Biomedical subjects

G Chen

Publications and source records attributed to G Chen.

At least 469 records · Page 26Linked to original sources

PubMed1998

A dose-response relationship between exposure to cockroach allergens and induction of sensitization in an experimental asthma in Hartley guinea pigs.

OBJECTIVE: An indoor allergen, cockroach allergen (CRa) has been partly implicated in the rising prevalence of inner-city asthma. This study investigates a dose-response relationship of exposure to CRa with the degree of sensitization and with airway inflammation through the use of our established guinea pig asthma model. METHODS: Four groups of Hartley guinea pigs were exposed to aerosolized saline (control) and three dose levels of CRa: low-dose, 0.5 mg (LD); medium-dose, 5 mg (MD); or high-dose, 25 mg (HD), nebulized twice a day, 5 days per week, for 4 weeks. The development of anaphylactic antibodies was measured by both allergy skin test and passive cutaneous anaphylaxis assay. Animals were challenged with CRa 5 days after the last sensitization, and specific airway resistance was measured continuously by a double-chamber plethysmograph while animals were in the conscious state. The inflammatory cells in bronchoalveolar lavage fluid (BALF) and the contractile responses of tracheal rings were analyzed in vitro at 24 hours after CRa challenge. RESULTS: The anaphylactic antibodies to CRa were detected in the CRa-sensitized animals by allergy skin test. Passive cutaneous anaphylaxis titers of IgG1a-like antibody were zero in control, 1:2 in LD, 1:40 in MD, and 1:160 in HD. Total leukocytes in BALF were increased by CRa challenge in all three CRa-sensitized groups compared with control (p < 0.0001). The tracheal rings from CRa-sensitized guinea pigs constricted upon addition of incremental doses of CRa challenge in vitro in a dose-responsive manner (p < 0.0001). The leukocytosis in BALF and the anaphylactic contractile responses of the tracheal rings in CRa-sensitized groups were correlated to the levels of CRa to which the groups had been exposed during sensitization (p < 0.001). CRa-provoked increase in SRaw was noted in all three groups of the CRa-sensitized guinea pigs compared with control (p < 0.01). Yet, among CRa-sensitized groups, a greater increase in specific airway resistance was noted in the LD group but not in the HD CRa group. CONCLUSIONS: The development of anaphylactic cockroach sensitivity in guinea pigs was dependent on the levels of CRa exposure during sensitization, and the CRa-sensitized animals showed antigen-specific airway inflammation along with airway smooth muscle contractions. However, the severity of bronchospasm in conscious animals was not in agreement with the degree of CRa sensitivity.

Allergens↗

PubMed1998

Parasitic worms: an ally in the war against the superbugs.

The entomopathogenic nematodes are now of considerable scientific interest not only because of their function as biological control agents, but because of the potential medical and agricultural importance of the metabolic products of their symbiotic bacteria. Initial exploration in Australia, a decade ago, has blossomed into a significant area of research activity as we discover the nematicidal, anticancer, antimycotic and antibiotic properties of these bacterially derived compounds. Some of the antibiotics are novel compounds, and they might form the basis of the next round of drugs against the superbugs, as discussed here by John Webster, Genhui Chen and Jianxong Li.

Journal Article↗

PubMed1998

Optical responses evoked by cerebellar surface stimulation in vivo using neutral red.

The pH sensitive dye, Neutral Red, was used with optical imaging techniques to map intracellular pH shifts elicited by cortical surface stimulation of the rat cerebellum. In the in vivo rat cerebellar cortex stained with Neutral Red, a brief stimulus train (three stimuli at 33 Hz) evoked a longitudinal beam of increased fluorescence (acidic shift) running parallel to the long axis of the folium within 100 ms of stimulation onset. A 5-10 s stimulus train (5-20 Hz) produced a biphasic optical response consisting of a beam of increased fluorescence (acidic shift) which returned to baseline in approximately 60 s, followed by a beam of decreased fluorescence (alkaline shift) for up to 120 s. A close spatial correspondence was observed between electrophysiological and optical maps of the response to surface stimulation. Application of acetazolamide enhanced the optical signals, acetabenzolamide-phenoxyethene had no effect, and the glutamate antagonist, 6-cyano-7-nitroquinoxaline-2,3-dione, decreased the optical signals. Increased fluorescence was produced by superfusion of the cerebellar cortex with acidic Ringer solutions and a decrease in fluorescence by basic solutions. These fluorescence changes also occurred in the presence of several ion channel/receptor blockers. Increased fluorescence resulted from superfusion with Ringer solution containing sodium propionate and decreased fluorescence with the transition from 5% carbon dioxide to nominally carbon dioxide-free Ringer solution. Recovery from acid loading with ammonium chloride was prevented by amiloride, an inhibitor of the Na+/H+ transporter. Application of Ringer solution with high potassium concentration produced an increase in fluorescence but only a decrease in fluorescence was detected when neuronal blockers were present, an effect consistent with a glial contribution. This decrease in fluorescence was blocked by adding barium. No epifluorescent optical signals were obtained from unstained preparations or preparations stained with cell-permeant fluorescence markers, suggesting little contribution from activity-dependent volume changes and other intrinsic signals. These results demonstrate that the Neutral Red optical signals evoked by cerebellar surface stimulation are primarily pH based and include a significant component related to intracellular pH shifts. The large amplitudes of these optical signals are particularly useful for mapping neuronal activity. Furthermore, this technique provides a novel tool for the study of pH changes in vivo at both high spatial and temporal resolution.

6-Cyano-7-nitroquinoxaline-2,3-dione↗

PubMed1998

Clarification of the relationship between free radical spin trapping and carbon tetrachloride metabolism in microsomal systems.

It has been proposed that the C-phenyl-N-tert-butylnitrone/trichloromethyl radical adduct (PBN/.CCl3) is metabolized to either the C-phenyl-N-tert-butylnitrone/carbon dioxide anion radical adduct (PBN/.CO2-) or the glutathione (GSH) and CCl4-dependent PBN radical adduct (PBN/[GSH-.CCl3]). Inclusion of PBN/.CCl3 in microsomal incubations containing GSH, nicotinamide adenine dinucleotide phosphate (NADPH), or GSH plus NADPH produced no electron spin resonance (ESR) spectral data indicative of the formation of either the PBN/[GSH-.CCl3] or PBN/.CO2- radical adducts. Microsomes alone or with GSH had no effect on the PBN/.CCl3 radical adduct. Addition of NADPH to a microsomal system containing PBN/.CCl3 presumably reduced the radical adduct to its ESR-silent hydroxylamine because no ESR signal was observed. The Folch extract of this system produced an ESR spectrum that was a composite of two radicals, one of which had hyperfine coupling constants identical to those of PBN/.CCl3. We conclude that PBN/.CCl3 is not metabolized into either PBN/[GSH-.CCl3] or PBN/.CO2- in microsomal systems.

Animals↗

PubMed1998

Herbimycin-A attenuates ischaemia-reperfusion induced pulmonary neutrophil infiltration.

OBJECTIVES: To determine whether pharmacological induction of heat shock proteins (HSPs) by herbimycin-A (a tyrosine-kinase inhibitor) would protect against neutrophil-mediated lung injury in an animal model of lower torso ischaemia-reperfusion. MATERIALS AND METHODS: Sprague-Dawley rats were randomised into three groups: the control group underwent midline laparotomy only; the ischaemia-reperfusion (IR) group underwent laparotomy and clamping of the infrarenal abdominal aorta for 30 min followed by 2 h of reperfusion; the third group (HerbIR) was pretreated with herbimycin-A 18 h prior to IR insult. Wet to dry lung weight ratio (W:D), bronchoalveolar lavage protein concentration (BALprot), tissue myeloperoxidase activity (MPO) and bronchoalveolar lavage neutrophil count (BALPMN) were measured. Heat shock protein 72 (HSP72) expression in lung, intestine, mesentery and liver was measured using Western immunoblotting. RESULTS: IR resulted in acute lung injury with tissue oedema (W:D) and neutrophil infiltration (PMO, BALPMN). Herbimycin-A, in vivo, induced HSP expression and attenuated neutrophil infiltration (MPO, BALPMN). CONCLUSION: These data indicate that herbimycin-A protects against ischaemia-reperfusion induced pulmonary neutrophil infiltration, possibly by increasing the expression of heat shock proteins.

Animals↗

PubMed1998

Recruitment of CBP/p300 by the IFN beta enhanceosome is required for synergistic activation of transcription.

Transcriptional activation of the IFN beta gene in response to virus infection requires the assembly of an enhanceosome, consisting of the transcriptional activators NF-kappa B, IRF1, ATF2/c-Jun, and the architectural protein HMG I(Y). The level of transcription generated by all of these activators is greater than the sum of the levels generated by individual factors, a phenomenon designated transcriptional synergy. We demonstrate that this synergy, in the context of the enhanceosome, requires a new protein-protein interaction domain in the p65 subunit of NF-kappa B. Transcriptional synergy requires recruitment of the CBP/p300 coactivator to the enhanceosome, via a new activating surface assembled from the novel p65 domain and the activation domains of all of the activators. Deletion, substitution, or rearrangement of any one of the activation domains in the context of the enhanceosome decreases both recruitment of CBP and transcriptional synergy.

Activating Transcription Factor 2↗

PubMed1998

Acetylation of HMG I(Y) by CBP turns off IFN beta expression by disrupting the enhanceosome.

The transcriptional coactivators CBP and P/CAF are required for activation of transcription from the IFN beta enhanceosome. We show that CBP and P/CAF acetylate HMG I(Y), the essential architectural component required for enhanceosome assembly, at distinct lysine residues, causing distinct effects on transcription. Thus, in the context of the enhanceosome, acetylation of HMG I by CBP, but not by P/CAF, leads to enhanceosome destabilization and disassembly. We demonstrate that acetylation of HMG I(Y) by CBP is essential for turning off IFN beta gene expression. Finally, we show that the acetyltransferase activities of CBP and P/CAF modulate both the strength of the transcriptional response and the kinetics of virus-dependent activation of the IFN beta gene.

Acetylation↗

PubMed1998

The 2G2 antibody recognizes an acidic 110-kDa human mitochondrial protein.

Using fluorescence microscopy, the mouse monoclonal antibody 2G2 was found to label mitochondria in human cells, as assessed by double staining with either Rhodamine 123 or a polyclonal antibody to mitochondrial matrix HSP-60 proteins. No reactivity to the 2G2 antibody was detected in cells from mouse, rat and chicken. Immunoblotting analysis demonstrated that the 2G2 antigen corresponds to a human protein with a relative mobility of 110kDa and an approximate isoelectric point of 6.5 that co-partitions with HSP-60 proteins during isolation of mitochondria from HeLa cells. Close examination of the 2G2 staining pattern in HeLa and Fanconi's anaemia cells revealed differences in the morphology and organization of mitochondria in these two cell types. In HeLa cells, mitochondria appear as individual tubular compartments of variable length and are closely associated with vimentin filaments, particularly at the periphery of the nucleus. In Fanconi's anaemia cells, mitochondria have a filamentous shape and form an interconnected cytoplasmic reticulum running in parallel with both vimentin filaments and microtubules. After stabilization with aldehyde- or alcohol-based fixation protocols that optimize the preservation of cytoskeletal components, the epitope targeted by the 2G2 antibody may serve as a valuable marker in the investigation of relationships between mitochondria and other cellular structures in human cells.

3T3 Cells↗

PubMed1998

Thermotolerance induces heat shock protein 72 expression and protects against ischaemia-reperfusion-induced lung injury.

BACKGROUND: Ischaemia-reperfusion injury is mediated by neutrophil-endothelial interaction. Induction of heat shock proteins attenuates neutrophil-endothelial interactions. The aim of this study was to determine whether thermal preconditioning could have a protective effect on neutrophil-mediated lung injury in an animal model of lower torso ischaemia-reperfusion. METHODS: Sprague-Dawley rats were randomized into: control, ischaemia-reperfusion, and ischaemia-reperfusion preconditioned with hyperthermia groups. Ischaemia-reperfusion injury was induced by infrarenal aortic clamping for 30 min and reperfusion for 120 min. Thermotolerance was induced by raising the core body temperature to 40.5-41.5 degrees C for 15 min, 18 h before ischaemia-reperfusion. Wet:dry lung (W:D) weight ratio, bronchoalveolar lavage protein (BALprot) concentration, tissue myeloperoxidase (MPO) activity and bronchoalveolar lavage polymorphonuclear neutrophil (BAL PMN) count were measured. Heat shock protein 72 (hsp72) expression in lung, intestine and mesentery was measured using Western immunoblotting. RESULTS: Ischaemia-reperfusion resulted in a significant increase in tissue oedema (W:D weight ratio) and BALprot concentration. In addition there was a marked increase in tissue neutrophil infiltration (MPO activity, BAL PMN concentration). Preconditioning with hyperthermia resulted in increased expression of hsp72 and significantly reduced tissue oedema and neutrophil infiltration. CONCLUSION: Thermal preconditioning protects against neutrophil-mediated ischaemia-reperfusion-induced lung injury, possibly by increasing the expression of heat shock proteins.

Animals↗

PubMed1998

Lithium increases tyrosine hydroxylase levels both in vivo and in vitro.

Lithium, a simple monovalent cation, is the mainstay in the treatment of manic-depressive illness, but despite extensive research, its mechanism of action remains to be elucidated. Because lithium requires chronic administration for therapeutic efficacy and because its beneficial effects last well beyond its discontinuation, it has been postulated that lithium may exert major effects at the genomic level. We have previously shown that lithium, at therapeutically relevant concentrations, increases gene expression through the activator protein-1 (AP-1) transcription factor pathway in vitro. In the present study, we have sought to determine if lithium also increases the expression of endogenous genes known to be regulated by AP-1 and have therefore investigated the effects of lithium on tyrosine hydroxylase (TH) levels. Male Wistar rats were treated with LiCl for 9 days (subacute) or 4 weeks (chronic), and TH levels were measured in frontal cortex, hippocampus, and striatum using immunoblotting. Chronic (but not subacute) lithium treatment resulted in significant increases in TH levels in rat frontal cortex, hippocampus, and striatum. Lithium (1 mM) also increased TH levels in human SH-SY5Y neuroblastoma cells in vitro, indicating that lithium increases TH levels in both rodent and human tissues, likely via a direct cellular effect. These effects are compatible with (but likely not exclusively due to) an effect on the DNA binding of the 12-O-tetradecanoylphorbol 13-acetate response element to the AP-1 family of transcription factors.

Animals↗

PubMed1998

In human skin, UVB initiates early induction of IL-10 over IL-12 preferentially in the expanding dermal monocytic/macrophagic population.

In contrast to Langerhans cells, which make interleukin (IL)-12, differentiated macrophages that infiltrate the epidermis 72 h after ultraviolet B (UV) irradiation potently produce IL-10 mRNA and secrete IL-10 protein. We asked whether differentiated UV macrophages in the epidermis acquired their activated, IL-10hi status as a result of entering the epidermis or as a result of encountering UV-induced changes in the dermal microenvironment. In this study, sequential section immunostaining directly showed dynamic and reciprocal changes of infiltrating CD11b+ macrophages and CD1a+ Langerhans cell loss in human epidermis and dermis after in vivo UV exposure in relation to the microanatomic localization of newly appearing dermal cells that stain for IL-10 mRNA by in situ hybridization. Using quantitative reverse transcriptase polymerase chain reaction on purified dermal cell subsets, the first significant rise in IL-10 mRNA occurred 6 h after UV in the dermal CD11b+ (CD1-, 3-, 24-, 56-) monocytic/macrophagic population. Significant induction of IL-10 mRNA 24 h post-UV was limited to the CD11b+ CD1- subset (p = 0.006). The fold increase of IL-10 mRNA relative to 0 h by the CD11b+ dermal monocytic/macrophagic population peaked at 24-48 h and tapered thereafter. Intense IL-10 production by macrophages in the epidermis appeared to follow dermal changes, with maximum production at 72 h, indicating migration/activation of this population from the dermis, and the remainder of dermal cells, depleted of monocyte/macrophages and Langerhans cell-like antigen-presenting cells, showed no increase in IL-10 at any time point post-UV. IL-10 protein-producing CD11b+ macrophages in the dermis were also documented by flow cytometry. IL-12 mRNA was differentially regulated from IL-10 after UV, in that IL-12 was consistently downregulated in the CD11b+ monocytic/macrophagic population (p < 0.0002). Taken together, monocytic/macrophagic cells with high IL-10 and low IL-12 expression initially appear in the dermis as early as 6 h, and then appear in the epidermis, implicating the dermis as the primary site of activation/signaling for IL-10 upregulation in cutaneous antigen-presenting cells.

Adult↗

PubMed1998

New imidazoles as probes of the active site topology and potent inhibitors of beta-glucosidase.

Series of 4-arylimidazoles, omega-N-acylhistamines and 4-(omega-phenylalkyl)imidazoles were synthesized in order to probe the active site topology of sweet almond beta-glucosidase. These imidazole derivatives were shown to be very powerful competitive inhibitors. Among the 20 tested compounds, omega-N-benzoylhistamine and 4-(3'-phenylpropyl)imidazole are the most potent inhibitors of the enzyme, with pH-independent Ki values of 0.06 and 0.07 microM, respectively. The inhibition of 4-(omega-phenylalkyl)imidazoles exhibited an interesting trend as to Ki values: 4-phenylimidazole (6.6 microM)>4-benzylimidazole (1.4 microM)>4-(2'-phenylethyl)imidazole (0.82 microM)>4-(3'-phenylpropyl)imidazole (0.07 microM)<4-(4'-phenylbutyl)imidazole (0.13 microM)<4-(5'-phenylpentyl)imidazole (0.3 microM). This revealed that the imidazole and aryl binding sites (which result from favorable interactions within the corresponding glycone and aglycone binding subsites) are separated by the optimal distance equivalent to the length of a -CH2-CH2-CH2- group. Substitutions of the phenyl moieties of 4-phenylimidazole and 4-benzoylhistamine result in weaker inhibition. These classes of imidazoles are particularly powerful inhibitors of sweet almond beta-glucosidase.

Binding Sites↗

PubMed1998

Antibody affinity maturation using bacterial surface display.

A quantitative system for screening combinatorial single-chain Fv (scFv) antibody libraries was developed utilizing surface display on Escherichia coli and fluorescence-activated cell sorting (FACS). This system was employed to isolate clones with high-affinity to a fluorescently-labeled hapten from libraries constructed by randomizing heavy and light-chain residues in the anti-digoxin 26-10 derived antibody, scFv(dig). The use of flow cytometry enabled the detection of rare library members directly in heterogeneous populations and the optimization of selection conditions prior to sorting. A heavy-chain mutant having wild-type affinity (KD = 0.91+/-0.22 nM) and an expected representation frequency of less than 1 x 10(6), was selected to homogeneity after three rounds utilizing increasingly stringent selection conditions. The isolated clone possessed two distinct point mutations relative to the wild-type DNA sequence, yet still coded for the wild-type amino acid sequence, suggesting that the wild-type residues may be optimal at the randomized positions. An affinity improved clone (KD = 0.30+/-0.05 nM), having a dissociation constant approximately threefold lower than the wild-type antibody, was isolated from a smaller light-chain library in a single sorting step. Flow cytometry was shown to be a simple and rapid method for the determination of the relative hapten dissociation rate constants of selected clones without requiring subcloning. The relative rate constants estimated by FACS were confirmed by producing the scFv antibodies in soluble form and measuring hapten binding kinetics by surface plasmon resonance (SPR). These results demonstrate that E.coli surface display, coupled with quantitative selection and analysis using FACS, has the potential to become a powerful tool for rapid isolation and characterization of desirable mutants from large polypeptide libraries.

Antibody Affinity↗

PubMed1998

Recombinant human CXC-chemokine receptor-4 in melanophores are linked to Gi protein: seven transmembrane coreceptors for human immunodeficiency virus entry into cells.

This article describes the transient expression of the CXC chemokine receptor-4 in Xenopus laevis melanophores and the resulting functional assay for the endogenous ligand for this receptor stromal cell-derived factor (SDF)-1alpha. Specifically, it will be shown that SDF-1alpha produces increased light transmittance in transfected cells that is consistent with the activation of Gi protein. This stimulus pathway is further implicated by the abolition of this response after pretreatment of the cells with pertussis toxin, a known method for the inactivation of Gi protein. The fact that SDF-1alpha does not produce responses in nontransfected cells and that treatment of the cells with 12G5, an antibody specific for the CXC chemokine receptor-4, eliminates this response indicates that this ligand produces responses by activation of this receptor in these cells. The possible relevance to human immunodeficiency virus (HIV) entry into cells was explored by observing the effects of SDF-1alpha on HIV-mediated cell fusion. It was found that SDF-1alpha blocked cell-to-cell fusion (as has been previously reported) at concentrations 1200-fold greater than those required to produce Gi protein mediated responses. The implications of the functional assay to screening for new drugs to block HIV-mediated fusion is discussed.

Amino Acid Sequence↗

PubMed1998

Characterization of the DNA-binding domain of the bovine papillomavirus replication initiator E1.

The bovine papillomavirus replication initiator protein E1 is an origin of replication (ori)-binding protein absolutely required for viral DNA replication. In the presence of the viral transcription factor E2, E1 binds to the ori and initiates DNA replication. To understand how the E1 initiator recognizes the ori and how E2 assists in this process, we have expressed and purified a 166-amino-acid fragment which corresponds to the minimal E1 DNA-binding domain (DBD). DNA binding studies using this protein demonstrate that the E1 DBD can bind to the palindromic E1 binding site in several forms but that binding of two monomers, each recognizing one half-site of the E1 palindrome, is the predominant form. This is reminiscent of the binding of the T-antigen DBD to the SV40 ori, and interestingly, the arrangement of E1 binding sites shows striking similarities to the arrangement of T-antigen binding sites in the SV40 ori even though the recognition sequences are unrelated. The E1 DBD is capable of interacting cooperatively with E2; however, the E2 DBD and not the E2 activation domain mediates this interaction. Furthermore, the E2 DBD stimulates binding of two monomers of the E1 DBD to the ori by binding cooperatively with one E1 monomer. Finally, we show that our results concerning the DNA-binding properties of the E1 DBD can be extended to full-length E1.

Animals↗

PubMed1998

Dorsal-mediated repression requires the formation of a multiprotein repression complex at the ventral silencer.

Dorsal functions as both an activator and repressor of transcription to determine dorsoventral fate in the Drosophila melanogaster embryo. Repression by Dorsal requires the corepressor Groucho (Gro) and is mediated by silencers termed ventral repression regions (VRRs). A VRR in zerknüllt (zen) contains Dorsal binding sites as well as an essential element termed AT2. We have identified and purified an AT2 DNA binding activity in embryos and shown it to consist of cut (ct) and dead ringer (dri) gene products. Studies of loss-of-function mutations in ct and dri demonstrate that both genes are required for the activity of the AT2 site. Dorsal and Dri both bind Gro, acting cooperatively to recruit it to the DNA. Thus, ventral repression may require the formation of a multiprotein complex at the VRR. This complex includes Dorsal, Gro, and additional DNA binding proteins, which appear to convert Dorsal from an activator to a repressor by enabling it to recruit Gro to the template. By showing how binding site context can dramatically alter transcription factor function, these findings help clarify the mechanisms responsible for the regulatory specificity of transcription factors.

Animals↗

PubMed1998

A role for Groucho tetramerization in transcriptional repression.

The Drosophila Groucho (Gro) protein is a corepressor required by a number of DNA-binding transcriptional repressors. Comparison of Gro with its homologues in other eukaryotic organisms reveals that Gro contains, in addition to a conserved C-terminal WD repeat domain, a conserved N-terminal domain, which has previously been implicated in transcriptional repression. We determined, via a variety of hydrodynamic measurements as well as protein cross-linking, that native Gro is a tetramer in solution and that tetramerization is mediated by two putative amphipathic alpha-helices (termed leucine zipper-like motifs) found in the N-terminal region. Point mutations in the leucine zipper-like motifs that block tetramerization also block repression by Gro, as assayed in cultured Drosophila cells with Gal4-Gro fusion proteins. Furthermore, the heterologous tetramerization domain from p53 fully substitutes for the Gro tetramerization domain in transcriptional repression. These findings suggest that oligomerization is essential for Gro-mediated repression and that the primary function of the conserved N-terminal domain is to mediate this oligomerization.

Amino Acid Sequence↗

PubMed1998

GABA-dependent firing of glutamate-evoked action potentials at AMPA/kainate receptors in developing hypothalamic neurons.

Although it plays a major inhibitory role in the adult mammalian CNS, gamma-aminobutyric acid (GABA) may have an excitatory function in developing neurons. The present study focuses on the dependence of glutamate on GABA to generate action potentials in developing hypothalamic neurons. Under conditions where glutamate by itself could not evoke an action potential, GABA facilitated glutamate-mediated depolarization to fire action potentials. This facilitation had a broad time window during the decaying phase of the GABA-mediated depolarization in developing neurons in culture. The glutamate-mediated depolarization was shunted only during the peak of GABA-mediated depolarization, but was facilitated after that. Similar results were obtained in the presence of 2-amino-5-phosphonopentanoic acid (AP5), indicating that GABA can facilitate glutamate responses independent of relief of the Mg2+ block of the N-methyl-D-aspartate (NMDA) receptor. This novel interaction between GABA- and glutamate-mediated excitation could play a role in strengthening neuronal circuits during early development and would exert a maximal effect if GABA and glutamate receptors were activated after a slight temporal delay.

2-Amino-5-phosphonovalerate↗