Post-ischemic regional changes in acetylcholine synthesis following transient forebrain ischemia in gerbils

The synthesis rate of brain acetylcholine (ACh) was estimated 30 min and 5 days following transient forebrain ischemia performed by 10 min bilateral carotid occlusion in gerbils. ACh synthesis was evaluated from the conversion of radiolabeled choline (Ch) into ACh after an i.v. administration of [methyl-³H]Ch. Endogenous and labeled Ch and ACh were quantified by HPLC. The synthesis rate of ACh was significantly decreased following 30 min of recirculation. The reductions reached 55.4% in the hippocampus, 51.2% in the cerebral cortex and 44.4% in the striatum. Five days after ischemia, the values returned to normal in the cerebral cortex and in the striatum, while ACh synthesis remained selectively lowered (–30.4%, p<0.01) in the hippocampus. These cholinergic alterations may account for both early and delayed post-ischemic behavioral and mnesic deficits.     

Effect of Dichloroacetate on Regional Energy Metabolites and Pyruvate Dehydrogenase Activity During Ischemia and Reperfusion in Gerbil Brain

The objective of this study was to determine whether administration of dichloroacetate (DCA), an activator of pyruvate dehydrogenase (PDH), improves recovery of energy metabolites following transient cerebral ischemia. Gerbils were pretreated with DCA, and cerebral ischemia was produced using bilateral carotid artery occlusion for 20 min, followed by reperfusion up to 4 h. DCA had no effect on the accumulation of lactic acid and the decrease in ATP and phosphocreatine (PCr) during the 20-min insult, nor on the recovery of these metabolites measured at 20 and 60 min reperfusion. However, at 4 h reperfusion, levels of ATP and PCr were significantly higher in DCA-treated animals than in controls, as PCr exhibited a secondary decrease in caudate nucleus of control animals. PDH was markedly inhibited at 20 min reperfusion in both groups, but was reactivated to a greater extent in DCA-treated animals at 60 min and 4 h reperfusion. These results demonstrate that DCA had no effect on the initial recovery of metabolites following transient ischemia. However, later in reperfusion, DCA enhanced the postischemic reactivation of PDH and prevented the secondary failure of energy metabolism in caudate nucleus. Thus, inhibition of PDH may limit the recovery of energy metabolism following cerebral ischemia.     

The analysis of metabolites in rainbow trout white muscle: a comparison of different sampling and processing methods

We have investigated the effects of different sampling and processing methods on metabolite concentrations [glycogen (Gly), glucose (Glu), lactate (Lac), pyruvate (Pyr), ammonia (Amm), creatine phosphate (PCr), creatine (Cr), and adenosine triphosphate (ATP)] measured in white muscle of rainbow trout at rest and immediately after exhaustive exercise. When samples were taken from resting fish by rapid needle biopsy (without anaesthesia), direct freezing of the needles in liquid N₂ yielded lower Lac and Glu levels than if the muscle cores were quickly blown out into liquid N₂. However, killing of the fish by an overdose of MS-222 followed by freeze-clamping of excised muscle was superior to the biopsy method in preserving high levels of PCr and Gly (91 and 62% higher, respectively). In parallel, the MS-222 method also yielded lower levels of Amm (80%) and Lac (47%). Samples freeze-clamped by the MS-222 method were used to evaluate three methods of subsequent processing for enzymatic analysis of metabolites: classic glass homogenization (GH) in 8% perchloric acid (PCA) c. mortar and pestle (MP) pulverization or freeze-drying (FD) prior to PCA extraction. For all metabolites, GH and MP methods produced similar values. However, the FD technique yielded 20% higher PCr levels which represented over 80% phosphorylation of the total Cr pool at rest, the highest ever reported via enzymatic analysis. Glu was also higher by FD, bul Gly, Lac, and ATP were not affected. Indeed ATP was relatively stable throughout all sampling and processing procedures. MP, GH, MP&GH combination, and high speed motor driven grinding techniques all yielded similar Amm levels in resting muscle. However, tests demonstrated that even brief thawing of tissue greatly elevated Amm, while FD resulted in artificially low Amm values due to evaporative losses during lyophilization. Overall, muscle sampling by freeze-clamping on trout killed by MS-222 overdose, followed by FD prior to PCA extraction, appears to be the best combination for the measurement of all white muscle metabolites except Amm, for which MP or GH are preferable.     

马桑内酯激活的星形胶质细胞条件培养液对正常大鼠脑内谷氨酸和GABA的影响

目的探讨星形胶质细胞对大鼠脑内谷氨酸(Glu)和γ-氨基丁酸(GABA)的影响及其在癫痫发病中的作用。方法将马桑内酯激活的星形胶质细胞条件培养液(astrocyte-conditioned medium,ACM)注射入正常SD大鼠侧脑室,观察大鼠的行为变化,运用免疫组织化学及HPLC的方法,观察大鼠大脑皮质、海马内Glu和GABA免疫反应的变化及脑组织匀浆、脑脊液内Glu和GABA含量的变化。结果ACM组大鼠在注射ACM后30min出现癫痫行为,2h恢复正常。免疫组织化学显示:ACM作用后2h,大鼠大脑皮质及海马内Glu免疫反应阳性神经元数和平均光密度值明显增高,4h达高峰(P<0.05),12h恢复正常水平;ACM作用后2h,大鼠大脑皮质及海马GABA免疫反应阳性神经元数和平均光密度值明显减弱(P<0.05),12h恢复正常水平。HPLC方法显示:ACM作用后2h大鼠大脑皮质、海马及脑脊液中Glu含量均开始增加,4h达高峰(P<0.05);ACM作用后2h大脑皮质、海马及脑脊液中GABA含量均开始降低,4h达最低(P<0.05)。结论马桑内酯激活的星形胶质细胞条件培养液可影响大鼠脑内Glu和GABA的表达,并导致动物痫性发作。     

Changes in levels of monoamines and their metabolites in incompletely ischemic brains of spontaneously hypertensive rats

In order to investigate changes in levels of monoamines and their related substances together with those of other neurotransmitters (acetylcholine and GABA), choline and substances related to energy metabolism (ATP, lactate and glucose) accompanying incomplete cerebral ischemia, a bilateral common carotid artery occlusion model of spontaneously hypertensive rats (SHR) was utilized. Animals were subjected to 1 or 2 h ischemia. Then the concentrations of substances were measured in the cerebral cortex, hippocampus and striatum and compared with control values. Due to the incomplete ischemia, ATP showed a moderate decrease, while lactate and choline increased remarkably, and GABA underwent a moderate increase. With regard to monoamines, both noradrenaline and serotonin levels were reduced in the cerebral cortex and hippocampus, whereas dopamine levels increased in the hippocampus. All monoamine metabolites, i.e. metabolites by monoamine oxidase (MAO), metabolites by catechol-O-methyltransferase (COMT), and metabolites by both MAO and COMT, underwent increases. The 3-methoxytyramine level in particular showed marked increases. Furthermore levels of precursor amino acids as well as 5-hydroxytryptophan rose. Acetylcholine decreased moderately only in the cerebral cortex. Among these changes, sustained increases in all the monoamine metabolites were characteristic in the incompletely ischemic brain, suggesting that both COMT and MAO retain their activities in the incompletely ischemic brain.     

The release of gamma-aminobutyric acid, glutamate, and acetylcholine from striatal slices: a mass fragmentographic study

The release processes of endogenous Acetylcholine (ACh), gamma-aminobutyric acid (GABA), glutamate (Glu) and glutamine (GLN) were studied in superfused guinea-pig caudatal slices. Basal ACh release remained constant for up to 2 h, while the basal release of GABA, Glu and GLN declined to half or less of its initial values after 1 h of superfusion. Electrical stimulation increased the ACh release by 700-800% and that of GABA by 80% whereas it decreased the output of Glu by 50% and failed to modify the GLN efflux. KCl (25 nM) increased the output of ACh by 400%, that of GABA by approximately 500% and decreased that of Glu by 40%. Substituting of CaCl(2) by MgCl(2) in the superfusion medium reduced the basal efflux of GABA, Glu and GLN. Under these conditions, no evoked release of ACh or of GABA was detected, following electrical or KCl stimulation. Tetrodotoxin 5 x 10(-7) decreased the basal ACh release by 60% and increased the GABA efflux by 40%. The toxin abolished the stimulus-evoked ACh efflux but scarcely affected that of GABA. These results are consistent with a possible neurotransmitter role of ACh and GABA in the striatum and show some differences in the ionic mechanisms underlying GABA and ACh release.     

Changes in regional levels of putative neurotransmitter amino acids in brain under unilateral forebrain ischemia

The levels of the neurotransmitter amino acids glutamate, aspartate, and GABA were determined in different brain regions during ischemia and post-ischemic recirculation periods using the unilateral carotid artery occlusion model of stroke in gerbils. The levels of glutamate, aspartate and GABA in ischemic hemisphere were increased significantly by 10 min of ischemia and later declined with time. Reperfusion for 30 min following 10 min. of ischemia further enhanced the levels of glutamate and aspartate. Increase in GABA levels were found during early periods of reperfusion. Regional variations in the changes of amino acids' levels were noticed following ischemia. Hippocampus showed the highest increase in glutamate levels followed by striatum and cerebral cortex. Aspartate levels in striatum and hippocampus increased during 10 min ischemia (46% and 30%) and recirculation (70% and 79%), whereas in cerebral cortex the levels were doubled only during recirculation. Ischemia induced elevations of GABA levels were observed in cerebral cortex (68%) and in hippocampus (30%), and the levels were normalized during recirculation. No changes in GABA levels were found in striatum. It is suggested that the large increase in the levels of excitatory neurotransmitter amino acids in brain regions specially in hippocampus during ischemia and recirculation may be one of the causal factors for ischemic brain damage.     

The Effect of Moderate Hypocapnic Ventilation on Nuclear Ca2+-ATPase Activity, Nuclear Ca2+ Flux, and Ca2+/Calmodulin Kinase IV Activity in the Cerebral Cortex of Newborn Piglets

Previous studies have shown that hypocapnia results in fragmentation of nuclear DNA in the cerebral cortex of newborn piglets. We tested the hypothesis that hypocapnia results in decreased ATP and phosphocreatine (PCr) levels and increased nuclear high-affinity Ca++-ATPase activity, intranuclear Ca++ flux, and CaM kinase IV activity in neuronal nuclei of piglets. Three groups of piglets were ventilated as either hypocapnic (a PaCO2 of 20 mm Hg), normocapnic (a PaCO2 of 40 mm Hg), or corrected hypocapnic (ventilated as hypocapnic but with CO2 added to maintain normocapnia) for 1 h. Tissue ATP levels were lower in the hypocapnic than in the normocapnic group. PCr levels were lower and 45Ca++-influx, Ca++-ATPase activity and CaM kinase IV activity were higher in hypocapnic than in normocapnic or corrected hypocapnic piglets. We conclude that hypocapnia alters nuclear membrane Ca++ flux mechanisms and may alter neuronal phosphorylation mechanisms in the cerebral cortex of piglets.     

The Release of γ-Aminobutyric Acid, Glutamate, and Acetylcholine from Striatal Slices: A Mass Fragmentographic Study

Abstract: The release processes of endogenous Acetylcholine (ACh), γ-aminobutyric acid (GABA), glutamate (Glu) and glutamine (GLN) were studied in superfused guinea-pig caudatal slices. Basal ACh release remained constant for up to 2 h, while the basal release of GABA, Glu and GLN declined to half or less of its initial values after 1 h of superfusion. Electrical stimulation increased the ACh release by 700–800% and that of GABA by 80% whereas it decreased the output of Glu by 50% and failed to modify the GLN efflux. KCl (25 mM) increased the output of ACh by 400%, that of GABA by approximately 500% and decreased that of Glu by 40%. Substituting of CaCl₂ by MgCl₂ in the superfusion medium reduced the basal ACh release by 70% whereas no differences were observed in the basal efflux of GABA, Glu and GLN. Under these conditions, no evoked release of ACh or of GABA was detected, following electrical or KCl stimulation. Tetrodotoxin 5 × 10^-7 M decreased the basal ACh release by 60% and increased the GABA efflux by 40%. The toxin abolished the stimulus-evoked ACh efflux but scarcely affected that of GABA. These results are consistent with a possible neurotransmitter role of ACh and GABA in the striatum and show some differences in the ionic mechanisms underlying GABA and ACh release.     

Decreased expression of vesicular GABA transporter, but not vesicular glutamate, acetylcholine and monoamine transporters in rat brain following focal ischemia

In nerve terminals, vesicular transporters pack neurotransmitters into synaptic vesicles, which is an essential prerequisite for transmitter release. To date, three distinct families of vesicular transporters have been identified which are specific for (a) excitatory amino acids (glutamate and aspartate), (b) inhibitory amino acids (GABA and glycine) and (c) acetylcholine and monoamines. The present study evaluated the effect of transient focal cerebral ischemia on the expression of these vesicular transporters in adult rat brain. Ischemia was induced by a 1 h transient middle cerebral artery occlusion (MCAO) in spontaneously hypertensive rats. At various reperfusion periods (3-72 h), mRNA levels of the vesicular transporters were estimated in the contralateral and the ipsilateral cerebral cortex by real-time PCR analysis. Following transient focal ischemia, mRNA expression of the vesicular GABA transporter (VGAT) decreased significantly by 3 h of reperfusion and remained at a significantly lower level than sham until at least 72 h of reperfusion. Western blotting showed a significant decrease in the VGAT immunoreactive protein levels in the ipsilateral cortex of rats subjected to focal ischemia and 24 h reperfusion. Immunohistochemistry demonstrated many VGAT immunopositive puncta in the contralateral cortex, which were significantly decreased in the ipsilateral cortex at 24 h reperfusion. Focal ischemia had no effect on the mRNA levels of the vesicular transporters specific for glutamate/aspartate, acetylcholine and monoamines at either 6 h or 24 h of reperfusion.     

Short- and long-term changes in extracellular glutamate and acetylcholine concentrations in the rat hippocampus following hypoxia

Hypoxia at birth is a major source of brain damage and it is associated with serious neurological sequelae in survivors. Alterations in the extracellular turnover of glutamate (Glu) and acetylcholine (ACh), two neurotransmitters that are essential for normal hippocampal function and learning and memory processes, may contribute to some of the neurological effects of perinatal hypoxia. We set out to determine the immediate and long-lasting effects of hypoxia on the turnover of these neurotransmitters by using microdialysis to measure the extracellular concentration of Glu and ACh in hippocampus, when hypoxia was induced in rats at postnatal day (PD) 7, and again at PD30. In PD7 rats, hypoxia induced an increase in extracellular Glu concentrations that lasted for up to 2.5 h and a decrease in extracellular ACh concentrations over this period. By contrast, perinatal hypoxia attenuated Glu release in asphyxiated rats, inducing a decrease in basal Glu levels when these animals reached PD30. Unlike Glu, the basal ACh levels in these animals were greater than in controls at PD30, although ACh release was stimulated less strongly than in control animals. These results provide the first evidence of the initial and long term consequences of the hypoxia on Glu and ACh turnover in the brain, demonstrating that hypoxia produces significant alterations in hippocampal neurochemistry and physiology.     

Output, Tissue Levels, and Synthesis of Acetylcholine During and After Transient Forebrain Ischemia in the Rat

Biochemical changes in the rat brain cholinergic system during and after 60 min of ischemia were studied using a four-vessel occlusion model. Extracellular acetylcholine (ACh) concentrations in the unanesthetized rat hippocampus markedly increased during ischemia and reached a peak (about 13.5 times baseline levels) at 5-10 min after the onset of ischemia. At 2-5 h after reperfusion, extracellular ACh concentrations were reduced to 64-72% of the levels of controls. ACh levels in the hippocampus, striatum, and cortex decreased significantly during ischemia and exceeded their control values just after reperfusion. A significant increase in hippocampal ACh level after 2 days of reperfusion and a decrease in [14C]ACh synthesis from [14C]glucose in hippocampal slices excised at 2 days after reperfusion were observed. The extracellular concentrations and tissue levels of choline markedly increased after ischemia. These results show that ACh is markedly released into the extracellular space in the hippocampus during ischemia, and they suggest that ACh synthesis is activated just after reperfusion and that cholinergic activity is reduced after 2-48 h of reperfusion in the hippocampus.     

NMR monitoring of the anaerobic metabolism of frog muscle at rest

The time dependence of Lactate (Lac), H+, Adenosine-triphosphate (ATP), Phosphocreatine (PCr), Hexose-monophosphate (PME), and Inorganic Phosphate (Pi) levels has been obtained for frog muscle at rest in anaerobic conditions by multinuclear NMR. All information has been collected on the same samples alternatively tuning the probehead on 1H- and 31P-NMR frequencies. ATP, PCr and H+ levels show the same time dependence for all the samples, while PME, Pi and Lac levels vary in time differently from one sample to another. No direct correlation between the Lac appearance and the H+ concentration has been found.     

Regional levels of glucose,amino acids,high energy phosphates,and cyclic nucleotides in the central nervous system during hypoglycemic stupor and behavioral recovery

The effects of insulin-induced hypoglycemic stupor and subsequent treatment with glucose on mouse cerebral cortical, cerebellar and brain stem levels of glucose, glycogen, ATP, phosphocreatine, glutamate, aspartate and GABA and on cerebral cortical and cerebellar levels of cyclic AMP and cyclic GMP have been measured. Hypoglycemia decreased glucose, glycogen and glutamate levels and had no effect on ATP levels in all three regions of brain. GABA levels were decreased only in cerebellum. Aspartate levels rose in cerebral cortex and brain stem, and creatine phosphate increased in cerebral cortex and cerebellum. In the hypoglycemic stuporous animals, cyclic GMP levels were elevated in cerebral cortex and depressed in cerebellum whereas cyclic AMP levels were unchanged from control values. Intravenous administration of 2.5-3.5 mmol/kg of glucose to the hypoglycemic stuporous animals produced recovery of near normal neurological function within 45 s. Only brain glucose and aspartate levels returned to normal prior to behavioral recovery. These results suggest that of the several substances examined in this study, only glucose and perhaps aspartate have important roles in the biochemical mechanisms producing neurological abnormalities in hypoglycemic animals.     

Neurochemical Changes in Brain Induced by Chronic Morphine Treatment: NMR Studies in Thalamus and Somatosensory Cortex of Rats

To investigate the effects of chronic morphine treatment and its cessation on thalamus and the somatosensory cortex, an ex vivo high resolution (500 MHz) ¹H nuclear magnetic resonance spectroscopy (NMRS), in the present study, was applied to detect multiple alterations of neurochemicals and/or neurometabolites in the rats. Ten days of chronic morphine administration was observed to markedly increase the total amount of lactate (Lac), myo-inositol (my-Ins) (each P < 0.01) and aspartate (Asp) (P < 0.05), and significantly decrease that of glutamate (Glu) and glutamine (Gln) in the rats thalamus (each P < 0.05). In the somatosensory cortex, chronic morphine was shown to increase the level of Lac and my-Ins, and decrease that of Glu (each P < 0.05). Interestingly, the ratio of Glu/GABA was found to decrease in these two brain areas after chronic morphine treatment, and among the detectable neurochemicals in those two cerebral areas, only taurine (Tau) showed to result in a significant increment in thalamus during the process of morphine discontinuation (P < 0.05). Moreover, the alterations of multiple neurochemicals due to chronic morphine exhibited a tendency of recovery to the normal level over the course of morphine withdrawal. The results suggested that, in thalamus and the somatosensory cortex, chronic morphine administration and its cessation could induce multiple neurochemical changes, which may involve in the brain energy metabolism, activity and transition of neurotransmitters.     

Effect of Insulin-Induced Hypoglycemia on the Concentrations of Glutamate and Related Amino Acids and Energy Metabolites in the Intact and Decorticated Rat Neostriatum

Abstract The glutamate (Glu) terminals in rat neostriatum were removed by a unilateral frontal decortication. One to two weeks later the effects of insulin-induced hypoglycemia on the steady-state levels of amino acids [Glu, glutamine (Gin), aspartate (Asp), γ-aminobutyric acid (GABA), tau-rine] and energy metabolites (glucose, glycogen, α-ketoglu-tarate, pyruvate, lactate, ATP, ADP, AMP, phosphocre-atine) were examined in the intact and decorticated neostriatum from brains frozen in situ. The changes in the metabolite levels were examined during normoglycemia, hypoglycemia with burst-suppression (BS) EEG, after 5 and 30 min of hypoglycemic coma with isoelectric EEG, and 1 h of recovery following 30 min of isoelectric EEG. In normoglycemia Glu decreased and Gin and glycogen increased significantly on the decorticated side. During the BS period no significant differences in the measured compounds were noted between the two sides. After 5 min of isoelectric EEG Glu, Gin, GABA, and ATP levels were significantly lower and Asp higher on the intact than on the decorticated side. No differences between the two sides were found after 30 min of isoelectric EEG. After 1 h of recovery from 30 min of isoelectric EEG Glu, Gin, and glycogen had not reached their control levels. Glu was significantly lower, and Gin and glycogen higher on the decorticated side. The Asp and GABA levels were not significantly different from control levels. The results indicate that the turnover of Glu is higher in the intact than in decorticated neostriatum during profound hypoglycemia.     

Excitatory and inhibitory amino acid changes in ischemic brain regions in spontaneously hypertensive rats

Excitatory (glutamate, aspartate) or inhibitory amino acids (-aminobutyric acid: GABA, taurine) and glutamine contents were examined in acutely induced cerebral ischemia in spontaneously hypertensive rats. At 20 min ischemia most of these amino acids remained unchanged, but glutamine significantly decreased by 14% in the CA3 hippocampal subfield. At 60 min ischemia glutamate significantly decreased by 14% in the CA3, aspartate by 17–26% in the CA3, cingulate cortex, septum and striatum. In contrast, GABA significantly increased by 48–106% in the cortices (frontal, parietal and cingulate), striatum and nucleus accumbens, but insignificantly in hippocampal subrïelds. Likewise, taurine increased in the parietal cortex and nucleus accumbens. Glutamine showed heterogeneous changes (increase in the nucleus accumbens and decrease in the CA3). Amino acid levels change during ischemia, but their changes are varied in each area, implying that different reaction of amino acids may explain the selective vulnerability to cerebral ischemia.     

Inhibition of choline efflux results in enhanced acetylcholine synthesis and release in the guinea-pig corticocerebral synaptosomes.

Synthesis and release of [3H]acetylcholine ([3H]ACh) were measured in synaptosomes from the guinea pig cerebral cortex after preloading with [3H]choline ([3H]Ch). We demonstrate here that inhibition of choline (Ch) efflux results in an increase in acetylcholine (ACh) synthesis and release. Our findings are as follows: (1) inhibition of [3H]Ch efflux by hemicholinium-3 (HC-3) (100 microM), increased the levels of both the released (116% of control) and the residing (115% of control) [3H]ACh. (2) The muscarinic agonist, McN-A-343 (100 microM), which was previously shown to inhibit Ch efflux, also increased the released (121% of control) and the residing (109% of control) [3H]ACh. (3) Omission of Na+ ions (which are required for Ch transport) from the incubation medium had similar effects to those observed with McN-A-343 and HC-3. These results suggest inverse relationships between Ch efflux on one hand, and ACh synthesis and release on the other hand. (4) Depolarization with 50 mM K+, or with the K+ channel blocker, 4-aminopyridine (100 microM), also increased the total level of [3H]ACh (113 and 107% of nondepolarized synaptosomes, respectively). However, whereas conditions that inhibit Ch transport such as HC-3, McN-A-343 and "no sodium" increased both the residing and the released [3H]ACh depolarization with high K+ or 4-aminopyridine reduced the residing (79 and 87% of control, respectively) and increased only the released [3H]ACh (182 and 148% of control, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of Ischemia on the In Vivo Release of Striatal Dopamine, Glutamate, and γ-Aminobutyric Acid Studied by Intracerebral Microdialysis

We have previously described a marked attenuation of postischemic striatal neuronal death by prior substantia nigra (SN) lesioning. The present study was carried out to evaluate whether the protective effect of the lesion involves changes in the degree of local cerebral blood flow (ICBF) reduction, energy metabolite depletion, or alterations in the extracellular release of striatal dopamine (DA), glutamate (Glu), or gamma-aminobutyric acid (GABA). Control and SN-lesioned rats were subjected to 20 min of forebrain ischemia by four-vessel occlusion combined with systemic hypotension. Levels of ICBF, as measured by the autoradiographic method, and energy metabolites were uniformly reduced in both the ipsi- and contralateral striata at the end of the ischemic period, a finding implying that the lesion did not affect the severity of the ischemic insult itself. Extracellular neurotransmitter levels were measured by microdialysis; the perfusate was collected before, during, and after ischemia. An approximately 500-fold increase in DA content, a 7-fold increase in Glu content, and a 5-fold increase in GABA content were observed during ischemia in nonlesioned animals. These levels gradually returned to baseline by 30 min of reperfusion. In SN-lesioned rats, the release of DA was completely prevented, the release of GABA was not affected, and the release of Glu was partially attenuated. However, excessive extracellular Glu concentrations were still attained, which are potentially toxic. This, taken together with the previous neuropathological findings, suggests that excessive release of DA is important for the development of ischemic cell damage in the striatum.     

Influence of vanadate on glycolysis,intracellular sodium,and pH in perfused rat hearts

Vanadium compounds have been shown to cause a variety of biological and metabolic effects including inhibition of certain enzymes, alteration of contractile function, and as an insulin like regulator of glucose metabolism. However, the influence of vanadium on metabolic and ionic changes in hearts remains to be understood. In this study we have examined the influence of vanadate on glucose metabolism and sodium transport in isolated perfused rat hearts. Hearts were perfused with 10 mM glucose and varying vanadate concentrations (0.7100 M) while changes in high energy phosphates (ATP and phosphocreatine (PCr)), intracellular pH, and intracellular sodium were monitored using 31P and 23Na NMR spectroscopy. Tissue lactate, glycogen, and (Na+, K+)-ATPase activity were also measured using biochemical assays. Under baseline conditions, vanadate increased tissue glycogen levels two fold and reduced (Na+, K+)-ATPase activity. Significant decreases in ATP and PCr were observed in the presence of vanadate, with little change in intracellular pH. These changes under baseline conditions were less severe when the hearts were perfused with glucose, palmitate and b-hydroxybutyrate. During ischemia vanadate did not limit the rise in intracellular sodium, but slowed sodium recovery on reperfusion. The presence of vanadate during ischemia resulted in attenuation of acidosis, and reduced lactate accumulation. Reperfusion in the presence of vanadate resulted in a slower ATP recovery, while intracellular pH and PCr recovery was not affected. These results indicate that vanadate alters glucose utilization and (Na+, K+)-ATPase activity and thereby influences the response of the myocardium to an ischemic insult.