Ganglioside GM1 preventsN-methyl-d-aspartate neurotoxicity in rabbit hippocampus in vivo

Microdialysis was used to apply 1 mM N-methyl-d-aspartate (NMDA) for 20 min to the hippocampus of rabbits, control and pretreated with GM1 ganglioside (im injections of 30 mg/kg for 3d, twice a day). Concentrations of ionized Ca²⁺ and 6-keto prostaglandin F_1α (6-keto PGF_1α)-immunoreactive material in the dialyzates and⁴⁵Ca and [¹⁴C]sucrose efflux from the prelabeled hippocampus were determined. After 24 h, the morphology of the hippocampal neurons was examined. In control animals, the application of NMDA resulted in 25% decrease in Ca²⁺ concentration and in 1000% increase in 6-keto PGF_1α concentration in the dialyzates. A 30% decrease in⁴⁵Ca efflux was accompanied by 20% increase in [¹⁴C]sucrose efflux, reflecting a corresponding reduction of the extracellular space volume. A degeneration of CA1 pyramidal neurons in the vicinity of a microdialysis probe was observed. In GM1-treated rabbits the NMDA-induced decrease in Ca²⁺ concentrations in the dialyzates was not reduced significantly, whereas a 70% stimulation of⁴⁵Ca efflux was noted, with a concomitant 40% reduction of 6-keto-PG F_1α release. NMDA-evoked increase in [¹⁴C]sucrose efflux did not differ from the control. In these animals CA1 neurons were well preserved. These results indicate that the pretreatment with GM1 results in activation of calcium extrusion from the NMDA-stimulated rabbit hippocampal neurons that alleviates destabilization of calcium homeostasis and reduces NMDA-evoked neuronal injury.     

NMDA-induced increase in [Ca]i andCa uptake in acutely dissociated brain cells derived from adult rats

A preparation of acutely dissociated brain cells derived from adult (3-month-old) rat has been developed under conditions preserving the metabolic integrity of the cells and the function of N-methyl-d-aspartate (NMDA) receptors. The effects of glutamate and NMDA on [Ca²⁺]_i measured with fluo3 and⁴⁵Ca²⁺ uptake have been studied on preparations derived from hippocampus and cerebral cortex. Glutamate (100 μM) and N-methyl-dl-aspartate (200 μM) increased [Ca²⁺]_i by 26-12 nM and 23-9 nM after 90 s in cerebral cortex and hippocampus, and stimulated⁴⁵Ca²⁺ uptake about 16–10% in the same regions. The increases in [Ca²⁺]_i and⁴⁵Ca²⁺ uptake were inhibited by 40% in the presence of 1 mM MgCl₂ and by 90–50% in the presence of MK-801. The results indicate (a) that a large fraction of the [Ca²⁺]_i response to glutamate in freshly dissociated brain cells from the adult rat involves NMDA receptors, (b) when compared with results in newborn rats, there is a substantial blunting of the [Ca²⁺]_i increase in adult age.     

Differential inhibition by ferrous ions of [H]MK-801 binding to native N-methyl- -aspartate channel in neonatal and adult rat brains

In vitro addition or pretreatment with ≥1 μM ferrous chloride markedly inhibited in a concentration-dependent manner [³H]dizocilpine (MK-801) binding to an open ion channel associated with the N-methyl- -aspartate (NMDA) receptor in rat brain synaptic membranes. The addition of NMDA agonists invariably attenuated the inhibition of [³H]MK-801 binding in hippocampal synaptic membranes previously treated with ferrous chloride, without significantly affecting that in cerebellar synaptic membranes. In the absence of spermidine, ferrous chloride was more potent in inhibiting binding in the cerebral cortex and hippocampus in adult rats than in those in rats at 3 days after birth, while in the striatum [³H]MK-801 binding was 10 times more sensitive to inhibition by added ferrous chloride in neonatal rats than in adult rats. Addition of spermidine significantly attenuated the potency of ferrous chloride to inhibit binding in the cerebral cortex of adult rats, with facilitation of the inhibition in newborn rats. Moreover, spermidine significantly reduced the inhibitory potency of ferrous chloride in neonatal rat striatum, without markedly affecting that in adult rat striatum. These results suggest that ferrous ions may interfere with opening processes of the native NMDA channel through molecular mechanisms peculiar to neuronal development in a manner associated with the polyamine recognition domain.     

Evidence that ibogaine releases dopamine from the cytoplasmic pool in isolated mouse striatum

Summary We measured the effect of ibogaine on the tritium efflux from isolated mouse striatum preloaded with [³H]dopamine ([³H]DA). Ibogaine increased the basal tritium outflow in a concentration-dependent manner, but it was without effect on electrical stimulation-induced tritium overflow. Separation of the released radioactivity after ibogaine administration showed that this drug increased the release of [³H]DA and [³H]-dihydroxyphenylacetic acid ([³H]DOPAC), but the efflux of O-methylated-deaminated metabolites was not changed. The dopamine (DA)-releasing effect of ibogaine was reduced by the DA uptake inhibitors cocaine and nomifensine. The tritium efflux evoked by ibogaine was not altered by omission of Ca²⁺ from the perfusion buffer or by inhibition of the voltage-sensitive Na⁺ channels with tetrodotoxin. Ibogaine maintained its effect on release from superfused striatum prepared from reserpine-pretreated mice. The ibogaine-induced tritium release measured from mouse striatum that was preloaded with [³H]DA was not affected by the D-2 DA receptor ligands (–)-quinpirole and (+/–)-sulpiride, indicating that the ibogaine-induced release is not subject to presynaptic autoreceptor regulation. Ibogaine failed to affect [³H]DA uptake and retention in mouse striatum. These data indicate that at the nerve terminal level ibogaine releases DA, and the primary source for the release is probably the cytoplasmic pool. The DA-releasing effect of ibogaine may have importance in mediation of its hallucinogenic action, as seen in a frequent practice in African cults.     

The entry of [1-C]glucose into biochemical pathways reveals a complex compartmentation and metabolite trafficking between glia and neurons: a study by C-NMR spectroscopy

Glial–neuronal interactions were investigated in rats injected intraperitoneally with [1-¹³C]glucose and killed after 15, 30, 45, or 60 min. Brain extracts were analyzed by ¹³C-NMR spectroscopy and the fractional ¹³C-enrichment at individual carbon positions was measured for amino acids, lactate, and N-acetyl-aspartate. [1-¹³C]Glucose was shown to be metabolized by both neurons and glia, with the anaplerotic pathway through pyruvate carboxylase (PC) accounting for 10% of total cerebral glucose metabolism. The PC-mediated pathway accounted for 39% of the glutamine synthesis, and for 8, 6, 14% of glutamate, GABA, and aspartate synthesis, respectively. These results reflect a compartmentation of the cerebral amino acids synthesis within glial and neuronal cells. The appearance of the ¹³C-label in C5 of glutamate and glutamine, C1 of GABA and C2 of lactate, is suggestive of pyruvate, formation from TCA cycle intermediates and provides evidence of metabolite trafficking between astrocytes and neurons.     

Studies on the relationship between Ca efflux from mitochondria and the release of amino acid neurotransmitters

It is known that transmitter release depends upon the entry of calcium ions into the synaptic terminal. Mitochondria have been suggested to play a key role on the regulation of intracellular Ca²⁺ concentration, thereby influencing transmitter liberation and synaptic transmission. Here we report the stimulatory effect of DNP and FCCP, uncouplers of oxidative phosphorylation, and quinidine, known to induce muscle contractures and increase Ca²⁺ efflux from muscle mitochondria, on both [¹⁴C]glutamic acid and [³H]GABA unstimulated release from synaptosomes and loss of⁴⁵Ca²⁺ from preloaded whole brain mitochondria. Results showed that the spontaneous efflux of non-putative neurotransmitters, leucine and α-aminoisobutyric acid, was less affected or not stimulated at all, under similar experimental conditions. Data suggest that calcium ions released from mitochondria are able to trigger neurotransmitter release.     

Differential regulation of dopamine release by N-methyl-d-aspartate receptors in rat striatum after partial and extreme lesions of the nigro-striatal pathway

The participation of N-methyl-d-aspartate (NMDA) receptors on dopamine (DA) efflux in the striatum of anaesthetized rats, which had their DA nigrostriatal pathway previously lesioned with different doses of 6-hydroxydopamine (6-OH-DA), was assessed by in vivo microdialysis methodology. In addition, the in vivo basal DA and dihydroxy-phenyl-acetic acid (DOPAC) effluxes and the effect of local K⁺-depolarization on DA release were also evaluated in the striatum of these 6-OH-DA treated rats. Lesioned rats were divided in three groups corresponding to animals with 25–75%, 75–95% and >95% of striatum tissue DA depletion, respectively. Striatal DA tissue depletion between 25–75% occurred in parallel with a 30% reduction in DA extracellular levels, with a moderate 10% increase in basal fractional DA efflux, and with no statistical changes in the fractional DA efflux induced by NMDA (500 μM) receptor stimulation by reverse dialysis. Rats with higher DA tissue depletion (between 75–95%) exhibited a 60% reduction in DA extracellular levels in the striatum and this reduction occurred in parallel with a modest rise in basal fractional DA efflux, but with a striking decrease in the NMDA-induced fractional DA efflux. In rats with extreme or >95% of striatal DA tissue depletion, basal fractional DA efflux in the striatum increased quite substantially along with a recovery in the ability of NMDA receptor stimulation to induce fractional DA release. The >95% striatal DA-depleted rats also exhibited a significant decrease in tissue and extracellular DOPAC/DA ratio when compared to sham and partially DA-depleted rats. In contrast to the previous results, fractional DA efflux induced by reverse dialysis with K⁺ (40 mM) remained the same in the striatum of sham and all groups of DA-tissue depleted rats. The present findings suggest the existence of at least three features associated to the regulation of basal and NMDA-induced extracellular levels of DA in the striatum of rats as a function of striatal tissue DA depletion produced by 6-OH-DA. They also support the view that a differential regulation of basal and NMDA-induced DA extracellular levels occur in partial and extreme DA-depleted striatum after 6-OH-DA treatment. Such findings may have implications as regard to the participation of the NMDA receptor in the compensatory mechanisms associated to the progress of Parkinson's disease, as well as in the therapeutic treatment of this neurological disorder.     

Cortical release of labeled compounds during arousal in the cat: correlations with carbon dioxide, brain temperature and EEG.

The release of ⁴⁵Ca²⁺, ³H₂O, [¹⁴C]-carboxyl-inulin, [³H]-γ-aminobutyric acid, [¹⁴C]-taurine, [³H]-5-hydroxytryptamine, [³H]-norepinephrine and [³H]-lysine from cerebral cortex into a superfusion medium has been studied in vivo, using locally anesthetized, immobilized cats. Peaks in the rate of release of all these compounds from the suprasylvian gyrus could be correlated with a diminished amplitude of the cortical EEG and with increases in brain temperature and levels of CO₂ in alveolar air. Peaks correlated with pCO₂ could still be observed after the topical application of 5 × 10^?4 NaCN. Death, produced by an overdose of pentobarbital, resulted in a 45% drop in the release of ⁴⁵Ca²⁺ and ³H-GABA followed by irregular peaks in efflux. Superfusion of the cortical surface with a low Ca²⁺ medium resulted in very regular oscillations in the efflux of a number of isotopes including ⁴⁵Ca and ³H₂O. These oscillations, which had a period of about 6 min, were best observed immediately before or after a train of seizures, while the efflux pattern during seizures was slightly more irregular. The ratio of ⁴⁵Ca²⁺ and ³H₂O released at this time also rose and fell in phase with the oscillations in efflux. At each individual seizure, the Ca/³H₂O ratio fell to a minimum. On two occasions marked long term changes in the amplitude of the EEG were observed to correlate with a change in the amplitude of the oscillations. Hemodynamic factors are considered to affect the rate of release of isotopes into the superfusate but cortical metabolism is also likely to play a role in controlling the rate of release, especially during the oscillations in efflux in low calcium media.     

Possible role of surface potential in the gating mechanism of Ca channels in cat adrenal chromaffin cells: studies with fura-2 microfluorometry

The cytosolic free Ca²⁺ concentration ([Ca]_in) in isolated cat chromaffin cells was measured by fura-2 microfluorometry. During 30 mM KCl depolarization or sucrose substitution for NaCl, a reduction in external Ca²⁺ concentration under optimal conditions paradoxically caused a rise in [Ca]_in and, in separate experiments, in catecholamine secretion. The results support a previously suggested role of surface potentials in the gating mechanism of Ca²⁺ channels.     

Comparative studies on binding of 3 different ligands to theN-methyl-d-aspartate recognition domain in brain synaptic membranes treated with Triton X-100

Treatment with a low concentration of Triton X-100 almost tripled the binding of [³H]d,l-(E)-2-amino-4-propyl-5-phosphono-3-pentenoic acid (CGP 39653), a novel competetive antagonist at anN-methyl-d-aspartate (NMDA)-sensitive subclass of brain excitatory amino acid receptors, in synaptic membranes of the rat brain. The binding linearly increased with increasing protein concentrations of up to 0.4 mg/ml and also increased in proportion to incubation time with a plateau within 60 min after the initiation of incubation at 2°C in Triton-treated membranes. Elevation of incubation temperature from 2°C to 30°C resulted in a marked decrease in the binding at equilibrium by 80%, and a maximal level was obtained within 1 min after the initiation of incubation at 30°C with a gradual decline of up to 10 min. Bound [³H]CGP 39653 was rapidly dissociated by the addition of excess unlabeledl-glutamic acid (Glu), and the time required to attain complete dissociation was 60 min at 2°C and 1 min at 30°C, respectively. Among several agonists and antagonists tested, Glu was the most potent displacer of [³H]CGP 39653 binding with progressively less potent displacement byd-2-amino-5-phosphonovaleric,(±)-3-(2-carboxypiperain-4-yl)propyl-1-phosphonic (CPP),d-2-amino-7-phosphonoheptanoic,N-methyl-d-aspartic andN-methyl-l-aspartic acids. Agonists at the glycine (Gly) domain on the NMDA receptor ionophore complex invariably inhibited the binding of [³H]CGP 39653 without virtually affecting the binding of [³H]CPP or [³H]Glu in a manner that was sensitive to antagonism by 4 different antagonists at the Gly domain. In contrast, the Gly antagonist 1-hydroxy-3-aminopyrrolidone-2 markedly potentiated [³H]CPP binding with the binding of both [³H]CGP 39653 and [³H]Glu being unaltered. These results suggest that [³H]CGP 39653 may predominantly label an antagonist-preferring form of the NMDA domain in a state different from that favorable to labeling by [³H]CPP.     

Blockade ofCa influx through theN-methyl-d-aspartate receptor ion channel by the non-psychoactive cannabinoid HU-211

The effects of the synthetic non-psychoactive cannabinoid(+)-(3S,4S)-7-hydroxy-Δ⁶-tetrahydrocannabinol 1,1-dimethylheptyl (HU-211) on the activity of theN-methyl-d-aspartate (NMDA) receptor/ion channel were examined. HU-211 non-competitively blocks the increase in binding of[³H]N-[1-(2-thienyl)-cyclohexyl]piperidine ([³H]TCP) induced by the polyamines spermine and spermidine or by glutamate and glycine. HU-211 does not, however, affect the direct binding of [³H]glycine and [³H]glutamate to their binding sites on the NMDA receptor, which suggests that the effects of HU-211 are not mediated via the binding sites of glutamate-, glycine- and phencyclidine-like drugs or of polyamines. HU-211 can also block⁴⁵Ca²⁺ uptake through the NMDA-receptor/ion channel in primary cell cultures of rat forebrain. All of the above inhibitory effects of HU-211 on the NMDA-receptor/ion channel activity are stereospecific, since the(−)(3R,4R) enantiomer (HU-210) is ineffective.     

4-Aminopyridine differentially affects the spontaneous release of radiolabelled transmitters from rat brain slices in vitro

4-Aminopyridine increased the release of [³H]noradrenaline from dorsal hippocampus slices in vitro in a concentration-dependent manner. When the slices were exposed to 4-aminopyridine for 5 min, the overflow of radioactivity returned to pre-exposure values within 20–25 min. When the exposure of the slices was continued, a sustained enhancement of the release of [³H]noradrenaline was observed for the duration of the exposure. 4-Aminopyridine, 10⁻⁴ M, had an effect of similar magnitude, or an even more pronounced effect, on the release of [³H]catecholamine from cortex, septum, periaqueductal gray and striatum slices. The effects of the compound on the release of [³H]5-hydroxytryptamine and [¹⁴C]acetylcholine were less pronounced. At this concentration 4-aminopyridine had no effect on the release of [³H]D-aspartate from hippocampus or septum slices, whereas the effect on the release of this transmitter in striatal slices was marginal. The effect of 4-aminopyridine on the release of [³H]noradrenaline in hippocampus slices was largely dependent on the presence of Ca²⁺ in the superfusion medium. This was also the case for the effect on the release of [³H]noradrenaline from preloaded dorsal hippocampus synaptosomes. In the presence of nitrendipine the effect of 4-aminopyridine was dose-dependently reduced, but the maximal reduction, at a nitrendipine concentration of 10⁻⁴ M, was only 40%. Cd²⁺ completely abolished the effect of 4-aminopyridine on the release of [³H]noradrenaline. These results confirm that the enhancing effect of 4-aminopyridine on the release of [³H]noradrenaline depends on the entry of extracellular Ca²⁺ into the nerve terminals. That the magnitude of the effect of 4-aminopyridine differs per neurotransmitters and is particularly small or even absent for [³H]d-aspartate supposedly reflects differences in the kinetics of Ca²⁺ entry into the terminals.     

On the mechanism of enhanced release of [C]glutamate in hippocampal long-term potentiation

K⁺-induced release of [¹⁴C]glutamate was studied in slices of dentate gyrus prepared from control rats and rats in which long-term potentiation (LTP) had been induced in vivo. At all concentrations of Ca²⁺ studied, release from potentiated slices was greater than from control slices. In the same preparations both Ruthenium Red and caffeine enhanced basal release but in potentiated tissue the Ruthenium Red-induced release was significantly greater than in control tissue. These results are discussed in the light of our recent finding that enhanced transmitter release is associated with LTP.     

Evidence for a striatal NMDA receptor modulation of nigral glutamate release. A dual probe microdialysis study in the awake freely moving rat

Dual probe microdialysis was employed to characterize dialysate glutamate levels from the substantia nigra pars reticulata of awake freely moving rats, and to test its sensitivity to alterations in striatal neurotransmission including striatal N-methyl-d -aspartic acid (NMDA) receptor stimulation and blockade. Intranigral perfusion with low (0.1 mm ) Ca²⁺ medium (60 min) did not affect nigral glutamate levels, whereas intranigral perfusion with tetrodotoxin (10 μm , 60 min) increased nigral glutamate levels. Perfusion of KCl (100 mm , 10 min) in the dorsolateral striatum transiently stimulated nigral glutamate levels (maximal increase + 60%), whereas intrastriatal perfusion (60 min) with low Ca²⁺ medium and tetrodotoxin gradually increased nigral glutamate levels. Intrastriatal perfusion with NMDA (0.1–100 μm , 10 min) dose-dependently stimulated glutamate levels in the substantia nigra pars reticulata. The NMDA (1 μm )-induced increase in nigral glutamate release was transient and maximal (+60% within 20 min), whereas that for NMDA (10 μm ) had a slow onset but was long lasting (+35% after 60 min). Lower (0.1 μm ) and higher (100 μm ) NMDA concentrations were ineffective. The effect of intrastriatal NMDA (1 μm ) was prevented by coperfusion with MK-801 (1 μm ). Intrastriatal MK-801 (10 μm ) alone gradually increased glutamate levels up to +50% after 60 min of perfusion. The present results suggest that glutamate levels in the substantia nigra pars reticulata are sensitive to changes in neuronal transmission in the dorsolateral striatum, and that striatal NMDA receptors regulate nigral glutamate release in both a tonic and phasic fashion.     

Effect ofd- andl-α-aminoadipate on the efflux ofl-aspartate,l-glutamate and γ-aminobutyrate from superfused rat brain slices

d-α-Aminoadipate (d-AA) andl-α-aminoadipate (l-AA) were found to significantly reduce spontaneous efflux of [¹⁴C]l-aspartate from preloaded rat brain slices. Onlyd-AA significantly reduced spontaneous efflux of [¹⁴C]l-glutamate and [³H]γ-aminobutyric acid (GABA);l-AA reduced but not significantly the efflux of these 2 labeled amino acids.d-AA reduced K⁺-stimulated release of [¹⁴C]l-aspartate and [^14]C]l-glutamate significantly, andl-AA that of [³H]GABA significantly. Since bothd-AA andl-AA inhibit the uptake ofl-aspartate,l-glutamate and GABA, their effects on the efflux of these amino acids are more specific. These results also suggest that it is unlikely that the depressant effect ofd-AA, and the excitant effect ofl-AA on neurons when applied locally by iontophoresis are secondary to the accelerated or decelerated release of more specific transmitter amino acids from neighboring cells.     

PET imaging of serotoninergic neurotransmission with [11C]DASB and [18F]altanserin after focal cerebral ischemia in rats

The use of selective serotonin reuptake inhibitors has shown functional improvement after stroke. Despite this, the role of serotoninergic neurotransmission after cerebral ischemia evolution and its involvement in functional recovery processes are still largely unknown. For this purpose, we performed in parallel in vivo magnetic resonance imaging and positron emission tomography (PET) with [¹¹C]DASB and [¹⁸F]altanserin at 1, 3, 7, 14, 21, and 28 days after middle cerebral artery occlusion (MCAO) in rats. In the ischemic territory, PET with [¹¹C]DASB and [¹⁸F]altanserin showed a dramatic decline in serotonin transporter (SERT) and 5-HT_2A binding potential in the cortex and striatum after cerebral ischemia. Interestingly, a slight increase in [¹¹C]DASB binding was observed from days 7 to 21 followed by the uppermost binding at day 28 in the ipsilateral midbrain. In contrast, no changes were observed in the contralateral hemisphere by using both radiotracers. Likewise, both functional and behavior testing showed major impaired outcome at day 1 after ischemia onset followed by a recovery of the sensorimotor function and dexterity from day 21 to day 28 after cerebral ischemia. Taken together, these results might evidence that SERT changes in the midbrain could have a key role in the functional recovery process after cerebral ischemia.     

Developmental maturation of the N-methyl- -aspartic acid receptor channel complex in postnatal rat brain

The N-methyl- -aspartate (NMDA) receptor plays an important role in developmental plasticity. Previous studies have reported differences between the NMDA receptor-channel complex in the rat pup brain and the adult brain. In the present study, modulation of the NMDA channel complex as a function of age was measured to determine when the temporal switching of the NMDA receptor from the immature form to the adult mature form takes place. [³H]MK-801 binding was measured in the rat forebrain from postnatal day 1 to day 21. Our data suggest the presence of two types of NMDA receptors — an immature type and a mature type. The immature NMDA receptor, seen during the early postnatal period (day 1–day 14) is highly sensitive to spermidine, -glutamate alone potentiates [³H]MK-801 binding, and glycine failed to potentiate an -glutamate-induced increase in [³H]MK-801 binding. During the late postnatal period (after day 14) spermidine alone did not increase [³H]MK-801 binding as potently as it did during the early postnatal period, high-affinity [³H]MK-801 binding was not seen in the presence of -glutamate alone, and -glutamate and glycine or -glutamate and spermidine or -glutamate, glycine and spermidine together, significantly increased [³H]MK-801 binding in a manner similar to that reported in the adult brain. Together, the pharmacology of the NMDA receptor during the early postnatal period differs from the adult-like receptor seen during the late postnatal period, and that in rats the apparent switching of the NMDA receptor from the immature type to the mature type takes place after the second postnatal week.     

Altered 13C glucose metabolism in the cortico–striato–thalamo–cortical loop in the MK-801 rat model of schizophrenia

Using a modified MK-801 (dizocilpine) N-methyl--aspartic acid (NMDA) receptor hypofunction model for schizophrenia, we analyzed glycolysis, as well as glutamatergic, GABAergic, and monoaminergic neurotransmitter synthesis and degradation. Rats received an injection of MK-801 daily for 6 days and on day 6, they also received an injection of [1-¹³C]glucose. Extracts of frontal cortex (FCX), parietal and temporal cortex (PTCX), thalamus, striatum, nucleus accumbens (NAc), and hippocampus were analyzed using ¹³C nuclear magnetic resonance spectroscopy, high-performance liquid chromatography, and gas chromatography–mass spectrometry. A pronounced reduction in glycolysis was found only in PTCX, in which ¹³C labeling of glucose, lactate, and alanine was decreased. ¹³C enrichment in lactate, however, was reduced in all areas investigated. The largest reductions in glutamate labeling were detected in FCX and PTCX, whereas in hippocampus, striatum, and Nac, ¹³C labeling of glutamate was only slightly but significantly reduced. The thalamus was the only region with unaffected glutamate labeling. γ-Aminobutyric acid (GABA) labeling was reduced in all areas, but most significantly in FCX. Glutamine and aspartate labeling was unchanged. Mitochondrial metabolites were also affected. Fumarate labeling was reduced in FCX and thalamus, whereas malate labeling was reduced in FCX, PTCX, striatum, and NAc. Dopamine turnover was decreased in FCX and thalamus, whereas that of serotonin was unchanged in all regions. In conclusion, neurotransmitter metabolism in the cortico–striato–thalamo–cortical loop is severely impaired in the MK-801 (dizocilpine) NMDA receptor hypofunction animal model for schizophrenia.     

Effects of Hg and CH3Hg on Ca fluxes in rat brain microsomes

A permanent increase in cytosolic Ca²⁺ levels seems to be associated with various pathological situations which may result in cell death. Hg²⁺ and CH₃Hg⁺ are potent neurotoxic agents, but the precise molecular mechanism(s) underlying their effects are not sufficiently understood. In the present study we investigated the potential role of Ca²⁺-ATPase located in the endoplasmic reticulum as a molecular target for mercury. Hg²⁺ and CH₃Hg⁺ inhibited Ca²⁺-ATPase and Ca²⁺ uptake by brain microsomes with similar potencies. However, the inhibitory potency of Hg²⁺ was higher than that of CH3Hg+, probably reflecting differences in the affinity for the sulfhydryl groups of these compounds. Passive or unidirectional Ca²⁺ efflux (measured in the absences of Ca²⁺-ATPase ligands) was increased significantly by CH₃Hg⁺ and Hg²⁺. Again, the potency of Hg²⁺ was higher than that of CH₃Hg⁺. Blockers of Ca²⁺ channels (ruthenium red, procaine, heparin) did not affect the increase in passive Ca t+ efflux induced by mercury compounds, possibly indicating that Ca²⁺ release occurs through Ca²⁺-ATPase. Addition of physiological concentrations of glutathione (GSH) simultaneously with mercury abolished the inhibitory effects of both forms of Hg on Ca Z+-transport. However, if the enzyme was first inhibited with Hg²⁺ or CH₃Hg⁺ and subsequently treated with GSH, the reversal of inhibition was about 50%, suggesting that part of the cysteinyl residues involved in the inhibitory actions of mercury in Ca t+-transport bind to mercury with an extremely high affinity.