猕猴在执行图形引导的有序运动过程中额叶皮层抑制性氨基酸变化的初步观察

本实验采用脑内微透析及同效液相色谱荧光分析技术,观察了猕猴在执行视觉图形引导的有序运动任务过程中额叶皮层（前额叶４６区,运动前区的Ｆ７和Ｆ２区以及初级运动皮层的Ｆ１区）透析液中γ－氨其丁酸（ＧＡＢＡ）和甘氨酸浓度的变化。观察到动物在执行ＦＲＳ任务时前额皮层透析液中ＧＡＢＡ浓度较操作前基础浓度明显升高,样品配对ｔ－检验具有显著统计意义;Ｇｌｙ浓度也有升高,但无统计意义。     

Metabolism of hibernating reptiles. Changes of free amino acids in blood, liver and brain.

1. Glutamic acid showed a significant decrease during hibernation in brain cortex. This is attributed to: (a) Transformation to glutamine to detoxicate ammonia. (b) The synthesis of GABA from glutamic acid. (c) It is suggested that the enzyme GAD is active during hibernation. 2. GABA showed a significant increase in liver and brain cortex. It was absent in the blood serum. (a) The present results show that non-neural tissues contain lower GABA than neural tissues. (b) GABA may be formed locally in tissues by decarboxylation of glutamate as well as from pathways connected with tricarboxylic acid cycle. 3. Aspartic acid showed increased levels in blood serum, liver and brain cortex, the greatest increase was observed in liver. 4. A significant increase was recorded in the level of arginine in brain cortex and liver, whilst a smaller percentage increase was recorded in ornithine level. It is assumed that transformation of arginine to ornithine was depressed during hibernation.     

Lithium: Effect on [3H]spiperone binding,ionic content,and amino acid levels in the brain of rats

After prolonged treatment of rats with lithium (pellets, 0.21% lithium carbonate, or 0.5 mg/ml lithium chloride in drinking water) for three months, the level of lithium in plasma was 0.87 meq/liter; in several brain regions, between 1.06–1.39 eq/g wet weight. The content of sodium and potassium in the plasma was normal. The level of potassium in the brain regions tested increased by 13–30% and that of sodium by about 10%. Glycine levels increased significantly in all the regions (cerebral cortex, midbrain, cerebellum, and spinal cord). In the cerebellum GABA was also increased, while glutamine was decreased. In midbrain, apart from increases in glycine levels, alamine, valine, GABA and lysine were also increased. In the spinal cord, glutamic acid was also increased. Changes were largely in the putative neurotransmitters. Long-term treatment with lithium also influenced the high-affinity binding of [³H]spiperone in the cerebral cortex and corpus striatum. Two specific binding sites were found in both brain regions; the main change was the reduction in the lower affinity binding site (B _max2).     

Effect of vibration on gamma-aminobutyric acid metabolism in the brain in various functional conditions of the adrenal cortex]

The low-frequency vibration during 30 min (20 Hz, A = 0.4 mm) has been studied for its influence on the level of components of the GABA system and dicarbonic ++amino acids in male rats at hypo- and hyperfunction of the adrenal cortex. It is shown that under these conditions of the experiment the GABA level and glutamate-decarboxylase activity increase. Hyperfunction of the adrenal cortex against the background of vibration causes a relatively less pronounced increase in the GABA content, than the vibration alone or against the background of inhibition of adrenocortical function in the organism.     

Evidence for net uptake of GABA into mouse astrocytes in primary cultures—Its sodium dependence and potassium independence

Content of GABA was measured in cultured, normal astrocytes (from the brain cortex of newborn mice) together with the effect of nonradioactive GABA on the efflux of labeled GABA from cells previously loaded with [¹⁴C]GABA. An increase of external GABA concentration from 0 to 25 M evoked a rise of the GABA content in the cells to a level which was approximately 50 times that of the incubation medium. Neither 200 nor 2000 M nonradioactive GABA had any effect on the rate of release of radioactivity from cells loaded with [¹⁴C]GABA. Both the high tissue/medium ratio and the lack of a GABA-induced enhancement of the release of radioactivity indicate that the previously observed high-affinity uptake of GABA in cultured astrocytes represents a net uptake and not a homoexchange with endogenous GABA. This uptake is sodium dependent but was found to be unaffected in potassium-free media; the quantitative correlation between GABA transport and sodium transport differed from that reported for synaptosomes.     

Acute effects of sodium valproate and γ-vinyl gaba on regional amino acid metabolism in the rat brain: Incorporation of 2-[14C]glucose into amino acids

Amino acid concentrations have been determined in rat brain regions (cortex, striatum, cerebellum, and hippocampus) by HPLC after administration of acute anticonvulsant doses of sodium valproate (400 mg/kg, i.p.) and -vinyl-GABA (1g/kg, i.p.). After valproate administration the GABA level increases only in the cortex; aspartic acid concentration decreases in the cortex and hippocampus, and glutamic acid decreases in the hippocampus and striatum and increases in the cortex and cerebellum. There are no changes in the concentrations of glutamine, taurine, glycine, serine, and alanine following valproate administration. Only the GABA level increases in all the regions after -vinyl-GABA administration. Cortical analyses 2, 4 and 10 minutes after pulse labeling with 2-[¹⁴C]glucose, i.v., shown no change in the rate of cortical glucose utilization in the valproate treated group. The rate of labeling of glutamic acid is also unchanged, but the rate of labeling of GABA is reduced following valproate administration. After -vinyl-GABA administration there is no change in the rate of labeling of GABA. These biochemical findings can be interpreted in terms of a primary anticonvulsant action of valproate on membrane receptors with secondary effects on the metabolism of amino acid neurotransmitters. This contrasts with the primary action of -vinyl-GABA on GABA-transaminase activity.This paper is dedicated to Dr. Derek Richter on his sevety-fifth birthday     

谷氨酸及γ-氨基丁酸在氯胺酮致大鼠精神分裂样表现中的变化

目的:观察大鼠前额皮层谷氨酸(Glu)及γ-氨基丁酸(GABA)在氯胺酮致精神分裂样表现中的变化。方法:雄性Wistar大鼠32只随机分为生理盐水组(S组,n=16)和氯胺酮组(K组,n=16)。腹腔注射生理盐水或氯胺酮30 mg/kg(容积1 mL),一天一次,连续5天,最后一次给药后0.5 h及2 h分别通过敞箱实验观察大鼠自主活动,并记录刻板行为评分。行为学测试后,取大鼠前额皮层,检测Glu及GABA含量。结果:与S组比较,K组大鼠给药后0.5 h自主活动增强、刻板行为评分增高(P0.05),符合精神分裂症大鼠表现;给药后2 h行为学评分则无显著差异(P0.05);给药后0.5 h及2 h大鼠前额皮层Glu水平均增加、GABA水平均下降(P0.05)。与氯胺酮给药后0.5 h组相比,给药后2 h Glu水平下降(P0.05)、GABA水平则无显著差异(P0.05)。结论:氯胺酮致精神分裂样表现可能与大鼠前额皮层Glu增加及GABA减少有关。     

METABOLITE LEVELS IN BRAIN FOLLOWING EXPERIMENTAL SEIZURES: THE EFFECTS OF ISONIAZID AND SODIUM VALPROATE IN CEREBELLAR AND CEREBRAL CORTICAL LAYERS

Abstract— Levels of glucose, lactate, GABA and cyclic nucleotides were examined in discrete layers of the cerebellum and cerebral cortex of mice following treatment with the anticonvulsant, sodium valproate, and/or the convulsant, isoniazid. The concentrations of the metabolites were essentially uniform among the layers of each region, whether from control or from drug-treated mice. Metabolite concentrations in the isoniazid-treated mice were determined either 30 min after administration (preconvulsive state), or immediatley after the onset of seizures. Glucose and lactate, two markers of energy status in the brain, were only minimally affected by drug treatment. However, the levels of GABA and cyclic nucleotides were markedly different from control values in the drug-treated animals. In the preconvulsive state, GABA levels in cerebellar layers were depressed and the cyclic nucleotides were elevated in most layers of both regions. At the onset of seizures, the reduction of GABA and the elevation of cyclic AMP in both regions was more pronounced than during the preconvulsive state. While the concentration of cyclic GMP remained elevated in the cerebellar layers at the onset of seizures, the level in the cerebral cortex returned to control values. Valproate elevated GABA in all the layers of both regions and decreased the cyclic GMP in the cerebellar layers. Generally, when valproate was administered in combination with isoniazid, it dampened the isoniazid induced changes in the metabolites. The events leading up to a seizure as well as those that sustain it may be reflected by the disparate responses of the metabolites in the cerebellum and cerebral cortex.     

THE UPTAKE OF [3H]GABA BY SLICES OF RAT CEREBRAL CORTEX

—A rapid accumulation of [³H]GABA occurs in slices of rat cerebral cortex incubated at 25° or 37° in a medium containing [³H]GABA. Tissue medium ratios of almost 100:1 are attained after a 60 min incubation at 25°. At the same temperature no labelled metabolites of GABA were found in the tissue or the medium. The process responsible for [³H]GABA uptake has many of the properties of an active transport mechanism: it is temperature sensitive, requires the presence of sodium ions in the external medium, is inhibited by dinitrophenol and ouabain, and shows saturation kinetics. The estimated K_m value for GABA is 2·2 × 10^?5m , and V_max is 0·115 μmoles/min/g cortex. There is only negligible efflux of the accumulated [³H]GABA when cortical slices are exposed to a GABA-free medium. [³H]GABA uptake was not affected by the presence of large molar excesses of glycine, l -glutamic acid, l -aspartic acid, or β-aminobutyrate, but was inhibited in the presence of l -alanine, l -histidine, β-hydroxy-GABA and β-guanidinopropionate. It is suggested that the GABA uptake system may represent a possible mechanism for the inactivation of GABA or some related substance at inhibitory synapses in the cortex.     

In Vivo Changes in γ-Aminobutyric Acid Output from the Cerebral Cortex Induced by Inhibitors of γ-Aminobutyric Acid Uptake and Metabolism

Abstract: The effects of inhibitors of γ-aminobutyric acid (GABA) metabolism or uptake on GABA output from the cerebral cortex was studied by means of a collecting cup placed on the exposed cortex of rats anaesthetized with urethane. GABA was identified and quantified by a mass-fragmentographic method. Ethanolamine-O-sulphate (10⁻² M ) applied directly on the cerebral cortex caused a long-lasting twofold increase in GABA output, whereas dl -2, 4-diaminobutyric acid (5 × 10⁻³ M ) caused a sevenfold increase and β -alanine was inactive. The results indicate that glial uptake has little effect on GABA inactivation in the cerebral cortex. The inhibition of neuronal uptake seems a more effective tool to increase GABA concentration in the synaptic cleft, and consequently also in GABA output, than the inhibition of GABA metabolism.     

REDUCTION OF γ-AMINOBUTYRIC ACID LEVEL IN THE CAT CEREBRAL CORTEX BY AFFERENT ELECTRICAL STIMULATION

—Electrical stimulation for 30 s of one brachial plexus in cat (afferent electrical stimulation = AES) produced a 20% decrease in GABA level of the stimulated (contralateral) cerebral cortex as compared to the non-stimulated (ipsilateral) cortex in the same animal. This change in GABA was reversed within a few seconds after cessation of stimulation. Inhibition of GABA catabolism by aminooxyacetic acid elevated considerably the cortical level of GABA but failed to prevent lowering GABA by AES. When AES was performed in preconvulsive condition induced by administration of picrotoxin, the decrease in GABA was negligible, while similar treatment with pentylenetetrazol had no influence on the decrease in GABA produced by AES. The observed lowering cortical GABA by AES is interpreted as being associated with some mechanism of the inhibitory transmitter inactivation.     

Relation of binding by metabolism of gamma-aminobutyric acid and various reactions of the Krebs cycle in the rat brain

The comparison has been made for the following items: intensity of pyruvate alpha-ketoglutarate, succinate oxidation, the gamma-aminobutyric acid (GABA) formation rate, utilization, total content of GABA, glutamate and alanine, the bound/free form ratio of GABA and glutamate, intensity of binding and desorption of exogenic [I-14C]GABA in homogenates of the cortex, cerebellum and brainstem of the Wistar rats. It is revealed that the intensity of ketoacids oxidation is significantly lower in the cerebellum than in the cortex, but the maximal activity of the enzymes of GABA formation and utilization is higher, due to which considerable oxidation of alpha-ketoglutarate transforming into succinate is possible proceeding the GABA shunt pathway. The cortex homogenates contrary to the cerebellum ones are characterized by the reliably higher intensity of ketoacid oxidation and by insignificant contribution of the GABA-shunt to the succinate production. These differences are in line with the reliably higher content of endogenic bound GABA in the cortex as compared to the cerebellum, with a higher level of binding of exogenic labelled GABA and with less pronounced desorption of the label from neurostructures. An assumption is advanced that the observed differences are related to the known high sensitivity of the cortex and to relative resistance of cerebellum to hypoxia and hypoglycemia.     

GABA对小鼠大脑皮质中GABA受体胚胎发育的调节

本文用ＧＡＢＡ及其受体激动剂和拮抗剂处理培养的胚胎小鼠大脑皮层神经细胞以及精确计时的妊娠小鼠,用放射配体结合法检测ＧＡＢＡＡ及ＧＡＢＡＢ的结合位点数目,研究了ＧＡＢＡ对小鼠大脑皮层ＧＡＢＡ受体胚胎发育的调节作用,结果表明：①ＧＡＢＡ可使培养１５—１７天妊龄的胚胎小鼠大脑皮层神经细胞及出生第１天的仔鼠大脑皮层中的ＧＡＢＡＡ及ＧＡＢＡＢ受体数目增加,这种作用可被蝇蕈醇（Ｍｕｓ）及巴氯芬（Ｂａｃ）分别模拟,对ＧＡＢＡＡ受体的作用可为荷包牡丹碱（Ｂｉｃ）所阻断;②用ＧＡＢＡ处理妊娠７—１３天的小鼠,仔鼠出生第１天其大脑皮层的ＧＡＢＡＡ及ＧＡＢＡＢ受体数目均无变化;③用ＧＡＢＡ处理妊娠１４—１９天的小鼠,仔鼠出生的第１天其大脑皮层中的ＧＡＢＡＡ受体数目增加而ＧＡＢＡＢ受体数目不变;④用ＧＡＢＡ处理妊娠７－１９天的小鼠,仔鼠出生第１天其大脑皮层中ＧＡＢＡＡ及ＧＡＢＡＢ受体数目增加。这说明在胚胎发育的特定时期内,ＧＡＢＡ可诱导其受体数目的增加,这个作用是由ＧＡＢＡ受体调节的。     

COMPARISON OF THE BINDING’ OF β-ALANINE AND y-AMINOBUTYRIC ACID IN SYNAPTOSOMAL-MITOCHONDRIAL FRACTIONS OF RAT BRAIN1

Abstract— Na⁺-dependent ‘binding’ of β-alanine and GABA was examined with synaptosomal-mitochondrial fractions of rat brain incubated for 10 min at 0°C. GABA was bound to a much greater extent than β-alanine to particles of cerebral cortex, whole cerebellum and brain stem. For cerebral cortex, the binding capacity (B_max) for GABA was about 18 limes greater than that for β-alanine. and the affinity of the particles for GABA was about 2′ times greater than for β-alanine. The order of potency of GABA binding to brain regions was cerebral cortex > cerebellum > brain stem, whereas that for β-alanine was the reverse. If the binding of β-alanine is taken to indicate the glial component of the Na⁺-dependent binding process for GABA, then most of the GABA was bound to neuronal elements under the conditions employed.     

Effects of sodium n-dipropylacetate on the GABA level in various areas of the mouse brain]

Regional brain GABA distribution studies show that after administration of sodium n dipropylacetate, a competitive inhibitor of GABA transaminase, the concentration of GABA increases in some regions i.e. Olfactory Bulbs, Hypothalamus, Cortex, Cerebellum. The GABA level remains unchanged in Caudate Nucleus, Pons Medulla, Hippocampus in our experimental conditions. These variations do not correlate with the initial GABA level.     

Early changes in GABA and glutamate levels and aminotransferase activity in parts of the rat brain following whole-body gamma irradiation at an absolutely lethal dose

The contents of gamma-aminobutyric acid (GABA) and glutamate (GL) as well as GABA-aspartate- and alanine aminotransferase activities were measured in rat cerebellum, cerebral cortex and truncus cerebri 1, 3, 6, 24 and 48 hr following total-body gamma-irradiation (60Co) with a dose of 30 Gy. All the indices under study changed in a similar way in the cortex and truncus cerebri while in the cerebellum, GABA level increased and GABA-alpha-ketoglutarate aminotransfearse activity decreased 60 min after irradiation. The levels of GABA and GL in the cortex and truncus cerebri decreased immediately and increased 24 hr after irradiation. Activity of aminotransferases changed in a phase manner: changes in aspartate- and alanine aminotransferase activity were more pronounced than those of GABA-alpha-ketoglutarate aminotransferase activity and correlated with the glutamate level changes.     

Uptake of [14C]GABA by rat brain slices; the effect of Ca2+

The [14C]GABA uptake by slices (0.3 mm thick) of Wistar rat brain cortex was studied for its dependence on the GABA concentration in the medium, time of incubation and the presence of Ca2+. This process is characterized by the absence of saturation; the uptake by slices increases sharply when the concentration of exogenous [14C]GABA reaches 200 microM. Bicucullin (10(-4) M), an antagonist of GABA, inhibits the accumulation of GABA in the concentration of 0.2 microM by 60%, that evidences for a considerable contribution of the receptor binding to this process. The [14C]GABA uptake when Ca2+ is absent in the incubation medium and when its concentration is 10(-3) M is practically the same and comparatively low concentrations of Ca2+ (10(-6)-10(-4] decrease the GABA uptake.     

Changes in brain energy metabolism,neurotransmitters, and choline during and after incomplete cerebral ischemia in spontaneously hypertensive rats

In order to investigate changes in energy metabolism, neurotransmitters, and membrane disorder accompanying incomplete cerebral ischemia, a bilateral common carotid artery occlusion model of spontaneously hypertensive rats was utilized. We measured concentrations of ATP, phosphocreatine (PCr), lactate (Lac), glucose (Glu), acetylcholine (ACh), choline (Ch), and -aminobutyric acid (GABA) in both the cerebral cortex and the subcortical regions after 1 h ischemia, 2 h ischemia, and 2 h reflow following 2 h ischemia, and then examined changes in concentrations of these substances during and after incomplete cerebral ischemia. Also examined were interrelations of changes in these substance levels during ischemia. In the cerebral cortex, levels of ATP, PCr, Glu, and ACh decreased, and levels of Lac, Ch, and GABA increased during ischemia. After recirculation, levels of ATP, PCr, Ch, and GABA tended to return to the normal range. On the other hand, the Lac level remained in the ischemic range and the Glu level rose and greatly exceeded the normal range. With regard to ACh, most animals showed normal levels but some exceeded the normal range. Changes in the subcortical regions were qualitatively the same as those in the cerebral cortex during and after ischemia (except with Glu), but only smaller in degrees. Glu levels remained unchanged during ischemia. Correlation of the levels of these substances in the cerebral cortex was examined using normal and ischemic values. A high correlation was generally observed between ATP and other substance levels. The relations between ATP and either PCr or Glu levels were linear. The relation between ATP and ACh levels was logarithmic. The relations between ATP and either Lac, Ch, or GABA levels were exponential. Namely, ACh, Lac, Ch, and GABA levels stayed constant until ATP fell to some fixed low level, suggesting the existence of a threshold. High correlations were also observed among Lac, Ch, and GABA levels.     

Effect of sodium n-dipropylacetate (sodium valproate) on GABA level of neuronal and glial cells in culture]

The effect of sodium n dipropylacetate (nDPA), a competitive GABA-T inhibitor with respect to GABA, has been investigated on glial and neuronal cellular GABA level. After 1 to 4 days incubation with nDPA in the culture medium, a decrease of GABA level in M5 neuroblastoma clonal cell lines and no modification of GABA level in C6 astrocytoma cells has been observed. The combined addition of nDPA 4 micrometer with dibutyryl cyclic AMP (1 mM) to the culture medium induces the same decrease in GABA level in C6 astrocytoma cells as the addition of DB-c-AMP alone. After shorter incubation time with nDPA (5-150 min), we observed a decreased GABA level in C6 astrocytoma glial cells.     

Mechanism of action of an anticonvulsant, sodium dipropylacetate

The hypothesis that the brain GABA level increase which is induced by a sodium dipropyl acetate treatment arises either through inhibition of succinic semialdehyde dehydrogenase (SSADH), or through inhibition of GABA transaminase by succinic semialdehyde (SSA), has been considered. It appeared that in vivo brain GABA level increase cannot be attributed to SSADH inhibition, and that SSA is not a GABA precursor. It has been shown that SSA is neither in vivo nor in vitro a GABA-transaminase inhibitor. 4-hydroxybenzaldehyde, a potent SSADH inhibitor did not increase GABA level at a dosage which induces a 99% inhibition of SSADH.