Delayed neurotoxicity from long-term low-level topical administration of leptophos to the comb of hens

Histological observations on the liver of Tilapia mossambica after exposure to monocrotophos, an organophosphorus insecticide

The histological changes in the liver of Tilapia mossambica were observed after exposure to a sublethal level (2.5 ppm) of monocrotophos. The changes observed after 2 days of exposure were characterized by necrosis and vacuolation of hepatocytes. Fatty degeneration was observed after 10 days of exposure. However, normalization of histological picture was evident after 15 days of treatment, though some patches of degenerating zones were also found to exist concomitantly. A wave of secondary intensively degenerative changes was observed from 30 days up to 45 days of experimentation. The possible significance of histological lesions and adaptation to exposure after sublethal doses as well as continuous exposure are discussed.

Percutaneous toxicity and delayed neurotoxicity of organophosphates in the scaleless hen

The acute toxicity of tri-ortho-cresyl phosphate (TOCP) and the development of delayed neurotoxicity were characterized in the scaleless hen, a featherless mutant, and compared to the responses observed in normally feathered birds. Brain acetylcholinesterase (AChE) activity was comparable between scaleless and normal hens, but nonspecific cholinesterase (ChE) activities of brain and plasma were significantly higher in scaleless birds. The acute ID50 of TOCP for plasma ChE activity was 690 mg/kg for scaleless birds and 240 mg/kg for normal ones following sc administration. However, there was no difference in the ID50 for plasma ChE activity between normal and scaleless hens treated sc with the active metabolite of TOCP, 2-(o-cresyl)-4H-1:3:2-benzodioxaphosphoran-2-one, or parathion. The onset of clinical signs of delayed neurotoxicity in scaleless birds was 8 to 14 days after sc or dermal treatment with TOCP and caused typical axonal fragmentation in the sciatic nerve. Plasma creatine phosphokinase activity was significantly increased following the onset of delayed neurotoxicity in both lines of birds. Dermal application of TOCP to a 50-cm2 area on the backs of scaleless hens inhibited plasma ChE activity in a dose-related manner (ID50 = 115 mg/kg), and the lowest dose of TOCP, 114 mg/kg, did not produce delayed neurotoxicity. The results show that the scaleless hen can be used to determine a no-observable effect level for delayed neurotoxicity which regulatory agencies could use to extrapolate a safe level of human dermal exposure to organophosphates that produce delayed neurotoxicity.

The injection of the delayed neurotoxin tri-O-tolyl phosphate into embryonating chicken eggs and its effects on subsequent chick development

Tri-o-tolyl phosphate (TOTP) was injected into the yolk sac of 120-h chicken embryos at concentrations equivalent to 200,100, 50, 25, or 0 (vehicle control) microgram TOTP/g egg. On d 22 of incubation, all live hatchlings were wing-banded, weighed, and housed in a brooder battery according to treatment level. Birds were examined daily for mortality as well as for development of clinical signs indicative of delayed neurotoxicity. Body weights were determined at weekly intervals for 4 wk. At the end of the fourth week, all birds were killed and necropsied. Liver, spleen, bursa of Fabricius, ovary or testes, and comb (male only) were removed and weighed. The injection of 200 microgram TOTP/g egg significantly depressed hatchability when compared to controls. Chick mortality was not significantly affected by TOTP injection. Clinical symptoms characteristic of delayed neurotoxicity did not develop during the 4-wk observation period. TOTP injection caused a transient growth depression that disappeared by 4 wk of age in both sexes. Organ weighs at 4 wk of age were not consistently affected by the treatment.

Effect of multiple diisopropyl fluorophosphate injections in hens: a behavioral, biochemical, and histological investigation

Delayed neurotoxicity after acute administration of organophosphates to hens can be predicted by using the neurotoxic esterase (NTE) assay. The present study was designed to compare results obtained with the assay after single or multiple diisopropyl fluorophosphate (DFP) injections in hens. Adult White Leghorn hens were given DFP in a single (1.0 mg/kg) or in multiple (0.05 mg/kg . d for 20 d) sc injections. Walking behavior was measured and both groups showed significant impairment by d 5 after the first or only DFP injection. However, impairment at the end of the study was greater in hens given a single injection of 1.0 mg/Kg. All DFP-treated hens exhibited axonal degeneration in brains, spinal cords, and peripheral nerves, and the changes in the two groups were of equal severity. Cervical and thoracic spinal cord lesions in hens given multiple DFP injections appeared to be primarily restricted to the myelinated spinocerebellar tracts. Inhibition of NTE was measured in brains, spinal cords, ilea, and thymuses 24 h after the single injection of 1.0 mg/kg DFP or after the 20th injection of 0.05 mg/kg DFP in additional hens. The NTE inhibition was significantly greater in all four tissues in the group given DFP as a single treatment. NTE in nerve and nonnerve tissues appeared to be differentially affected by single and multiple DFP treatments. Walking impairment and NTE inhibition were more marked when DFP was given in a single rather than 20 daily injections. However, in hens given multiple DFP injections the severity of central and peripheral nerve lesions was greater than was expected from the clinical and biochemical results.

Delayed neurotoxicity of subchronic oral administration of leptophos to hens: recovery during four months after exposure

Daily oral administration of small doses of technical grade O-methyl O-4-bromo-2,5-dichlorophenyl phenylphosphonothioate (leptophos, 0.5-20.0 mg/kg) caused delayed neurotoxicity in hens. Severity of clinical condition and progression or improvement of signs of delayed neurotoxicity depended on the dose and duration of administration. Hens given 20.0 mg/kg suffered ataxia, paralysis, and death. Intermediate doses (5 and 10 mg/kg) caused ataxia, with most treated hens showing no change in clinical condition during the 4-mo observation period. Hens given small doses (2.5 and 1.0 mg/kg) demonstrated regression of neurological deficits after administration of leptophos was stopped. Hens given the smallest tested dose (,.5 mg/kg) developed mild ataxia and showed total recovery during the observation period. Days of administration and total administered dose before onset of ataxia depended on the daily dose. Degeneration of axons and myelin i, the spinal cord was the most consistent histopathologic change and was identical to that observed in tri-o-cresyl phosphate (TOCP) control hens. Only one hen, which died early in the treatment period, showed peripheral nerve degeneration. Controls consisted of 3 groups of hens given a daily oral dose of 10.0 mg/kg TOCP, 1.0 mg/kg O,O-diethyl O-4-nitrophenyl phosphorothioate (parathion), or an empty gelatin capsule. TOCP-treated hens developed delayed neurotoxicity, whereas those given parathion showed initial leg weakness but subsequently recovery without developing delayed neurotoxicity. Controls given gelatin capsules remained normal.

Delayed neurotoxicity of phenylphosphonothioate esters

Administration of a single oral dose of five phenylphosphonothioate esters produced delayed neurotoxicity in hens; their potency was, in descending order, cyanofenphos, EPN, desbromoleptophos, leptophos, and EPBP (Seven). Histological examination showed that in some hens there was marked axonal and myelin degeneration in the spinal cord and peripheral nerves. The results suggest that delayed neurotoxicity may be a general feature of phenylphosphonothioate insecticides.