A recent chemical spill of 4-Methylcyclohexanemethanol (4-MCHM) in West Virginia left 300,000 people without water. Officials claimed that this compound is not lethally toxic, but potentially harmful if swallowed or inhaled, and can cause eye and skin irritation. Sittig's Handbook of Toxic and Hazardous Chemical Carcinogens reports high exposures from skin contact or inhalation may cause damage to the heart, liver, kidneys, and lungs, and may result in death. However, no quantitative data seem to exist and no references can be found on neurotoxicity. We have investigated the neurotoxicity of 4-MCHM using mammalian nerve cell networks grown on microelectrode arrays. Network spontaneous activity from multiple units (range 48 – 120 per network) were used as the primary readout. Individual units were followed based on spike waveforms digitized at 40 kHz (Plexon MNAP system). Dose response curves show the effective inhibitory concentration at 50 percent decrease (EC50) to average 27.4 microM SD±6.17. However, in the presence of 40 microM bicuculline, a competitive GABAA antagonist, the EC50 shifts to 70.63uM SD ±4.3; implying that early, low concentration exposures to 4-MCHM involve GABA activation. Initial activity loss occurs without active unit loss (defined as 10 or more template threshold crossing per min), indicating functional interference with spike production. Full recovery has not been seen at concentrations above 130 microM, unless the culture was given bicuculline. Direct exposure to 400uM results in immediate, irreversible loss of spike production, followed by necrosis of glia and neurons.

Introduction: Neuroactive steroids represent a class of both synthetic and naturally occurring steroids that have an effect on neural function. In addition to classical genomic mechanism by the hormones progesterone, deoxycorticosterone and testosterone 3α-OH metabolites of these hormones enhance GABAA receptor through rapid non-genomic mechanism. The site(s) of action of these neuroactive steroids namely 3α-OH-5α-pregnan-20 one, (3α,5α)-3,21-deoxycorticosterone(3α5α-THDOC) and 5α androstane-3α,17β-diol on GABAA receptor are distinct from that of benzodiazepines and barbiturate binding sites. The modulation site(s) has a well-defined structure activity relationship with a 3α-hydroxy and a 20-ketone configuration in the pregnane molecule required for agonistic action. Pregnenolone sulfate is a noncompetitive GABAA receptor antagonist and inhibit GABA activated Cl- current in an activation dependant manner. 3β-hydroxy A-ring reduced pregnane steroids are also GABAA receptor antagonist and inhibit GABAA receptor function and its potentiation induced by their 3α-diesteromers in a noncompetitive manner. Aim: The aim was to investigate if the effect of GABA, pentobarbital antagonism by bicuculline and if the effect of GABA-agonist and antagonist neuroactive steroids including pregnenolone sulfate is dependant on the α-subunits of GABAA receptor. Furthermore, the studies aimed at investigating the binding site of pregnenolone sulfate and if its effect is dependent on γ-subunit. In addition, the inhibitory effect of pregnenolone sulfate and 3β-hydroxy steroids has been characterized. We also wanted to investigate if the neuroactive steroids effect vary between the human and rat recombinant α1β2γ2L receptors and between the long (L) and short (S) variants of γ2-subunit. Method: Experiments were performed by the two electrodes voltage-clamp technique using oocytes of Xenopus laevis expressed with recombinant GABAA receptors containing α1, α4 or α5, β2, γ2L and γ2S-subunits. Results: There was no difference between the α1, α4 and α5-containing subunits regarding GABA and pentobarbital inhibition by bicuculline. GABA-activated current in the binary αβ was potent than that of ternary αβγ receptor. Unlike Zn2+ effect, inhibition by pregnenolone sulfate on the GABAA receptor is not dependant on the γ-subunit. It is likely that the 2’ residue closest to the N-terminus of the protein at M2 helix on both α1 and β2 subunit are critical to the inhibitory actions of PS and the function of Cl- channels. Point mutation at M2 helix of the β2-subunit (b2A252S) can dramatically reduce the inhibitory effect of PS on the GABAA receptors without affecting the inhibitory properties of 3β-hydroxysteroids. Agonist and antagonist steroids also varied in their efficacy between the human and rat α1β2γ2L receptor. Neuroactive steroids also showed difference between human γ2L and γ2S-containing receptor. Conclusions: GABA and pentobarbital antagonism by bicuculline is not dependant on α-subunit. Pregnenolone sulfate binding site is different from that of Zn2+. 3β-hydroxysteroids and pregnenolone sulfate inhibit GABAA receptor through different mechanisms. Neuroactive steroids also differ between species and between the long and short variant of γ- subunit.

As a major public health problem affecting more that 76.5 million Americans, chronic pain is one main reason why people seek medical attention. It is a pathological nervous system disorder that persists for months or years. Sensitization of nociceptive neurons in the dorsal horn of the spinal cord is crucial in the development of allodynia and hyperalgesia. The work presented in this thesis will focus on spinal protein kinase M zeta (PKMζ)-mediated plasticity and GABAergic disinhibition as spinal amplification mechanisms that orchestrate persistent changes in the dorsal horn of the spinal cord. As a result of central sensitization following peripheral nerve injruy, GABAergic disinhibition occurs due to an alteration in Cl- homeostasis via reduced KCC2 expression and function. Intrathecal administration of acetazolamide (ACT), a carbonic anhydrase inhibitor, attenuated neuropathic allodynia and spinal co-adminitation of ACT and midazolam (MZL), an allosteric modulator of the benzodiazepine class of GABAA receptors, synergistically inhibited neuropathic allodynia. Further studies concerning the impact of altered Cl-homeostasis via reduced KCC2-mediated Cl-extrusion capacity on the analgesic efficacy and potency of GABAA receptor agonist and allosteric modulators revealed that there is a differential regulation of the agonists and allosteric modulators at the GABAA receptor complex when Cl-homeostasis is altered. Another spinal amplification mechanism leading to central sensitization is PKMζ-mediated spinal LTP. In model of persistent nociceptive sensitization, allodynia induced by IL-6 injection or plantar incision was abolished by both the inhibition of protein translation machinery and PKMζ inhibitor, ZIP. However, only PKMζ inhibition prevented the enhanced pain hypersensitivity precipitated by a subsequent stimulus after the initial hypersensitivity had resolved, asserting that spinal PKMζ underlies the maintenance mechanisms of persistent nociceptive sensitization. Also, these results confirmed that the initiation mechanisms of persistent sensitization parallel LTP initiation mechanisms and the maintenance mechanisms of persistent sensitization parallel LTP maintenance mechanisms. Taken together, these results indicate that these amplification mechanisms drive a chronic persistent state in these models such that inhibition of these spinal amplication mechanisms will serve as an effective approach in the quenching chronic pain hypersensitivity in chronic pain models.

A blockade of GABAergic inhibition increases the receptive field(RF) size of most somatosensory cortex (SI) and some ventrobasal thalamus (VB) neurons. The results suggest RF size of cuneate neurons may be modulated through GABAa and GABAb receptors, independent of firing frequency.

Fast postsynaptic inhibition in the brain is mediated by ionotropic GABA_A receptors (GABA_ARs), which are activated by the release of the neurotransmitter GABA from presynaptic interneurons. The GABA_AR is primarily permeable to chloride ions (Cl-) and therefore the transmembrane gradient for Cl- sets the reversal potential of the receptor (E_GABA-A). When intracellular Cl^- concentrations are relatively low, E_GABA-A is more negative than the membrane potential and GABA_AR responses will have a hyperpolarising and inhibitory effect upon the postsynaptic cell. In contrast, when intracellular Cl^- concentrations are relatively high, E_GABA-A will be more positive and GABA_AR activation will have a depolarising effect. How a neuron controls its intracellular Cl^- concentrations is a fundamental question that has direct relevance to hyperexcitability conditions such as epilepsy. Recently, it has become clear that Cl^- homeostasis is altered in epileptic tissue such that postsynaptic inhibition via the GABA_AR is reduced and, under some conditions, GABA_AR signalling may even be excitatory. In my thesis I explore some of the mechanisms and factors that are responsible for regulating postsynaptic GABA_AR signalling in the context of epileptic seizure activity in the rat hippocampus. In the first series of experiments I combined pharmacological approaches with electrophysiological recordings from pyramidal neurons in the CA3 region of the hippocampus to trigger seizure activity. My results show that intense neuronal activity during a seizure leads to a transient accumulation of intracellular Cl^-, which generates a pronounced depolarising shift in E_GABA-A. Under these conditions, GABAergic synapses become excitatory and contribute to ongoing neuronal activity rather than exerting their normal inhibitory role. I found that the same seizure activity also induces the release of a neuromodulator called adenosine, which serves to limit the deleterious effects of excitatory GABA_AR responses. Adenosine exerts these effects by activating downstream potassium channels, which increase the postsynaptic cell’s membrane conductance and, in doing so, ‘shunt’ incoming GABA_AR responses. In the second series of experiments I examined Cl^- homeostasis and E_GABA-A in the context of neonatal seizures. One of the main mechanisms by which neurons maintain their intracellular Cl^- levels is through the activity of ion transporter proteins that reside in the membrane and move Cl^- either into, or out of, the cell. I discovered that the intracellular trafficking of an important Cl^- transporter protein, NKCC1, correlates with changes in Cl^- homeostasis. Using a combination of biochemical and molecular techniques, I then identified a novel molecular association between NKCC1 and a motor protein, Myosin Va, which has been implicated in the intracellular trafficking of membrane proteins. Using electrophysiological recordings I found that Myosin Va is required for NKCC1’s contribution to Cl^- homeostasis, which may be important for E_GABA-A changes in epilepsy. In the final series of experiments I developed methods to study the temporal dynamics in E_GABA-A during a single seizure. These revealed a Cl^- unloading mechanism that emerges at the end of a seizure and which depends upon hyperpolarisation of the postsynaptic membrane potential. This mechanism aids E_GABA-A recovery after the seizure and moves E_GABA-A to more hyperpolarised values. This mechanism could boost postsynaptic inhibition after a seizure and thereby help to protect against further seizure episodes. In conclusion, this work extends our understanding of postsynaptic GABAergic transmission in the context of epileptic seizure activity and suggests new mechanisms that could be relevant for the development of rational anti-epileptic treatments.

Quelque 30 % de la population neuronale du cortex mammalien est composée d’une population très hétérogène d’interneurones GABAergiques. Ces interneurones diffèrent quant à leur morphologie, leur expression génique, leurs propriétés électrophysiologiques et leurs cibles subcellulaires, formant une riche diversité. Après leur naissance dans les éminences ganglioniques, ces cellules migrent vers les différentes couches corticales. Les interneurones GABAergiques corticaux exprimant la parvalbumin (PV), lesquels constituent le sous-type majeur des interneurones GABAergiques, ciblent spécifiquement le soma et les dendrites proximales des neurones principaux et des neurones PV+. Ces interneurones sont nommés cellules à panier (Basket Cells –BCs) en raison de la complexité morphologique de leur axone. La maturation de la connectivité distincte des BCs PV+, caractérisée par une augmentation de la complexité de l’axone et de la densité synaptique, se déroule graduellement chez la souris juvénile. Des travaux précédents ont commencé à élucider les mécanismes contrôlant ce processus de maturation, identifiant des facteurs génétiques, l’activité neuronale ainsi que l’expérience sensorielle. Cette augmentation marquante de la complexité axonale et de la synaptogénèse durant cette phase de maturation suggère la nécessité d’une synthèse de protéines élevée. La voie de signalisation de la cible mécanistique de la rapamycine (Mechanistic Target Of Rapamycin -mTOR) a été impliquée dans le contrôle de plusieurs aspects neurodéveloppementaux en régulant la synthèse de protéines. Des mutations des régulateurs Tsc1 et Tsc2 du complexe mTOR1 causent la sclérose tubéreuse (TSC) chez l’humain. La majorité des patients TSC développent des problèmes neurologiques incluant des crises épileptiques, des retards mentaux et l’autisme. D’études récentes ont investigué le rôle de la dérégulation de la voie de signalisation de mTOR dans les neurones corticaux excitateurs. Toutefois, son rôle dans le développement des interneurones GABAergiques corticaux et la contribution spécifique de ces interneurones GABAergiques altérés dans les manifestations de la maladie demeurent largement inconnus. Ici, nous avons investigué si et comment l’ablation du gène Tsc1 perturbe le développement de la connectivité GABAergique, autant in vitro que in vivo. Pour investiguer le rôle de l’activation de mTORC1 dans le développement d’une BC unique, nous avons délété le gène Tsc1 en transfectant CRE-GFP dirigé par un promoteur spécifique aux BCs dans des cultures organotypiques provenant de souris Tsc1lox. Le knockdown in vitro de Tsc1 a causé une augmentation précoce de la densité des boutons et des embranchements terminaux formés par les BCs mutantes, augmentation renversée par le traitement à la rapamycine. Ces données suggèrent que l’hyperactivation de la voie de signalisation de mTOR affecte le rythme de la maturation des synapses des BCs. Pour investiguer le rôle de mTORC1 dans les interneurones GABAergiques in vivo, nous avons croisé les souris Tsc1lox avec les souris Nkx2.1-Cre et PV-Cre. À P18, les souris Tg(Nkx2.1-Cre);Tsc1flox/flox ont montré une hyperactivation de mTORC1 et une hypertrophie somatique des BCs de même qu’une augmentation de l’expression de PV dans la région périsomatique des neurones pyramidaux. Au contraire, à P45 nous avons découvert une réduction de la densité des punctas périsomatiques PV-gephyrin (un marqueur post-synaptique GABAergique). L’étude de la morphologie des BCs en cultures organotypiques provenant du knock-out conditionnel Nkx2.1-Cre a confirmé l’augmentation initiale du rythme de maturation, lequel s’effondre ensuite aux étapes développementales tardives. De plus, les souris Tg(Nkx2.1Cre);Tsc1flox/flox montrent des déficits dans la mémoire de travail et le comportement social et ce d’une façon dose-dépendante. En somme, ces résultats suggèrent que l’activation contrôlée de mTOR régule le déroulement de la maturation et la maintenance des synapses des BCs. Des dysfonctions de la neurotransmission GABAergique ont été impliquées dans des maladies telles que l’épilepsie et chez certains patients, elles sont associées avec des mutations du récepteur GABAA. De quelle façon ces mutations affectent le processus de maturation des BCs demeuret toutefois inconnu. Pour adresser cette question, nous avons utilisé la stratégie Cre-lox pour déléter le gène GABRA1, codant pour la sous-unité alpha-1 du récepteur GABAA dans une unique BC en culture organotypique. La perte de GABRA1 réduit l’étendue du champ d’innervation des BCs, suggérant que des variations dans les entrées inhibitrices en raison de l’absence de la sous-unité GABAAR α1 peuvent affecter le développement des BCs. La surexpression des sous-unités GABAAR α1 contenant des mutations identifiées chez des patients épileptiques ont montré des effets similaires en termes d’étendue du champ d’innervation des BCs. Pour approfondir, nous avons investigué les effets de ces mutations identifiées chez l’humain dans le développement des épines des neurones pyramidaux, lesquelles sont l’endroit privilégié pour la formation des synapses excitatrices. Somme toute, ces données montrent pour la première fois que différentes mutations de GABRA1 associées à des syndromes épileptiques peuvent affecter les épines dendritiques et la formation des boutons GABAergiques d’une façon mutation-spécifique. / About 30% of the total neuronal population in the mammalian cortex is composed by a very heterogeneous population of GABAergic interneurons. These interneurons differ in their morphology, gene expression, electrophysiological properties and subcellular targets, thus establishing a rich diversity. After birth in the ganglionic eminences these cells migrate to distinct cortical layers. Parvalbumin (PV) expressing cortical GABAergic cells which constitute the major GABAergic subtype specifically targets the soma and proximal dendrites of principal neurons and PV+ cells. These cells are often referred as Basket cells (BCs) because of the intricate morphological complexity of their axons. The maturation of the distinct connectivity of PV+ BCs, characterized by an increase of axon complexity and synapse density, occurs gradually in juvenile mice. Previous studies started to elucidate the mechanisms controlling this maturation process, including genetic factors, neuronal activity and sensory experiences. The striking increase in axonal complexity and synaptogenesis occurring during the maturation phase suggests the requirement for elevated proteins synthesis in order to sustain the developmental process. The Mechanistic Target Of Rapamycin (mTOR) pathway has been implicated in controlling several aspects of neurodevelopment by regulating protein synthesis. Mutations in the regulatory components Tsc1 and Tsc2 of mTOR-Complex1 (mTORC1) cause the disease Tuberous Sclerosis (TSC) in humans. The majority of TSC patients develop neurological problems including seizures, mental retardation and autism. Recent studies investigated the role of mTOR pathway dys-regulation in excitatory cortical cells, however its role in the development of cortical GABAergic interneurons and the specific contribution of altered GABAergic cells in disease manifestation remain largely unknown. Here, we investigated whether and how Tsc1 knockout perturbs GABAergic circuit development, both in vitro and in vivo. To investigate the role of mTORC1 activation in BC development, we knocked out Tsc1 expression, by transfecting Cre-GFP driven by a promoter specific for BCs in cortical organotypic cultures prepared from Tsc1lox mice. Tsc1 knockdown in vitro caused a precocious increase in bouton density and terminal branching formed by mutant BCs, which was reversed by Rapamycin treatment. These data suggest that mTOR pathway hyperactivation affects the timing of BC synapse maturation. To investigate the role of mTORC1 in GABAergic cells in vivo, we bred Tsc1lox mice with Nkx2.1-Cre and PV-Cre mice. At P18, Tg(Nkx2.1Cre),Tsc1flox/flox mice showed both mTORC1 hyperactivation and somatic hypertrophy in BCs along with increased expression of PV in the perisomatic region of pyramidal neurons. In contrast, by P45 we found a reduction of PV-gephyrin (post-synaptic GABAergic marker) perisomatic puncta density. Study of BC morphology in organotypic cultures from the Nkx2.1-Cre conditional knockout confirmed the occurrence of a faster maturation rate initially which however collapsed at later stages. Additionally Tg(Nkx2.1Cre),Tsc1flox/flox mice exhibit Tsc1 dose-dependent deficits in working memory and social behaviour. All together, these results suggest that controlled mTOR activation regulates both the time course and the maintenance of BC synapses. Dysfunction of GABAergic neurotransmission has been implicated in several disease states like epilepsy and in some patients it is associated with mutations in the GABAA receptor. How these mutations affect the BC cell maturation process remains largely unknown. To address this question, we used the Cre-lox strategy to knockout the endogenous GABRA1 gene coding for the GABAA-receptor alpha-1 subunit in single PV-expressing basket cells (BCs) in organotypic cultures. Cell-autonomous loss of GABRA1 reduced the extent of BC innervation field suggesting changes in inhibitory inputs caused by the absence of GABAAR α1 subunit may alter BC development. Over-expression of mutant GABAAR α1 subunits (found in patients diagnosed with epilepsy) show similar effects in terms of BC target coverage. Further studies involved the effect of these human mutations in the development of Pyramidal cell dendritic spines, which are the preferential site for excitatory synapse formation. Altogether, this data show for the first time that different GABRA1 mutations associated with genetic epilepsy syndromes can affect dendritic spine and GABAergic bouton formation in a mutation-specific manner.

Ziel dieser Arbeit war die Synthese von (RS)-5-Amino-3-aryl(methyl)-pentansäure Hydrochloride, 3-Aminomethyl-5-chlor-benzolsäure Hydrochlorid und(RS)-4-Amino-3-(4´-ethynyl(jod)-phenyl)-butansäure Hydrochloride und die Testung der pharmakologischen Aktivität dieser Verbindungen. Die synthetisierten Verbindungen wurden als GABAB-Rezeptor Agonisten, in einem auf Ca2+-Messungen basierenden Funktional-Assay (in vitro tsA Zellen mit GABAB1b/GABAB2/Gαq-z5 transfektiert), getestet und daraus ein Struktur-Aktivitäts Modell abgeleitet. Im allgemein Teil dieser Arbeit wird ein Überblick, über die Neurotransmitter- Rezeptoren (Liganden gesteuerte Ionen-Kanal-Rezeptoren und G Protein-gekoppelte Rezeptoren) des zentralen Nervensystems und deren Agonisten und Antagonisten, gegeben. Eine ausführliche Diskussion zur Synthesestrategie der Verbindungen der Zwischenstufen und der Ausgangsmaterialien wird in den Schemata 2-6 beschrieben. Die synthetisierten Verbindungen wurden als GABAB Agonisten geprüft. Zusätzlich wurden diese im 3D Homologie Modell mit FlexiDock Programm gedockt. Daraus wurde ein Modell zur Voraussage der Aktivität von Analogen und Homologen des Baclofens abgeleitet. Letztendlich wurde ein Pharmakophor-Modell für GABAB Agonisten mit DISCO (DIStance COmparisons) Programm erstellt. / Synthesis of (RS)-5-amino-3-aryl (methyl)-pentanoic acid hydrochlorides, 3 aminomethyl-5-chloro-benzoic acid hydrochloride and (RS)-4-amino-3-(4`-ethynyl(iodo)-phenyl)-butanoic acid hydrochlorides have been accomplished. The aim of their synthesis was to evaluate their GABABR agonist activity and to derive a model which will correlate their structure with the observed pEC50. The GABABR agonist activity of the prepared compounds has been determined in functional assay based on calcium measurement in vitro using tsA cells transfected with GABAB1b/GABAB2/Gαq-z5. Reviews on the neurotransmitter receptors (ligand-gated ion channel receptors and G protein-coupled receptors), their agonists and antagonists have been given in the general part of this work. A detailed discussion on the strategy followed for the synthesis of the designed compounds as well as the starting materials and intermediates has been described and illustrated in Schemes 2-6. The synthesized compounds were evaluated for their GABABR agonist activity. Furthermore, these compounds were docked in the available 3D homology model of GABABR using the program FlexiDock implemented in SYBYL software. Subsequently, we derived a predictive model which correlates the experimentally determined pEC50 with the calculated binding energy of certain baclofen analogues and homologues. In addition, we used the program DISCO (DIStance COmparisons) implemented in SYBYL software to find the pharmacophore features of GABAB agonists.

Thesis advisor: Stephen C. Heinrichs / This study investigated the effects of baclofen, a GABAB agonist, on modulating drug seeking and drug reward in a novel model of reinstatement. To investigate drug seeking, rats were trained to nosepoke for cocaine infusions, given a drug holiday, and under a baclofen pretreatment (0, 0.2, 1, or 5 mg/kg i.p.), were exposed to an odor conditioned discriminative stimulus (DS+) that reinstated cocaine self-administration. To investigate drug reward, an odor reactivity test was used. Rats were tested for changes in odor preference after the acquisition, drug holiday, and reinstatement phases of self-administration behavior were each completed. Pretreatment with the low dose of baclofen (0.2) attenuated cocaine seeking primed by a conditioned DS+. Medium doses (1.0) caused no change in drug seeking. High doses (5.0) caused a reduction in drug seeking, but this was due to motor impairment. No doses of baclofen had any affect on the rewarding properties of cocaine or cocaine-associated stimuli. It can be concluded that GABAB receptors have no role in modulating the rewarding properties of drug rewards or drug-associated stimuli, but instead play a role in modulating drug seeking. In rats that were exposed to a drug in the past, low levels of GABAB receptor activation reduce drug-seeking, while medium to high levels could have reduced dopamine levels to the point that increased drug seeking or motor impairment was seen. / Thesis (BA) — Boston College, 2004. / Submitted to: Boston College. College of Arts and Sciences. / Discipline: Psychology. / Discipline: College Honors Program.

Recent research had shown a correlation between aging and decreasing Gamma-aminobutyric acid (GABA) the primary inhibitory neurotransmitter in the brain. However, how GABA level varies with age in the medial portion of the brain has not yet been studied. The purpose of this study was to investigate the GABA level variation with age focusing on posterior cingulate cortex, which is the 'core hub' of the Default mode network. In this study, 14 monkeys between 4 and 21 years were recruited and MEGA-PRESS to measure GABA level in order to explorea potential link between aging and GABA. Our results showed that a correlation between age and GABA+/Creatine ratio was at the edge of significance (r= -0.523, p=0.081). There was also a near-significant trend between grey matter/ white matter ratio and GABA+/Creatine ratio (r = -0.518, p=0.0848). Meanwhile, the correlation between age and grey matter showed no significance (r= -0.028, p = 0.93). Therefore, age and grey matter/ white matter ratio accounts for different part of R-squared as independent variables for predicting GABA levels. These finding suggest that there the internal neurochemical variation of GABA levels in the nonhuman primate is associated with normal aging and brain structural decline.

Chan, Chi Yung Savio. / "January 2002." / Thesis (Ph.D.)--Chinese University of Hong Kong, 2002. / Includes bibliographical references (p. 130-182). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Mode of access: World Wide Web. / Abstracts in English and Chinese.