Biomedical subjects

Xilong Zhao

Publications and source records attributed to Xilong Zhao.

16 recordsLinked to original sources

PubMed2025

ProgModule: A novel computational framework to identify mutation driver modules for predicting cancer prognosis and immunotherapy response.

BACKGROUND: Cancer originates from dysregulated cell proliferation driven by driver gene mutations. Despite numerous algorithms developed to identify genomic mutational signatures, they often suffer from high computational complexity and limited clinical applicability. METHODS: Here, we presented ProgModule, an advanced computational framework designed to identify mutation driver modules for cancer prognosis and immunotherapy response prediction. In ProgModule, we introduced the Prognosis-Related Mutually Exclusive Mutation (PRMEM) score, which optimizes the balance between exclusive mutation coverage and the incorporation of mutation combination mechanisms critical for cancer prognosis. RESULTS: Applying to BLCA and HNSC cohorts, ProgModule successfully identified driver modules that stratify patients into distinct prognostic subgroups, and the combination of these modules could serve as an effective prognostic biomarker. Extending our method to diverse cancers, ProgModule presented robust prognostic performance and stability across model parameters, including stopping criteria and network topology. Moreover, our analysis suggested that driver modules can predict immunotherapeutic benefit more effectively than existing signatures. Further analyses based on published CRISPR data indicated that genes within these modules may serve as potential therapeutic targets. CONCLUSIONS: Altogether, ProgModule emerges as a powerful tool for identifying mutation driver modules as prognostic and immunotherapy response biomarkers, and genes within these modules may be used as potential therapeutic targets for cancer, offering new insights into precision oncology.

Humans↗

PubMed2007

Effects of ethanol on excitatory and inhibitory synaptic transmission in rat cortical neurons.

BACKGROUND: The gamma-aminobutyric acid-A (GABA(A)) receptor and glutamate receptors are among the most important target sites for the behavioral effects of ethanol. However, data in the literature concerning the ethanol modulation of the GABA(A) and glutamate receptors have been controversial. The activity of the neuronal nicotinic acetylcholine (ACh) receptors (nAChRs) has recently been reported to be potently augmented by ethanol. The activation of nAChRs is also known to cause the release of various neurotransmitters including GABA and glutamate. Thus, ethanol potentiation of nAChRs is expected to stimulate the GABAergic and glutamatergic systems. METHODS: Whole-cell patch clamp experiments were performed using rat cortical neurons in primary culture to record spontaneous miniature inhibitory postsynaptic currents (mIPSCs) and spontaneous miniature excitatory postsynaptic currents (mEPSCs). RESULTS: Two types of neurons were distinguished: bipolar neurons possessed alpha4beta2 nAChRs generating a steady current in response to 30 nM ACh, and multipolar neurons that did not generate a current by ACh application. Acetylcholine greatly increased the frequency of mEPSCs and mIPSCs in bipolar neurons but not in multipolar neurons. The amplitude of neither type of neuron was affected by ACh. Ethanol at 10 to 100 mM suppressed the amplitude of mEPSCs while augmenting the amplitude of mIPSCs in both bipolar and multipolar neurons, indicating the direct action on the respective receptors. In bipolar neurons, ACh plus 100 mM ethanol greatly increased the frequency of mIPSCs beyond the levels achieved by ACh alone, while no such increases were observed in multipolar neurons. CONCLUSIONS: It is concluded that ethanol stimulation of nAChRs modulates the activity of both glutamate and GABA receptors in rat cortical bipolar neurons.

2-Amino-5-phosphonovalerate↗

PubMed2006

Nefiracetam potentiates N-methyl-D-aspartate (NMDA) receptor function via protein kinase C activation and reduces magnesium block of NMDA receptor.

Nicotinic acetylcholine receptors and N-methyl-D-aspartate (NMDA) receptors are known to be down-regulated in the brain of Alzheimer's disease patients. We have previously demonstrated that the nootropic drug nefiracetam potentiates the activity of both nicotinic acetylcholine and NMDA receptors and that nefiracetam modulates the glycine binding site of the NMDA receptor. Because the NMDA receptor is also modulated by Mg2+ and protein kinases, we studied their roles in nefiracetam action on the NMDA receptor by the whole-cell patch-clamp technique and immunoblotting analysis using rat cortical or hippocampal neurons in primary culture. The nefiracetam potentiation of NMDA currents was inhibited by the protein kinase C (PKC) inhibitor chelerythrine, but not by the protein kinase A (PKA) inhibitor N-[2-(4-bromocinnamylamino)ethyl]-5-isoquinoline (H89). In immunoblotting analysis, nefiracetam treatment increased the PKCalpha activity with a bell-shaped dose-response relationship peaking at 10 nM, thereby increasing phosphorylation of PKC substrate and NMDA receptor. Such an increase in PKCalpha-mediated phosphorylation was prevented by chelerythine. Nefiracetam treatment did not affect the PKA activity. Analysis of the current-voltage relationships revealed that nefiracetam at 10 nM largely eliminated voltage-dependent Mg2+ block and that this action of nefiracetam was sensitive to PKC inhibition. It was concluded that nefiracetam potentiated NMDA currents not by acting as a partial agonist but by interacting with PKC, allosterically enhancing glycine binding, and attenuating voltage-dependent Mg2+ block.

Allosteric Regulation↗

PubMed2006

In vitro galantamine-memantine co-application: mechanism of beneficial action.

Several drugs are in clinical use for symptomatic treatment of Alzheimer's disease patients. Since Alzheimer's disease is known to be associated with down-regulation of the cholinergic and N-methyl-D-aspartate (NMDA) systems, most of these drugs inhibit acetylcholinesterase, potentiate the activity of nicotinic acetylcholine receptors (nAChRs), or modulate NMDA receptors. Galantamine is an anticholinesterase and allosterically potentiates the activity of the nicotinic receptors. We have recently found that galantamine potentiates the activity of NMDA receptors as well. Memantine is unique in that it inhibits the NMDA receptors. We have developed a hypothesis that combining galantamine and memantine will be more effective for improving the patient's conditions than monotherapy with either drug. Patch clamp and intracellular Ca(2+) imaging experiments using rat cortical and hippocampal neurons clearly provided the in vitro bases for our hypothesis. Memantine blocked the extrasynaptic NMDA receptor 100 times more potently than the synaptic NMDA receptor at negative membrane potentials and the block of both types of NMDA receptors was attenuated with depolarization. However, galantamine potentiation of the NMDA receptors was not voltage dependent. Thus, co-application of memantine with galantamine prevented the galantamine potentiation and the activation of extrasynaptic NMDA receptors, but membrane depolarization revealed the galantamine potentiation. Therefore, cell death is expected to be prevented by memantine near the resting potential while the NMDA-mediated synaptic transmission, which is down-regulated in the patients, is maintained and potentiated by galantamine. These results provide in vitro bases for the beneficial actions of galantamine and memantine combinations.

6-Cyano-7-nitroquinoxaline-2,3-dione↗

PubMed2005

Modulation of N-methyl-D-aspartate receptors by donepezil in rat cortical neurons.

Nicotinic acetylcholine receptors and N-methyl-D-aspartate (NMDA) receptors are known to be down-regulated in the brain of patients with Alzheimer's disease. It was previously shown that the nootropic drugs nefiracetam and galantamine potentiate the activity of both nicotinic and NMDA receptors. We hypothesized that donepezil, a nootropic with a potent anticholinesterase activity, might also affect the NMDA system. NMDA-induced currents were recorded from rat cortical neurons in primary culture using the whole-cell patch-clamp technique at a holding potential of -70 mV in Mg2+-free solutions. In multipolar neurons, NMDA currents were decreased by bath and U-tube applications of 1 to 10 microM donepezil but were increased by 30 to 100 microM donepezil. Donepezil suppression occurred in a manner independent of NMDA concentrations ranging from 3 to 1000 microM. The donepezil suppression of NMDA currents was prevented by inhibition of protein kinase C (PKC) but unaffected by protein kinase A (PKA) and G proteins. In bipolar neurons, however, NMDA currents were potently augmented by bath and U-tube applications of 0.01 to 100 microM donepezil. Donepezil potentiation occurred at high NMDA concentrations that evoked the saturating responses and in a manner independent of NMDA concentrations ranging from 3 to 1000 microM. The potentiation of NMDA currents by donepezil was decreased by inhibition of PKC and abolished by modulation of G proteins but not by PKA inhibition. It was concluded that donepezil at low therapeutic concentrations (0.01-1 microM) potentiated the activity of the NMDA system and that this action together with cholinesterase inhibition would contribute to the improvement of learning, memory, and cognition in patients with Alzheimer's disease.

Acetylcholine↗

PubMed2005

Block of two subtypes of sodium channels in cockroach neurons by indoxacarb insecticides.

Indoxacarb, a novel insecticide, and its decarbomethoxyllated metabolite, DCJW, are known to block voltage-gated Na(+) channels in insects and mammals, but the mechanism of block is not yet well understood. The present study was undertaken to characterize the action of indoxacarb and DCJW on cockroach Na(+) channels. Na(+) currents were recorded using the whole-cell patch clamp technique from neurons acutely dissociated from thoracic ganglia of the American cockroach Periplaneta americana L. Two types of tetrodotoxin-sensitive Na(+) currents were observed, with different voltage dependencies of channel inactivation. Type-I Na(+) currents were inactivated at more negative potentials than type-II Na(+) currents. As a result, these two types of Na(+) channels responded to indoxacarb compounds differentially. At a holding potential of -100 mV, type-I Na(+) currents were inhibited reversibly by 1 microM indoxacarb and irreversibly by 1 microM DCJW in a voltage-dependent manner, whereas type-II Na(+) currents were not affected by either of the compound. However, type-II Na(+) currents were inhibited by indoxacarb or DCJW at more depolarizing membrane potentials, ranging from -60 to -40 mV. The slow inactivation curves of type-I and type-II Na(+) channels were significantly shifted in the hyperpolarizing direction by indoxacarb and DCJW, suggesting that these compounds have high affinities for the inactivated state of the Na(+) channels. It was concluded that the differential blocking actions of indoxacarb insecticides on type-I and type-II Na(+) currents resulted from their different voltage dependence of Na(+) channel inactivation. The irreversible nature of DCJW block may be partially responsible for its potent action in insects.

Animals↗

PubMed2005

Sulfone metabolite of fipronil blocks gamma-aminobutyric acid- and glutamate-activated chloride channels in mammalian and insect neurons.

Fipronil sulfone, a major metabolite of fipronil in both insects and mammals, binds strongly to GABA receptors and is thought to play a significant role in poisoning by fipronil. To better understand the mechanism of selective insecticidal action of fipronil, we examined the effects of its sulfone metabolite on GABA- and glutamate-activated chloride channels (GluCls) in cockroach thoracic ganglion neurons and on GABA(A) receptors in rat dorsal root ganglion neurons using the whole-cell patch-clamp technique. Fipronil sulfone blocked both desensitizing and nondesensitizing GluCls in the cockroach. Activation was required for block and unblock of desensitizing GluCls. In contrast, activation was not prerequisite for block and unblock of nondesensitizing channels. After repetitive activation of the receptors, the IC50 of fipronil sulfone to block the desensitizing GluCls was reduced from 350 to 25 nM and that for blocking nondesensitizing GluCls was reduced from 31.2 to 8.8 nM. This use-dependent block may be explained by its slow unbinding rate. In cockroach and rat neurons, fipronil sulfone blocked GABA receptors in both activated and resting states, with IC50 values ranging from 20 to 70 nM. In conclusion, although fipronil sulfone is a potent inhibitor of cockroach GABA receptors, desensitizing and nondesensitizing GluCls, and rat GABA(A) receptors, its selective toxicity in insects over mammals appears to be associated with its potent blocking action on both desensitizing and nondesensitizing GluCls, which are lacking in mammals.

Animals↗

PubMed2004

Mechanism of action of galantamine on N-methyl-D-aspartate receptors in rat cortical neurons.

Galantamine, a new Alzheimer's drug approved in the United States, is known to inhibit acetylcholinesterase and potentiate acetylcholine-induced currents in brain neurons. However, because both cholinergic and N-methyl-D-aspartate (NMDA) systems are down-regulated in the brain of Alzheimer's patients, we studied the effects of galantamine on NMDA receptors. NMDA-induced whole-cell currents were recorded from the rat multipolar cortical neurons in primary culture. NMDA currents recorded in Mg2+-free media without addition of glycine were reversibly potentiated by bath and U-tube applications of galantamine at 10 to 10,000 nM, showing a bell-shaped dose-response relationship. However, alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid and kainate currents were not affected by galantamine. The maximum potentiation of NMDA currents to approximately 130% of the control was obtained at 1 microM galantamine. The potentiation was due to a shift of the NMDA dose-response curve in the direction of lower NMDA concentrations. Glycine at 1 to 3000 nM enhanced NMDA currents, and potentiation by 1 microM galantamine and 1 to 300 nM glycine was additive. The glycine site antagonist 7-chlorokynurenic acid did not prevent the galantamine action. These results suggested that galantamine did not interact with the glycine binding site. Experiments with various concentrations of Mg2+ indicated that galantamine did not affect the Mg2+ blocking site of the NMDA receptor. PKC was involved in galantamine potentiation of NMDA currents, but protein kinase A, Gi/Go proteins, and Gs proteins were not involved. Potentiation of the activity of NMDA receptors is deemed partially responsible for the improvement of cognition, learning, and memory in Alzheimer's patients.

Animals↗

PubMed2004

Fipronil is a potent open channel blocker of glutamate-activated chloride channels in cockroach neurons.

Fipronil, a phenylpyrazole insecticide, displays high insecticidal activity and reduced mammalian toxicity. To better elucidate the mechanism of its selective toxicity between insects and mammals and activity against dieldrin-resistant insects, we studied fipronil action on glutamate-gated chloride channels (GluCls), unique invertebrate ligand-gated chloride channels, in cockroach thoracic ganglion neurons, using the whole-cell patch clamp technique. Glutamate evoked two types of chloride currents, a desensitizing current and a nondesensitizing current. Fipronil differentially inhibited these two types of currents with different potencies and with different rates of reversibility. Fipronil inhibited the desensitizing and nondesensitizing GluCls with IC50 values of 801 and 10 nM, respectively. Kinetic analysis revealed that fipronil blocks required channel opening. Recovery of the desensitizing current from fipronil block required channel opening, whereas recovery of nondesensitizing current from block was independent of channel opening. The high potency of fipronil against the nondesensitizing current was due to a slow unblocking rate constant. In addition, when the nondesensitizing GluCls were occupied by picrotoxinin, the receptors became less sensitive to fipronil block. It is concluded that GluCls are a critical target for fipronil, especially for the selective toxicity between mammals and insects, and that fipronil block of GluCls may play a role in the lack of the cross-resistance with dieldrin.

Animals↗

PubMed2004

Kinetic and pharmacological characterization of desensitizing and non-desensitizing glutamate-gated chloride channels in cockroach neurons.

Glutamate-gated chloride channels (GluCls) are found only in invertebrate nerve and muscle, where they mediate inhibitory synaptic transmission, and are important target sites of insecticides. Two GluCl subtypes have previously been distinguished in isolated cockroach CNS neurons based on differential pharmacology. The present study characterizes the kinetics and pharmacological properties of desensitizing and non-desensitizing GluCls. Both types of GluCls were sensitive to glutamate and ibotenic acid. The non-desensitizing GluCl subtype was elicited by glutamate with an EC(50) of 115.8 microM and a Hill coefficient of 2.6 and was also sensitive to the agonist ibotenic acid with an EC(50) of 42 microM and a Hill coefficient of 1.7. The desensitizing and non-desensitizing currents were carried by chloride ions, and occurred either separately or in combination in individual neurons. The GluCls were also found to coexist with and function independently of the GABA-activated chloride channels. The desensitizing and non-desensitizing GluCls exhibited different sensitivities to the ligand-gated channel blocker picrotoxinin. The desensitizing GluCls were blocked only 8% by 30 microM picrotoxinin, whereas the non-desensitizing GluCls were potently blocked by picrotoxinin with an IC(50) of 4.1 microM. The insecticides fipronil and dieldrin at 1 microM inhibited the desensitizing currents by 56 and 13%, respectively, and the non-desensitizing currents by 98 and 43%, respectively. It is concluded that the two types of GluCls found in cockroach neurons exhibit significantly different electrophysiological and pharmacological characteristics.

Animals↗

PubMed2004

Mechanisms of action of cognitive enhancers on neuroreceptors.

No strategies for curing Alzheimer's disease have been developed yet as we do not know the exact cause of the disease. The only therapy that is available for patients is symptomatic treatment. Since Alzheimer's disease is associated with downregulation of the cholinergic system in the brain, its stimulation is expected to improve the patients' cognition, learning, and memory. Four anticholinesterases have been approved in the U.S.A. for the treatment of Alzheimer's disease patients. However, because of the inhibition of cholinesterases, these drugs have side effects and their effectiveness does not last long. Thus new approaches are needed. One approach is to stimulate directly nicotinic acetylcholine (nACh) receptors in the brain, and another is to stimulate NMDA receptors which are also known to be downregulated in Alzheimer's patients. Nefiracetam has been shown to potentiate ACh currents in the alpha4beta2 receptor of rat cortical neurons with a bell-shaped dose-response relationship and the maximum effect at 1 nM. This effect was exerted via G(s) proteins. The alpha7 receptor was almost unaffected by nefiracetam. Nefiracetam also potentiated NMDA currents with the maximum effect at 10 nM via interaction with the glycine-binding site of the receptor. Galantamine had a moderate potentiating effect on the alpha4beta2 receptor and potentiated NMDA currents with the maximum effect at 1 microM. However, galantamine did not interact with the glycine-binding site. Donepezil, a potent anticholinesterase, also potentiated NMDA currents at 1-10000 nM. In conclusion, these three drugs potentiate the activity not only of the cholinergic system but also of the NMDA system, thereby stimulating the downregulated nACh receptors and NMDA receptors to improve patients' learning, cognition, and memory.

Alzheimer Disease↗

PubMed2003

Unique mechanism of action of Alzheimer's drugs on brain nicotinic acetylcholine receptors and NMDA receptors.

While a variety of hypotheses have been proposed for the cause of Alzheimer's disease, our knowledge is far from complete to explain the disease making it difficult to develop the methods for treatment. In the brain of Alzheimer's patients, both neuronal nicotinic acetylcholine (nACh) receptors and NMDA receptors are known to be down-regulated. Thus four anticholinesterases have been developed and approved for the treatment in the U.S.A. However, these are not ideal drugs considering their side effects and limited effectiveness. Nefiracetam is being developed for the treatment of Alzheimer's and other patients with dementia, and has unique actions in potentiating the activity of both nACh and NMDA receptors as demonstrated by in vitro patch clamp experiments using rat cortical neurons in primary culture. Nefiracetam potentiated alpha4beta2-like ACh- and NMDA-induced currents at nanomolar concentrations forming bell-shaped dose-response curves with the maximum potentiation occurring at 1 and 10 nM, respectively. Nefiracetam potentiated nACh receptor currents via G(s) proteins, but not G(i)/G(o) proteins, PKA or PKC. Nefiracetam potentiation of NMDA currents occurred via interactions with the glycine binding site of the NMDA receptor. The nefiracetam potentiation of both nACh and NMDA receptors in a potent and efficacious manner is deemed responsible for its cognitive enhancing action.

Acetylcholine↗

PubMed2003

Potentiation of N-methyl-D-aspartate-induced currents by the nootropic drug nefiracetam in rat cortical neurons.

Nefiracetam is a new pyrrolidone nootropic drug being developed for the treatment of Alzheimer's type and post-stroke vascular-type dementia. In the brain of Alzheimer's disease patients, down-regulation of both cholinergic and glutamatergic systems has been found and is thought to play an important role in impairment of cognition, learning and memory. We have previously shown that the activity of neuronal nicotinic acetylcholine receptors is potently augmented by nefiracetam. The present study was undertaken to elucidate the mechanism of action of nefiracetam on glutamatergic receptors. Currents were recorded from rat cortical neurons in long-term primary culture using the whole-cell patch-clamp technique at a holding potential of -70 mV in Mg2+-free solutions. N-Methyl-D-aspartate (NMDA)-evoked currents were greatly and reversibly potentiated by bath application of nefiracetam resulting in a bell-shaped dose-response curve. The minimum effective nefiracetam concentration was 1 nM, and the maximum potentiation to 170% of the control was produced at 10 nM. Nefiracetam potentiation occurred at high NMDA concentrations that evoked the saturated response, and in a manner independent of NMDA concentrations ranging from 3 to 1,000 microM. Glycine at 3 microM potentiated NMDA currents but this effect was attenuated with an increasing concentration of nefiracetam from 1 to 10,000 nM. 7-Chlorokynurenic acid at 1 microM prevented nefiracetam from potentiating NMDA currents. Nefiracetam at 10 nM shifted the dose-response relationship for the 7-chlorokynurenic acid inhibition of NMDA currents in the direction of higher concentrations. Alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid- and kainate-induced currents were not significantly affected by application of 10 nM nefiracetam. It was concluded that nefiracetam potentiated NMDA currents through interactions with the glycine binding site of the NMDA receptor.

Animals↗

PubMed2003

Differential actions of fipronil and dieldrin insecticides on GABA-gated chloride channels in cockroach neurons.

Fipronil and dieldrin are known to inhibit GABA receptors in both mammals and insects. However, the mechanism of selective toxicity of these insecticides between mammals and insects remains to be seen. One possible mechanism is that insect GABA receptors are more sensitive than mammalian GABAA receptors to fipronil and dieldrin. We examined differential actions of fipronil and dieldrin on GABA-gated chloride channels in insects and compared them with the data on mammalian GABAA receptors. Neurons were acutely dissociated from the American cockroach thoracic ganglia, and currents evoked by GABA were recorded by the whole-cell patch-clamp technique. GABA-evoked currents were carried by chloride ions, blocked by picrotoxinin, but not by bicuculline. Fipronil inhibited GABA currents with an IC50 value of 28 nM, whereas dieldrin exhibited a dual action potentiation with an EC50 value of 4 nM followed by inhibition with an IC50 value of 16 nM. Fipronil and dieldrin acted on the resting receptor at comparable rates, whereas fipronil blocked the activated receptor 10 times faster than dieldrin. Fipronil inhibition was partially reversible, whereas dieldrin inhibition was irreversible. Fipronil was 59 times more potent on cockroach GABA receptors than on rat GABAA receptors. However, the potentiating and inhibitory potencies of dieldrin in cockroach GABA receptors were comparable with those in rat GABAA receptors. It was concluded that the higher toxicity of fipronil in insects than in mammals is due partially to the higher sensitivity of GABA receptors. The mechanism of dieldrin's selective toxicity must lie in factors other than the sensitivity of GABA receptors.

Animals↗

PubMed2003

Voltage-dependent block of sodium channels in mammalian neurons by the oxadiazine insecticide indoxacarb and its metabolite DCJW.

Indoxacarb is a newly developed insecticide with high insecticidal activity and low toxicity to non-target organisms. Its metabolite, DCJW, is known to block compound action potentials in insect nerves and to inhibit sodium currents in cultured insect neurons. However, little is known about the effects of these compounds on the sodium channels of mammalian neurons. We compared the effects of indoxacarb and DCJW on tetrodotoxin-sensitive (TTX-S) and tetrodotoxin-resistant (TTX-R) sodium channels in rat dorsal root ganglion neurons by using the whole-cell patch clamp technique. Indoxacarb and DCJW at 1-10 microM slowly and irreversibly blocked both TTX-S and TTX-R sodium channels in a voltage-dependent manner. The sodium channel activation kinetics were not significantly modified by 1 microM indoxacarb or 1 microM DCJW. The steady-state fast and slow inactivation curves were shifted in the hyperpolarization direction by 1 microM indoxacarb or 1 microM DCJW indicating a higher affinity of the inactivated sodium channels for these insecticides. These shifts resulted in an enhanced block at more depolarized potentials, thus explaining voltage-dependent block, and an apparent difference in the sensitivity of TTX-R and TTX-S channels to indoxacarb and DCJW near the resting potential. Indoxacarb and its metabolite DCJW cause toxicity through their action on the sodium channels.

Action Potentials↗

PubMed2003

Fipronil modulation of glutamate-induced chloride currents in cockroach thoracic ganglion neurons.

Fipronil is the first phenylpyrazole insecticide introduced for pest control. It is effective against some insects that have become resistant to other insecticides, and exhibits low mammalian toxicity. Although fipronil is known to block GABA receptors, the mechanisms of its selective toxicity and efficacy against insects with dieldrin-resistant GABA receptors are not fully understood. We studied the effects of fipronil on the inhibitory glutamate receptor-chloride channel complex, which is found only in invertebrates. Glutamate-activated chloride currents were recorded from neurons isolated from cockroach thoracic ganglia using the whole-cell patch clamp technique. When glutamate was applied to a neuron, it evoked inward currents with an EC50 of 36.8 +/- 3.0 microM and a Hill coefficient of 1.56 +/- 0.17. The similarity between the reversal potential and the calculated chloride equilibrium potential indicated that glutamate-induced currents were carried by chloride ions. Fipronil suppressed the glutamate-induced peak currents in a dose-dependent manner with an IC50 of 0.73 +/- 0.27 microM and a Hill coefficient of 0.68 +/- 0.15. The current decay phases were greatly prolonged after fipronil application in a concentration-dependent manner. Picrotoxinin (PTX) at 100 microM slightly suppressed glutamate-induced currents to 87.8 +/- 3.7% of the control, and dieldrin at 100 microM had no effect (96.7 +/- 3.1%). AP5 and CNQX, mammalian glutamate receptor antagonists, were without effect on glutamate-induced Cl- currents. It is concluded that the potent blocking action of fipronil against glutamate-gated chloride channels may contribute to the higher toxicity against insects than mammals, as well as the efficacy against insects resistant to other insecticides.

Animals↗