Ultrastructure of tri-ortho-cresyl phosphate poisoning in the chicken. II. Studies on spinal cord alterations

Atg7 Knockout Alleviated the Axonal Injury of Neuro-2a Cells Induced by Tri-Ortho-Cresyl Phosphate

Autophagy is believed to be essential for the maintenance of axonal homeostasis in neurons. However, whether autophagy is causally related to the axon degeneration in organophosphorus-induced delayed neuropathy (OPIDN) still remains unclear. This research was designed to investigate the role of autophagy in axon degeneration following tri-ortho-cresyl phosphate (TOCP) in an in vitro model. Differentiated wild-type and Atg7-/- neuro-2a (N2a) cells were treated with TOCP for 24 h. Axonal degeneration in N2a cells was quantitatively analyzed; the key molecules responsible for axon degeneration and its upstream signaling pathway were determined by Western blotting and real-time PCR. The results found that Atg7-/- cells exhibited a higher resistance to TOCP insult than wild-type cells. Further study revealed that TOCP caused a significant decrease in pro-survival factors NMNATs and SCG10 and a significant increase in pro-degenerative factor SARM1 in both cells. Notably, Atg7-/- cells presented a higher level of pro-survival factors and a lower level of pro-degenerative factors than wild-type cells in the same setting of TOCP administration. Moreover, DLK-MAPK pathway was activated following TOCP. Altogether, our results suggest that autophagy is able to affect TOCP-induced axonal injury via regulating the balance between pro-survival and pro-degenerative factors, providing a promising avenue for the potential therapy for OPIDN patients.

Involvement of autophagy in tri-ortho-cresyl phosphate- induced delayed neuropathy in hens

Autophagy is a highly conserved cellular self-degradative process that plays a housekeeping role in removing aggregated proteins and damaged organelles. Our recent work has found that tri-ortho-cresyl phosphate (TOCP), a neuropathic organophosphate (OP), decreased the level of beclin 1 (a key molecule in the process of autophagy) in hen nerve tissues (Song et al., 2012). However, the role of autophagy in the pathogenesis of organophosphorus ester-induced delayed neuropathy (OPIDN) remains unclear. Here, we investigated whether dysfunctional autophagy was associated with the initiation and development of TOCP-induced delayed neuropathy. Adult hens were given a single dose of 750mg/kg TOCP (p.o.) and sacrificed on days 1, 5, 10, and 21 after dosing, respectively. The formation of autophagosomes in spinal cord motor neurons was observed by transmission electron microscopy, the level of autophagy-related proteins in hen spinal cords and tibial nerves was determined by Western blot analysis. The results demonstrated that the number of autophagosomes was markedly increased in the myelinated and unmyelinated axons of hen spinal cords after TOCP exposure. In the meantime, the level of two molecular markers for autophagy, microtubule-associated protein light chain-3 (LC3) and p62/SQSTM1 in hen nerve tissues was significantly decreased and increased, respectively. Furthermore, a marked reduction in autophagy-regulated proteins including ULK 1, AMBRA 1, ATG 5, ATG 7, ATG 12 and VPS34 expression was also observed. Our results suggested that the administration of TOCP resulted in a significant inhibition of autophagy activity in neurons, which might be associated with the pathogenesis of OPIDN.

Calcium-dependent neutral cysteine protease and organophosphate-induced delayed neuropathy

A few organophosphorus compounds (OPs) can cause toxic neuropathy known as organophosphorus ester-induced delayed neuropathy (OPIDN). Although the incidents of OPIDN have been documented for over a century, its molecular mechanisms underlying the axonopathy are still unclear. Recently, increasing evidences suggest that proteases are closely associated with OPIDN. Herein, we have summarized the roles of calcium-dependent cysteine proteases (calpains) in OPIDN. The activation of calpains should be an early molecular event during the onset and development of OPIDN. However, the understanding of the mechanism underlying the disruption of Ca(2+) homeostasis and the activation of calpain by neurotoxic OPs is still limited. Therefore, a better understanding of molecular mechanisms that can prevent the disturbance in cellular Ca(2+) homeostasis can facilitate to establish the novel therapeutic strategies for OPIDN.

Changes in beclin-1 and micro-calpain expression in tri-ortho-cresyl phosphate-induced delayed neuropathy

Tri-ortho-cresyl phosphate (TOCP) can cause toxic neuropathy known as organophosphate-induced delayed neuropathy (OPIDN), which is pathologically characterized by the swollen axon containing aggregations of neurofilaments, microtubules, and multivesicular vesicles. Autophagy is a self-degradative process which plays a housekeeping role in removing misfolded proteins and damaged organelles. The current study was designed to investigate the possible roles of autophagy in the pathogenesis of OPIDN. Adult hens were treated with a dose of 750mg/kg TOCP by gavage, or injected subcutaneously with 60mg/kg phenylmethanesulfonyl fluoride (PMSF) dissolved in DMSO 24h earlier and subsequently treated with TOCP, then sacrificed on the time-points of 0, 1, 5, 10, and 21 days after dosing of TOCP respectively. The levels of beclin-1 and μ-calpain in tibial nerves and spinal cords were determined by immunoblotting. The results showed that in both tissues TOCP increased the expression of μ-calpain while decreased that of beclin-1. When given before TOCP administration, PMSF pretreatment could protect hens against the delayed neuropathy. In the meantime, pretreatment with PMSF reduced calpain expression below basal and increased beclin-1 expression above basal in tibial nerve, whereas it simply returned calpain and beclin-1 expression to their basal levels in spinal cord. In conclusion, the intoxication of TOCP was associated with a significant change of beclin-1 in hen nervous tissues, which suggested that disruption of autophagy-regulated machinery in neurons might be involved in the pathogenesis of OPIDN.

Reduction of retrograde axonal transport associated-proteins motor proteins, dynein and dynactin in the spinal cord and cerebral cortex of hens by tri-ortho-cresyl phosphate (TOCP)

Tri-ortho-cresyl phosphate (TOCP) can cause a type of neurotoxicity known as organophosphate-induced delayed neuropathy (OPIDN). The characteristic axonal swelling containing aggregations of neurofilaments, microtubules, and multivesicular vesicles is consistent with a disturbance of axonal transport. We hypothesized that there existed a disturbance of molecular motor in the pathogenesis of OPIDN. In the present study, adult hens were treated with a dosage of 750 mg/kg TOCP by gavage, or pretreated 24h earlier with phenylmethanesulfonyl fluoride (PMSF) and subsequently with TOCP, then sacrificed on the time-points of 0, 1, 5, 10, and 21 days after dosing of TOCP, respectively. The level of kinesin-1, dynein, and dynactin in spinal cords and cerebral cortexes of hens was determined. Immunoblotting analysis showed a progressive decline of dynein and dynactin in spinal cords after dosing TOCP. Furthermore, a significant reduction in dynactin and dynein was observed in cerebral cortexes at several time-points post dosing TOCP. In contrast, no significant changes of kinesin-1 were observed throughout the period of experiment. When given before TOCP administration, PMSF could inhibit TOCP-induced motor protein disruption, while it protected hens against the delayed neuropathy. In conclusion, the reduction of the motor proteins, dynein and dynactin, might be associated with the disruption of retrograde neuronal axonal transport in OPIDN.

Changes of mitochondrial ultrastructures and function in central nervous tissue of hens treated with tri-ortho-cresyl phosphate (TOCP)

Tri-ortho-cresyl phosphate (TOCP), an organophosphorus ester, is capable of producing organophosphorus ester-induced delayed neurotoxicity (OPIDN) in humans and sensitive animals. The mechanism of OPIDN has not been fully understood. The present study has been designed to evaluate the role of mitochondrial dysfunctions in the development of OPIDN. Adult hens were treated with 750 mg/kg·bw TOCP by gavage and control hens were given an equivalent volume of corn oil. On day 1, 5, 15, 21 post-dosing, respectively, hens were anesthetized by intraperitoneal injection of sodium pentobarbital and perfused with 4% paraformaldehyde. The cerebral cortex cinerea and the ventral horn of lumbar spinal cord were dissected for electron microscopy. Another batch of hens were randomly divided into three experimental groups and control group. Hens in experimental groups were, respectively, given 185, 375, 750 mg/kg·bw TOCP orally and control group received solvent. After 1, 5, 15, 21 days of administration, they were sacrificed and the cerebrum and spinal cord dissected for the determination of the mitochondrial permeability transition (MPT), membrane potential (Δψ(m)) and the activity of succinate dehydrogenase. Structural changes of mitochondria were observed in hens' nervous tissues, including vacuolation and fission, which increased with time post-dosing. MPT was increased in both the cerebrum and spinal cord, with the most noticeable increase in the spinal cord. Δψ(m) was decreased in both the cerebrum and spinal cord, although there was no significant difference in the three treated groups and control group. The activity of mitochondrial succinate dehydrogenase assayed by methyl thiazolyl tetrazolium (MTT) reduction also confirmed mitochondrial dysfunctions following development of OPIDN. The results suggested mitochondrial dysfunction might partly account for the development of OPIDN induced by TOCP.

Phenylmethylsulfonyl fluoride protects against the degradation of neurofilaments in tri-ortho-cresyl phosphate (TOCP) induced delayed neuropathy

Tri-ortho-cresyl phosphate (TOCP) is an organophosphorus ester, which can cause a type of neurotoxicity known as organophosphate-induced delayed neuropathy (OPIDN). Our recent study has shown that the enhanced degradation of neurofilament (NF) in peripheral nerve of hens is an early event of TOCP-induced OPIDN (Song et al., 2009). The main objective of this investigation is to study the effect of TOCP administration on NF content and NF degradation when OPIDN is blocked by pretreatment with phenylmethylsulfonyl fluoride (PMSF). The hens were pretreated 24h earlier with PMSF and subsequently treated with a single dosage of 750 mg/kg TOCP, then sacrificed on the corresponding time points of 0, 1, 5, 10, and 21 days after dosing TOCP, respectively. The tibial nerves were dissected, homogenized, and centrifuged at 100,000 x g. The level of NF triplet protein in both pellet and supernatant fractions of tibial nerves was determined. Western blotting analysis showed a significant increase of three NF subunits in hens treated with PMSF and TOCP compared with the control. These changes were observed within 24h of PMSF administration and then followed by an obvious recovery. Furthermore, accompanied with the increase of NF content, a significant decline in NF-L degradation rate was observed in both fractions of tibial nerves. Taken together, these results demonstrated the pretreatment with PMSF could inhibit TOCP-induced NF degradation while it protected hens against the development of OPIDN, which suggested the inhibition of NF-associated protease in peripheral nerves might be an underlying protective mechanism of PMSF against OPIDN.

Time-dependent changes of lipid peroxidation and antioxidative status in nerve tissues of hens treated with tri-ortho-cresyl phosphate (TOCP)

Tri-ortho-cresyl phosphate (TOCP) could induce a delayed neurodegenerative condition known as organophosphorus easter-induced delayed neurotoxicity (OPIDN) in human beings and sensitive animals. However, the mechanisms of OPIDN remain unknown. This study investigated the time-dependent changes of the lipid peroxidation (malondialdehyde, MDA) and antioxidative status (glutathione, GSH; glutathione peroxidase, GSH-Px; glutathione reductase, GR; superoxide dismutase, SOD and anti-reactive oxygen species, anti-ROS) in nerve tissues for elucidating the mechanism of OPIDN induced by TOCP. Adult hens were treated with TOCP by gavage at a single dosage of 750 mg/kg. TOCP was dissolved in corn oil and administered at 0.65 ml/kg. The control hens received an equivalent volume of corn oil by gavage. Hens were sacrificed after 0, 5, 10, 15 and 21 days of treatment and the cerebrum, spinal cord, sciatic nerve were dissected, homogenized and used for the determination of lipid peroxidation and antioxidative status. The results showed that treatment with TOCP increased lipid peroxidation and reduced the antioxidative status in cerebrum, spinal cord and sciatic nerve. The levels of MDA increased by 33% (P<0.01) in cerebrum on 5th day after TOCP treatment and at clinical sign score of 1-2, and increased respectively by 32% and 15% (P<0.01) in spinal cord and sciatic nerve on 10th day after TOCP treatment and at clinical sign score of 3-4. Further changes of MDA were also observed after 15 and 21 days post-dosing and at clinical sign score of 5-6 and 7-8. There is a decrease in the activities of SOD, GSH-Px, GR, anti-ROS, and GSH content in cerebrum, spinal cord and sciatic nerve of hens after 5, 10, 15 and 21 days post-dosing and at clinical sign score of 1-2, 3-4, 5-6 and 7-8. Thus, OPIDN induced by TOCP was associated with elevation of lipid peroxidation and reduction of antioxidative status, and the time-dependent changes of these indexes in hens nerve tissues occurred. Sciatic nerve was the main target tissue and MDA was most sensitive among all indexes. The time-dependent and tissue specific changes of lipid peroxidation and antioxidative status in cerebrum, spinal cord and sciatic nerve suggest that ROS and concomitant lipid peroxidation, at least in part, are involved in the toxic effects of TOCP on nerve tissues and that oxidative stress may play a role in the occurrence and development of OPIDN induced by TOCP.

Neuropathy Target Esterase and Its Yeast Homologue Degrade Phosphatidylcholine to Glycerophosphocholine in Living Cells

Eukaryotic cells control the levels of their major membrane lipid, phosphatidylcholine (PtdCho), by balancing synthesis with degradation via deacylation to glycerophosphocholine (GroPCho). Here we present evidence that in both yeast and mammalian cells this deacylation is catalyzed by neuropathy target esterase (NTE), a protein originally identified by its reaction with organophosphates, which cause nerve axon degeneration. YML059c, a Saccharomyces cerevisiae protein with sequence homology to NTE, had similar catalytic properties to the mammalian enzyme in assays of microsome preparations and, like NTE, was localized to the endoplasmic reticulum. Yeast lacking YML059c were viable under all conditions examined but, unlike the wild-type strain, did not convert PtdCho to GroPCho. Despite the absence of the deacylation pathway, the net rate of [(14)C]choline incorporation into PtdCho in YML059c-null yeast was not greater than that in the wild type; this was because, in the null strain diminished net uptake of extracellular choline and decreased formation of the rate-limiting intermediate, CDP-choline, resulted in a reduced rate of PtdCho synthesis. In [(14)C]choline labeling experiments with cultured mammalian cell lines, production of [(14)C]GroPCho was enhanced by overexpression of catalytically active NTE and was diminished by reduction of endogenous NTE activity mediated either by RNA interference or organophosphate treatment. We conclude that NTE and its homologues play a central role in membrane lipid homeostasis.

Protein levels of neurofilament subunits in the hen central nervous system following prevention and potentiation of diisopropyl phosphorofluoridate (DFP)-induced delayed neurotoxicity(1)

Diisopropyl phosphorofluoridate (DFP) is an organophosphorus ester, which produces delayed neurotoxicity (OPIDN) in hens in 7-14 days. OPIDN is characterized by mild ataxia in its initial stages and severe ataxia or paralysis in about 3 weeks. It is marked by distal swollen axons, and exhibits aggregations of neurofilaments (NFs), microtubules, proliferated smooth endoplasmic reticulum, and multivesicular bodies. These aggregations subsequently undergo disintegration, leaving empty varicosities. Previous studies in this laboratory have shown an increased level of medium-molecular weight NF (NF-M) and decreased levels of high- and low-molecular weight NF (NF-H, NF-L) proteins in the spinal cord of DFP-treated hens. The main objective of this investigation was to study the effect of DFP administration on NF subunit levels when OPIDN is prevented or potentiated by pretreatment or post-treatment with phenylmethylsulfonyl fluoride (PMSF), respectively. Hens pretreated or post-treated with PMSF were killed 1, 5, 10, and 20 days after the last treatment. The alteration in NF subunit protein levels observed in DFP-treated hen spinal cords was not observed in protected hens. Estimation of NFs in the potentiation experiments, however, showed a different pattern of alteration in NF subunit levels. The results showed that an alteration in NF subunit levels in DFP-treated hens might be related to the development of OPIDN, since these changes were suppressed in PMSF-protected hens. However, results from PMSF post-treated hen spinal cords suggested that potentiation of OPIDN by PMSF was mediated by a mechanism different from that followed by DFP alone to produce OPIDN.

Enhanced activity and level of protein kinase A in the spinal cord supernatant of diisopropyl phosphorofluoridate (DFP)-treated hens. Distribution of protein kinases and phosphatases in spinal cord subcellular fractions

Diisopropyl phosphorofluoridate (DFP) is a type I organophosphorus compound and produces delayed neurotoxicity (OPIDN) in adult hens. A single dose of DFP (1.7 mg/kg, s.c.) produces mild ataxia in hens in 7-14 days, which develops into severe ataxia or paralysis as the disease progresses. We have previously shown altered expression of several proteins (e.g. Ca2+/calmodulin-dependent protein kinase II (CaM kinase II) alpha-subunit, tau, tubulin, neurofilament protein (NF), vimentin, GFAP) and an immediate early gene (e.g. c-fos) in DFP-treated hens. Here we show an increase in protein kinase A (PKA) protein level and activity in the spinal cord at 1-day and 5-days time periods after DFP administration. We also determined the protein levels of protein kinase C (PKC), CaM kinase II and several phosphatases (i.e. phosphatase 1 (PP1), phosphatase 2A (PP2A), phosphatase 2B (PP2B) in the spinal cord of DFP-treated hens after 1, 5, 10, and 20 days). There was increase in CaM kinase II alpha subunit level after 10 and 20 days of treatment, and decrease in PKC level at 1-day and 20-days time periods in spinal cord mitochondria. In contrast, the cerebrum, which is resistant to DFP-induced axonal degeneration, did not show change in PKA and CaM Kinase II levels at any time period DFP post-administration. No alteration was found in the protein levels of PP1, PP2A, and PP2B at any time period. An early induction in PKA, which is an important protein kinase in signal transduction, followed by that of CaM kinase might be contributing towards the development of OPIDN in DFP-treated hens.

Effect of prevention and potentiation of diisopropyl phosphorofluoridate (DFP)-induced delayed neurotoxicity on the mRNA expression of neurofilament subunits in hen central nervous system

Diisopropyl phosphorofluoridate (DFP) is an organophosphorus ester, which produces mild ataxia in 7–14 days and severe ataxia or paralysis in about 20 days (OPIDN) in hens. Previous studies in this laboratory have shown enhanced temporal expression of neurofilament (NF) subunit mRNAs in the spinal cord (SC) of DFP-treated hens. The main objective of this investigation was to study the effect of DFP administration on NF subunit mRNAs expression, when OPIDN is protected or potentiated by pre-treatment or post-treatment, respectively, with phenylmethylsulfonyl fluoride (PMSF). The hens were sacrificed 1, 5, 10, and 20 days after the last treatment. In contrast with enhanced mRNA expression of NF subunits reported in OPIDN, there was no alteration in the expression of NF subunits in the SC of PMSF-protected hens that did not develop OPIDN. PMSF post-treatment of DFP-treated hens, which enhanced delayed neurotoxicity produced by a low dose of DFP, exhibited decrease in the mRNA expression of NF subunits in SC at all time periods (1–20 days) of observation. The expression of NF subunits was also studied in the degeneration-resistant tissue cerebrum of treated hens. The results from protected hens suggested that temporal enhanced expression of NF subunit mRNAs in DFP-treated hens might be contributing to the development of OPIDN in hens. By contrast, PMSF post-treatment seemed to potentiate OPIDN by a mechanism different from that followed by DFP alone to produce OPIDN.Key words: diisopropyl phosphorofluoridate, phenylmethylsulfonyl fluoride, hen, spinal cord, neurofilament mRNAs.

Alteration in cytoskeletal protein levels in sciatic nerve on post-treatment of diisopropyl phosphorofluoridate (DFP)-treated hen with phenylmethylsulfonyl fluoride

Diisopropyl phosphorofluoridate (DFP) is an organophosphorus ester, and a single dose (1.7 mg/kg, sc.) of this compound produces mild ataxia in hens in 7-14 days and a severe ataxia or paralysis (OPIDN) in three weeks. OPIDN is associated with axonal swelling and their degeneration. We have previously observed alteration in neurofilament (NF) protein levels in the spinal cord of DFP-treated hens. The main objective of this investigation was to study NF protein levels in the sciatic nerves (SN) of hens, in which OPIDN has been potentiated by phenylmethylsulfonyl fluoride (PMSF) post-treatment. PMSF is known to protect DFP-treated (1.7 mg/kg) hens from developing OPIDN if injected before, and potentiate OPIDN if injected after the administration of DFP (0.5 mg/kg). The potentiation of OPIDN was accompanied by earlier elevation of NF proteins in the SN particulate fraction. In contrast, SN supernatant fraction showed a transient fall in NF protein levels in potentiation OPIDN. Out of the two other cytoskeletal proteins (i.e., tubulin, tau) studied in this investigation, tubulin also showed earlier elevation in its level in the particulate fraction in potentiated OPIDN. The earlier elevation of NF protein levels in SN particulate fraction in potentiated OPIDN suggested the possible involvement of NFs in delayed neurotoxicity.

Altered expression of neurofilament subunits in diisopropyl phosphorofluoridate-treated hen spinal cord and their presence in axonal aggregations

Diisopropyl phosphorofluoridate (DFP) is an organophosphorus ester, which produces organophosphorus ester-induced delayed neuropathy (OPIDN) in hen and other sensitive species. A single dose of DFP (1.7 mg/kg, sc.) produces mild ataxia in 7-14 days in hens, which develops into severe ataxia or paralysis with the progression of disease. OPIDN is associated with axonal swellings and degeneration of axons. This study was carried out to investigate the expression of neurofilament (NF) subunits in the spinal cord of DFP-treated hens. Hens were treated with a single dose of DFP and sacrificed 1, 5, 10, and 20 days post-treatment. Western blot analysis showed increased expression of middle molecular weight neurofilament protein (NF-M), and decreased expression of high molecular weight (NF-H) and low molecular weight (NF-L) neurofilament proteins in the 2 M urea extracts of spinal cord particulate fraction. These changes were observed within 24 h of DFP administration and persisted for 10-20 days. Thus, there was increase in the stoichiometry of NF-M:NF-L in the spinal cord of DFP-treated hens. Immunoprecipitation, cross-linking, and two-dimensional polyacrylamide gel electrophoresis showed the presence of heterodimers, but not heterotetramers, in the hen spinal cord extract. Immunohistochemical staining revealed the presence of all three NF subunits in the cytoskeletal inclusions in DFP-treated hen spinal cord cross-sections. The results suggested that each NF subunit might be accumulated by a different mechanism in the axonal aggregations of DFP-treated hen.

Alterations in levels of mRNAs coding for glial fibrillary acidic protein (GFAP) and vimentin genes in the central nervous system of hens treated with diisopropyl phosphorofluoridate (DFP)

Diisopropyl phophorofluoridate (DFP) produces organophosphorus-ester induced delayed neurotoxicity (OPIDN) in the hen, human and other sensitive species. We studied the effect of DFP admimistration (1.7 mg/kg/s.c.) on the expression of Intermediate Filament (IF) proteins: Glial Fibrillary Acidic Protein (GFAP) and vimentin which are known indicators of neurotoxicity and astroglial pathology. The hens were sacrificed at different time points i.e. 1,2,5,10 and 20 days. Total RNA was extracted from the following brain regions: cerebrum, cerebellum, and brainstem as well as spinal cord. Northern blots prepared using standard protocols were hybridized with GFAP and vimentin as well as beta-actin and 18S RNA cDNA (controls) probes. The results indicate a differential/spatial/temporal regulation of GFAP and vimentin levels which may be due to the result of disruption of glial-neuronal network. The GFAP transcript levels reached near control levels (88% and 95%) at 20 days post DFP treatment after an initial down-regulation (60% and 73%) in highly susceptible tissues like spinal cord and brainstem respectively. However vimentin transcript levels remained down-regulated (61% and 53%) at 20 days after an early reduced levels(47% and 55%) for spinal cord and brainstem respectively. This may be due to the astroglial pathology resulting in neuronal alterations or vice-versa. In cerebellum (less susceptile tissue) GFAP levels were moderately down-regulated at 1,2 and 5 days and reached near control values at 10 and 20 days. Vimentin was rapidly reinduced (128%) in cerebellum at 5 days and remained at the same level at 10 days and then returned to control values at 20 days after an initial down-regulation at 1 and 2 days. Thus these alterations were less drastic in cerebellum as indicated by initial susceptibility followed by rapid recovery. On the other hand both GFAP and vimentin levels were upregulated from 2 days onwards in the non-susceptible tissue cerebrum, implying protective mechanisms from the beginning. Hence the DFP induced astroglial pathology as indicated by the complex expression profile of GFAP and vimentin mRNA levels may be playing an important role in the delayed degeneration of axons or is the result of progressive degeneration of axons in OPIDN.

Neural development and neurodegeneration: two faces of neuropathy target esterase

Neuropathy target esterase (NTE) is an integral membrane protein in vertebrate neurons. Recent evidence suggests that NTE plays an important role in neural development, possibly via involvement in a signalling pathway between neurons and glial cells. NTE is a member of a novel protein family, represented in organisms from bacteria to man. NTE comprises an N-terminal regulatory domain (with some sequence similarity to cyclic nucleotide-binding proteins) and a C-terminal catalytic domain: the latter has three predicted transmembrane segments and requires membrane-association for activity. In vitro, NTE potently catalyses hydrolysis of phenyl valerate: however, its physiological substrate is likely to be a metabolite of a much longer chain carboxylic acid, possibly associated with cell membranes. NTE was discovered originally as the primary target for those organophosphorus esters (OPs) which cause a delayed neuropathy with degeneration of long axons in peripheral nerves and spinal cord. Paradoxically, NTE's catalytic activity appears redundant in adult vertebrates. Neuropathic OPs react covalently with NTE in a rapid two-step process which not only inhibits catalytic activity but also leaves a negatively-charged OP group attached to the active site serine. The latter event is proposed to induce a toxic gain of function in NTE. OP-modified NTE somehow engenders a "chemical transection of the axon". In turn, this leads to calcium entry, elevation of axonal calpain activity and Wallerian-type degeneration. The net damage to peripheral nerve axons is a balance between ongoing degenerative and repair processes: the latter involve serine hydrolases which can be inhibited by the same OPs used to modify NTE.

C-fos mRNA induction in the central and peripheral nervous systems of diisopropyl phosphorofluoridate (DFP)-treated hens

A single dose of diisopropyl phosphorofluoridate (DFP), an organophosphorus ester, produces delayed neurotoxicity (OPIDN) in hen. DFP produces mild ataxia in hens in 7-14 days, which develops into severe ataxia or paralysis as the disease progresses. Since, OPIDN is associated with alteration in the expression of several proteins (e.g., Ca2+/calmodulin-dependent protein kinase II (CaM kinase II) alpha-subunit, tau, tubulin, neurofilament (NF) protein, vimentin, GFAP) as well as their mRNAs (e.g., NF, CaM kinase II alpha-subunit), we determined the effect of a single dose of DFP on the expression of one of the best known immediate-early gene (IEG), c-fos. C-fos expression was measured by Northern hybridization in cerebrum, cerebellum, brainstem, midbrain, spinal cord, and the sciatic nerves of hens at 0.5 hr, 1 hr, 2 hr, 1 day, 5 days, 10 days, and 20 days after a single 1.7 mg/kg, sc. injection of DFP. All the tissues (cerebrum, 52%; cerebellum, 55%; brainstem, 49%; midbrain, 23%; spinal cord, 80%; sciatic nerve, 157%) showed significant increase in c-fos expression in 30 min and this elevated level persisted at least up to 2 hr. Expressions of beta-actin mRNA and 18S RNA were used as internal controls. The significant increase in c-fos expression in DFP-treated hens suggests that c-fos may be one of the IEGs involved in the development of OPIDN.

Mechanisms of toxic injury in the peripheral nervous system: neuropathologic considerations

The anatomical distribution and organization of the peripheral nervous system as well as its frequent ability to reflect neurotoxic injury make it useful for the study of nerve fiber and ganglionic lesions. Contemporary neuropathologic techniques provide sections with excellent light-microscopic resolution for use in making such assessments. The histopathologist examining such peripheral nerve samples may see several patterns of neurotoxic injury. Most common are axonopathies, conditions in which axonal alterations are noted; these axonopathies often progress toward the Wallerian-like degeneration of affected fibers. These are usually more severe in distal regions of the neurite, and they affect both peripheral and central fibers. Examples of such distal axonopathies are organophosphorous ester-induced delayed neuropathy, hexacarbon neuropathy, and p-bromophenylacetylurea intoxication. These axonopathies may have varying pathologic features and sometimes have incompletely understood toxic mechanisms. In such neuropathies with fiber degeneration, peripheral nerve axons may regenerate, which can complicate pathologic interpretation of neurotoxicity. On occasion neurotoxins elicit more severe injury in proximal regions of the fiber (not included in this review). Axonal pathology is also a feature of the neuronopathies, toxic states in which the primary injuries are found in neuronal cell bodies. This is exemplified by pyridoxine neurotoxicity, where there is sublethal or lethal damage to larger cytons in the sensory ganglia, with failure of such neurons to maintain their axons. Lastly, one may encounter myelinopathies, conditions in which the toxic effect is on the myelin-forming cell or sheath. An example of this is tellurium intoxication, where demyelination noted in young animals is coincident with toxin-induced interference of cholesterol synthesis by Schwann cells. In this paper, the above-noted examples of toxic neuropathy are discussed, with emphasis on mechanistic and morphologic considerations.

Enhanced mRNA expression of neurofilament subunits in the brain and spinal cord of diisopropyl phosphorofluoridate-treated hens

Diisopropyl phosphorofluoridate (DFP) is an organophosphorus ester, and a single injection of this compound (1.7 mg/kg, s.c.) produces delayed neurotoxicity (OPIDN) in hens in 7-14 days. Clinically, the disease is marked by hindlimb ataxia followed by paralysis after some time. A characteristic feature of this neuropathy is axonal swelling in the initial stages and comparative dissolution of the accumulated material and degeneration of distal axons with disease progression. Axonal swelling consists of aggregated neurofilaments, microtubules, and proliferated smooth endoplasmic reticulum. We studied expression of neurofilament (NF) mRNAs in brain regions and spinal cord to elucidate their role in OPIDN. There was a 50-200% increase in NF transcripts in 24 hr after DFP administration. The NF-L mRNA level started falling after 1-5 days and came down to control level in susceptible brain regions (i.e. cerebellum and brainstem) and spinal cord, but not in cerebral cortex, which does not show degeneration of axons in OPIDN. Cerebral cortex exhibited elevated levels of both NF-L and NF-M transcripts in DFP-treated hens throughout the period of observation. The induction of NF messages is consistent with the previously reported effect on extension of neurites of human neuroblastoma cells in culture. The transient increase in NF messages in susceptible tissues either may be responsible for the delayed degeneration of axons in OPIDN or is the result of interruption of regulatory signal due to progressive degeneration of axons.

cDNA cloning and sequencing of Ca2+/calmodulin-dependent protein kinase IIalpha subunit and its mRNA expression in diisopropyl phosphorofluoridate (DFP)-treated hen central nervous system

Diisopropyl phosphorofluoridate (DFP) produces delayed neurotoxicity, known as organophosphorus ester-induced delayed neurotoxicity (OPIDN), in hen, human, and other sensitive species. A single dose of DFP (1.7 mg/kg, se.) produces first mild ataxia followed by paralysis in 7-14 days in hens. DFP treatment also increases in vitro autophosphorylation of Ca2+ calmodulin-dependent protein kinase II (CaM kinase II) and the phosphorylation of several cytoskeletal proteins in the hen brain. To investigate whether increase in CaM kinase II activity is associated with increased expression of its mRNA, we cloned and sequenced CaM kinase II alpha subunit cDNA, and used it to study CaM kinase II expression in brain regions and spinal cord. Hen CaM kinase II alpha subunit differs in 7 amino acids from that of rat CaM kinase II. Its mRNA occurs predominantly as a 6.7 kb message, which is very close to that of human CaM kinase II alpha subunit. Northern blot analysis showed a transient increase in CaM kinase II alpha subunit mRNA in the cerebellum and spinal cord of DFP-treated chickens. The increase in CaM kinase II mRNA expression is consistent with the previously reported increase in its activity in brain and spinal cord, and its increased expression only in cerebellum and spinal cord, which are sensitive to the Wallerian-type degeneration characteristic of OPIDN, suggests the probable role of this enzyme in delayed neurotoxicity.

Alteration in neurofilament axonal transport in the sciatic nerve of the diisopropyl phosphorofluoridate (DFP)-treated hen

Diisopropyl phosphorofluoridate (DFP) is an organophosphorus ester that produces organophosphorus ester-induced delayed neurotoxicity (OPIDN) in hens 7-14 days after a single s.c. dose of 1.7 mg/kg. In this study, hens were treated with a single dose of DFP (1.7 mg/kg, s.c.) 24 hr after [35S]methionine injection into the sacrolumbar region of their spinal cord, and killed 3, 7, 14, or 27 days post-DFP treatment. The rates of transport of labeled high (NF-H), medium (NF-M), and low (NF-L) molecular weight neurofilaments, and tubulin were faster in DFP-treated birds than in controls after 3 days. Subsequently, the rate of transport of these proteins started falling, so that the peaks of labeled proteins in control and DFP-treated hens were overlapping after 7 days. At 14 days, the peaks of NF-H, NF-M, and NF-L in treated hens were distinctly behind the corresponding peaks in control hens. This was again followed by an increase in transport of NF-H and NF-L, but not of NF-M, so that the labeled NF-H and NF-L showed the same pattern in control and treated hens after 27 days. The transient decrease in NF-H and NF-L axonal transport rate, and recovery correlated in a temporal manner with the previously reported increase of Ca2+/calmodulin-dependent protein kinase-mediated phosphorylation of neurofilament proteins and inhibition of calpain activity in the sciatic nerve in OPIDN. Proteinase inhibition has been reported recently to result in enhanced phosphorylation of neurofilaments in some cells. The present study suggests that the enhanced phosphorylation of neurofilaments by DFP-increased Ca2+/calmodulin-dependent protein kinase activity may be contributing toward alteration in NF axonal transport and the development of OPIDN.

Neuropathology of organophosphate-induced delayed neuropathy (OPIDN) in young chicks

To examine the phenomenon of apparent age resistance of young chicks to organophosphate-induced delayed neuropathy (OPIDN), groups of either 2- or 10-week-old chicks were exposed subcutaneously daily for 4 days to the neuropathic organophosphate (OP), di-isopropylfluorophosphate (DFP, 1 mg/kg), the non-neuropathic OP, paraoxon (PO, 0.25 mg/kg) or atropine (20 mg/kg). Subsequently, all birds were examined at post-exposure intervals (calculated from the last day of exposure) for up to 56 days for neurological deficits and morphological lesions in the central and peripheral nervous systems (CNS, PNS). Clinically, none of the birds in the 2-week-old groups, or in the 10-week-old PO or atropine exposed groups had neurological deficits. However, all birds in the 10-week-old DFP exposed group developed ataxia by 7 days post-exposure (DPE) and then progressive paralysis. Therefore, all birds in the 10-week-old groups were killed at 14 DPE. Pathologically, the 2-week-old DFP exposed chicks had increasingly severe lesions of Wallerian-like degeneration predominantly in the spinal cord from 7 DPE and subsequently. In the 10-week-old DFP exposed chicks, the degenerative lesions of OPIDN were first detected in the CNS at 3 DPE and then with equally increasing severity in the CNS and PNS up to 14 DPE. A higher incidence of neuronal necrosis and chromatolysis in ventral motor horn neurons of spinal cord grey matter and in dorsal root ganglia occurred in both the DFP exposed age groups compared with those lesions in other groups.(ABSTRACT TRUNCATED AT 250 WORDS)

In vivo and in vitro effects of diisopropyl phosphorofluoridate (DFP) on the rate of hen brain tubulin polymerization

Diisopropyl phosphorofluoridate (DFP) produces organophosphorus ester-induced delayed neurotoxicity (OPIDN) in sensitive species. We have investigated the in vivo and in vitro effects of DFP on hen brain tubulin polymerization. Hens were treated with a single dose of DFP (1.7 mg/kg, sc.), and were sacrificed after 18-21 days. Tubulin from DFP-treated hen brains showed small but significant decrease (14.42%) in the rate of polymerization and 11.05% decrease in rise in O.D. at 340 nm in 30 min. DFP in vivo treatment also resulted in decreased concentration of tau and an enhanced concentration of two peptides (45 kDa, 35 kDa) in the brain supernatant. These peptides seemed to be the degradation products of MAP-2. The decrease in the rate of brain tubulin polymerization in treated hens is consistent with neurochemical alterations and the focal degeneration and aggregation of these filamentous structures in OPIDN.

Neurology and neuropathology of Soman-induced brain injury: an overview

Battlefield use of nerve agents poses serious medical threats to combat troops and to civilians in the immediate or adjacent environment. The experiments reported herein were carried out in the 1980s to help to define both the neurological and neuropathological consequences of exposure to the organophosphate nerve agent Soman. These data contributed to the scientific foundation for a program of drug development to find agents that would prevent or reduce the risk of injury to the central nervous system and specifically pointed to the importance of including an anticonvulsant in the treatment of agent exposure. Since these experiments were conducted, research efforts have continued to improve pretreatment and treatment, such as the inclusion of the anticonvulsant diazepam in the medical treatment of exposed personnel.

Giant axonopathy in streptozotocin diabetes of rats

The ultrastructure of peripheral sensory nerves was investigated in adult Wistar rats suffering from experimental diabetes mellitus 6 and 10 weeks after the injection of streptozotocin. Giant axons were seen in sections from the nerves of streptozotocin-treated rats; some contained masses of neurofilaments, others were predominantly filled with ill-defined vesicles. At the swollen axons, the myelin sheath was thinned or absent. In other regions, large intramyelinic vacuoles were observed. A number of nerve fibers broke down completely and underwent Wallerian degeneration. This was accompanied by Schwann cell proliferation and formation of Büngner bands. Concomitantly with axonal degeneration, nerve regeneration started from intact internodes. The pathomorphology of streptozotocin diabetic neuropathy closely resembles that of some toxic distal axonopathies. This points to a common metabolic basis of giant axonopathies of different etiology.

Enhanced calmodulin binding concurrent with increased kinase-dependent phosphorylation of cytoskeletal proteins following a single subcutaneous injection of diisopropyl phosphorofluoridate in hens

Diisopropyl phosphorofluoridate (DFP) produces Type I organophosphorus compound-induced delayed neurotoxicity (OPIDN) in adult female chickens. We have proposed that calcium/calmodulin protein kinase II (CaM kinase II) plays a role in the development of OPIDN by increasing the phosphorylation of cytoskeletal proteins. We investigated in vivo the effects of treatment of DFP on CaM kinase II-dependent phosphorylation. In isolated brain supernatants from DFP-treated hens, calmodulin binding increased concurrent with increases in CaM kinase II-dependent autophosphorylation and phosphorylation of cytoskeleton proteins. There were no changes in the relative amounts of the enzyme based on immunobinding studies of antibodies to the CaM kinase II. In the absence of any exogenously added substrate. CaM kinase II and microtubule associated protein-2 (MAP-2) exhibited substantially increased phosphorylation, 833 and 275%, respectively, over brain supernatants from untreated hens. Moreover, isolated brain supernatants from treated hens with exogenously added cytoskeletal proteins and myelin basic protein (MBP) exhibited significant increases in phosphorylation over control, 233, 332 and 60%, for MAP-2, tubulin, and MBP, respectively. 125I-Calmodulin binding studies revealed a 136% increase in calmodulin binding to CaM kinase II in treated hens when compared to control groups. The data suggest that in vivo DFP treatment increases the percentage of unphosphorylated, active CaM kinase II resulting in increased calmodulin binding and subsequent enhanced phosphorylation of cytoskeletal proteins that leads to their aggregation and the production of axonal degeneration.

Anomalous phosphorylated neurofilament aggregations in central and peripheral axons of hens treated with tri-ortho-cresyl phosphate (TOCP)

Previous biochemical studies demonstrated a dramatic increase in phosphorylation of cytoskeletal proteins that occurs early in organophosphorus ester-induced delayed neurotoxicity (OPIDN). In this report we present immunohistochemical evidence that there is anomalous aggregation of phosphorylated neurofilaments within central and peripheral axons following organophosphate exposure. The morphology, location, and time of appearance of these aggregations are consistent with the hypothesis that the aberrant phosphorylation of cytoskeletal elements is an antecedent to the focal axonal swelling and degeneration characteristic of OPIDN.

The Sertoli cell cytoskeleton: a target for toxicant-induced germ cell loss

Numerous studies in recent years have elucidated fundamental properties of axoplasmic structure, biochemistry, and function. The structural role of the cytoskeletal elements, the orientation of MTs within the axon, the phenomenon of MT-dependent transport, and the identity and direction of movement of two MT motors--kinesin and MAP-1C--have been revealed. For many years to come, researchers investigating the structure and function of the Sertoli cell cytoskeleton will be able to adapt techniques gleaned from work on the axonal cytoskeleton. Innovative thinking will be required to apply these techniques to the special circumstances of the male reproductive system; however, the underlying questions are similar. For example, knowledge of several fundamental properties of transport processes in the Sertoli cell would facilitate the toxicologic evaluation of this system. What is the orientation of MTs within the Sertoli cell cytoplasm? Are the fast-growing (+) ends of all MTs in the Sertoli cell cytoplasm directed toward the lumen? This is an important question because the direction of MT-dependent transport involving known MT motors is dependent upon the MT orientation. Which of the Sertoli cell transport pathways are MT-dependent pathways? What are the MT motors involved in these pathways? Ultrastructural examination following exposure to specific cytoskeleton-disrupting agents has highlighted the importance of AFs, IFs, and MTs in the Sertoli cell. Future research will focus on the nature of those molecules which integrate these cytoskeletal components into a dynamic whole, the regulatory systems which control this integration, and the role of an integrated cytoskeleton in Sertoli cell function and testicular homeostasis. Toxicology will be an active participant in this process of scientific discovery. The selective nervous system and testicular toxicants may be useful tools in revealing similarities in the cytoskeletal organization of these apparently disparate organ systems. By searching for common targets in the testis and nervous system, the mechanisms of action of these agents may be more easily, and more confidently, determined.

Degeneration patterns in the chicken central nervous system induced by ingestion of the organophosphorus delayed neurotoxin tri-ortho-tolyl phosphate. A silver impregnation study

Exposure to certain organophosphorus compounds results in a neurological condition known as organophosphorus-induced delayed neurotoxicity (OPIDN). OPIDN is characterized clinically by an initial post-exposure delay period of 8-14 days after which signs of progressively developing ataxia and paralysis of the hindlimbs are observed. Although several studies have reported the presence of degeneration induced by organophosphorus delayed neurotoxins in specific central nervous system (CNS) structures, none have systematically examined CNS changes seen in the most frequently studied animal model for OPIDN--the domestic fowl. In the present study, we assessed the location and extent of anterograde degeneration in the chicken CNS following exposure to tri-o-tolyl phosphate (TOTP). All birds were dosed with 500 mg TOTP/kg body weight and killed after post-exposure periods of 1, 2, 3, or 4 weeks. The brains and spinal cords were processed with Fink-Heimer and Nissl stains. In the spinal cord, axon degeneration was noted in the fasciculus gracilis at cervical levels two weeks after exposure to TOTP. At 3 weeks, degeneration was also present in the cervical part of the dorsal spinocerebellar tract, in the lumbar part of the medial pontine-spinal tract, and in lamina VII in the lumbar ventral horn. In the medulla, moderate amounts of terminal and preterminal degeneration appeared at two weeks in the lateral vestibular, gracile, external cuneate, and lateral cervical nuclei. Lesser amounts of degeneration were noted in the solitary, inferior olivary, and raphae nuclei, in the medial, descending and lateral vestibular nuclei, and in the lateral paragigantocellular, gigantocellular, and lateral reticular nuclei. Fiber degeneration was also present in the medullary portions of the dorsal and ventral spinocerebellar tracts and spinal lemniscus. In the cerebellum, moderate amounts of terminal degeneration appeared in the deep cerebellar nuclei at one week while moderate mossy fiber degeneration was first noted in the granular layers of cerebellar folia I-V at 3 weeks. These results indicate (1) that, in the CNS, axonal and terminal degeneration resulting from TOTP intoxication appears to be confined to the spinal cord, medulla and cerebellum, (2) that the time of onset of degeneration in different fiber tracts and nuclei ranges from one to three weeks post-exposure, and (3) that the delay in the appearance of clinical signs of OPIDN is consistent with the delayed onset of degeneration in many of the affected CNS fiber systems.

Electromyographic, neuropathologic, and functional correlates in the cat as the result of tri-o-cresyl phosphate delayed neurotoxicity

To investigate the cat as a test animal for organophosphorous compound-induced delayed neurotoxicity, tri-o-cresyl phosphate (TOCP) was applied directly on the unprotected back of the neck of young adult cats. Single dermal doses, ranging from 250 to 2000 mg/kg TOCP, or subchronic daily administration of 1 to 100 mg/kg produced delayed neurotoxic effects in the cat. Severity of delayed neurotoxicity depended on the dose and duration. Clinical signs were characterized by hindlimb weakness, ataxia, and paresis. Electromyographic abnormalities resulting from acute denervation were observed in most cats that developed a neurologic deficit. No changes were seen in the motor nerve conduction, thus suggesting that the deficits were in the terminal branch rather than being diffuse lesions in the peripheral nerves. These results correlated well with histopathologic results showing lesions in the most distal portion of the longest tracts in both central and peripheral nervous systems. In the spinal cord, histopathologic studies showed that the ascending tracts of the upper cervical levels and descending tracts of the lumbosacral regions were affected most frequently. Although this study shows that the cat, like the chicken, is susceptible to TOCP-induced delayed neurotoxicity, it demonstrates two differences between the cat and the chicken: greater sensitivity of the cat to the acute effect of TOCP, and greater extent of recovery or improvement of the cat from delayed neurotoxicity. This recovery was demonstrated by: improvement of clinical signs, gain in body weight, disappearance of electromyographic abnormalities, and regeneration of peripheral nerves. Dermal administration of a single 100-mg/kg dose or subchronic 0.5-mg/kg doses of TOCP did not produce delayed neurotoxicity.

Changes in in vitro brain and spinal cord protein phosphorylation after a single oral administration of tri-o-cresyl phosphate to hens

The effect of a single oral 750 mg/kg dose of tri-o-cresyl phosphate (TOCP) on the endogenous phosphorylation of brain and spinal cord proteins was assessed in hens during the development of and recovery from delayed neurotoxicity. Crude membrane and cytosolic fractions were prepared from the brains and spinal cords of control and TOCP-treated hens at 1, 7, 14, 21, 35, and 55 days after treatment. Brain and spinal cord protein phosphorylation with [gamma-32P]ATP was analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), autoradiography, and microdensitometry. TOCP administration conferred calcium and calmodulin dependence on the phosphorylation of a few brain cytosolic proteins and caused an increase in the phosphorylation of a number of other cytosolic and membrane proteins. This effect of TOCP was large in magnitude, and its time course reflected the onset of and recovery from the signs of ataxia and paralysis associated with delayed neurotoxicity in the hen. The molecular weights (Mr) and maximal phosphorylation (percent of control) for the most prominently affected bands were as follows: brain cytosol--50K (183%), 55K (575%), 60K (529%), 65K (273%), and 70K (548%); brain membranes--50K (622%) and 60K (697%); and spinal cord cytosol--20K (182%). The role of endogenous phosphorylation reactions in and their potential usefulness as biochemical indicators of delayed neurotoxicity are being explored further.

Morphologic alterations in leg muscles of chicks treated with triorthocresyl phosphate in ovo

Chick embryos were injected on incubation Day 14 with 62 microliter of triorthocresyl phosphate (TOCP)/kg egg. Muscles of the leg were examined from 5 to 25 days after hatching. The sartorius from the thigh and the external gastrocnemius and peroneus longus from the tibial leg region were compared for muscle fiber size and end-plate length over this period. Treated chicks showed no acute toxic effects or overt ataxia and were equal in body weight to controls. At 5, 15, and 25 days after hatching, morphologic alterations consistent with denervation were detected. Muscle fibers were smaller than controls on Day 5 and were hypertrophic on Days 15 and 25. On Day 5 growth of fibers was retarded, an effect consistent with denervation, and the subsequent hypertrophy is predicted as compensation for denervated fibers. Small end plates were seen on Day 15, characteristic of end plates that were delayed in development by denervation. Each of these differences was greater in the tibial muscles than in the more proximally located sartorius. This is consistent with a distal neuropathy, such as that caused by TOCP in adult hens. Some recovery was apparent at the low dose 25 days after hatching. It is suggested that this resulted from reinnervation by repaired axons. This study of the myoneural apparatus and muscle fiber response to TOCP adds evidence to the possibility that the developing chick embryo may develop delayed neuropathy from organophosphorus compounds which produce this effect in adult hens.

Peripheral nerve damage in chicks following treatment with organophosphorus compounds in ovo

Chick embryos were treated with tri-o-cresyl phosphate (TOCP) or leptophos, organophosphorus compounds that cause delayed neurotoxicity. Embryos received either TOCP (62 or 250 microliter/kg egg) or leptophos (125 to 750 mg/kg egg) Day 14 of incubation and were examined after hatching for nerve damage. The high doses caused high embryo mortality. Chicks which survived the high doses were grossly ataxic from hatching until the study was ended at 3 weeks posthatching. On Posthatching Day 2, many degenerating nerve fibers were observed in the profundus/superficialis peroneus nerve in chicks surviving the high doses. TOCP-treated chicks were followed in detail for neuromuscular changes. Twenty days after hatching there were fewer large nerve fibers in the distal ischiadic nerve compared with controls and the largest nerve fibers were absent in the peroneus profundus nerve. Consistent with the evidence of denervation there was increased terminal branching of motor axons in femoral (sartorius) and tibial (external gastrocnemius and peroneus longus) leg muscles. The leg nerves of chicks treated with the low dose of TOCP did not show either an excessive number of degenerating nerve fibers or a detectable loss of large nerve fibers. However, terminal branching of motor axons was increased in the external gastrocnemius and peroneus longus muscles of 5- and 15-day-old chicks, followed by recovery by Day 25. The evidence is interpreted as a distal axonopathy in chicks treated with TOCP during late embryonic development.

The relationship between neurological damage and neurotoxic esterase inhibition in rats acutely exposed to tri-ortho-cresyl phosphate

A rodent model of organophosphorus-induced delayed neuropathy (OPIDN) has been developed using Long-Evans adult male rats exposed to tri-ortho-cresyl phosphate (TOCP). In the present study an attempt was made to relate neurochemical with neuropathological changes in rats exposed to single dosages of TOCP ranging from 145 to 3480 mg/kg. The degree of neurotoxic esterase (NTE) inhibition, measured at 20 and 44 hr and at 14 days postexposure was correlated with the appearance of spinal cord pathology 14 days postexposure in a separate group of similarly dosed rats. Those dosages that inhibited mean NTE activity in spinal cord greater than or equal to 72% and brain greater than or equal to 66% of control values within 44 hr postexposure produced marked spinal cord pathology 14 days postexposure in greater than or equal to 90% of similarly dosed animals. In contrast, dosages of TOCP which inhibited mean NTE activity in the spinal cord less than or equal to 65% and in the brain less than or equal to 57% produced spinal cord pathology in less than or equal to 15% of the animals. These data indicate that NTE inhibition may be used as a biochemical predictor for TOCP-induced neurological damage in rats.

The evolution of intracellular responses to acrylamide in rat spinal ganglion neurons

Acrylamide (30 mg or 50 mg/kg/day, 5 days each week) was injected intraperitoneally into rats for up to 4 weeks. Lumbar spinal ganglia, spinal cord and lumbrical muscle spindles were examined by light and electron microscopy at various times during this period. The first abnormalities in spinal ganglion neurons were seen at 7 days when an apparent increase in numbers of mitochondria, some being hypertrophic, were found in a few large light cells. This was 10 days before any significant Wallerian degeneration was found in muscle spindle sensory fibres. Mitochondrial changes became more marked with time and were later associated with RER disruption, loss of neurofilaments and peripheral displacement of the nucleus thus mimicking chromatolysis of the axon reaction. All these changes began, however, before axon degeneration. Evidence of increased satellite cell activity was maximal at 21 days. These changes are discussed in the light of the possibility that calcium entry into the cell may be seriously increased early in the intoxication as a direct result of the presence of acrylamide and that many of these cellular features are secondary responses to such an event. Distal degeneration of axons seems likely to be secondary to the perikaryal changes.

Fine structural changes in cat L7 ventral horn neurones after chronic sub LD50 DFP

The fine structural changes in the ventral anterior horn of spinal segment L7, have been studied in adult cats after single and chronic sub LD50 (0.1 to 0.75 mg/kg SC with a cumulative range of 1.3 mg/kg to 10.5 mg/kg) low dose exposure to diisopropylfluorophosphate (DFP). Only the motoneurons of the chronically treated animals show an increase in the number of lysosomes, neurofilaments and vesicle-like structures. A large number of coated vesicles is observed within axons and axon terminals of both acute and chronically treated animals. Morphological evidence of axon and terminal degeneration is seen only in chronically treated animals. The present study shows that chronic sub LD50 low dose administration of DFP over periods from 5 to 21 days results in degenerative changes of presynaptic terminals and axons, with the severity of the changes being dependent on dose and duration of treatment. The data are interpreted by comparison with single high dose exposure reported in the literature with a discussion of acute and delayed neurotoxic effects of DFP, on the central nervous system.

Clinical and electrophysiological study of neuropathy after organophosphorus compounds poisoning

Clinical and electrophysiological examinations were performed on 12 patients with toxic neuropathy following accidental ingestion of alcohol polluted by triorthocresyl phosphate (TOCP). Concurrent PNS and CNS lesions were found in all patients. Two to three months after ingestion, five of them showed prevalent signs of mixed, sensorimotor polyneuropathy, especially motor and distal, and the electrophysiological data pointed to the mixed process of axonal degeneration and secondary demyelination. In two of these five patients in whom examinations were repeated 13 years after TOCP ingestion, there was a marked clinical and electrophysiological improvement of signs of PNS lesions. Improvement of signs of CNS lesions was very poor even after 13 years. Signs of CNS lesions prevailed in the remaining seven patients. The clinical picture resembled that in amyotrophic lateral sclerosis and the electrophysiological data suggested a neuronal and axonal degeneration. Apart from the 12 cases of TOCP neuropathy, we also studied two cases of poisoning with organophosphorus insecticides, Dipterex and Divipan, in which a pure motor form of neuropathy was found.

Neuropathy due to phytosol (agritox). Report of a case

A case of intoxication with Phytosol (an insecticide) in a 29-year-old man is described. Ingestion of Phytosol (suicide attempt) produced signs of cholinergic crisis followed, after 16 days, by features of peripheral neuropathy and later, with the regression of signs of polyneuropathy, gradually increasing spastic paralegia. Electrophysiological investigation of nerves which were clinically moderately involved demonstrated sparing of sensory fibers and damage to motor fibers. There was no change in maximal motor conduction velocity. Histology of the clinically involved sural nerve revealed axonal changes together with demyelination, presumed to be secondary in type. This case shows that the susceptibility to delayed nervous system damage in man is greater than it might be expected from experimental studies and calls for caution in human exposure to these compounds.

Differential susceptibility of peripheral nerves of the hen to triorthocresyl phosphate and to trauma

The nerve fibres of largest diameter and of greatest length are considered to be the most vulnerable to triorthocresyl phosphate (TOCP). In this study, the differential vulnerability of the particular sciatic nerve branches was determined in the course of TOCP neuropathy and of Wallerian degeneration. The branch innervating the lateral gastrocnemius muscle, made up predominantly of large-diameter fibres, proved most susceptible to TOCP. By contrast, after proximal sciatic-nerve transection, degeneration commenced in the lateral nerve of the third digit, containing long nerve fibres of small diameter.