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1.
The action of insecticides on the spontaneous electrical activity of neurohemal tissue in the stick insect, Carausius morosus, has been studied using extracellular electrodes. The pyrethroid, permethrin, causes a massive increase in the frequency of the spontaneously generated action potentials at concentrations between 5 × 10?5 and 5 × 10?8M. Concentrations as low as 5 × 10?11M are still effective in producing bursting activity.DDT, at concentrations between 5 × 10?5M and 5 × 10?6M, produces an overall increase in activity although the bursting activity is less violent than that shown with permethrin. DDT, 5 × 10?7M, is ineffective at altering the resting pattern.Carbaryl and coroxon cause a transitory increase in electrical activity at 1 × 10?4M, but are ineffective at 1 × 10?5M.It is concluded that insecticides could have a direct effect upon the neurohormonal balance in insects.  相似文献   

2.
Selection with pp'-DDT was applied to fourth-stage larvae of Aedes aegypti along four lines, starting with larvae of the F2 generation from crosses between a susceptible strain and each of four resistant strains (two of Trinidad origin and two of Bangkok origin). Larval resistance increased substantially along each line but there was little or no change in the percentage breakdown of DDT to 1,1-dichloro-2,2-bis(4-chloro-phenyl)ethylene (pp'-DDE) in vivo and in no line were these two variables significantly correlated. Percentage breakdown was generally higher at 10 mg than at 50 mg litre?1. DDT uptake (defined as content of DDT+pp'-DDE) was generally higher after exposure to 50 mg than to 10 mg litre?1. It increased significantly with selection in the TE×NS line; it remained unchanged in the T8 × NS line; and in the other two lines (BSJ × NS and B51 × NS), it increased initially but dropped as selection progressed, the reduction being highly significant in the second of these lines. The amount of internal residual (unmetabolised) DDT tolerated by larvae of the TE × NS line also increased significantly with resistance. The levels in the other lines followed the pattern of uptake, remaining steady in T8 × NS despite the increase in survival, rising at first and then declining in the two Bangkok lines. Thus selection produced a higher tolerance to internal unmetabolised DDT in the two Trinidad lines but led ultimately to a lower content of DDT+pp'-DDE in the two Bangkok lines. The reasons for this behaviour are discussed.  相似文献   

3.
Deltamethrin and NRDC 157, pyrethroid insecticides that produce different poisoning syndromes in mammals, enhanced veratridine-dependent, sodium channel-mediated 22Na+ uptake in mouse brain synaptosomes. Concentrations producing half-maximal enhancement were 2.5 × 10?8M (deltamethrin) and 2.2 × 10?7M (NRDC 157). This effect was stereospecific: The nontoxic 1S enantiomers had no significant effect on veratridine-dependent activation. At high deltamethrin concentrations, enhancement was maximal at 5 × 10?5?1 × 10?4M veratridine. Pyrethroid enhancement was completely blocked by 5 × 10?6M tetrodotoxin, and neither pyrethroid affected 22Na+ uptake in the absence of veratridine at concentrations up to 1 × 10?5M. The relative potencies of deltamethrin and NRDC 157 in the synaptosomal sodium channel assay agree well with their relative acute toxicities to mice when administered by intracerebral injection. These findings demonstrate that pyrethroids exemplifying both characteristic poisoning syndromes are potent, stereospecific modifiers of sodium channel function in mammalian brain.  相似文献   

4.
The binding behavior of mercuric chloride (HgCl2), phenylmercuric acetate (PMA), and ethylmercuric chloride (EMC) to the spinach chloroplasts in relation to the inhibition of the Hill reaction was studied at pH 6.8 and 7.8 using 203Hg labeled compounds. The pH of the reaction medium did not influence the amount of mercury binding of the chloroplast at various mercurial concentrations, but it altered the inhibition curve of the Hill reaction. Between 0–1 × 10?5M the binding of Hg2+ and EMC were similar and increased linearly with the concentration, while the binding of PMA was similar to the binding of Hg2+ only at a concentration below 4 × 10?6M and was less when the concentration was above 4 × 10?6M. However, the inhibition of the Hill reaction by these mercury compounds was quite different; at pH 7.8, the I50 values for Hg2+, PMA, and EMC were 5 × 10?6, 2.5 × 10?6, and 2.5 × 10?6M, respectively, while at pH 6.8, these values were 4 × 10?6, 4 × 10?5, and 2 × 10?4M, respectively. The differential block of electron flow by the mercury compounds at pH 6.8 and 7.8 was further confirmed by electron spin resonance study.  相似文献   

5.
DDT inhibits the ATPase activity of the intact eel electroplaque. At a concentration of 10?5M, DDT inhibited 46% of the total ATPase activity, and 10?4M DDT inhibited 62% of the total ATPase activity and 62% of the ouabain-sensitive ATPase activity. The latter concentration of DDT reduced the rate of Na efflux from intact electroplaques and slowed the rate of recovery of the membrane potential following a large depolarization produced by carbamylcholine application. Repetitive direct stimulation of the innervated membrane at 10 Hz during the application of 10?4M DDT produced a significant irreversible depolarization. Ouabain, 10?4M, produced similar effects. The possible role of the inhibition of active NaK transport in producing the symptoms of DDT poisoning is discussed.  相似文献   

6.
Helicoverpa armigera is a strong insecticidal resistance developed insect pest. The understanding of its innate immune responses to emerging biocontrol agent entomopathogenic nematode-bacterial complex can provide an opportunity to control this insect in an environmentally benign manner. Study was focused on role of hemocytes changes and PO activity in Steinernema abbasi-Xenorhabdus indica challenged larvae of H. armigera over the time. Total cell count changed effectively from 10.2?±?1.81?×?105 to 15.5?±?3.3?×?105 cells/mm3 upto 9 h and reduced distinctly up to 8.0?±?2.49?×?105 cells/ mm3 in 24 h. PO activity inclined significantly and was recorded highest at 9 h (24.67?±?1.08?×?102 units) and lowest at 24 h (14.34?±?0.74?×?102 units) in total hemolymph with a similar pattern in plasma and the cellular fraction. Phenoloxidase activity in total and cellular component of hemolymph was positively correlated with prohemocytes, granulocytes and oenocytoids. Study showed the hemocytes and PO accounted as active immune responses against nematode infection. The results provide the first insight to understand the hemolytic activity, quick immunosuppression responses of S. abbasi-X. indica and vulnerability of H. armigera.  相似文献   

7.
At concentrations near 2 × 10?4M, barban, chlorpropham, and phenmedipham are inhibitors of the electron transfer in potato and mung bean mitochondria. The inhibition seems to be localized in the flavoprotein region. It affects preferentially the exogenous NADH dehydrogenation, in potato mitochondria (I50, 10?4M). Succinate dehydrogenation is less inhibited. At noninhibiting concentrations, the studied carbamates cannot uncouple the oxidative phosphorylations. Photosynthesis is completely inhibited by 2.10?7M phenmedipham, 5 × 10?5M barban, and 2 × 10?4M chlorpropham. The inhibition takes place at the PS II level. Moreover, barban and chlorpropham are uncouplers of the photophosphorylations for concentrations between 5 × 10?5 and 5 × 10?4M. The effects observed on mitochondrial respiration can also be found on respiration of Acer cultured cells. The effects on isolated chloroplast photosynthesis are also observed for slightly higher concentrations on cultured Chlorella and on pea and oat leaf fragments.  相似文献   

8.
The actions of a range of formamidines have been investigated biochemically and physiologically on octopamine receptors in the locust Schistocerca gregaria. All the formamidines tested [chlordimeform (CDM), demethylchlordimeform (DCDM), amitraz, and UK 16353] mimicked the action of octopamine by (1) increasing the amplitude and relaxation rate of slow motorneurone tension in the extensor-tibiae muscle of the hind leg and (2) changing the levels of cyclic AMP in this muscle. UK 16353 was most effective in changing these parameters, followed by DCDM then amitraz and CDM. The formamidine-induced increase in cyclic AMP levels was reduced or completely blocked by phentolamine, an antagonist of insect octopamine receptors. The time course for the increase in cyclic AMP was followed for 30 min by incubating muscles in 10?5M DCDM. The increase was potentiated by the phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine. In the presence of this compound, the response peaked within 5 min, before declining to a lower plateau after 12 min. The response to 10?5M CDM was lower and the maximum increase occurred after 7 min, then rapidly declined. Both formamidines increased cyclic AMP in a dose-dependent way with a threshold of between 5 × 10?7 and 10?8M. The results are discused in terms of the relationship between the biochemical and physiological actions of the formamidines in this preparation.  相似文献   

9.
The effects of pyrethroids on the on-going electrical activity of the axons of neurosecretory cells from the brain of fifth instar Rhodnius prolixus have been studied using extracellular electrodes. Low concentrations of the pyrethroids decamethrin, bioresmethrin, permethrin, and bioallethrin all produce dramatic increases in the overall frequency and dramatic changes in the pattern of electrical activity when applied directly to the exposed brain and corpora cardiaca in an otherwise intact insect. This change in activity was brought about by a recruitment in active units and the production of phasic acivity. A doubling of frequency over that of controls was brought about by low doses of the pyrethroids, namely decamethrin, 1 × 10?10M; bioresmethrin, 2 × 10?10M; permethrin, 1 × 10?9M; and bioallethrin, 2 × 10?7M. Similar hyperactivity of this system occurred during intoxication of intact insects following topical application of LD95 bioresmethrin. The enhanced sensitivity shown by neurosecretory cells over that of other cell types is discussed, as is the possibility that the increases in electrical activity of neurosecretory axons may result in massive neurohormonal release and thereby contribute to the eventual poisoning of the insect.  相似文献   

10.
Formetanate, a formamidine-type pesticide, and U-40481 (N-methyl-N′-2,4-xylylformamidine), a metabolite of amitraz, also a formamidine pesticide, contract the rabbit central ear artery with their maximal contractions being 22 ± 8% and 49 ± 6% of norepinephrine contractions, respectively. Maximal contractions were obtained with 10?3M formetanate and 10?4M U-40481, and cumulatively added higher concentrations caused a decrease in tension from that maximum. Their contractions were antagonized by 10?6M and 3 × 10?6M phentolamine. U-40481 reversibly antagonized contractions induced by serotonin, norepinephrine, and histamine, and to some extent potassium. Formetanate had little antagonist activity. Neither compound altered the resting rate of washout of radioactivity from [3H]norepinephrine preloaded strips. Both reduced electrically induced release, which may be related to local anesthetic-like actions on sympathetic neurones. Thus both compounds are partial agonists at the α-adrenergic receptor, and reduce electrically induced norepinephrine release, and U-40481 antagonizes contractions induced by certain other vasoactive agents.  相似文献   

11.
A range of compounds were tested as inhibitors of the enzyme epoxide hydrase, using a cyclodiene epoxide (HEOM) as substrate. Rat and rabbit liver microsomes and pupal homogenates of the blowfly (Calliphora erythrocephala) and the yellow mealworm (Tenebrio molitor) were compared as sources of the enzyme. Only minor differences were found between the four enzyme preparations, when considering I50 values and percentage inhibition at standard concentration. The simple epoxide 1,1,1-trichloropropane-2,3-epoxide and two glycidyl ethers p-nitrophenyl glycidyl ether and p-ethylphenyl glycidyl ether tended to have lower I50 values (1.8×10?6 to 8.0×10?5M) than triphenyl phosphate and SKF 525A (4.5×10?5 to 1.4×10?4M). Triphenyl phosphate and SKF 525A were competitive inhibitors for both the rat and Tenebrio enzymes. The only clear difference found between these two epoxide hydrase preparations was with respect to their inhibition by 1,1,1-trichloropropane-2,3-epoxide, which was an uncompetitive inhibitor with the rat enzyme, but showed kinetics of mixed inhibition with the insect preparation.  相似文献   

12.
Over a concentration range of 5.0 × 10?6?7.5 × 10?4M, the selective herbicide difenzoquat (1,2-dimethyl-3,5-diphenyl-1H-pyrazolium) caused more pronounced inhibition of potassium ion (K+) absorption by excised seedling roots of susceptible wild oat (Avena fatua L.) compared to those of tolerant barley (Hordeum vulgare L. cv. Bonanza) or wheat (Triticum aestivum L. cv. Neepawa). At 2.5 × 10?5M difenzoquat, the relative inhibition of K+ (86Rb) absorption by wild oat root segments inceased from 30% with a 10-min uptake period to 75% with an uptake period of 90 min, whereas no inhibition at all was evident for wheat root segments even after a 90-min exposure to the herbicide. An ion efflux compartmental analysis procedure demonstrated that difenzoquat did not affect the passive permeability properties of the plasma membrane of wild oat root cells. The experimental findings indicated that difenzoquat interfered directly with the process of active ion transport across the plasma membrane of root cells.  相似文献   

13.
In apterous adults of the spirea aphid, Aphis citricola van der Goot, the optimum conditions for determining acetylcholinesterase (AChE) activity consist of reaction mixture of 0.1 M phosphate buffer (pH 7.5), 10?3M acetylthiocholine (ASCh), and enzyme extract equivalent to 80 ± 3 μg protein incubated for 15 min at 30°C. The Km value for ASCh (6.7 × 10?5M) was much lower than that of butyrylthiocholine (BuSCh) (1.25 × 10?2M). The enzyme activity was almost completely inhibited by 10?6M paraoxon or 10?5M eserine and was 84% inhibited by 10?5M BW284C51 (a specific AChE inhibitor). DTNB was found to inhibit the enzyme activity and was therefore added at the end of the reaction. AChE activity of A. citricola was inhibited in vitro and in vivo by dimethoxon > dimethoate, and aldicarb sulfoxide > aldicarb > aldicarb sulfone. The in vivo effect correlates well with the toxicity level of the various toxicants. A neurotoxicity index which combines both mortality and in vivo inhibition of the aphid AChE activity is suggested as a measure for determining the toxicity of organophosphorus and carbamate compounds toward aphids.  相似文献   

14.
Methyl-1-(butylcarbamoyl)-2-benzimidazolecarbamate (benomyl) severely decreased DNA synthesis when applied at 3.5 × 10?6M during the G1 phase of germinating conidia of Fusarium oxysporum; nuclear divisions were completely inhibited at a fungicide concentration of 10 × 10?6M. The same concentration applied only after the S phase also completely inhibited the nuclear divisions. This dual interference of benomyl with DNA formation and mitosis might be related to a disturbed phosphorus metabolism.  相似文献   

15.
Methamidophos (O,S-dimethylphosphoramidothioate, Monitor) is an organophosphorus, cholinesterase-inhibiting insecticide. The rate constant (ki) for inhibiting rat plasma cholinesterase (ChE) was 1.57 ± 0.03 × 103M?1 min?1, for rat erythrocyte ChE was 8.86 ± 1.10 × 103M?1 min?1, and for rat brain ChE was 6.58 ± 0.42 M?1 min?1. Brain and plasma cholinesterases spontaneously recovered from over 90% inhibition at 30 min to 50% inhibition in 4 and 14 hr, respectively. Pralidoxime increased the rate of reactivation in vitro. In vivo, rats poisoned with methamidophos exhibited signs of cholinergic stimulation. The LD50 of ip methamidophos in male rats was 15 ± 0.7 mg/kg. Pralidoxime (60 mg/kg) and atropine (10 mg/kg) given with the methamidophos increased the LD50 to 52 ± 4.9 mg/kg and 60 ± 0.4 mg/kg, respectively. In rats given 12.5 mg methamidophos (an LD20), ChE activity was depressed 95 ± 12.5% in plasma, 92 ± 0.6% in stomach, and 88 ± 1% in brain at 1 hr after injection. At 48 hr after injection ChE activity had returned to 60% or more of control values in each of the tissues. Administration of a single dose of 60 mg/kg of pralidoxime along with methamidophos did not increase ChE activities at the times and places it was measured.  相似文献   

16.
Several aryl N-hydroxy- and N-methoxy-N-methylcarbamates were examined as inhibitors of bovine erythrocyte acetylcholinesterase (AChE). These carbamate derivatives were generally strong inhibitors of AChE, but, unlike the typical N-methyl- and N,N-dimethylcarbamates which are carbamylating agents, they proved to be reversible, competitive inhibitors of the enzyme. The values for the dissociation constant (Ka) for the enzyme-inhibitor complex to enzyme and inhibitor were in the range of 2 × 10?5?1 × 10?7M.  相似文献   

17.
Proctolin-induced, dose-dependent (10?8-2 × 10?6 M) contraction of the isolated foregut of Schistocerca gregaria was antagonised non-competitively by sulfotep (2 × 10?6-10?5 M). A higher dose of sulfotep (5 × 10?5 M) caused restoration of the proctolin dose-response curve to its control value. Neostigmine (10?5 M) caused non-competitive inhibition of proctolininduced tissue contraction. Increasing the dose of neostigmine to 10?4 M restored the proctolin response to control values. Sulfotep (10?5 M) and neostigmine (10?4 M) caused inhibition of acetylcholinesterase (AChE) activity in tissue homogenates obtained from guts pretreated with either drug for 20 min. The stimulatory effect of sulfotep (5 × 10?5 M) on proctolin-induced gut contraction was abolished by pretreatment of tissues with atropine (10?6 M). Under these conditions, 5 × 10?5 M sulfotep caused further antagonism of the action of proctolin. The results suggest that sulfotep is a proctolin receptor antagonist in the locust foregut. However, higher concentrations inhibit tissue AChE activity, thereby allowing endogenous acetylcholine to activate muscarinic receptors. This leads to enhanced tissue contractility which masks the antagonistic effect of sulfotep on proctolin-induced contraction.  相似文献   

18.
Long-term experiments with dactyl cells of Nitella flexilis showed that the herbicide 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) at a concentration of 1 × 10?5M affected not only O2 evolution in the light but also O2 uptake in the dark. The inhibition of O2 production was transitory, but dark respiration did not recover. DCMU induced the formation of giant mitochondria which disappeared before cell death. It was concluded that the algicidic effect of 1 × 10?5M DCMU on N. flexilis, but not necessarily the elongation of mitochondria, was due to the inhibition of mitochondrial respiration and not of photosynthesis.  相似文献   

19.
Brown rot on cherry and plum, caused by Monilinia laxa, is an important disease, for which overwintered mummified fruit is a significant inoculum source for infection of flowers and fruit in the spring. Experiments were conducted to assess the potential of applying plant protection products in winter and/or early spring to suppress sporulation on mummified fruit. Products tested included Indar 5 EW (a commercial fungicide, a.i. fenbuconazole), Aureobasidium pullulans Y126 [a candidate biocontrol agent (BCA)]), Bacillus sp. B91 (a candidate BCA) and Serenade (a commercially formulated BCA of Bacillus subtilis strain QST 713) in addition to control treated with tap water. Indar and A. pullulans Y126 significantly reduced sporulation when applied once in winter. Overall, a single treatment in early spring (February) was slightly more effective than single treatment in winter (November). Application of all products in both winter and early spring led to significant reduction in sporulation. Indar had the highest efficacy, reducing the number of spores from 9?×?105 to 5?×?103 per mummified plum when applied twice. Of the three BCAs applied on both occasions, A. pullulans Y126 had the highest efficacy, reducing the number of spores from 9?×?105 to 5?×?104 per mummified plum. There were no synergistic but additive effects between the two applications in winter and early spring based on the Bliss independence test. These results suggest that reducing overwintering inoculum in dormant season is effective and may be part of an integrated management strategy for brown rot on stone fruit.  相似文献   

20.
Cells were isolated from the developing leaves of Ipomoea aquatica (water spinach), a C3 plant, and three kinds of C4 plants, namely, Digitaria sanguinalis (NADP+-specific malate dehydrogenase type), Panicum miliaceum (NAD+-specific malic enzyme type), and Panicum texanum (phosphoenopyruvate carboxy kinase type), to study the effect of monuron on light-dependent 14CO2 fixation and oxygen evolution. Bundle sheath cells, except for those of D. sanguinalis, and mesophyll cells of all plants fixed approximately the same amount of 14CO2. Monuron, at the range used (2 to 10 × 10?7M), showed strong inhibition in the mesophyll cells of water spinach and in bundle sheath cells of P. miliaceum and P. texanum and moderate inhibition in the mesophyll cells of all C4 plants. In the bundle sheath cells of D. sanguinalis the low rate of 14CO2 fixation was stimulated to some extent by the addition of malate and ribose 5-phosphate. The I50 value was 6 × 10?7M for the sensitive cells. Monuron inhibited the oxygen evolution of all seven cell types and their I50 values varied between 3 × 10?7 to 6 × 10?7M. The differential response of isolated plant cells from different species to light-dependent CO2 fixation in the presence of monuron may also be involved in urea herbicide selectivity and undoubtedly is due to the differential photosynthetic pathways present nn them.  相似文献   

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