Effects of DDT on the cockroach nervous system at three temperatures

Some effects of DDT on the cockroach nervous system have been correlated with poisoning symptoms, using free-walking cockroaches with implanted electrodes. Experiments at 16.5°C and 32°C used LD₉₅ doses and at 25°C, an estimated LD₉₅. DDT had excitant actions on each nerve studied; cercal afferent and efferent neurones, and abdominal interneurones. The effects on the central nervous system became more marked as temperature was reduced, despite the smaller quantity of DDT employed, but the excitant actions on the peripheral nervous system were not quantified. It is suggested that the effects of DDT on the cockroach nervous system could account for the negative temperature coefficient of toxicity of DDT.     

Mode of action of nereistoxin on the neuromuscular transmission in the frog

The effects of nereistoxin on the neuromuscular transmission of the frog have been studied by means of intracellular microelectrode and voltage clamp techniques. Nereistoxin blocked the neuromuscular transmission without causing depolarization of end-plate membranes. A small end-plate potential was elicited upon nerve stimulation. The frequency and amplitude of miniature end-plate potentials decreased after exposure to nereistoxin, and the quantum content of the end-plate potential tended to decrease also. Chemical sensitivity of the end-plate membrane as examined by iontophoretic application of acetylcholine was markedly reduced. Both sodium and potassium components of the end-plate current were suppressed almost equally by application of nereistoxin. It is concluded that inhibition of the mechanisms whereby the end-plate membrane conductances to sodium and potassium ions are increased is the major action of nereistoxin responsible for neuromuscular blockade.     

Effects of deltamethrin on ventral nerve cord activity in the cockroach

The effects of varying concentrations of deltamethrin on a number of the parameters of electrophysiological activity in the cockroach ventral nerve cord have been studied. Deltamethrin, at concentrations greater than 100 nM, caused repetitive firing in the central nervous system (CNS), prior to conduction block, the effect getting faster as the concentration was increased. Whilst 10-nM deltamethrin eventually caused conduction block with no apparent increase in the level of CNS activity, it induced a gradual decrease in the amplitudes of all spike activity. Deltamethrin at 10μM induced a significant increase in the latency of electrically evoked responses, and this was attributed to a synaptic mechanism. It was shown for the first time that 10-μM deltamethrin causes a significant elevation of the extra-axonal K⁺ activity; the possible consequences of this are discussed.     

Action of avermectin B1a on the leg muscles and the nervous system of the American cockroach

The action of avermectin was studied in the leg muscle and the central nervous system of the American cockroach, Periplanata americana L. Avermectin at a low concentration (10^?7M) causes a failure of the leg muscles to respond to external stimuli within 30 min without affecting the magnitude of contraction. Avermectin was found to stimulate Cl^? uptake by the leg muscles within 4 min at 10^?7M. The threshold concentration to cause such stimulation was on the order of 10^?8M. This stimulatory action could be antagonized by picrotoxinin (10^?4M) and to a lesser extent by bicuculline methiodide (10^?4M). The phenomenon is observable under both Na⁺-free and K⁺-free conditions. It was concluded that the action of avermectin is to open the chloride channel on the plasma membrane. This action of avermectin does not seem to be mediated through GABA, GABA receptors, diazepine receptors, or picrotoxinin receptor in this insect species, and therefore suggests that avermectin directly attacks the chloride channel proper both in the central nervous and the neuromuscular systems.     

杀螟丹在水稻植株及稻田土壤、水中的残留降解动态研究

本文通过田间试验和气相色谱检测,分析了杀螟丹在水稻叶片和根中,以及对稻田土壤和水中的降解动态.结果表明:在苗床上施用杀螟丹,杀螟丹在水稻叶和根中的降解半衰期分别为16.92和10.94d.水稻移栽后60d,水稻叶片和根中均未检出杀螟丹.在稻田土壤和水中的降解速度较植株中快,半衰期分别为3.71和1.88d.水稻移栽后30d,稻田水中未检出杀螟丹;移后60d,稻田土壤中也未检测到杀螟丹.     

Cholinergic properties of pinched-off synaptic nerve endings from the central nervous system of the cockroach Periplaneta americana

The preparation and cholinergic properties of a subcellular fraction, enriched in pinched-off nerve-endings (synaptosomes) from the central nervous system of the cockroach Periplaneta americana, are described. The endings retained their cytoplasmic components, as shown by the presence of marker enzymes and by ultrastructural examination. A carrier-mediated, high-affinity uptake of [³H] choline into the synaptosomes was demonstrated, and this uptake was saturable, depended on a Na⁺-gradient, and was inhibited by hemicholinium-3. It had an apparent K_m value of 0.6 (±0.1) μM, and a V_max of 20.5 (±2.5) pmol min^?1 per mg of protein. The high-affinity [³H]choline uptake was associated with the synthesis of [³H]phosphocholine and [³H]O-acetylcholine. The rate of [³H]choline uptake in synaptosomes was increased by DDT [1,1,1-trichloro-2,2-bis(4-chlorophenyl) ethane] at 100 nM concentration, and this increase was inhibited by tetrodotoxin, while neostigmine appeared to be a potent inhibitor (I₅₀ = 10 pM) of the DDT-activated uptake of [³H]choline. The site of action of the insecticides was specifically on the pre-synaptic nerve terminals because the synaptosomes preparation did not retain the post-synaptic membrane of the original nerve-endings. Cockroach synaptosomes provided a useful in-vitro preparation for studying the effects of insecticides on the pre-synaptic nerve endings.     

取食不同寄主的小菜蛾对呋喃威和巴丹敏感性变化

取食不同寄主植物的小菜蛾３龄幼虫对呋喃威和巴丹的敏感性发生了变化。其中取食萝卜的小菜蛾最为敏感，其次为甘蓝、菜心、白菜和西洋菜，取食花椰菜的最不敏感。但用不同寄主植物饲养小菜蛾１个世代后，统一用菜心饲养至３龄，再分别用上述药剂测定，其结果敏感性差异不明显。     

Phenylpyrazoles,a new class of pesticide: Effects on neuromuscular transmission and acetylcholine responses

Phenylpyrazoles constitute a newly developed class of chemicals with insecticidal and herbicidal properties. In acute toxicity experiments in rats, near-lethal doses of phenylpyrazoles produce neurotoxic symptoms with an unknown mode of action. We have investigated the effects of two phenylpyrazoles, SLA4722 and SLA4685, in the frog neuromuscular junction and in the clonal muscle cell line BC3H-1. In the frog neuromuscular junction SLA4722 at concentrations ? 10^?5 M caused a pronounced increase in the frequency of miniature endplate potentials (MEPPs). SLA4685 caused a similar increase but was less potent. In the clonal muscle cell line BC3H-1, SLA4685 produced a concentration-dependent block of the acetylcholine (ACh) response (IC₅₀ = 2.4(±0.3) × 10^?5 M). At 10^?6 M a slight potentiating effect of SLA4685 on the ACh response was observed. SLA4722 was less potent in this preparation. The increased transmitter release might, at least partly, be responsible for the excitatory effects of the phenylpyrazoles in intact animals.     

Deltamethrin raises potassium activity in the microenvironment of the central nervous system of the cockroach: An assessment of the potential role of the blood-brain barrier in insecticide action

The effect of deltamethrin (10μm) on extracellular K ⁺ activity in the micro-environment of the central nervous system of the cockroach has been studied. At normal room temperature, deltamethrin induced a rise in the K ⁺ concentration of about 3 mM, representing some 75% increase from normal Deltamethrin also caused a transient surge in the frequency of spontaneous activity, which preceded the K ⁺ effect. At a lowered temperature, the final value of the deltamthrin-induced rise in extracellular K ⁺ concentration was very similar to normal. However, when the structural component of the blood-brain barrier was disrupted, the effect of deltamethrin was much reduced. Possible consequences of the deltamethrin-induced rise in extracellular K ⁺ concentration and the potential role of the blood-brain barrier in insecticide action are discussed.     

The effects of dieldrin and isomeric aldrin diols on synaptic transmission in the American cockroach and their relevance to the dieldrin poisoning syndrome

Dieldrin and two of its metabolites, 6,7-trans-dihydroaldrindiol, and 6,7-cis-dihydroaldrindiol, were studied with regard to their toxicity to the American cockroach, effects on ganglia of the ventral nerve cord, and penetration into the ventral nerve cord of poisoned cockroaches. An approximate LD₅₀ for injected doses of dieldrin was 0.45 mg/kg. After injection at 115 mg/kg, the trans isomer of aldrin diol caused about 70%, and the cis isomer about 50% mortality. Injected doses of 40 mg/kg of the three compounds appeared in the ventral nerve cord to the extent of 0.13–0.26% of the doses. Dieldrin was more potent, but slower acting than the diols in causing synaptic after-discharge and elevated spontaneous activity in isolated nerve cords. The results are discussed in relation to other studies on these compounds. It was concluded that, in the American cockroach, dieldrin, rather than either of the diols, is the insecticidal agent in dieldrin poisoning, and that metabolic conversion of dieldrin to the cis and/or trans aldrindiol constitutes a detoxification.     

Effects of chlordimeform and lindane on monoamine levels in the central nervous system of the american cockroach, Periplaneta americana L

The effects of chlordimeform and lindane on levels of 5-hydroxytryptamine, tryptophan, and N-acetyl dopamine were studied in the cerebral ganglia of the american cockroach, Periplaneta americana. The effects of chlordimeform on nerve cord levels of 5-hydroxytryptamine, tryptophan, dopamine, and octopamine, and the effect of lindane on cerebral ganglia levels of dopamine were also investigated in this species. Topical applications of chlordimeform deplete 5-hydroxytryptamine and tryptophan from the cerebral ganglia whereas levels of n-acetyl dopamine are elevated. The effect of chlordimeform on these compounds is dose-dependent. Similar chlordimeform-induced effects are observed in the nerve cord, and octopamine levels are also depleted in this tissue following treatment with chlordimeform. A biphasic response to chlordimeform is observed in the nerve cord for dopamine levels with a 40% decrease evident after 2 hr and a 30% increase apparent after 6 hr. In contrast to chlordimeform, lindane does not affect 5-hydroxytryptamine and tryptophan levels in the cebral ganglion but low doses of this insecticide effect increases in brain levels of dopamine and n-acetyl dopamine.     

Effect of thiamethoxam on cockroach locomotor activity is associated with its metabolite clothianidin

BACKROUND: In the present study, the effect of thiamethoxam and clothianidin on the locomotor activity of American cockroach, Periplaneta americana (L.), was evaluated. Because it has been proposed that thiamethoxam is metabolised to clothianidin, high‐performance liquid chromatography coupled with mass spectrometry was used to evaluate the amount of clothianidin on thiamethoxam‐treated cockroaches. RESULTS: One hour after neonicotinoid treatment, the time spent in the open‐field‐like apparatus significantly increased, suggesting a decrease in locomotor activity. The percentage of cockroaches displaying locomotor activity was significantly reduced 1 h after haemolymph application of 1 nmol g^?1 neonicotinoid, while no significant effect was found after topical and oral administration. However, at 24 and 48 h, all neonicotinoids were able to reduce locomotor activity, depending on their concentrations and the way they were applied. Interestingly, it was found that thiamethoxam was converted to clothianidin 1 h after application, but the amount of clothianidin did not rise proportionately to thiamethoxam, especially after oral administration. CONCLUSION: The data suggest that the effect of thiamethoxam on cockroach locomotor activity is due in part to clothianidin action because (1) thiamethoxam levels remained persistent 48 h after application and (2) the amount of clothianidin in cockroach tissues was consistent with the toxicity of thiamethoxam. Copyright © 2010 Society of Chemical Industry     

Picrotoxinin receptor in the central nervous system of the American cockroach: Its role in the action of cyclodiene-type insecticides

The nature of the picrotoxinin receptor was studied using the central nervous system (CNS) of the American cockroach. It first was confirmed by using an electrophysiological technique that the abdominal nerve cord of the American cockroach was sensitive to picrotoxinin. By using a $\text{[}{}^3\text{H]α-dihydropicrotoxinin}$ binding test it was determined that the picrotoxinin receptor in CNS of this insect had a higher affinity toward picrotoxinin and heptachlor epoxide than the corresponding receptor in the rat brain. Also, the cockroach brain preparation had a higher percentage of specific binding in the total binding, making this material suitable for receptor studies. By using a sucrose density centrifugation technique, it was determined that the fraction sedimented at the interphase of 1.0 to 1.2 M sucrose at 100,000g contained the highest level of specific binding site. The receptor showed a sensitivity to all insecticidal cyclodienes tested, namely photodieldrin, oxychlordane, endrin, heptachlor epoxide, γ-chlordane, dieldrin, aldrin, heptachlor, and isodrin (expressed in the order of potency). Among four BHC isomers, the γ-isomer showed the highest potency to bind with this receptor.     

Recent studies on the effects of DDT and pyrethroid insecticides on nervous activity in cockroaches

A summary is given of the results of three sets of electrophysiological experiments on the American cockroach (Periplaneta americana). The effects of DDT and S-bioallethrin [bioallethrin (S)-cyclopentenyl isomer] on single giant axons were studied using the voltage-clamp technique. Whereas both molecules induced long tails of inward (sodium ion) current, the voltage and time-dependency of these tails differed. With DDT, the tail was proportional to the activation of the peak current and decreased with the duration of the pulse, suggesting that the molecules were bound to open sodium channels and delayed their closing. With S-bioallethrin, the voltage dependency of the tail was different from that of the peak current, and the tail current increased exponentially with the duration of the depolarisation, suggesting that the pyrethroid insecticide modified resting (or silent) sodium channels into slowly activating channels. Modified action potentials, mimicking those produced by the two molecules, were computed on the basis of these results. Deltamethrin, one of the most potent pyrethroid insecticides, was applied topically on a leg mechanoreceptor and was found to have little effect on the local ‘receptor potential’ but to inhibit action potential production. The effects of topical applications of deltamethrin on the dorsal part of the abdomen, on nervous activity in the abdominal connectives, were studied under different experimental conditions. The results suggest that the insecticide molecules diffused rapidly through the cuticle, were concentrated in the haemolymph, and eventually reached the central nervous system, where they inhibited nerve activity.     

Effects of the pyrethroids bioallethrin,deltamethrin and RU-15525 on the electrical activity of a cuticular mechanoreceptor of the cockroach Periplaneta americana

A study has been made of the effects of bioallethrin, RU-15525 [5-benzyl-3-furylmethyl (1R)-cis-2,2-dimethyl-3-(tetrahydro-2-oxo-3-thienylidenemethyl)-cyclopropanecarboxylate, ‘Kadethrin’], and deltamethrin on the electrical activity, measured in vivo, of a cuticular mechanoreceptor of Periplaneta americana. The modifications induced by these pyrethroids on the membrane excitability can be classified into two groups: Type I effects (bioallethrin) are characterised by a substantial increase in the number of action potentials triggered at the initiation site by a given mechanical stimulation, by an electrical activity persisting after mechanical stimulus has been stopped (repetitive activity), and possibly, by an inhibition of excitability of the cell membrane. Type II effects (RU-15525 and deltamethrin), are characterised by an inhibition of the excitability of the initiation site. In the case of RU-15525, there was a transient spontaneous electrical activity. Both types of effects have been linked to an action on the sodium channel, particularly at the initiation site. The preparation studied, which possessed no synapses, was shown to be more sensitive to deltamethrin (which is also the most insecticidal of the three pyrethroids) than to either allethrin or RU-15525. These results suggest that it is unnecessary to envisage a main target (sodium channel) that is different for the two types of pyrethroid.     

Effects of topical and bath applications of the insecticide deltamethrin on electrical activity in a leg mechanoreceptor of the cockroach,Periplaneta americana

Two different methods were used to analyze the effects of topical and bath applications of low concentrations of deltamethrin. The first method enabled the analysis of the receptor potential as well as that of the spike activity generated by mechanical or electrical stimulation of the mechano-receptor. The second method enabled recording of the conducted spike activity originating from a mechanical stimulation of the receptor and propagated along the sensory nerve. Topical application of small amounts of deltamethrin (10⁻⁹ to 10⁻⁷ g) had little effect on the receptor potential induced by mechanical stimulation of the sensory hair but blocked the action potentials within a few minutes. Electrical stimulation of the receptor cell revealed that conduction in the dendrite was affected first by the insecticide. The effects of topical application on conducted activity were compared with those of bath applications (2 × 10⁻⁸ to 2 × 10⁻⁷ M) and no significant difference was found, suggesting a rapid penetration of the insecticide through the cuticle. These effects were not reversible and this absence of reversibility was not correlated with the integrity of the barrier which protects the receptor cell from rapid changes in the ionic composition of the hemolymph. Deltamethrin was never found to induce bursts of activity in the mechanoreceptor cell under investigation either at rest or following mechanical or electrical stimulation. There are, however, some indications that other receptor cells may respond differently to this insecticide.     

Long-term effects of DDT on the behavior and central nervous system activity in Periplaneta americana

The effects of p,p′-DDT and four of its analogs on electrical activity in the central nervous system of the cockroach, Periplaneta americana (L.), were investigated. Cockroaches were injected intraabdominally with an organochlorine compound at LD₅₀ 96-hr doses (except for p,p′-DDE). Extracellular recordings were made from the central nervous system at 1 hr, 24 hr, or 3 weeks postinjection. p,p′-DDT, methoxychlor, and p,p′-DDD induced behavioral changes (tremors, jitters, hyperexcitability) and repetitive firing in the central nervous system prior to 1 hr postinjection. By 24 hr postinjection, most behavioral signs of poisoning had disappeared, though repetitive firing could still be readily elicited in the central nervous system. Cockroaches injected with o,p′-DDT, however, usually required about 48 hr before overt signs of poisoning became apparent. Cockroaches treated with p,p′-DDT or o,p′-DDT behaved normally at 3 weeks postinjection but still displayed a significant occurrence of repetitive firing in the central nervous system. A mechanism is proposed to explain how a cockroach might recover behaviorally from a sublethal dose of an organochlorine compound but still display repetitive firing in its central nervous system. A direct “cause and effect” relationship between repetitive firing in the central nervous system and mortality (and external signs of poisoning) is therefore questioned.     

Inhibition of juvenile hormone biosynthesis and methyl farnesoate epoxidase activity by 1,5-disubstituted imidazoles in the cockroach,Diploptera punctata

Seventeen substituted imidazoles were tested as inhibitors of juvenile hormone (JH) III synthesis by cockroach corpora allata in an in-vitro radio-chemical assay. Most of these 1,5-disubstituted imidazoles were highly potent, with IC₅₀ values of less than 100nM. The compounds differed in their ability to cause an accumulation of the precursor methyl farnesoate in the glands. Four of the imidazoles were tested by topical application to previtellogenic adult females, and all caused a significant inhibition of JH synthesis and an accumulation of intraglandular methyl farnesoate for at least three days after treatment. Methyl farnesoate epoxidase activity of homogenates of corpora allata was inhibited by the compounds TH -14 and TH -27. This P450-dependent epoxidase activity was inhibited at less than 10 nM. The results show that the 1,5-disubstituted imidazoles are powerful inhibitors of the last step of juvenile synthesis in this cockroach.     

Biophysical aspects of nervous activity in relation to studies on the mode of action of insecticides

The spread to the nervous system of topically applied neurotoxic insecticides is discussed. During spread different insecticides may distribute themselves between fluid and solid phases within the insect's tissues in greatly differing ratios. These differences are reflected in their concentrations in the haemolymph, which is probably the medium mainly responsible for distributing insecticides within the insect, and also the main source from which insecticides enter the nervous system. Evidence for spread via more restricted pathways, such as tracheae or the nerves themselves, is conflicting. The mode of action of neurotoxic insecticides is briefly reviewed, including the role of secondarily released neuroactive stress substances, and the extent to which resistance is expressed at the site of action is also discussed. Finally, the nervous system is examined for new sites of insecticidal action which, if attacked, could give greater specificity.