Structure-related effects of pyrethroid insecticides on the lateral-line sense organ and on peripheral nerves of the clawed frog, Xenopus laevis

The effects of seven different pyrethroid insecticides on the lateral-line sense organ and on peripheral nerves of the clawed frog, Xenopus laevis, were investigated by means of electrophysiological methods. The results show that two classes of pyrethroid can be clearly distinguished. (i) Pyrethroids without an α-cyano group (permethrin, cismethrin, and bioresmethrin). These noncyano pyrethroids induce short trains of nerve impulses in the lateral-line sense organ. In peripheral nerve branches they induce a depolarizing afterpotential and repetitive firing. These effects are very similar to those previously reported for allethrin. (ii) Pyrethroids with an α-cyano-3-phenoxybenzyl alcohol (cypermethrin, fenpropathrin, deltamethrin, and fenvalerate). In the lateral-line sense organ these α-cyano pyrethroids induce very long trains of nerve impulses which may last for seconds and may contain hundreds or even thousands of impulses. The α-cyano compounds do not cause repetitive activity in peripheral nerves. Instead they induce a quickly reversible, stimulus frequency-dependent suppression of the action potential. Since the chemical structure of cypermethrin differs from that of permethrin only in the α-cyano group and because all four α-cyano compounds act in a very similar way, it is concluded that the α-cyano substituent is responsible for the large differences in neurotoxic effects. In the lateral-line sense organ the duration of nerve impulse trains induced by the noncyano as well as the α-cyano pyrethroids increases dramatically when the temperature is lowered. Further, in sensory fibers the effects of both classes of pyrethroid on the nerve action potential are more pronounced compared to their effects on motor fibers. It is argued that the different neurotoxic effects reported here originate from a common mechanism of action of pyrethroids, which is a prolongation of the transient increase of sodium permeability of the nerve membrane associated with excitation.It is concluded that the sodium channel in the nerve membrane is the major target site of noncyano and α-cyano pyrethroids.     

The effects of organophosphorus poisoning on dopamine and 5-hydroxytryptamine concentrations in the brain of the cricket, Acheta pennsylvanicus, and the cockroach, Periplaneta americana

Liquid chromatography with electrochemical detection was used to measure dopamine and 5-hydroxytryptamine concentrations in the brains of crickets (Acheta (Gryllus) pennsylvanicus) and cockroaches (Periplaneta america) treated with the organophosphate dicrotophos. Organophosphate treatment did not cause depletion in dopamine and 5-hydroxytryptamine concentrations although reserpine treatment caused a reduction in the concentrations of both amines in the brains of these insects. Fluorescent histochemical studies of cricket brains confirmed these observations.     

Comparative inhibition of the juvenile hormone esterases from Trichoplusia ni,Tenebrio molitor, and Musca domestica

Twenty-seven compounds were screened as potential inhibitors of juvenile hormone esterases. Of these compounds O-ethyl-S-phenyl phosphoramidothiolate provided the best inhibition for the cabbage looper, Trichoplusia ni (Hubner), and the yellow mealworm, Tenebrio molitor L., while the juvenile hormone esterases of the house fly, Musca domestica L., were best inhibited by a juvenoid carbamate (1-(m-phenoxy-N-ethyl carbamate)-3,7-dimethyl-7-methoxy-2E-octene). The inhibition patterns of T. ni and T. molitor are similar, while those of M. domestica are relatively different. Further studies on the juvenile hormone and α-napthyl acetate esterases of T. ni showed that they could be differentially inhibited. Diisopropyl phosphorofluoridate and an alkyl trifluoromethyl ketone selectively inhibit the hydrolysis of α-naphthyl acetate and juvenile hormone, respectively, while O-ethyl-S-phenyl phosporamidothiolate inhibits both enzymes. The juvenile hormone esterases of T. ni also appear to be unique enzymes that are selective for juvenile-hormone-like molecules. The in vivo inhibition of T. ni juvenile hormone esterases by O-ethyl-S-phenyl phosphoramidothiolate slows the in vivo hydrolysis of juvenile hormone and results in delayed pupation and malformed larvae that resemble larval-pupal intermediates. Thus, the esterases involved in juvenile hormone metabolism appear to be important in juvenile hormone regulation.     

Myotoxic and neurotoxic activity of Bacillus thuringiensis var. israelensis crystal toxin

The mechanism of the entomocidal action of Bacillus thuringiensis var. israelensis (BTI) in Periplaneta americana has been studied. Cockroaches treated with the alkali-solubilized BTI crystal gradually became sluggish and immobile. A physiological examination of poisoned cockroaches indicated that BTI possessed both myotoxic and neurotoxic activity. Following hemocoel or foregut administration of BTI, myotoxic effects were observed within 10–20 min whereas the onset of neurotoxic effects was considerably delayed. The results of this study suggest that the myotoxic action of BTI is probably important for the initial manifestation of its toxicity. The neurotoxic effects of BTI were ascribed to its ability to interfere with transmitter release. BTI exerted a dual action on transmitter release in the cockroach sixth abdominal ganglion. At lower doses (2–4 μg/ml) BTI was found to suppress transmitter release by interfering with calcium uptake. At higher concentrations (12 μg/ml or higher), however, BTI caused blockage of synaptic transmission which was preceded by massive transmitter release. In either case, the synapse blocking action of BTI was probably due to its effects upon presynaptic terminals. Postsynaptic membranes and axons in the ventral nerve cord apparently remained unaffected.     

The effect of O,S,S,-trimethyl phosphorodithioate on the in vivo metabolism of phenthoate in the rat

The in vivo metabolism of phenthoate (O,O-dimethyl S-[α-(carboethoxy)benzyl]phosphorodithioate) was followed in rats after oral administration of a nontoxic dose of 100 mg/kg. The same metabolic study was conducted following coadministration of 0.5% O,S,S-trimethyl phosphorodithioate (OSS-Me). When administered alone, phenthoate was metabolized principally by carboethoxy ester hydrolysis and cleavage of the PO and CS bonds, resulting in at least six metabolites. The primary urinary metabolite excreted was phenthoate acid. Coadministration of 0.5% OSS-Me did not alter the types of metabolites excreted. However, a reduction of the carboxylesterase-catalyzed product (phenthoate acid) was observed, indicating that the enzyme responsible for the major pathway of phenthoate detoxication was inhibited. Alternate detoxication processes did not compensate for the reduction in carboxylesterase-catalyzed detoxication. It was concluded that inhibition of the carboxylesterase enzymes is the major cause of the potentiation of phenthoate toxicity by OSS-Me.     

Effects of glyphosate on uptake,translocation, and intracellular localization of metal cations in soybean (Glycine max) seedlings

Root-fed or foliar-applied glyphosate [N-(phosphonomethyl) glycine] reduced uptake and translocation of Ca²⁺ and Mg²⁺, but not K⁺, by soybean [Glycine max (L.) Merr. “Hill”] seedlings as measured by atomic absorption spectrometry. Histochemical techniques revealed that cells of secondary roots that were formed after glyphosate treatment were deficient in Ca²⁺. The relative distribution of Ca²⁺ in control root and leaf cells was mitochondria > plastids > cytoplasm. Glyphosate severely reduced Ca²⁺ content and eliminated intracellular concentration of Ca²⁺ in the mitochondria of both root and leaf cells. Glyphosate had no effects on K⁺ distribution at the ultrastructural level. These results support the view that glyphosate effects on distribution of divalent metal cations may be related directly or indirectly to the phytotoxicity of the herbicide.     

Enhancement of dye-sensitized phototoxicity to house fly larvae in vivo by dietary ascorbate,diazabicyclooctane, and other additives

Several reagents reported to be singlet oxygen quenchers and/or radical scavengers and to be protectants against photooxidative damage to isolated systems in vitro were examined, in vivo, for protective effect on the larvae of the house fly (Musca domestica L.; Diptera:Muscidae). A standardized erythrosine-sensitized phototoxic test procedure was used. β-Carotene appeared to show some protective effect. Other dietary additives exhibited no measurable degree of protection to the larvae in vitro; on the contrary, mortality increased in the presence of butylated hydroxytoluene, ascorbate, and diazabicyclooctane.     

Metabolism of fenitrothion in red-backed voles (Clethrionomys gapperi)

To estimate the impact of fenitrothion on small mammals, a breeding colony of wild southern red-backed voles (Clethrionomys gapperi) was successfully maintained. The red-backed vole is a nontarget species inhabiting coniferous forests that are subjected to aerial spraying of the pesticide for the control of spruce budworm infestations. The voles were used to examine toxicity and the metabolic pathways involved in the elimination of fenitrothion after intraperitoneal injection of the purified, undiluted organophosphate. The 96-hr LD₅₀ was 1330 mg/kg. Toxicities toward males and females were not significantly different. All observed symptoms of intoxication and 99% of the mortality occurred within 48 hr of dose application. All major metabolites of fenitrothion metabolism in nonruminant mammals were identified and quantified by gas chromatography. At all doses, fenitrothion was rapidly metabolized and excreted. No body accumulation of residues was implied. The toxicity of fenitrothion was not correlated with increasing proportion of the dose converted into fenitrooxon. The low toxicity to red-backed voles is probably due, in part, to rapid metabolic detoxication by the two mechanisms cleaving fenitrothion at the P-O-aryl and PO-alkyl bonds, the latter becoming more prominent at high dose levels.     

Inhibition of permethrin-hydrolyzing esterases from Wiseana cervinata larvae

Inhibition of permethrin-hydrolyzing enzymes from larvae of the porina moth Wiseana cervinata has been examined in vivo and in vitro. Significant inhibition was shown by carbaryl and pirimiphos-methyl. 1-Dodecylimidazole substantially inhibited permethrin hydrolysis only in liver insects. The triphenylmethane dye tetrabromophenolphthalein was a moderate inhibitor only in vitro. TMDM (bis(N-dimethyl-4-aminophenyl)methane) had little effect on hydrolysis. These observations extend the range of species and substrates for which the triphenylmethane dyes and 1-dodecylimidazole are useful inhibitors of insecticide metabolism.     

Disposition and metabolism of [14C]chlorpyrifos in the black imported fire ant, Solenopsis richteri Forel

The short-term disposition and metabolism of topically administered [¹⁴C]chlorpyrifos was assessed in the black imported fire ant (Solenopsis richteri Forel) in the presence and absence of the mixed-function oxidase inhibitor piperonyl butoxide. Chlorpyrifos is readily absorbed into an internal organosoluble fraction which was quickly converted into a water-soluble fraction. The radioactivity was slowly excreted over a 24-hr period. Piperonyl butoxide slowed the conversion of the internal organosoluble radioactivity to the water-soluble fraction. Thin-layer chromatography indicated that piperonyl butoxide slowed the conversion of chlorpyrifos to material remaining at the origin, presumably water-soluble metabolites. The results of acid hydrolysis studies indicated that the water-soluble radioactivity was comprised mainly of conjugates. Although very little chlorpyrifos oxon was recovered in the metabolism experiments, in vitro studies on fire and head homogenates showed the compound to be an extremely potent anticholinesterase, with an I₅₀ of 4.6 × 10^?10M, while a major metabolite, 3,5,6-trichloropyridinol, was an ineffective acetylcholinesterase inhibitor.     

The effect of organophosphorous insecticides upon catecholamine fluorescence in the corpus centrale and frontal ganglion of the house cricket, Acheta domesticus (L.)

Treatment of the house cricket Acheta domesticus (L.) with tetraethyl pyrophosphate and dicrotophos causes a depletion of the catecholamine stores of the central nervous system. Fluorescence microscopy of the brain and frontal ganglion 30 min after knock-down revealed a reduction in the catecholamine-specific fluorescence of the corpus centrale and frontal ganglion neuropile. In the corpus centrale the effect was much more pronounced and less variable with dicrotophos than with tetraethyl pyrophosphate, whereas both compounds appeared to have similar effects on the frontal ganglion. The possible relationship of this depletion to symptoms of intoxication requires further investigation.     

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.     

Physiological effects of a benzyl-1,3-benzodioxole chemosterilant on Sarcophaga bullata

Ovarian development of adult female Sarcophaga bullata was arrested by benzyl-1,3-benzodioxole (J2581) when fed in concentrations of 5–10 mg/g sugar. An accumulation of hemolymph protein, especially vitellogenin, was associated with the disruption of ovarian development, indicating that the benzyl-1,3-benzodioxole affects the sequestration of vitellogenin from the hemolymph into the ripening follicles. Exogenous supplementation with ecdysterone or juvenile hormone analog (ZR515) did not restore normal ovarian growth.     

Effects of herbicides and herbicide analogs on [14C]leucine incorporation by suspension-cultured Solanum nigrum cells

Assays of [¹⁴C]leucine incorporation were used to measure effects of herbicides on suspensioncultured heterotrophic Solanum nigrum cells. Most herbicidal vs. nonherbicidal chemicals in a set of 47 compounds could be distinguished from each other based on their extent of inhibition of leucine incorporation by S. nigrum cells. Herbicides which failed to inhibit leucine incorporation were photosynthetic inhibitors. Both phytotoxic and nonphytotoxic thiocarbamate analogs (as determined by whole-plant studies) tended to inhibit leucine incorporation. It was concluded that the leucine incorporation screen could detect a majority of compounds tested which are herbicidal, and that it may also be useful to detect compounds which have cellular toxicity which is not observed in the whole plant.     

On the mode of action of 3-phenylindole towards Aspergillus niger

3-Phenylindole is an antimicrobial compound active towards many fungi and gram-positive bacteria. At 5 μg/ml it inhibits growth of Aspergillus niger. Higher concentrations (50 μg/ml) also suppress spore germination; they do not kill the fungus. Dry weight of the fungus still increases for 1 or 2 days after fungicide treatment. The toxicant has no effect on O₂ uptake even at higher concentrations (100 μg/ml). The compound markedly affects composition of the lipid fraction of A. niger inducing a decrease in phospholipid concentration with a coincident increase in free fatty acids. Sterol pattern and sterol concentration were not affected. Antifungal activity was reversed by phospholipids added to the medium. 3-Phenylindole induced a slight leakage of ³²P-labeled compounds from the treated cells under growth conditions but not under nongrowth conditions. A strain of A. niger resistant to 3-phenylindole had the same phospholipid and sterol pattern as the wild type, but the level of both components was higher (40–60%). The 3-phenylindole-resistant strain showed resistance to triarimol and pimaricin. The wild type and the resistant strain both took up 3-phenylindole quite rapidly and accumulated it in the mycelium. 3-Phenylindole possibly interferes with phospholipid function in cell membranes, although the specific site of action has not yet been elucidated.     

Induction of the mixed-function oxidase system in the liver of the barn owl Tyto alba by PCBs

Injection of 30 mg/kg body wt of polychlorinated biphenyl (Aroclor 1254) into liver parenchymal tissue of nestling and adult barn owls Tyto alba resulted in increases in the level of cytochrome P-450. Concomitantly, there were increases in catalytic activity of the microsomal enzyme system as measured by aldrin epoxidation and aminopyrine N-demethylation. However, the ratio $\text{455}\text{430}\text{nm}$ in the ethylisocyanide-difference spectrum remained unchanged. Of particular interest is the sudden drop in the level and catalytic activity of cytochrome P-450 in nestling owls at age 40 days. Treatment with Aroclor 1254 produced small hemorrhages in the liver of nestling owls and the liver appeared much enlarged (hepatomegaly), indicating a toxic effect and resulting in little induction of microsomal enzymes. In adult owls the inductive effect was much greater. Aroclor 1254 produced a spectral shift in the cytochrome P-450-difference spectrum from 450 to 448 nm and in the ethylisocyanide-difference spectrum from 455 to 453 nm and from 430 to 427 nm.     

Comparative metabolism of 1,1-Bis-(p-chlorophenyl)-2-nitropropane (Prolan) in mouse,insects, and in a model ecosystem

¹⁴C-labeled Prolan or 1,1-bis-(p-chlorophenyl)-2-nitropropane was found to be some-what more biodegradable than DDT. This insecticide, although highly resistant to microsomal metabolism, was degraded by elimination to 1,1-bis-(p-chlorophenyl)-1-propene, and by reduction to 1,1-bis-(p-chlorophenyl)-2-aminopropane. The major degradative pathway, however, was by oxidation to 1,1-bis-(p-chlorophenyl)-2-propanone, to 1,1-bis-(p-chlorophenyl)-pyruvic acid, to bis-(p-chlorophenyl)-acetic acid, and ultimately to p,p′-dichlorobenzophenone. Therefore the ultimate degradative products of Prolan are identical to those produced from DDT.     

Interaction with phospholipids as a possible mode of action of 3-phenylindole on Aspergillus niger

Low concentrations of 3-PI(3-phenylindole) inhibit several uptake and biosynthetic processes in liquid cultures of Aspergillus niger. The incorporation of ³²P_i into phospholipids, [¹⁴C]uridine into nucleic acids, and [¹⁴C]phenylalanine into proteins was inhibited and the uptake of all three precursors was reduced. Studies on an in vitro interaction between 3-phenylindole and phospholipids showed, that at about equimolar concentrations 3-phenylindole prevents phospholipids from swelling in water. At the same ratio a decrease of the absorption intensity of the NH-band of 3-phenylindole was observed in ir spectra. Moreover, the maxima of the uv spectrum of 3-phenylindole shifted after addition of a sonicated phospholipid suspension. It is suggested that binding to phospholipids is the first effect of 3-phenylindole. Apparently this affects, consequently, several membrane-bound reactions, i.e., transport and biosynthetic processes.     

Metabolism of the methoxychlor isostere,dianisylneopentane, in mouse,insects, and a model ecosystem

Dianisylneopentane or 1,1-bis(p-methoxyphenyl)-2,2-dimethylpropane was metabolized largely by O-demethylation to form mono- and diphenol derivatives. Only a small percentage was degraded by α-hydroxylation and rearrangement. In the model ecosystem, dianisylneopentane reacted very similarly to methoxychlor, accumulating in fish to about the same extent and yielding a slightly higher ratio of polar to nonpolar metabolites. The neopentyl group proved to be approximately as stable in biological systems as the isosterically equivalent trichloromethyl group.     

Paraoxon-induced release of β-glucuronidase from rat hepatocytes in vitro

A suspension culture of isolated rat hepatocytes was used to reproduce in vitro the paraoxon-induced release of hepatic β-glucuronidase observed in vivo. After a short latent period, exposure of hepatocytes to paraoxon at 10^?7 to 10^?4M resulted in a typical dose-dependent response, with highest release occurring at 10^?4M paraoxon. With 10^?3M paraoxon, however, response was anomalous with a much-decreased enzyme release. As expected from earlier results in vivo, SV₁-oxon exhibited less effect than paraoxon.