspartate receptor antagonist MK-801: effect of concurrent administration of haloperidol or scopolamine on preproenkephalin mRNA levels of the striatum and nucleus accumbens of the rat brain

We injected rats three times at 3 h intervals (from 0900 h to 1500 h) with the N-methyl-D-aspartate (NMDA) receptor antagonist MK-801 at 0.1 or 0.5 mg/kg of body weight. Three hours after the last injection, animals were sacrificed and the brains were processed for in situ hybridization histochemistry. Preproenkephalin (PPE) mRNA levels were significantly decreased throughout the caudate-putamen (CPu) and nucleus accumbens (NAc) at the lower dose. The higher dose produced significant decreases only in anterior CPu (aCPu) and NAc. Concurrent administration of the muscarinic cholinergic receptor antagonist scopolamine at 2 or 5 mg/kg neither potentiated nor prevented the effect of MK-801 on PPE mRNA levels in the neostriatum. In contrast, co-administration of haloperidol (dopamine receptor antagonist) with MK-801 blocked the effect of the latter in the NAc, and elevated PPE mRNA levels throughout the CPu. The data demonstrate that the acute effects of glutamate receptor activity on striatal and accumbal PPE mRNA expression via the NMDA receptor can be modulated by the dopaminergic system in the brain of the rat.

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.

New horizons in molecular mechanisms underlying Parkinson's disease and in our understanding of the neuroprotective effects of selegiline

There have been many claims that the selective monoamine oxidase type B (MAO-B) inhibitor selegiline may have distinct properties in slowing the progression of Parkinson's disease (PD). Degeneration of nigro-striatal dopaminergic neurons is the primary histopathological feature of PD. Although many different hypotheses have been advanced, the cause of chronic nigral cell death and the underlying mechanisms remain elusive as yet. Therefore, there is no clear knowledge regarding an understanding of the reported effects of selegiline on the progression of PD. However, there is a considerable body of indirect evidence that oxidative stress may play a role in the pathogenesis of this illness. Oxidative stress refers to cytotoxic consequences of hydrogen peroxide and oxygen-derived free radicals such as the hydroxyl radical (.OH), the superoxide anion (.O2), and nitric oxide (NO), which are generated as byproducts of normal and aberrant metabolic processes that utilize molecular oxygen. On the other hand, an increasing body of experimental data has implicated excitotoxicity as a mechanism of cell death in both acute and chronic neurological disease. One of the receptor which is particularly involved in the toxic effects of excitatory amino acids is the NMDA (N-methyl-D-aspartate) receptor. Excessive stimulation of this type of receptor by glutamic acid or NMDA agonists leads to a massive influx of calcium ions into the neuron followed by activation of a variety of calcium-dependent enzymes, impaired mitochondrial function, and the generation of free radicals. This article will consider the concept that excitotoxicity is linked with the generation of free radicals. In view of this idea it will be further discussed how selegiline might exert its neuroprotective effects via indirect actions on the polyamine binding site of the NMDA receptor. Under treatment with the MAO-B inhibitor selegiline, the degradation of putrescine via MAO, a key factor in regulating the polyamine metabolism, might be diminished in the Parkinsonian brain, which in turn would suppress the polyamine synthesis. Hence, the reported neuroprotective effect of selegiline might also receive a contribution from the diminished potentiation of the NMDA receptor by the polyamine binding site. On the other hand, since N1-acetylated spermine and spermidine are also good substrates of MAO-B, it is likely that these compounds will be present in the brain in increased concentrations. It therefore seems possible that they will exert a neuroprotective effect via an antagonistic modulation of the polyamine binding site of the NMDA receptor.

The subsensitivity of striatal glutamate receptors induced by chronic haloperidol in rats

The aim of the present study was to investigate the influence of chronic treatment with haloperidol on the contralateral head turns and rotations induced by intrastriatal agonists of NMDA and non-NMDA receptors in rats. N-Methyl-D-aspartate (NMDA, 500 ng/0.5 mu l), alpha-amino-3-hydroxy-5-methyl-4-isoxasole-propionic acid (AMPA, 1000 ng/0.5 mu l) or kainic acid (50 ng/0.5 mu l), injected into the intermediate and caudal parts of the caudate-putamen, induced contralateral head turns and rotations. Haloperidol was given to animals in a dose of ca. 1 mg/kg per day in drinking water for 6 weeks. On day 5 of withdrawal, haloperidol decreased the number of contralateral head turns, but did not significantly influence the contralateral rotations induced by NMDA, AMPA and kainic acid. At the same time, haloperidol enhanced the stereotypy induced by apomorphine (0.25 mg/kg s.c.). The present results seem to suggest that, apart from supersensitivity to dopamine, chronic treatment with haloperidol also induces subsensitivity of striatal NMDA and non-NMDA receptors.

An NMDA receptor on isolated secretory nerve endings

While the presence of post-synaptic NMDA receptors in the CNS is well-established, the present study addressed the question of whether NMDA receptors may also be present on secretory nerve endings. Using microspectrofluorometry of fura-2 loaded isolated neurohypophysial nerve endings of the rat, we found that both glutamate (EC50 = 50 microM) and NMDA (EC50 = 30 microM) induced a rapid rise in (Ca2+]i. These responses were glycine-dependent and abolished by 1 mM Mg2+, 1 microM dizocilpine, and removal of extracellular Ca2+. Responses were not significantly affected by treatment with Ca2+ channel blockers or 10 microM CNQX.

NMDA-induced glutamate and aspartate release from rat cortical pyramidal neurones: evidence for modulation by a 5-HT1A antagonist

1. We have investigated an aspect of the regulation of cortical pyramidal neurone activity. Microdialysis was used to assess whether topical application of drugs (in 10 microliter) to fill a burr hole over the frontal cortex, where part of the corticostriatal pathway originates, would change concentrations of the excitatory amino acids glutamate and aspartate in the striatum of the anaesthetized rat. 2. Topical application of N-methyl-D-aspartate (NMDA, 2 and 20 mM) dose-dependently increased glutamate and aspartate concentrations in the striatum. Coapplication of tetrodotoxin (10 microM) blocked the NMDA-evoked rise in these amino acids. A calcium-free medium, perfused through the probe also blocked the rise, indicating that it was due to an exocytotic mechanism in the striatum. 3. It was hypothesized that the rise observed was due to an increase in the activity of the corticostriatal pathway. As 5-hydroxytryptamine1A (5-HT1A) receptors are enriched on cell bodies of corticostriatal neurones, a selective 5-HT1A-antagonist (WAY 100135) was coapplied with the lower dose of NMDA. Compared to NMDA alone, coapplication of 50 microM WAY 100135 significantly increased glutamate release. This effect was sensitive to tetrodotoxin and calcium-dependent. Application of 50 microM WAY 100135 alone significantly enhanced glutamate release above baseline; this was also tested at 100 microM (not significant). 4. Compared to NMDA alone, coapplication of WAY 100135 (20 microM) significantly enhanced aspartate release; the mean value was also increased (not significantly) with 50 microM. This rise was calcium-dependent, but not tetrodotoxin-sensitive. WAY 100135 (100 microM) reduced NMDA-induced aspartate release. WAY 100135 (100 microM) reduced NMDA-induced aspartate release. Application of the drug alone had no effect on basal aspartate release.5. Coapplication of the 5-HT1A agonist, 8-OHDPAT (5 sanM) with NMDA did not affect the NMDA evoked increase in glutamate and aspartate.6. Topical application of high potassium (100 sanM) to the surface of the cortex did not result in a detectable rise in striatal glutamate or aspartate.7. Perfusion of WAY 100135 (tested at 50 microM) through the dialysis probe did not affect glutamate oraspartate concentrations.8. It was concluded that a selective 5-HT1A-antagonist can increase the activity of corticostriatal pyramidal neurones. As in Alzheimer's disease hypoactivity of pyramidal neurones almost certainly exists, a selective 5-HT1A-antagonist may be potentially useful in the treatment of the cognitive symptoms of this disease.

Attenuation of neostriatal preproenkephalin and preprotachykinin mRNA abundance by chronic treatment with the kainate/quisqualate receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione in the rat brain

The present investigation assessed the effect of chronic blockade of kainate/quisqualate binding sites with 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) on preproenkephalin (PPE) and preprotachykinin (PPT) mRNA abundance in the neostriatum of the rat brain. Daily injection of CNQX for seven consecutive days decreased PPE mRNA abundance approximately 25% below vehicle-injected controls in dorsolateral, dorsomedial, anterior caudate-putamen (dlCPu, dmCPu and aCPu, respectively) and nucleus accumbens (NAc). Similarly, PPT mRNA abundance was significantly decreased in dlCPu, dmCPu and aCPu but not in the accumbens. The data demonstrate that non-NMDA receptor activity modulates basal levels of expression of PPE and PPT mRNAs in the neostriatum of the rat brain.

Regulation of N-methyl-D-aspartate receptor-mediated calcium transport and norepinephrine release in rat hippocampus synaptosomes by polyamines

The role of polyamines (PA) synthesis in NMDA receptor-mediated 45Ca2+ fluxes and norepinephrine release was studied in rat hippocampal synaptosomes. NMDA (50 microM) caused a sharp (> 2-fold) transient increase in PA synthesis regulating enzyme, ornithine decarboxylase (ODC) activity with concomitant elevation in PA levels in the order putrescine > spermidine > spermine. ODC inhibitor, alpha-difluoromethylornithine (DFMO), and NMDA antagonist, 2-amino-5-phosphonovaleric acid (D-AP5), both blocked increases in ODC activity and PA levels. Activation of NMDA receptors induced a sharp (3 to 4-fold) and quick (15 seconds) increase in 45Ca2+ uptake by synaptosomes within 15 seconds of exposure at 37 degrees C. The efflux of 45Ca2+ and 3H-norepinephrine (NE) release at 22 degrees C from pre-loaded synaptosomes was also significantly (2 to 4-fold) enhanced by NMDA within 15 seconds. These NMDA receptor-mediated effects on calcium fluxes and NE release were blocked by NMDA receptor-antagonists (DAP-5 and MK-801) and PA synthesis inhibitor, DFMO and the DFMO inhibition nullified by exogenous putrescine. These observations establish that ODC/PA cascade play an important role in transduction of excitatory amino acid mediated signals at NMDA receptors.

Glutamate-dopamine interactions in the ventral striatum: role in locomotor activity and responding with conditioned reinforcement

Previous evidence suggests that glutamatergic limbic afferents participate in the potentiation of responding with conditioned reinforcement produced by intra-accumbens d-amphetamine. The present experiments were designed to investigate glutamate-dopamine interactions in the ventral striatum in both conditioned reinforcement and locomotor activity. Glutamate receptor agonists and antagonists were infused into the nucleus accumbens both alone and in combination with 3 micrograms d-amphetamine, and the effects of these interactions on responding with conditioned reinforcement and locomotor activity were measured. The glutamate receptor agonists NMDA, AMPA and quisqualate (agonists at the NMDA, AMPA and metabotropic glutamate receptor subtypes, respectively) and the antagonists AP5 and CNQX, (antagonists at the NMDA and AMPA receptor subtypes, respectively) were used in these investigations. These compounds were used in a dose range of 0.3 to 3 nmol, except CNQX, which was used in 0.2 to 2 nmol doses. While all agonists and antagonists increased locomotor activity when administered alone, the antagonists attenuated the locomotor response to d-amphetamine. In contrast, the agonists AMPA and quisqualate enhanced d-amphetamine-induced locomotor activity, although NMDA interfered with the effects of d-amphetamine. In the conditioned reinforcement paradigm, both the agonists and the antagonists abolished amphetamine's potentiation of responding with conditioned reinforcement, suggesting that the glutamatergic transmission of information about the conditioned reinforcer could be blocked by glutamate receptor antagonists and disrupted by administration of the agonists. The dissociation between the effects of these excitatory amino acids on amphetamine-induced locomotor activity versus their effects on amphetamine's potentiation of responding with conditioned reinforcement provides insight into the nature of the reward enhancement by accumbens dopamine versus its locomotor stimulant effects.

Localization of AMPA-selective excitatory amino acid receptor subunits in identified populations of striatal neurons

Two-color immunofluorescence histochemistry and immunohistochemistry in combination with retrograde tract-tracing techniques were used to examine the relationship of alpha-amino-3-hydroxy-5-methyl-4-isoxazole proprionic acid (AMPA)-selective glutamate receptor subunits (GluR1, GluR2/3/4c and GluR4) to identified populations of striatal projection neurons and interneurons. The majority of striatonigral and striatopallidal neurons were double-labeled for GluR2/3/4c. These findings were confirmed using calbindin to label matrix projection neurons. In contrast, immunostaining of the GluR1 subunit was not observed to co-localize with any striatal projection neurons. Striatal interneurons immunostained for parvalbumin were also labeled by antibodies directed against the GluR1 subunit. Approximately 50% of parvalbumin neurons also contained GluR2/3/4c. Somatostatin immunoreactivity did not co-localize with either the GluR1 or GluR2/3/4c subunits. GluR4-immunoreactive neurons were not observed in striatum. This study demonstrates that AMPA-selective glutamate receptors are differentially localized on subpopulations of striatal neurons and interneurons. These findings suggest that discrete striatal neuron populations may express different AMPA receptor subunit combinations which may account for their functional specificity.

NMDA and carbachol but not AMPA affect differently the release of [3H]GABA in striosome- and matrix-enriched areas of the rat striatum

The effects of alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA; 10(-3) M), N-methyl-D-aspartate (10(-3) M, in the absence of magnesium or presence of AMPA) and carbachol (10(-3) M) on the release of preloaded [3H]gamma-aminobutyric acid ([3H]GABA) from microdiscs of tissue punched out from sagittal brain slices in striosome- or matrix-enriched areas of the rat striatum have been compared. Although AMPA stimulated similarly the release of [3H]GABA in both striatal compartments, the release of [3H]GABA evoked by either N-methyl-D-aspartate (in the presence of AMPA) or carbachol was more pronounced in matrix- than in striosome-enriched areas. AMPA- and N-methyl-D-aspartate- (in the absence of magnesium) evoked responses were reduced but not abolished in the presence of tetrodotoxin (10(-6) M) in both compartments while the carbachol-evoked release of [3H]GABA was decreased by tetrodotoxin only in the matrix. The interruption of cholinergic transmission by the combined application of atropine (10(-5) M) and pempidine (10(-4) M) was without effect on the AMPA-evoked release of [3H]GABA, but it reduced the N-methyl-D-aspartate- (in the absence of magnesium or presence of AMPA) evoked release of [3H]GABA in both compartments, these reductions being of similar amplitude than those observed with tetrodotoxin.

Glutamate receptor expression in rat striatum: effect of deafferentation

The cerebral cortex is the primary source of glutamatergic afferents to the neostriatum. We used in situ hybridization to examine the effect of removal of the glutamatergic input to the striatum by unilateral frontal cortical ablation on the expression of genes encoding subunits from three families of glutamate receptors: N-methyl-D-aspartate receptors (NMDAR1, NMDAR2A, and NMDAR2B); alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) receptors (GluR1-4, flip and flop splice variants); and metabotropic receptors (mGluR1-5). Significant changes were restricted to the dorsolateral quadrant of the ipsilateral striatum, the main projection area of the sensorimotor cortex. The expression of those messages which are normally abundant, NMDAR1, NMDAR2A, GluR1-4 flop and mGluR1, 3 and 5, was decreased in the deafferented dorsolateral striatum by 10-39% at 3 days after cortical ablation and subsequently increased to 120-165% of control at 15 and 60 days. mRNAs encoding the flip isoforms of GluR1-4, mGluR2 and 4, and an alternatively spliced region of NMDAR1 (Insertion I) which are undetectable or present at low levels in the striatum were not induced by cortical ablation. In contrast, both glial fibrillary acid protein and beta-actin mRNA expression were markedly enhanced at 3 and 15 days, returning to near normal at 60 days. Striatal NMDA, AMPA and metabotropic type 1 ligand binding sites were increased as early as 3 days after cortical ablation, reached a peak at 15 days and remained increased for up to 60 days, while metabotropic type 2 binding was slightly but significantly reduced at 3 and 15 days and [3H]kainate binding did not change significantly. These results demonstrate that cortical ablation, and subsequent loss of glutamatergic afferents to the striatum, results in alterations in the expression of genes encoding glutamate receptor subunits in striatal neurons. The regulation of these genes appears to be coordinate, so that the relative abundance of the different messages is preserved.

Organization of N-methyl-D-aspartate glutamate receptor gene expression in the basal ganglia of the rat

Glutamate is an important neurotransmitter in the circuitry of the basal ganglia. Of the four pharmacological classes of receptors that may mediate the actions of glutamate, the N-methyl-D-aspartate (NMDA) type is of particular interest insofar as it has been implicated in the neural processes underlying long-term synaptic plasticity as well as excitotoxic injury. NMDA ligand binding sites are abundant in the structures of the basal ganglia, and NMDA receptors have been linked to neuronal excitability, neuropeptide gene expression, and regulation of dopamine release in these regions. NMDA receptors are believed to be heterooligomers of subunits from two families: NMDAR1, encoded by a single gene but alternatively spliced to produce eight distinct isoforms (NMDAR1A-H), and NMDAR2, encoded by four separate genes (NMDAR2A-D). We have used in situ hybridization with a total of 13 oligonucleotide probes to examine the expression of these genes in the rat basal ganglia. NMDAR1 subunits are expressed throughout the basal ganglia as well as in the rest of the brain; however, the alternatively spliced amino-terminal region Insertion I is abundantly expressed only in the subthalamic nucleus and is not detectable in the neostriatum, globus pallidus, or substantia nigra pars compacta. In contrast, expression of the carboxy terminus segment Deletion I is prominent in the striatum but is not observed in other elements of the basal ganglia. NMDAR2 subunits also exhibit differential expression: NMDAR2B is abundant in the striatum, but NMDAR2A is present within the striatum only at low levels. NMDAR2C is present in the substantia nigra pars compacta only, while NMDAR2D exhibits an unusual distribution, with high levels of expression in the substantia nigra pars compacta, the subthalamic nucleus, the globus pallidus, and the ventral pallidum. Since each isoform of the NMDAR1 and NMDAR2 subunits can confer distinct properties on the resultant NMDA receptor, these data imply that there is a high degree of regional specialization in the properties of NMDA receptors within the basal ganglia.

Excitatory amino acid receptors mediate the orofacial stereotypy elicited by dopaminergic stimulation of the ventrolateral striatum

The present experiments examined the role of excitatory amino acid receptors in the orofacial stereotypy induced by direct amphetamine microinjection into the ventrolateral striatum. In these experiments, the influence of prior intra-ventrolateral striatum treatment with various excitatory amino acid antagonists on the expression of amphetamine-stimulated oral stereotypy was observed. In all experiments, behavioral observations were conducted in the home cage using a time-sampling procedure. In the first experiment, different groups of rats received bilateral microinfusions of either kynurenic acid, 2-amino-5-phosphonopentanoic acid, 6,7-dinitroquinoxaline or dizocilpine maleate. The excitatory amino acid antagonists were administered immediately prior to bilateral microinfusions of d-amphetamine. Both N-methyl-D-aspartate and non-N-methyl-D-aspartate antagonists dose-dependently attenuated or blocked the expression of dopamine-mediated stereotypy. 2-Amino-5-phosphonopentanoic acid was the most potent of these compounds, totally suppressing stereotypy at a dose of 0.3 micrograms (equivalent to 1.5 nmol). In the second experiment, the same compounds were tested for their ability to suppress physostigmine-induced mouth movements. Cholinergic stimulation of the ventrolateral striatum has previously been shown to elicit non-directed mouth movements, quite distinguishable from stimulus-directed, amphetamine-induced biting. Excitatory amino acid antagonists were administered in the same doses prior to bilateral infusion of physostigmine (2.5 micrograms/0.5 microliters). The expression of physostigmine-induced mouth movements was for the most part not affected by excitatory amino acid antagonists, although dizocilpine maleate slightly reduced this oral behavior. In a third experiment, behavior was observed following infusion of the antagonists alone, using the same doses as in the previous experiments. No behavioral alterations were observed with the exception of a small increase in nonspecific mouth movements induced by kynurenic acid and 2-amino-5-phosphonopentanoic acid. These findings indicate that the expression of dopamine-mediated oral stereotypy, induced by amphetamine stimulation of the ventrolateral striatal region, is highly dependent on activation of striatal excitatory amino acid receptors. In contrast, oral behavior induced by cholinergic stimulation of the ventrolateral region is not mediated by glutamate input. These results are discussed in relation to the synaptic organization of neuronal elements within the striatum. Moreover, the relevance to further understanding of orofacial dyskinesias is noted.

Role of a 35 kDa fos-related antigen (FRA) in the long-term induction of striatal dynorphin expression in the 6-hydroxydopamine lesioned rat

D1 dopamine (DA) receptor agonists induce the expression of the opioid peptide dynorphin (DYN) in the striatum, an effect accentuated several fold by removing the dopaminergic innervation to the striatum (e.g., by lesioning the DA cell bodies in the substantia nigra [SN]). D1 receptor-mediated effects are thought to involve cAMP and/or phosphoinositides as second messengers. However, it is unclear what third messengers are involved in the regulation of DYN expression. The present experiments evaluated the possible role of two families of immediate-early gene (IEG) proteins, Fos and Jun, in the induction of DYN biosynthesis following repeated treatment with DA agonists. In addition, the role of N-methyl-D-aspartate (NMDA) receptors in modulating DA-induced changes in DYN and IEG protein expression was assessed. Adult male rats received unilateral 6-hydroxydopamine (6-OHDA) or sham lesions of the SN. Following a recovery period, animals were injected twice daily with the DA agonist, apomorphine (APO; 5 mg/kg), for 4 or 7 days. As expected, APO induced DYN biosynthesis, at both the peptide and mRNA level, several fold more in the striatum ipsilateral to the 6-OHDA lesion than in the contralateral control side (or a sham lesioned striatum). These effects appeared to be mediated by D1 receptors since the D1 agonist, SKF 38393 (5 mg/kg), caused the same changes in DYN expression as APO whereas a D2 agonist, quinpirole (1 mg/kg), had no effect. Paralleling the increase in DYN expression, APO also induced the expression of c-Fos and Fos-related antigens (FRA's), in particular a 35 kDa FRA, but had no effect on the expression of various Jun-related IEG proteins (i.e., c-Jun, Jun B, Jun D). Consistent with the notion that Fos and FRA proteins alter transcriptional activity by binding to AP-1 (or AP-1-like) DNA sequences in the promoter regions of target genes, we found that repeated APO treatment caused large increases in AP-1 binding activity in striata ipsilateral to 6-OHDA lesions. These data indicate that repeated activation of D1 receptors increases both the expression of a 35 kDa FRA and AP-1 binding, events which may mediate the large increases in DYN expression in the DA denervated striatum. While co-administration of the NMDA receptor antagonist, MK-801, inhibited APO-induced increases in DYN and Fos/FRA expression in the intact striatum, its only effect in the DA-denervated striatum was a partial (35%) inhibition of the APO-induced increase in DYN-ir concentrations.(ABSTRACT TRUNCATED AT 400 WORDS)

Receptor function in cortical rat brain regions after lesion of nucleus basalis

The present study was undertaken to study the interaction of cholinergic and glutamatergic mechanisms in cholinoceptive cortical target regions which is assumed to play an important role for realizing cognitive functions. The densities of cortical muscarinic cholinergic receptor subtypes and corresponding receptor genes m1 through m4, as well as NMDA, AMPA and kainate glutamate receptor subtypes were measured in rats one week after unilateral mechanical lesion of the anterior part of the nucleus basalis magnocellularis (NbM) applying quantitative receptor autoradiography and in situ hybridization. The studies revealed that in cortical regions displaying a low amount of acetylcholinesterase activity due to forebrain cholinergic lesion, NMDA receptor binding was markedly reduced in comparison to the unlesioned side, whereas AMPA and kainate binding has been significantly increased in these regions. M1-muscarinic cholinergic receptor binding was not changed in any of the cortical regions studied, whereas M2-receptor densities are slightly reduced in frontal and parietal cortices following lesion. These alterations in cortical M2-muscarinic receptor binding are complemented by corresponding changes in the m2- and m4-mRNA transcripts. The comparison of binding profiles through selected cortical regions of both lesioned and normal brain side revealed that lesion of the NbM affects NMDA receptors in all cortical layers of the lesioned side, whereas AMPA receptors are affected preferentially in the upper and kainate receptors preferentially in the middle and deeper cortical layers. The differential changes in glutamate receptor subtypes following lesion might be regarded as the consequence of a cortical reorganization compensating for the reduced cholinergic presynaptic input. The data further suggest that presynaptic cortical cholinergic deficits might affect glutamatergic functions with different intensity and different directions.

Localisation of muscarinic (m1) and other neurotransmitter receptors on corticofugal-projecting pyramidal neurones

Experimental lesions and quantitative autoradiography were used to investigate the cellular localisation of receptors. Lesions were produced by intrastriatal injections of either volkensin or ricin, only the former is retrogradely transported. Volkensin treatment caused significant losses in Fr1/Fr2 of neocortex in the number of infragranular pyramidal neurones and binding to deep cortical layers of both [3H]pirenzepine (muscarinic cholinergic m1 receptors) and [3H]kainate (kainate sensitive glutamate receptors). In common with previous findings, which also showed sparing of interneurones, supragranular pyramidal neurones were not reduced in number and the binding to deep cortical layers of [3H]8-hydroxy-2-(n-dipropylamino)tetralin (serotonin 1A receptors) was reduced. Significant increases in [3H]prazosin binding to both total alpha adrenoceptors and the alpha 1b subtype were observed in superficial layers. Adrenoceptors were not decreased in any layer. The binding of [3H] GABA to GABAA receptors was not affected at all. Muscarinic receptors and pyramidal neurones were also reduced in deep cortical layers of Par1/Par2 in common with serotonin 1A (5-HT1A) receptors and total alpha receptors were significantly decreased in the middle layers. Overall m1 and kainate receptors were less affected than 5-HT1A receptors. The results are discussed in terms of the biology of cortical pyramidal neurones, drugs for Alzheimer's disease and novel ligands for improving human brain in vivo scanning techniques.

NMDA and AMPA receptors in transgenic mice expressing human beta-amyloid protein

The human beta-amyloid protein may play an important, possibly primary, role in the pathogenesis of Alzheimer's disease (AD), and it appears to potentiate the susceptibility of neurons to excitotoxicity. AD is associated with alterations in the N-methyl-D-aspartate (NMDA) and alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) subtypes of glutamate receptors, and it has been suggested that excitotoxicity may play a role in neuronal damage in AD. In this study, we have used quantitative receptor autoradiography to examine NMDA and AMPA receptors in transgenic mice that contain the gene for the carboxyl-terminal 100 amino acids of the human amyloid precursor protein, beginning with the beta-amyloid region, which is under the control of the JC viral early region promoter. Reverse transcriptase-polymerase chain reaction confirmed that the brains of transgenic mice expressed beta-amyloid mRNA and that control mice did not. NMDA receptors, assessed with [3H]MK-801, were unchanged in the transgenic compared with the control mice. In the transgenic mice, there were no significant changes in [3H]AMPA receptor binding compared with controls. This study represents the first attempt to evaluate in transgenic mice the in vivo interaction between beta-amyloid expression and excitatory amino acid receptors.

Local GABAergic regulation of the N-methyl-D-aspartate-evoked release of dopamine is more prominent in striosomes than in matrix of the rat striatum

Using an in vitro microsuperfusion device we have previously demonstrated that in the absence of magnesium, the N-methyl-D-aspartate-evoked release of [3H]dopamine (continuously synthesized from [3H]tyrosine) is more prominent in matrix- than in striosome-enriched areas of the rat striatum and that in the matrix, the response is partially tetrodotoxin-sensitive. Since the medium-sized GABAergic neurons are the main targets of the corticostriatal glutamatergic fibers, the involvement of local GABAergic regulation in the N-methyl-D-aspartate-evoked release of [3H]dopamine was investigated in both striatal compartments using the same experimental approach. Firstly, bicuculline alone (5 microM, 25-min application) was shown to enhance the release of [3H]dopamine similarly in both compartments revealing the existence of a tonic GABAergic control of the spontaneous release of [3H]dopamine. Secondly, the N-methyl-D-aspartate (50 microM, 25-min application)-evoked release of [3H]dopamine was markedly amplified in the presence of bicuculline (5 microM, continuous delivery). This effect being more important in striosome- than in matrix-enriched areas (5.5- and two-times the N-methyl-D-aspartate-evoked response observed in the absence of the GABAA antagonist, respectively). Thirdly, the tetrodotoxin (1 microM, continuous delivery)-resistant N-methyl-D-aspartate-evoked responses were also enhanced in the presence of bicuculline, but in this case, the amplification of the N-methyl-D-aspartate-evoked release of [3H]dopamine was less marked than in the absence of tetrodotoxin and identical in both compartments (about two-times the tetrodotoxin-resistant N-methyl-D-aspartate-evoked responses observed in the absence of bicuculline). Altogether, these results indicate that GABAergic neurons exert locally an important inhibitory regulation of the N-methyl-D-aspartate-evoked release of dopamine and that this effect is more prominent in the striosome-enriched area. Both tetrodotoxin-sensitive (striosome) and tetrodotoxin-resistant (striosome and matrix) processes intervene in this inhibitory GABAergic presynaptic regulation of dopamine release.

The chemical nature of the main central excitatory transmitter: a critical appraisal based upon release studies and synaptic vesicle localization

The chemical nature of the central transmitter responsible for fast excitatory events and other related phenomena is analysed against the historical background that has progressively clarified the structure and function of central synapses. One of the problems posed by research in this field has been whether one or more of the numerous excitatory substances endogenous to the brain is responsible for fast excitatory synaptic transmission, or if such a substance is, or was, a previously unknown one. The second question is related to the presence in the CNS of three main receptor types related to fast excitatory transmission, the so-called alpha-amino-3-hydroxy-5-methylisoxazole propionic acid, kainate and N-methyl-D-aspartate receptors. This implies the possibility that each receptor type might have its own endogenous agonist, as has sometimes been suggested. To answer such questions, an analysis was done of how different endogenous substances, including L-glutamate, L-aspartate, L-cysteate, L-homocysteate, L-cysteine sulfinate, L-homocysteine sulfinate, N-acetyl-L-aspartyl glutamate, quinolinate, L-sulfoserine, S-sulfo-L-cysteine, as well as possible unknown compounds, were able to fulfil the more important criteria for transmitter identification, namely identity of action, induced release, and presence in synaptic vesicles. The conclusion of this analysis is that glutamate is clearly the main central excitatory transmitter, because it acts on all three of the excitatory receptors, it is released by exocytosis and, above all, it is present in synaptic vesicles in a very high concentration, comparable to the estimated number of acetylcholine molecules in a quantum, i.e. 6000 molecules. Regarding a possible transmitter role for aspartate, for which a large body of evidence has been presented, it seems, when this evidence is carefully scrutinized, that it is either inconclusive, or else negative. This suggests that aspartate is not a classical central excitatory transmitter. From this analysis, it is suggested that the terms alpha-amino-3-hydroxy-5-methylisoxazole propionic acid, kainate and N-methyl-D-aspartate receptors, should be changed to that of glutamate receptors, and, more specifically, to GLUA, GLUK and GLUN receptors, respectively. When subtypes are described, a Roman numeral may be added, as in GLUNI, GLUNII, and so on.

Inhibition of succinate dehydrogenase by malonic acid produces an "excitotoxic" lesion in rat striatum

Excitotoxicity and defects in neuronal energy metabolism have both been implicated in the pathogenesis of neurodegenerative disease. These two mechanisms may be linked through the NMDA receptor, activation of which is dependent on neuronal membrane potential. Because the ability to maintain membrane potential is dependent on neuronal energy metabolism, bioenergetic defects may affect NMDA receptor-mediated excitotoxicity. We now report that reversible inhibition of succinate dehydrogenase (SDH), an enzyme central to both the tricarboxylic acid cycle and the electron transport chain, produces an "excitotoxic" lesion in rat striatum that can be blocked by the NMDA antagonist MK-801. Male Sprague-Dawley rats received intrastriatal stereotaxic injections of the SDH inhibitor malonic acid (1 or 2 mumol) in combination with intraperitoneal injections of vehicle or MK-801 (5 mg/kg) 30 min before and 210 min after malonic acid. Animals were killed 72 h after surgery, and brains were processed for histology, cytochrome oxidase activity, and [3H]MK-801 and [3H]AMPA autoradiography. The higher dose of malonic acid (2 mumol) produced large lesions that were markedly attenuated by treatment with MK-801 (28.1 +/- 3.6 vs. 4.7 +/- 2.6 mm3; p < 0.001). [3H]MK-801 and [3H]AMPA binding were reduced in the lesions by 60 and 63%, respectively. One micromole of malonic acid produced smaller lesions that were almost completely blocked by MK-801 treatment (9.6 +/- 1.3 vs. 0.06 +/- 0.04 mm3; p < 0.0001). The toxic effects of malonic acid were due specifically to inhibition of SDH inasmuch as coinjection of a threefold excess of succinate with the malonic acid blocked the striatal lesions (p < 0.002).(ABSTRACT TRUNCATED AT 250 WORDS)

Development of NMDA receptor-channel complex and L-type calcium channels in mouse hippocampus

In vitro binding autoradiography was used to examine the pattern and intensity of binding of [3H]glutamate to NMDA receptors, [3H]MK 801 to NMDA receptor associated channels, and [3H]PN-200 110 to L-type calcium channels in the hippocampus of mice aged 3-70 days. The distribution of NMDA receptors and NMDA receptor associated channels was similar but not identical at the tested ages. Beginning with postnatal day 8, high binding levels were confined mostly to the hippocampal strata: the oriens and radiatum (CA1 and CA3 with [3H]MK 801 labeling but only CA1 with NMDA displaced [3H]glutamate labeling), the moleculare (higher labeling with [3H]MK 801 than with NMDA displaced [3H]glutamate binding), and the lucidum. The binding values for NMDA receptor-channel complex rose in the examined period (especially within the second and third week), reaching a plateau at the end of the third postnatal week. Sharp growth of binding within the second and third week of life was about 50% greater with [3H]MK 801 than with NMDA displaced [3H] glutamate labeling. L-type calcium channels were found to be most abundant in the strata: the oriens of the CA3 field, the moleculare, and the lucidum. The time course of binding value changes for the calcium channel was similar to the time course found for the NMDA receptor-channel complex.

N-methyl-D-aspartic acid differentially regulates extracellular dopamine, GABA, and glutamate levels in the dorsolateral neostriatum of the halothane-anesthetized rat: an in vivo microdialysis study

The effects of local perfusion with the glutamate receptor agonist NMDA and the noncompetitive NMDA receptor antagonist dizolcipine (MK-801) on extracellular dopamine (DA), GABA, and glutamate (Glu) levels in the dorsolateral striatum were monitored using in vivo microdialysis in the halothane-anesthetized rat. In addition, the sensitivity of both the basal and NMDA-induced increases in levels of these neurotransmitter substances to perfusion with tetrodotoxin (TTX: 10(-5) M) and a low Ca2+ concentration (0.1 mM) was studied. The results show that the local perfusion (10 min) with both the 10(-3) and 10(-4) M dose of NMDA increased striatal DA and GABA outflow, whereas only the (10(-3) M) dose of NMDA was associated with a small and delayed increase in extracellular Glu levels. The NMDA-induced effects were dose-dependently counteracted by simultaneous perfusion with MK-801 (10(-6) and 10(-5) M). Both the basal and NMDA (10(-3) M)-induced increase in extracellular striatal DA content was reduced in the presence of TTX and a low Ca2+ concentration, whereas both basal and NMDA-stimulated GABA levels were unaffected by these treatments. Both the basal and NMDA-stimulated Glu levels were enhanced following TTX treatment, whereas perfusion with a low Ca2+ concentration reduced basal Glu levels and enhanced and prolonged the NMDA-induced stimulation. These data support the view that NMDA receptor stimulation plays a role in the regulation of extracellular DA, GABA, and Glu levels in the dorso-lateral neostriatum and provide evidence for a differential effect of NMDA receptor stimulation on these three striatal neurotransmitter systems, possibly reflecting direct and indirect actions mediated via striatal NMDA receptors.

AMPA glutamate receptor subunits are differentially distributed in rat brain

To demonstrate the regional, cellular and subcellular distributions of non-N-methyl-D-aspartate glutamate receptors in rat brain, we generated antipeptide antibodies that recognize the C-terminal domains of individual subunits of the alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA)-preferring glutamate receptors (i.e. GluR1, GluR4, and a region highly conserved in GluR2, GluR3 and GluR4c). On immunoblots, antibodies detect distinct proteins with mol. wts ranging from 102,000 to 108,000 in homogenates of rat brain. Immunocytochemistry shows that glutamate receptor subunits are distributed abundantly and differentially within neuronal cell bodies and processes in cerebral cortex, basal ganglia, limbic system, thalamus, cerebellum and brainstem. The precise patterns and cellular localizations of glutamate receptor subunit immunoreactivities are unique for each antibody. In neocortex and hippocampus, pyramidal neurons express GluR1 and GluR2/3/4c immunoreactivities; many non-pyramidal, calcium-binding, protein-enriched neurons in cerebral cortex are selectively immunoreactive for GluR1. In striatum, the cellular localizations of GluR1, GluR2/3/4c and GluR4 immunoreactivities are different; in this region, GluR1 co-localizes with many cholinergic neurons but is only present in a minor proportion of nicotinamide adenine dinucleotide phosphate diaphorase-positive striatal neurons. GluR1 co-localizes with most dopaminergic neurons within the substantia nigra. In several brain regions, astrocytes show GluR4 immunoreactivity. Within the cerebellar cortex, cell bodies and processes of Bergmann glia express intense GluR4 and GluR1 immunoreactivities; perikarya and dendrites of Purkinje cells show GluR2/3/4c immunoreactivity but no evidence of GluR1 or GluR4. Ultrastructurally, GluR subunit immunoreactivities are localized within cell bodies, dendrites and dendritic spines of specific subsets of neurons and, in the case of GluR1 and GluR4, in some populations of astrocytes. This investigation demonstrates that individual AMPA-preferring glutamate receptor subunits are distributed differentially in the brain and suggests that specific neurons and glial cells selectively express glutamate receptors composed of different subunit combinations. Thus, the co-expression of all AMPA receptor subunits within individual cells may not be obligatory for the functions of this glutamate receptor in vivo.