Effects of subchronic treatment of methamphetamine haloperidol on the rat brain levels of GABA, glutamate and aspartate

Centrally active amino acids (GABA, glutamate, aspartate) were assayed enzyme-fluorometrically in five brain regions of the rat after a 16-day administration of methamphetamine (2.5 mg/kg, i.p.) and haloperidol (2.5 mg/kg, i.p.), or both agents together. Methamphetamine caused no statistically-significant changes in the GABA contents in any brain areas, a significant decrease in the glutamate content of the striatum, hippocampus and midbrain and an increase in the aspartate content of the hypothalamus. Haloperidol treatment resulted in no changes in the GABA content, a significant decrease in the glutamate content of the striatum and a significant increase in the aspartate content in the frontal cortex. The treatment with both agents caused a significant decrease in the GABA content of the hypothalamus. The combined administration normalized a lowering of the glutamate levels in the striatum caused by methamphetamine and haloperidol, respectively, and increased the level of aspartate in the hypothalamus caused by methamphetamine and in the frontal cortex caused by haloperidol.     

Effects of Subchronic Treatment of Methamphetamine Haloperidol on the Rat Brain Levels of GABA, Glutamate and Aspartate

Abstract: Centrally active amino acids (GABA, glutamate, asparate) were assayed enzyme-fluorometrically in five brain regions of the rat after a 16-day administration of methamphetamine (2.5 mg/kg, i.p.) and haloperidol (2.5 mg/kg, i.p.), or both agents together. Methamphetamine caused no statistically-significant changes in the GABA contents in any brain areas, a significant decrease in the glutamate content of the striatum, hippocampus and midbrain and an increase in the aspartate content of the hypothalamus. Haloperidol treatment resulted in no changes in the GABA content, a significant decrease in the glutamate content of the striatum and a significant increase in the aspartate content in the frontal cortex. The treatment with both agents caused a significant decrease in the GABA content of the hypothalamus. The combined administration normalized a lowering of the glutamate levels in the striatum caused by methamphetamine and haloperidol, respectively, and increased the level of aspartate in the hypothalamus caused by methamphetamine and in the frontal cortex caused by haloperidol.     

大鼠全脑缺血再灌流后4个脑区的谷氨酸、门冬氨酸、甘氨酸及γ—氨基丁酸含量的测定

应用高效液相色谱仪,紫外分光光度检测器监测,测定大鼠全脑缺血再灌流后6h～7d的海马、纹状体、丘脑和新皮层组织匀浆中谷氨酸(Glu)、门冬氨酸(Asp)、甘氨酸(Gly)和γ-氨基丁酸(GABA)含量变化。结果显示在海马和丘脑Glu含量于再灌流后6h～3d下降(P<0.05和0.01),GABA含量升高(P<0.05和0.01),在纹状体和新皮层除GABA外,分别于6h～5d均有不同呈度的升高。比较有规律的变化是当GABA升高时Glu含量下降。这可能是由于缺血及再灌流早期Glu等兴奋性氨基酸(EAAs)大量释放,反射性GABA的合成与释放增多使Glu向GABA方向转化有关。     

Brain amino acid concentrations in rats killed by decapitation and microwave irradiation

The effect of death by decapitation or focused beam microwave irradiation (FBMI) on rat brain amino acid concentrations was investigated. Twenty-nine amino acids and related compounds were measured by ion-exchange chromatography in the cerebral cortex, hippocampus, striatum and substantia nigra of male Sprague-Dawley rats killed by decapitation (n = 5) or by FBMI (n = 5). Alanine, GABA, ethanolamine and NH3 concentrations were significantly lower in all 4 brain regions of the FBMI group animals. Valine, leucine, tyrosine and phenylalanine levels were also lower in the hippocampus, striatum and substantia nigra of the FBMI group. The FBMI group showed less aspartate in the hippocampus and substantia nigra as well as less glycine in the cortex, hippocampus and striatum. In the FBMI group, the only amino acids exhibiting significantly higher levels were GSH in the striatum and substantia nigra and glutamate in the substantia nigra. These results show a significant impact of method of killing on the determination of baseline concentrations of brain amino acids.     

帕金森病大鼠黑质纹状体中氨基酸含量的变化

目的：观察帕金森病大鼠黑质纹状体中氨基酸神经递质的变化。方法：将６－羟多巴胺（６－ＯＨＤＡ）注入鼠右侧黑质内以建立偏侧帕金森病模型,检测其黑质和纹状体中四种氨基酸的含量。结果：帕金森病大鼠损毁侧谷氨酸（Ｇｌｕ）、天门冬氨酸（Ａｓｐ）、甘氨酸（Ｇｌｙ）、和ｒ－氨丁酸（ＧＡＢＡ）的含量较未损毁侧显著增加（Ｐ〈０．０１）。结论：兴奋性氨基酸可能参与了６－ＯＨＤＡ所致的黑质纹状体内神经元损伤。     

Characterization of a neutral, divalent cation-sensitive endopeptidase: a possible role in neuropeptide processing

A trypsin-like endopeptidase which cleaves the synthetic substrate Dansyl-Phe-Leu-Arg-Arg-Ala-Ser-Leu-Gly-COOH (Dansyl-Phe-Kemptide) primarily at the Arg4-Ala5 bond has been partially purified from bovine adrenal chromaffin granules, brain and liver. The enzyme appears to have a relatively homogeneous tissue distribution, although highest levels were found in brain regions such as the hippocampus and corpus striatum. Sucrose density gradient fractionation established that enzyme activity assayed at pH 8.5 is not associated with lysosomes. Purified enzyme displays a dimeric structure with subunit molecular weights of 40 kDa and 42 kDa and a native molecular weight of 85,000 Da. The endopeptidase has a neutral pH optimum, is sensitive to divalent cations and thiol reagents, and can cleave on either the amino or carboxyl side of some but not all internal basic amino acids.     

Time-sequential change of amino acid neurotransmitters--GABA, aspartate and glutamate--in the rat basal ganglia following middle cerebral artery occlusion

To clarify the involvement of neurotransmitters in the remote metabolic effect following focal ischaemia, amino acid neurotransmitter candidates--GABA, aspartate and glutamate--were measured time-sequentially in the basal ganglia following middle cerebral artery occlusion in the rat, which is known to produce a change in glucose metabolism and blood flow in the remote basal ganglia. GABA and aspartate content decreased in the ipsilateral substantia nigra from the second to the 28 th postoperative day. The same tendency was observed in the ipsilateral globus pallidus. Glutamate did not change significantly in either nucleus. In the contralateral side, GABA increased significantly in the substantia nigra throughout the experimental period and in the striatum during the first seven days. These results indicate that the destruction of strionigral tract by focal ischaemia induced the decrease of inhibitory GABA in the ipsilateral substantia nigra. The increase of metabolism in this nucleus may be caused by the decrease of the inhibitory effect.     

Effects of valproate on amino acid and monoamine concentrations in striatum of audiogenic seizure-prone balb/c mice

The effects of aalproate on CNS concentrations of γ-aminobutyric acid (GABA), glutamate (GLU), glutamine (GLN), dopamine (DA), serotonin (5-HT), and metabolites were examined in tissue extracts of caudate nucleus of genetic substrains of Balb/c mice susceptible (EP) or resistant (ER) to audiogenic seizures. Generalized tonic-clonic seizures observed in EP mice were inhibited by valproate, administered 1 h prior to testing, in a dose-response fashion. Concentrations of GABA, GLU, and GLN, which were lower in EP mice than in ER mice, were significantly increased by valproate at doses of 180 and 360 mg/kg. Concentrations of homovanillic acid (HVA) and hydroxyindoleacetic acid (5-HIAA), metabolites of DA and 5-HT were substantially increased by valproate at these doses. Thein situ activity of tyrosine hydroxylase (TH) was not significantly influenced by valproate, whereas a valproate-induced increase in tryptophan hydroxylase (TPH) activity was observed in both striatum and in midbrain tegmentum. The data are consistent with the interpretation that anticonvulsive doses of valproate influences the intraneuronal metabolism of monoamines, GABA, and glutamate concurrently. Valproate’s influence on the metabolism of both major inhibitory (GABA) and excitatory (GLU) amino acids in striatum could contribute to its anticonvulsive effects in genetically seizure-prone mice, as well as to the accumulation of DA and 5-HT metabolites.     

The ketogenic diet influences the levels of excitatory and inhibitory amino acids in the CSF in children with refractory epilepsy

The ketogenic diet (KD) is an established treatment for medically refractory pediatric epilepsy. Its anticonvulsant mechanism is still unclear. We examined the influence of the KD on the CSF levels of excitatory and inhibitory amino acids in 26 children (mean age 6.1 years) with refractory epilepsy. Seventeen amino acids were determined before and at a mean of 4 months after the start of the KD. Seizures were quantified. Highly significant changes were found in eight amino acids: increases in GABA, taurine, serine, and glycine and decreases in asparagine, alanine, tyrosine and phenylalanine. However, aspartate, glutamate, arginine, threonine, citrulline, leucine, isoleucine and valine/methionine remained unchanged. A significant correlation with seizure response was found for threonine (P=0.016). The GABA levels were higher in responders (>50% seizure reduction) than in nonresponders during the diet (P=0.041). In the very good responders (>90% seizure reduction), the GABA levels were significantly higher at baseline as well as during the diet. Age differences were found with significantly larger decreases in glutamate and increases in GABA in connection with the diet in younger children. Our results indicate that the KD significantly alters the levels of several CSF amino acids that may be involved in its mechanism of action and the increase in GABA is of particular interest.     

Modulation of acetylcholine release via GABAA and GABAB receptors in rat striatum

In order to investigate whether changes in acetylcholine (ACh) release induced by GABA receptors are due to a direct or indirect effect on cholinergic neurons in the striatum, GABA_A and GABA_B receptor bindings were assayed in the striatum microinjected with ethylcholine mustard aziridinium ion (AF64A), a cholinergic neurotoxin. Intra-striatal injection of a selective concentration of AF64A (10 nmol) reduced GABA_A receptor binding without significantly altering GABA_B receptor binding. Treatment with a higher, less selective concentration of AF64A (20 nmol) reduced all markers examined. These results suggest that GABA_A, but not GABA_B receptors, are located on cholinergic neurons in the striatum, and that GABA can directly modulate ACh release through stimulation of GABA_A receptors. Findings further suggest that GABA can also indirectly modulate ACh release through stimulation of GABA_B receptors located on non-cholinergic neuronal elements in the striatum.     

The selective A2A receptor antagonist SCH 58261 reduces striatal transmitter outflow,turning behavior and ischemic brain damage induced by permanent focal ischemia in the rat

Adenosine A(2A) receptor antagonists have been proved protective in different ischemia models. In this study we verified if the protective effect of the selective A(2A) antagonist, SCH 58261, could be attributed to the reduction of the excitatory amino acid outflow induced by cerebral focal ischemia. A vertical microdialysis probe was inserted into the striatum of male Wistar rats and, after 24 h, permanent right intraluminal middle cerebral artery occlusion (MCAo) was induced. Soon after waking, rats showed a definite contralateral turning behavior, which persisted up to 7 h after MCAo. During 4 h after MCAo, glutamate, aspartate, GABA, adenosine and taurine outflow increased. SCH 58261 (0.01 mg/kg, i.p.), administered 5 min after MCAo, suppressed turning behavior and significantly reduced the outflow of glutamate, aspartate, GABA and adenosine. At 24 h after MCAo, the rats showed severe sensorimotor deficit and damage in both the striatum and cortex. SCH 58261 significantly reduced cortical damage but did not protect against the sensorimotor deficit. The protective effect of SCH 58261 against turning behavior and increased outflow of excitatory amino acids in the first hours after MCAo suggests the potential utility of selective adenosine A(2A) antagonists when administered in the first hours after ischemia. Furthermore, this study, for the first time, proposes that turning behavior after permanent intraluminal MCAo, be used as a precocious index of neurological deficit and neuronal damage.     

Decreased pallidal GABA following reverse microdialysis with clozapine, but not haloperidol.

Changes in striatopallidal GABA are believed to play a significant role in the motor side effects produced by antipsychotic drugs (APDs). In the current study, we measured extracellular GABA in the globus pallidus (GP) of rats. GABA release was partially impulse- and Ca2+-dependent, as evidenced by decreased efflux following tetrodotoxin (TTX) or removal of Ca2+. In addition, GABA release was significantly increased by high K+ (100 mM KCl) stimulation. Reverse dialysis of the atypical APD, clozapine (1-100 microM), produced a concentration dependent decrease in extracellular GABA. In contrast, the typical APD, haloperidol (1-100 microM), had no significant effect on GABA levels. These results suggest that clozapine has direct actions within the GP, while the effects of haloperidol are most likely mediated through its effects in the striatum. The clozapine-induced decrease in pallidal GABA may account for its low motor side effect liability.     

Effects of intranigral injection of taurine and GABA on striatal dopamine release monitored voltammetrically in the unanaesthetized rat

Linear sweep voltammetry with carbon-paste electrodes was used to detect changes in the extracellular concentration of homovanillic acid (HVA) in the striatum of unanaesthetized rats; under the present experimental conditions, changes in the HVA signal were used as an index of striatal dopamine release. The effects of unilateral intranigral infusion of saline, sucrose, taurine, GABA and the putative taurine-receptor antagonist, 6-aminomethyl-3-methyl-4H-1,2,4-benzothiadiazine-1,1-dioxide (TAG), on the HVA signal were monitored in the striatum on the two sides of the brain. Both taurine and GABA caused an increase in the extracellular concentration of HVA which was significantly greater in the striatum on the side of the injection compared with the contralateral side. The effect of TAG varied between animals. The results are discussed in terms of the role of taurine as a possible neuromodulator in the substantia nigra and in the light of the suggestion that different pathways are involved in taurine- and GABA-induced contraversive circling.     

Neurotransmitter amino acids in the CNS. I. Regional changes in amino acid levels in rat brain during ischemia and reperfusion

The levels of amino acids in 6 regions of the brain (cortex, hippocampus, striatum, diencephalon, stem and cerebellum) were determined during an ischemic insult of 30 min and after recovery periods of up to 10 h. The results were analyzed in two groups: putative neurotransmitters (GABA, aspartate, glutamate, taurine, glycine and alanine) and non-neurotransmitters. In the neurotransmitter group, it was found that at the end of 30 min ischemia the levels of aspartate and glutamate slightly decreased whereas those of GABA and alanine rose substantially. The amounts of glycine and taurine remained unchanged. In 30 min after the ischemic insult, there were much larger decreases in aspartate and glutamate and increases in GABA and alanine with no change in glycine and taurine. At 2 h recovery the levels of the neurotransmitter amino acids had almost returned to control values and were fully recovered by 10 h after ischemia. It is postulated that glutamate and aspartate are released during ischemia into the extracellular space and subsequently ‘washed-out’ into the blood during the reperfusion. Release of GABA, if it occurs, is however, compensated by increase in its synthesis and decrease in its degradation under anaerobic conditions, both of which contribute to the rise in its steady-state level. In the non-transmitter category, increases were seen in amino acids present normally in very small concentrations; tyrosine, lysine, leucine and 3 hydrophobic amino acids: valine, methionine and phenylalanine, which were most pronounced at 2 h after ischemia. It is suggested that the rise in the levels of these molecules is the consequence of stimulation of protein breakdown caused by activation of intracellular proteases by calcium and H⁺ during the ischemic episode. Regional variations in the patterns of changes were small although in the ischemic model used the brainstem seemed to be least affected.     

The environmental enrichment effect upon cortical growth is neutralized by concomitant pharmacological suppression of active sleep in female rats

D-alpha-Aminoadipate (D-AA) and L-alpha-aminoadipate (L-AA) were found to significantly reduce spontaneous efflux of [14C]L-aspartate from preloaded rat brain slices. Only D-AA significantly reduced spontaneous efflux of [14C]L-glutamate and [3H]gamma-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 [14C]L-glutamate significantly, and L-AA that of [3H]GABA significantly. Since both D-AA and L-AA inhibit the uptake of L-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 of D-AA, and the excitant effect of L-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.     

Hyperthermia influences excitatory and inhibitory amino acid neurotransmitters in the central nervous system. An experimental study in the rat using behavioural, biochemical, pharmacological, and morphological approaches

Summary. Role of excitatory amino acids, glutamate, aspartate, and inhibitory amino acids, gamma aminobutyric acid (GABA) and glycine in brain damage caused by heat stress was examined in a rat model. Subjection of rats to 4 h heat stress at 38°C in a biological oxygen demand (BOD) incubator resulted in a marked increase in glutamate and aspartate in some brain regions, whereas a significant decline in GABA and glycine was observed in several brain areas. Profound behavioural alterations and impairment of motor and cognitive functions were seen at this time. Breakdown of the blood–brain barrier (BBB), reduction in regional cerebral blood flow (CBF), edema formation and cell injuries are prominent in several parts of the brain. Pretreatment with multiple opioid receptor antagonist, naloxone (10 mg/kg, i.p.) significantly restored the heat stress induced decline in GABA and glycine and thwarted the elevation of glutamate and aspartate in various brain areas. The motor or cognitive deficits were also attenuated. A significant reduction in BBB permeability, cerebral blood flow abnormalities, edema formation and cell injuries was evident. These novel observations suggest that (i) glutamate, aspartate, GABA and glycine are involved in the pathophysiology of heat stress, and (ii) a balance between excitatory and inhibitory amino acids in brain is crucial in hyperthermia induced brain injuries or repair.     

Biochemical studies of the cerebral ischemia in the rat--changes in cerebral free amino acids, catecholamines and uric acid

Changes in cerebral free amino acids, catecholamines and uric acid levels were explored for up to 7 days after cerebral ischemia in the rat. Fifty male Sprague-Dawley rats were subjected to occlusion of the middle cerebral artery on the olfactory tract, under halothane anesthesia. The animals were decapitated at 2, 4, 6, 12, 24 hours and 2, 3, 5, 7 days after the surgery, respectively. The brains were rapidly removed. The cerebral hemispheres were divided into right and left halves, and homogenized in sulfosalicylic acid solution. Free amino acids were analyzed by colormetric method. Cathecholamines and uric acid were analyzed by high-performance liquid chromatography. Each parameters were measured both on the ischemic and contralateral hemispheres. The time course of changes in each parameters were observed by means of the ratio, which is the value of ischemic side divided by that of contralateral side. Free amino acids Dicarboxylic group; Decreases in glutamate and increases in glutamine suggest one aspect of detoxication of ammonia within the ischemia tissue. Monocarboxylic group; GABA, glycine, alanine were increased in early ischemic state, and gradually lowered to the normal values. These suggest the impairment of tricarboxylic acid (TCA) cycle in the ischemic tissues, since these amino acids are closely related to TCA cycle. Essential amino acids, except for tryptophan, were increased until the end of study. These increases suggest the utilization of essential amino acids for protein synthesis might be disturbed in the ischemic tissues. Catecholamines and precursors; Norepinephrine and dopamine were lowered gradually. On the other hand, phenylalanine and tyrosine were increased during ischemia.(ABSTRACT TRUNCATED AT 250 WORDS)     

Changes in serum and striatal free amino acids after Venezuelan equine encephalomyelitis virus infection

The infection with the Venezuelan equine encephalomyelitis virus produced a significant increase in the concentration of alanine, arginine, asparagine, glutamine, isoleucine, leucine, methionine, phenylalanine, threonine, tryptophan, tyrosine, and valine in the striatum of rats. On the contrary, the concentrations of aspartate, GABA, glutamate, and taurine were reduced. Arginine, aspartate, glycine, methionine, phenylalanine, taurine, and tyrosine concentrations were increased in the serum of infected rats. However, the modifications in the content of free amino acids in the striatum and serum of rats that survived the infection were qualitatively and quantitatively different from those detected during the acute phase of the infection.     

Kindling increases the K(+)-evoked Ca2(+)-dependent release of endogenous GABA in area CA1 of rat hippocampus

The release of endogenous amino acids from hippocampal CA1 subslices under basal conditions and the release evoked by high potassium (50 mM K+) depolarization was studied during kindling epileptogenesis. Emphasis was put on the release of the amino acid neurotransmitters gamma-aminobutyric acid (GABA) and glutamate. Kindling was induced by tetanic stimulation of the Schaffer-collaterals/commissural fibers of the dorsal hippocampus of the rat. The calcium-dependent GABA release in the presence of high K+ was significantly increased (40-46%) in fully kindled animals, 24 h after the last seizure, in comparison to controls. At long-term, 28 days after the last seizure, the calcium-dependent GABA release was still significantly increased (45-49%). An increased release of GABA in kindled animals was still found when GABA uptake was blocked by nipecotic acid. In contrast, no significant alterations were encountered in the basal or high potassium induced release of the excitatory amino acids aspartate and glutamate. These results suggest that kindling epileptogenesis is accompanied by a specific and long-lasting enhancement of GABA exocytosis which may lead to a desensitization of the GABA receptor, and thus determine the increase of seizure sensitivity.     

L-DOPA Reverses the Increased Free Amino Acids Tissue Levels Induced by Dopamine Depletion and Rises GABA and Tyrosine in the Striatum

Perturbations in the cerebral levels of various amino acids are associated with neurological disorders, and previous studies have suggested that such alterations have a role in the motor and non-motor symptoms of Parkinson’s disease. However, the direct effects of chronic L-DOPA treatment, that produces dyskinesia, on neural tissue amino acid concentrations have not been explored in detail. To evaluate whether striatal amino acid concentrations are altered in peak dose dyskinesia, 6-hydroxydopamine (6-OHDA)-lesioned hemiparkinsonian mice were treated chronically with L-DOPA and tissue amino acid concentrations were assessed by HPLC analysis. These experiments revealed that neither 6-OHDA nor L-DOPA treatment are able to alter glutamate in the striatum. However, glutamine increases after 6-OHDA and returns back to normal levels with L-DOPA treatment, suggesting increased striatal glutamatergic transmission with lack of dopamine. In addition, glycine and taurine levels are increased following dopamine denervation and restored to normal levels by L-DOPA. Interestingly, dyskinetic animals showed increased levels of GABA and tyrosine, while aspartate striatal tissue levels are not altered. Overall, our results indicate that chronic L-DOPA treatment, besides normalizing the altered levels of some amino acids after 6-OHDA, robustly increases striatal GABA and tyrosine levels which may in turn contribute to the development of L-DOPA-induced dyskinesia.