蓝斑核对上呼吸道阻力肌—颏舌肌功能的影响

本实验在３８只经氨基甲酸乙酯麻醉的健康家兔上进行,观察了电、化学刺激蓝斑核（ＬＣ）对颏舌肌功能的影响。结果如下：（１）长串电脉冲刺激蓝斑核使颏舌肌肌电活动明显增强,表现为长吸性肌电积分幅度升高,膈肌亦出现与颏舌肌同步的肌电活动增强。（２）ＬＣ内微量注射胞体兴奋剂谷氨酸钠,也引起明显的颏舌肌和膈肌肌电活动增强。（３）上述电、化学刺激的区域对照和盐水对照实验,均未出现有意义的肌电改变。提示：电、化学刺激ＬＣ可特异性增强上呼吸道阻力肌──颏舌肌的紧张性活动,具有减小上呼吸道阻力的作用,这对于某些上呼吸道阻塞性疾病发病机制的研究可能具有重要的意义。     

Oxic and anoxic growth of a new Citrobacter species on amino acids

A facultatively anaerobic bacterium, strain P-88, was enriched selectively under dual limitation by glutamate and oxygen in a chemostat. The new strain is a gram-negative motile rod. The mol% guanine plus cytosine of the DNA is 51.4±0.6 mol%. The organism grows on citrate as a sole source of carbon and energy, does not form acetoin, does not induce lysine decarboxylase and was thus classified as a species of the genus Citrobacter. A remarkable characteristic of the new isolate is its ability to grow on several amino acids with either a respiratory or a fermentative type of metabolism. Under strictly anoxic conditions glutamate was fermented to acetate, H₂, CO₂ and ammonia. Asparagine, aspartate and serine could also be fermented. Furthermore, all type strains of the genus Citrobacter were shown to have the same fermentative abilities. Based on enzyme activities determined in cell-free extracts a combination of the methylaspartate pathway and the mixed acid fermentation of Enterobacteriaceae is proposed to explain the glutamate fermentation pattern observed in cultures of strain P-88. Analysis of the growth of strain P-88 in continuous culture with various degrees of oxygen supply, demonstrated that the bacterium can rapidly switch between oxic and anoxic metabolism. Cultures of strain P-88 grown under oxygen limitation simultaneously respire and ferment glutamate, suggesting that the organism is particularly well adapted to growth in microoxic environments.     

Transmitter amino acid levels in rat brain regions after amygdala-kindling or chronic electrode implantation without kindling: Evidence for a pro-kindling effect of prolonged electrode implantation

Kindling is a chronic model of epilepsy characterized by a progressive increase in response to the same regularly applied stimulus. The biological basis of the kindling phenomenon requires to be determined, but several studies indicate that alterations in amino acidergic neurotransmission may be involved. In the present experiments, levels of glutamate, aspartate, GABA, glycine, and taurine were determined in 12 brain regions by HPLC in 3 groups of animals: (a) a group which was kindled via electrical stimulation of intraamygdala electrodes and was sacrificed 36 days after the last fully kindled seizure for neurochemical determinations; (b) a group of implanted but nonstimulated rats (surgical control group) in which neurochemical measurements were done at the same time after electrode implantation as the kindled group, and (c) a group of non-implanted, naive control rats. Compared to surgical controls, kindling induced a significant reduction of glutamate, GABA, and taurine in the brain stem (pons/medulla), whereas no differences between both groups were found in any of the other regions. However, both electrode-implanted groups differed significantly from non-implanted naive rats in several regions, indicating that electrode-implantation per se induced long-lasting alterations in transmitter amino acids. The most striking difference to naive controls was an increase of glycine levels in several regions in which this amino acid is known to potentiate glutamatergic transmission. In order to examine the functional consequences of prolonged electrode implantation, seizure thresholds were determined in groups of rats with short and prolonged electrode implantation. Data from these experiments indicated that prolonged electrode implantation per se induces pro-kindling effects, i.e. a dramatic decrease of seizure threshold. The data of this study thus demonstrate that the choice of adequate controls is critical in neurochemical and functional studies on the kindling phenomenon.     

Effect of beta-N-oxalylamino-l-alanine on cerebellar cGMP level in vivo

Beta-N-oxalylamino-l-alanine (BOAA), a non-protein amino acid present in the seeds of Lathyrus Sativus (LS), is one of several neuroactive glutamate analogs reported to stimulate excitatory receptors and, in high concentrations, cause neuronal degeneration. In the present study, the in vivo acute effects of synthetic BOAA and LS seed extract were investigated on rat cerebellar cyclic GMP following intraperitoneal (10–100 mg/kg) or oral (100 mg/kg) administration of subconvulsive doses of toxin. Furthermore, the BOAA content in LS seeds and in the cerebellum of injected rats was determined by high performance liquid chromatograph analysis. A dose- and time-dependent increase of cerebellar cyclic guanosine monophosphate (cGMP) level was observed after intraperitoneal administration of synthetic BOAA or LS extract. The neurotoxin evoked a maximum stimulation 90 min after injection within the dose range of 50–75 mg/kg, elevating cGMP from basal levels of 5.3±0.5 pmol/mg protein to 15±1.3 pmol/mg protein. Similarly, the oral intake of LS-extracted neurotoxin resulted in the elevation of cGMP content. Kynurenic acid (300 mg/kg i.p.), a non specific excitatory amino acid antagonist, was effective in blocking LS BOAA-elicited cGMP enhancement. The data suggest that in the cerebellum acute administration of low concentrations of BOAA exert in vivo activation of glutamate receptors involved in the regulation of cGMP level.     

新生大鼠脊髓切片运动神经元的电生理参数测定

用微电极技术对新生大鼠脊髓横切薄片运动神经元(MN)进行细胞内记录,测得静息电位为-62±4mV(n=26),膜电阻为67±31MΩ,时间常数3.8±1.6ms,动作电位幅度68±7mV(n=26),阈电位-50±8mV,超射值6±4mV。灌流谷氨酸(1～30mmol/L)诱导伴膜电阻降低的缓慢去极化反应,5-羟色胺(50μmol/L)介导伴膜电导降低的电压依赖性内向电流。结果表明新生大鼠脊髓切片MN的细胞内生物电记录是一种稳定可靠的电生理学和药理学研究方法。     

Inorganic nitrogen regulation of glutamate uptake in the cyanobacterium Nostoc muscorum

In Nostoc muscorum (Anabaena ATCC 27893) glutamate was not metabolised as a fixed nitrogen source, rather it functioned as an inhibitor of growth. The latter effect was nitrogen source specific and occurred in N₂-fixing cultures but not in cultures assimilating nitrate or ammonium. NO₃^--grown cultures lacked heterocysts and nitrogenase activity and showed a nearly 50% reduction in glutamate uptake rates, as well as in the final extent of glutamate taken up, compared to N₂-fixing or nitrogen-limited control cultures. NH₄⁺-grown cultures showed a similar response, except that the reduction in glutamate uptake rates and the final exten of glutamate taken up was over 80%. The present results suggest a relation between nitrate/ammounium nitrogen-dependent inhibition of glutamate uptake, probably via repression of the glutamate transport system, and glutamate toxicity.     

Neuronal apoptosis versus necrosis induced by glutamate or free radicals

The type of cell death encountered in neuronal cell cultures exposed to excitatory amino acids — such as glutamate, the major excitatory neurotransmitter in the central nervous system, or free radicals, such as nitric oxide (NO^.) and superoxide anoin (O2^{. –}), which react to form peroxynitrite (ONOO^–) — appears to depend on the intensity of the exposure and may involve two temporarily distinct phases. Following relatively fulminant insults, an initial phase of necrosis — associated with extreme energy depletion — may simply reflect the failure of neurons to carry out the default apoptotic death program used to efficiently dispose of aged or otherwise unwanted cells. Neurons recovering mitochondrial energy potential after an initial fulminant insult or following a more subtle inciting injury may subsequently undergo apoptosis, possibly associated with a factor released from mitochondria that triggers this death program. The maintenance of balanced energy production may be a decisive factor in detemining the degree, type, and progression of neuronal injury caused by excitotoxins and free radicals. Similar events could possibly occur in vivo after ischemia or other insults.     

Glutamate-induced swelling of cultured astrocytes is mediated by metabotropic glutamate receptor

The effects of glutamate and its agonists and antagonists on the swelling of cultured astrocytes were studied. Swelling of astrocytes was measured by [3H]-O-methyl-D-glucose uptake. Glutamate at 0.5, 1 and 10mmol/L and irons-l-aminocyclopentane-1,3-dicarboxylic acid (trans-ACPD), a metabotropic glutamate receptor (mGluR) agonist, at 1 mmol/L caused a significant increase in astrocytic volume, whereas alpha-amino-3-hydroxy-5-methyl-4-isoxazole proprionic acid (AMPA) was not effective. L-2-amino-3-phosphonopropionic acid (L-AP3), an antagonist of mGluR, blocked the astrocytic swelling induced by trans-ACPD or glutamate. In Ca2+-free condition, glutamate was no longer effective. Swelling of astrocytes induced by glutamate was not blocked by CdCl2 at 20 μmol/L, but significantly reduced by CdCl2 at 300 μmol/L and dantrolene at 30 μmol/L. These findings indicate that mGluR activation results in astrocytic swelling and both extracellular calcium and internal calcium stores play important roles in the genes     

Synapse maturation and structural plasticity at Drosophila neuromuscular junctions

The Drosophila larval neuromuscular junction has recently emerged as a powerful model system to characterize the cellular and molecular events involved in the formation and flexibility of synapses. The combination of molecular, genetic, electrophysiological and anatomical approaches has revealed, for example, the functional significance of the discs-large gene product (a novel synapse-organizing protein) in the nervous system. This protein is involved in the clustering of at least one ion channel and in the structural modification of glutamatergic synapses during target muscle growth. The manipulation of the genes encoding ion channels, components of second-messenger cascades, and cell adhesion molecules is beginning to tease apart the mechanisms underlying structural synaptic plasticity.     

谷氨酸钠流化床吸附脱色的柱过程研究

以颗粒活性炭(GAC)为吸附剂,采用多柱串联流化床进行味精中和液脱色,对柱过程进行了模拟研究。测定了平衡数据、传质动力学及流体流动参数,建立了具有广泛适应性的,包括颗粒分级、粒度分布、内外扩散及两相返混的宽粒度液固流化床吸附过程模型。对所研究体系的模拟计算与实验结果符合较好。