The ultrastructure of tri-ortho-cresyl phosphate-poisoning. I. Studies on myelin and axonal alterations in the sciatic nerve

Subchronic Neurotoxicity of Oil Formulations Containing Either Tricresyl Phosphate or Tri-Orthocresyl Phosphate

This study was conducted to determine the threshold concentration of tricresyl phosphate (TCP) in aviation engine oil able to cause delayed peripheral neuropathy in adult hens after repeated exposure. The study also evaluated the predictive value of endpoints usually used to measure acute peripheral neurotoxicity (neurotoxic esterase [NTE] inhibition, ataxia, and histopathologic changes), as measures of neurotoxicity in a subchronic study. Animals that received oil containing 3% TCP showed significant neurotoxicity that could not be accounted for by the small amount of TOCP present. Oil containing 1% TCP was without neurotoxic activity. There was an excellent correlation between percentage inhibition of NTE and development of neuropathy. An association was also seen for ataxia and neuropathology. Further study is needed to determine the phosphate ester isomers responsible for the significant neurotoxic potency demonstrated by the aviation engine oil containing 3% TCP.

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.

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.

Morphological effects of neuropathy-inducing organophosphorus compounds in primary dorsal root ganglia cell cultures

Chick embryo dorsal root ganglia (DRG) cultures were used to explore early pathological events associated with exposure to neuropathy-inducing organophosphorus (OP) compounds. This approach used an in vitro neuronal system from the species that provides the animal model for OP-induced delayed neuropathy (OPIDN). DRG were obtained from 9-day-old chick embryos, and grown for 14 days in minimal essential medium (MEM) supplemented with bovine and human placental sera and growth factors. Cultures were then exposed to 1 microM of the OP compounds phenyl saligenin phosphate (PSP) or mipafox, which readily elicit OPIDN in hens, paraoxon, which does not cause OPIDN, or the DMSO vehicle. The medium containing these toxicants was removed after 12 h, and cultures maintained for 4-7 days post-exposure. Morphometric analysis of neurites was performed by inverted microscopy, which demonstrated that neurites of cells treated with mipafox or PSP but not with paraoxon had decreased length-to-diameter ratios at day 4 post-exposure. Ultrastructural alterations of neurons treated with PSP and mipafox included dissolution of microtubules and neurofilaments and degrading mitochondria. Paraoxon-treated and DMSO control neuronal cell cultures did not show such evident ultrastructural changes. This study demonstrates that chick DRG show pathological changes following exposure to neuropathy-inducing OP compounds.

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.

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.

Tau phosphorylation by diisopropyl phosphorofluoridate (DFP)-treated hen brain supernatant inhibits its binding with microtubules: role of Ca2+/Calmodulin-dependent protein kinase II in tau phosphorylation

Diisopropyl phosphorofluoridate (DFP) produces organophosphorus ester-induced delayed neurotoxicity (OPIDN) in hen, human, and other sensitive species. This is characterized by mild ataxia, which progresses to severe ataxia or paralysis in a few days. Ultrastructurally, OPIDN is associated with the degeneration of axons in central and peripheral nervous systems. Bacterially expressed longest human tau protein (htau40) phosphorylated by DFP-treated hen brain supernatant showed a decrease in microtubule binding in a shorter time than that phosphorylated by control hen brain supernatant. The decrease in htau40-microtubule binding observed on htau40 phosphorylation by the recombinant Ca2+/calmodulin (CaM)-dependent protein kinase II (CaM kinase II) alpha-subunit showed that CaM kinase II present in brain supernatant could participate in tau phosphorylation even in the absence of Ca2+/CaM and decrease tau-microtubule binding. In addition, use of htau40 mutants, htau40m1 (Ala416) and htau40m6 (Asp416), suggested that replacement of Ser416 by neutral or acidic amino acid produced some change in htau40 conformation that caused diminished binding with microtubules phosphorylated by brain supernatant in the presence of ethylene glycol bis(beta-aminoethyl ether) N, N'tetraacetic acid (EGTA). The change in conformation produced by Ser416 phosphorylation, however, was different from that produced by mutants since only nonmutated htau40 showed a significant decrease in binding with microtubules on phosphorylation by recombinant CaM kinase II in the presence of Ca2+/CaM compared to that obtained by phosphorylation in the presence of EGTA. This study showed that enhanced Ca2+/CaM-dependent protein kinase activity in DFP-treated hen brain supernatant may cause decreased tau-microtubule binding and destabilization of microtubules and may be involved in axonal degeneration in OPIDN.

Tau proteins-enhanced Ca2+/calmodulin (CaM)-dependent phosphorylation by the brain supernatant of diisopropyl phosphorofluoridate (DFP)-treated hen: tau mutants indicate phosphorylation of more amino acids in tau by CaM kinase II

Diisopropyl phosphorofluoridate (DFP) produces organophosphorus ester-induced delayed neurotoxicity (OPIDN) in hen, human, and other sensitive species. A single dose of DFP (1.7 mg/kg, s.c.) produces mild ataxia in 7-14 days in hens, followed by progression to severe ataxia or paralysis. We studied the effect of DFP administration on Ca2+/calmodulin-dependent phosphorylation of tau proteins by the brain supernatants of control and DFP-treated hens. Brain supernatants from DFP-treated hens showed enhanced in vitro phosphorylation of htau40 and its various mutants, but no change in the two-dimensional phosphopeptide pattern, when compared to control hen brain supernatants. Analysis of tau mutants phosphorylated by brain supernatant and recombinant CaM kinase II alpha-subunit showed that (1) brain supernatant CaM kinase II is mainly responsible for the phosphorylation of Ser416, (2) Ser356, but probably not Ser262, is phosphorylated by CaM kinase II, (3) no amino acid between Lys395-Ala437 except Ser416 is phosphorylated by CaM kinase II, (4) a number of amino acids in the tau molecule, which are phosphorylated by the brain supernatant in the absence of Ca2+/calmodulin are also mildly phosphorylated by CaM kinase II. The enhanced Ca2+/calmodulin-dependent phosphorylation of tau proteins by brain supernatant of DFP-treated hens that includes phosphorylation of a number of amino acids is likely to alter the functional properties of tau proteins in OPIDN. The hyperphosphorylated tau may destabilize microtubules, alter axonal transport, and result in degeneration of axons in OPIDN.

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.

Diisopropyl phosphorofluoridate (DFP) treatment alters calcium-activated proteinase activity and cytoskeletal proteins of the hen sciatic nerve

Diisopropyl phosphorofluoridate (DFP) produces delayed neurotoxicity (OPIDN) in hens that is characterized by peripheral and central axonal degeneration. DFP administration resulted in mCANP activity inhibition in sciatic nerve and significant decrease in total NF-H, phosphorylated NF-H, vimentin, GFAP, tubulin, and tau. The degradation of cytoskeletal proteins even in the presence of decreased CANP activity may be ascribed to the release of intracellular Ca2+, elevation of other proteinase activity, or modification of cytoskeletal proteins resulting in their increased susceptibility in OPIDN.

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.

Neuroaxonal dystrophy in distal symmetric sensory polyneuropathy of the diabetic BB-rat

We and others have previously described neuroaxonal dystrophic changes as one of the hallmarks of structural diabetic autonomic polyneuropathy involving sympathetic nerves. In the present study, a systemic search for similar changes was undertaken in the mainly sensory symmetric polyneuropathy of the spontaneously diabetic BB-rat. Changes identical to those described in sympathetic nerves in this model were found in sensory ganglion cells, in their proximal extramedullary axons, and in proximal and distal myelinated axons of the spinal dorsal columns. The dystrophic substructures consisted of tubulovesicles, tubular rings, layered membranes, electron-dense membranous bodies, and neurofilamentous changes. Neuroaxonal dystrophic abnormalities increased with increasing duration of diabetes, and exhibited a topographic distribution along the sensory neuroaxonal axis, suggesting metabolic abnormalities as well as abnormalities in the turn-around mechanism of fast axonal transport in the pathogenesis of dystrophic changes in diabetic nerves.

Cytoskeletal proteins as targets for organophosphorus compound and aliphatic hexacarbon-induced neurotoxicity

Concurrent exposures to organophosphorus insecticide leptophos and the industrial solvents n-hexane and toluene were implicated in causing an outbreak of neuropathy in workers. Although both leptophos and n-hexane produce central-peripheral distal axonopathy, the morphology and distribution of neuropathic lesions are distinct, reflecting different modes of action. The molecular mechanisms of organophosphorus compound-induced delayed neurotoxicity (OPIDN) and aliphatic hexacarbon-induced neurotoxicity have been investigated utilizing various biochemical techniques, (i.e. one- and two-dimensional gel electrophoresis, immunoblotting, peptide mapping). Oral administration of tri-o-cresyl phosphate (TOCP) produced delayed neurotoxicity and increased in vitro Ca2+ and calmodulin-dependent kinase protein phosphorylation of cytoskeletal proteins in brain, spinal cord, and sciatic nerve of chickens. This enhanced protein phosphorylation correlated well with the following characteristics of OPIDN: test chemical, whether an OPIDN-producing or not; dose-dependence and time course of the effect; and the animal sex sensitivity, age selectivity, and species susceptibility. The proteins that showed an increased phosphorylation were identified to be; alpha- and beta-tubulin, microtubule-associated protein-2 (MAP-2), and the 3 neurofilament proteins 70 kDa, 160 kDa, and 210 kDa. Further studies suggested that the increased protein phosphorylation is not related to an effect on protein phosphatase or ATPase activity, but rather to altered Ca2+-calmodulin kinase II activity. Aliphatic hexacarbon-induced neurotoxicity is characterized by an accumulation of 10 nm neurofilaments above the nodes of Ranvier in the spinal cord and peripheral nerve. Treatment of rats with 2,5-hexanedione, the active neurotoxic metabolite of n-hexane, produced protein crosslinking in a dose-dependent manner. This treatment also decreased protein phosphorylation of neurofilament proteins as well as MAP-2. These studies demonstrate the involvement of cytoskeletal proteins in the molecular pathogenesis of chemical-induced neurotoxicity.

Gait analysis of chicks following treatment with tri-ortho-cresyl phosphate in ovo

Chick embryos were treated during late embryonic development with tri-ortho-cresyl phosphate (TOCP), an organophosphate compound that causes delayed neurotoxicity in humans and some other species. Embryos were treated on incubation d 14 with either 62 or 250 microliters TOCP/kg egg. The higher dose reduced the number hatched, and signs of cholinergic toxicity were apparent in the newly hatched chick. All chicks that survived this dose were unable to stand. Recovery from the cholinergic effects occurred within a few days after hatching, but the chicks remained severely ataxic through 3 wk of observation. The mortality of embryos treated with 62 microliters TOCP/kg egg was not higher than that of controls, and young chicks showed no overt signs of cholinergic toxicity or ataxia. Motor impairment was detected by measuring gait parameters. These chicks had a short stride and walked with a more open angle of foot placement. These are adjustments in gait that provide a more steady base of support. The change in gait developed over a 3-wk period after hatching. The hindlimb motor impairment detected at both doses is consistent with neuropathy such as is seen in the adult chicken. The value of gait analysis is the ability to quantify effects that are not apparent by simple observation.

Calcium and calmodulin-enhanced in vitro phosphorylation of hen brain cold-stable microtubules and spinal cord neurofilament triplet proteins after a single oral dose of tri-o-cresyl phosphate

The effect of a single 750-mg/kg oral dose of tri-o-cresyl phosphate (TOCP) on the endogenous phosphorylation of brain microtubule preparations and spinal cord neurofilaments was assessed in hens after the development of delayed neurotoxicity. Protein phosphorylation with [gamma-32P]ATP was analyzed by one-dimensional and two-dimensional gel electrophoresis, autoradiography, and microdensitometry. TOCP treatment enhanced the Ca2+- and calmodulin-dependent phosphorylation of tubulin in crude chicken brain cytosol (160% for alpha-tubulin and 140% for beta-tubulin) and cold-stable microtubules (165% and 155% for alpha- and beta-tubulin, respectively). Microtubule-associated protein 2 (MAP-2) phosphorylation was also increased in brain fractions studied--i.e., brain cytosol (145%), cold-stable microtubules (133%), and cold-labile microtubules (328%). There was significant increase in phosphorylation of a 70-kDa protein in the brain cytosol and in the cold-stable microtubule fractions. TOCP also stimulated the phosphorylation of spinal cord proteins of 70 kDa (119%) and 160 kDa (129%) in a Mg2+-dependent manner. Addition of Ca2+ and calmodulin further enhanced the phosphorylation of these 70-kDa (563%) and 160-kDa (221%) proteins as well as of 52-, 59-, and 210-kDa proteins by as much as 126%, 160%, and 196%, respectively. Two-dimensional electrophoresis was carried out to identify these proteins. They were confirmed as alpha- and beta-tubulin (52 and 59 kDa) in brain and spinal cord preparations and the neurofilament triplet proteins (70, 160, and 210 kDa) in the spinal cord preparation. The 70-kDa protein in brain was not neurofilament in origin. Peptide mapping using Staphylococcus aureus V8 protease showed the brain and spinal cord cytoskeletal proteins have identical phosphopeptide patterns in control and TOCP-treated hens, indicating that it was unlikely that the phosphorylation sites were altered by TOCP treatment.

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.

The joint neurotoxic action of inhaled methyl butyl ketone vapor and dermally applied O-ethyl O-4-nitrophenyl phenylphosphonothioate in hens: potentiating effect

The neurotoxic action of inhaled technical grade methyl butyl ketone and dermally applied (O-ethyl O-4-nitrophenyl phenylphosphonothioate (EPN) was studied. Three groups of five hens each were treated 5 days/week for 90 days with a dermal dose of 1.0 mg/kg of EPN (85%) on the unprotected back of the neck. These groups were exposed simultaneously to 10, 50, or 100 ppm of technical methyl butyl ketone (MBK; methyl n-butyl ketone:methyl isobutyl ketone, 7:3) in inhalation chambers. A fourth group was treated only with the dose of EPN and a fifth group with only 100 ppm MBK. The control consisted of a group of five hens treated with a dose of 0.1 ml acetone. Treatment was followed by a 30-day observation period. Simultaneous exposure to EPN and MBK greatly enhanced the neurotoxicity produced when compared to the neurotoxicity produced by either chemical when applied alone. Continued exposure to EPN and MBK resulted in earlier onset and more severe signs of neurotoxicity than exposure to either individual compound. The severity and characteristics of histopathologic lesions in hens given the same daily dermal dose of EPN in combination with inhaled MBK depended on the MBK concentration. Histopathologic changes were more severe and prevalent in the 100 ppm MBK:1 mg/kg EPN group than in the others. In this group, Wallerian-type degeneration was seen along with paranodal axonal swellings. The morphology and distribution of these lesions were characteristic of those induced by MBK. In the 50 ppm MBK:1 mg/kg EPN group axonal swelling was evident but not clearly identifiable as paranodal. Hens treated with 10 ppm MBK:1 mg/kg EPN had minimal lesions with low incidence of axonal swellings. These were not as large as those seen in MBK neurotoxicity, but instead resembled the histopathologic lesions caused by EPN. The results indicate that the combined treatment gave a value for neurotoxicity coefficient which was two times the additive neurotoxic effect of each treatment alone. Pretreatment with three daily ip doses of 5 mmol/kg technical grade MBK or methyl n-butyl ketone (MnBK), equally increased chicken hepatic microsomal cytochrome P-450 content. Also, hepatic microsomes from MBK-treated hens metabolized [14C]EPN in vitro to [14C]EPN oxon to a much greater extent than those from control hens. These results suggest that MBK potentiates the neurotoxic effect of EPN, at least in part, by increasing the metabolic activation of EPN to the more neurotoxic metabolite EPN oxon.(ABSTRACT TRUNCATED AT 400 WORDS)

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.

Pattern of neurotoxicity of n-hexane, methyl n-butyl ketone, 2,5-hexanediol, and 2,5-hexanedione alone and in combination with O-ethyl O-4-nitrophenyl phenylphosphonothioate in hens

This investigation was designed to study the neurotoxicity produced in hens by the aliphatic hexacarbons n-hexane, methyl n-butyl ketone (MnBK), 2,5-hexanediol (2,5-HDOH), and 2,5-hexanedione (2,5-HD) following daily dermal application of each chemical alone and in combination with O-ethyl O-4-nitrophenyl phenylphosphonothioate (EPN). Dermal application was carried out on the unprotected back of the neck. To assess whether the joint neurotoxic action of various chemicals is caused by the enhancement of absorption through the skin or by interaction at the molecular level, two additional experiments were performed. In the first experiment, EPN was dissolved in each of the aliphatic hydrocarbons prior to their topical application. In the second experiment, EPN was dissolved in acetone and applied at a different location from that of the aliphatic hexacarbons. Dermal application was carried out for 90 d followed by a 30-d observation period. The results show that hens treated with EPN developed severe ataxia followed by improvement during the observation period; n-hexane produced leg weakness with subsequent recovery, whereas the same dose of MnBK, 2,5-HDOH, or 2,5-HD produced clinical signs of neurotoxicity characterized by gross ataxia; concurrent dermal application of EPN with n-hexane or 2,5-HDOH at the same site or at different sites produced an additive neurotoxic action; simultaneous dermal application of EPN and MnBK at different sites resulted in an additive effect, whereas it caused potentiation when applied at the same site; and concurrent topical application of EPN and 2,5-HD produced a potentiating neurotoxic effect. While no histopathologic lesion was produced at the end of the observation period when any test chemical was applied alone, binary treatments of EPN and aliphatic hexacarbons resulted in histopathologic changes in some hens, with morphology and distribution characteristic of EPN neurotoxicity. The joint potentiating or additive action of aliphatic hexacarbons on EPN neurotoxicity was: 2,5-HD greater than MnBK greater than 2,5-HDOH greater than n-hexane. The mechanism of this joint action seems to be related both to enhancing skin absorption of EPN and/or its metabolic activation by n-hexane and its related chemicals.

Effects of soman on neuritic outgrowth and substrate utilization by explants of the rat superior cervical ganglion

The influence of the organophosphate, soman (pinacolyl methylphosphonofluoridate), on neuritic growth and substrate utilization by mammalian autonomic neural tissue was studied using explants of the rat superior cervical ganglion as a model. Soman produced a dose-dependent decrease in neuritic outgrowth from explants of this tissue maintained in a serum-free medium. Acetylcholinesterase in the explant as well as in culture media also decreased. In contrast, the effects of soman on explant metabolism were modest. Total protein and DNA content of the tissue was not affected. Only marginal changes in substrate utilization were detected; glucose use was unaltered, lactate production increased 20% with the highest soman tested. Soman increased the content of phosphocreatine in ganglion explants. This increase occurred in the absence of changes in the oxidation-reduction state of NAD calculated from pyruvate/lactate ratios. The results indicated that soman inhibited neuritic outgrowth from explants of the rat superior cervical ganglion in the absence of major effects on substrate utilization by this tissue.

A rodent model of organophosphorus-induced delayed neuropathy: distribution of central (spinal cord) and peripheral nerve damage

Central and peripheral nerve fibre damage has been produced in Long-Evans hooded male rats with tri-ortho-cresyl phosphate. Animals were dosed by gavage with intermittent or daily amounts of the organophosphate and examined after 2, 6, 12, 18 and 24 weeks. The distribution of central nervous system (spinal cord) damage and the differential vulnerability among various peripheral nerves supported a "dying-back' classification for the neuropathy. Giant axonal swellings, containing massive accumulations of smooth endoplasmic reticulum, hallmarked the neuropathy. In spite of severe neurological damage the animals displayed only moderate functional disturbances. These findings have shown that the rat is highly sensitive to the structural damage caused by organo-phosphates, although resistant to the ataxia.

Sensitivity of the cat to delayed neurotoxicity induced by O-ethyl O-4-nitrophenyl phenylphosphonothioate

Delayed neurotoxicity was produced in cats following the administration of either a single dermal dose of 22.5 to 225 mg/kg (0.2 to 5.0 times the LD50) or subchronic (90 days) administration of 0.5 to 2.0 mg/kg of technical grade O-ethyl O-4-nitrophenyl phenylphosphonothioate (EPN). The study showed three differences from the condition produced in the chicken: difficulty to protect from acute poisoning, slower progression of delayed neurotoxicity, and propensity for improvement. These animals received atropine sulfate and pyridine-2-aldoxime methyl chloride (PAM) to protect them against acute poisoning, but most developed signs of acute cholinergic neurotoxicity, the degree of severity being dose dependent. Also cats given small single doses of EPN showed only leg weakness, while those treated with large doses progressed to severe ataxia and death. In cats treated with subchronic dermal daily doses of EPN, the extent and permanence of injury and progression or improvement of neurologic deficit also depended on the dose size and duration of exposure. Histopathologic changes were present in the most distal portion of the longest tracts in both the central and peripheral nervous system. Ascending tracts were most affected in the cervical spinal cord, while change in the descending tracts was concentrated in the lumbosacral spinal cord. Recovery to a varying degree from delayed neurotoxicity was seen in all surviving cats. The recovery was demonstrated as improvement in clinical signs, increase in body weight, and regeneration of peripheral nerves.

Morphological and biochemical changes in muscle and peripheral nerve in Fabry's disease

In a case of Fabry's disease, microscopic, ultrastructural, and biochemical studies of a muscle biopsy were performed, as well as microscopic, ultrastructural, and morphometric studies of a nerve biopsy. Pleomorphic lipid inclusions were observed in muscle fibers, fibroblasts, and endomysial capillaries. Moreover, the thermolabile isoenzyme A of alpha-D-galactosidase was almost completely absent. In the nerve specimen, polymorphous lysosomes were noted in perineural cells, in fibroblasts, and in endothelial and perithelial cells in association with some nonspecific degenerative changes. The morphometric data revealed a loss of large myelinated fibers, an uncommon finding in Fabry's disease, and a decrease of the average diameter of the unmyelinated fibers, which was related to axonal sprouting. The relationship between the pain attacks and the increased number of the small unmyelinated fibers is discussed.

'Acrylamide-induced' neuropathy and impairment of axonal transport of proteins. II. Abnormal accumulations of smooth endoplasmic reticulum as sites of focal retention of fast transported proteins. Electron microscope radioautographic study

The distribution of fast axonally transported proteins was studied by electron microscope radioautography in ciliary ganglia of chickens treated or not treated with acrylamide. At 3 h after the intracerebral injection of [3H]lysine, the preganglionic axons of the untreated chickens displayed few silver grains, mainly associated with smooth endoplasmic reticulum (SER) profiles. In most axons of acrylamide-treated chickens, a similar pattern was observed, except in axons which exhibited focal and intense labeling underneath the axolemma: clusters of silver grains indeed overlayed peripheral accumulations of tubulovesicular profiles of SER, dense core vesicles and mitochondria. After impregnation with heavy metals, electron microscope observation of 1 micrometer thick sections showed a locally disorganized SER forming a complex network of tubules intermingled with vesicles and mitochondria. Such a local disorganization of the peripheral SER in the distal part of the axons, could be responsible for the focal stasis of fast transported proteins; it seems to be one of the earliest changes detectable in axons damaged by acrylamide treatment.

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.

The neuropathology of DFP at cat soleus neuromuscular junction

The fine structure of the cat soleus neuromuscular junction was studied following a single intra-arterial injection of di-isopropylfluorophosphate (DFP) into the right femoral artery. DFP induced separate subacute and delayed morphologic changes in soleus non-myelinated motor nerve terminals. Three days after DFP administration motor nerve terminals were reduced in number. Subacute DFP damage was also noted in the subneural apparatus and in the immediate subjacent muscle. Both pre- and post-junctional subacute changes were resolved two weeks post-DFP. One week following this initial regeneration, soleus motor nerve terminals underwent a delayed transient degeneration, followed by reinnervation of damaged endplates 6--8 weeks following DFP. Quantitative analysis of methylene blue-stained intramuscular nerves indicated that both subacutely and chronically denervated soleus muscle fibres were reinnervated by regeneration of the original motor axon. Reinnervation by means of collateral sprouting was insignificant. This mechanism of reinnervation and the rapidity with which it occurred suggests that both subacute and delayed soleus motor nerve damage is initiated from local actions of DFP on the non-myelinated terminal. The subacute reaction probably results from a direct cytotoxic action of DFP at pre- and post-junctional sites. The delayed nerve terminal degeneration may also stem from an acute effect not immediately detrimental to nerve function.

Unmyelinated nerve fibres in feline acrylamide neuropathy

Electronmicroscope studies have been performed on the greater splanchnic nerve and the nerve to the medial head of gastrocnemius muscle of control and acrylamide poisoned cats. Degeneration of unmyelinated as well as of myelinated fibres was observed in both nerves. In cats severely poisoned with acrylamide, some very large unmyelinated axons undergoing early degeneration were seen in the splanchnic nerve. In the nerve to medial head of gastrocnemius, there was a decrease in the proportion of large diameter unmyelinated axons.

Studies on the etiology of the experimental neuropathy from industrial adhesive (glues)

Chickens treated by paintbrushing with glue distillate (used in shoe industries), hydrocarbon mixture and TOCP in hexane, developed paralysis (4/5); in these, we have demonstrated a diffuse degeneration of the myelinic sheath of the peripheral and central neurites. Besides TOCP, cyclohexane (because of its higher concentration in the glue distillate and in the hydrocarbon mixture) may be indicated as responsible for occupational neuropathy.

Toxic polyneuropathies in Italy due to leather cement poisoning in shoe industries. A light- and electron-microscopic study

The peripheral nerve biopsy specimens of 4 cases of toxic polyneruopathies induced by exposure to leather cement in shoe industries were studied. Analysis of the cements used in the manufacturing process proved them to contain n-hexane as a volatile substance. Light- and electron-microscopic examination of nerve biopsies showed segmental swelling of axons due to the accumulation of packed filaments and thinning of the overlying myelin sheath. Neither active nerve fibre degeneration nor regeneration were frequently seen. It has been suggested that features of so-called giant axonal neuropathy are the most common pattern of peripheral nerve degeneration in chronic n-hexane intoxication.

Studies on drug-induced neuropathies. III. Motor nerve deficit in cats with experimental acrylamide neuropathy

To assess motor nerve and motor nerve terminal function in acrylamide neuropathy, cats were given i.m. injections of acrylamide (15 mg/kg) daily for 10 days to induce a peripheral neuropathy. Tests of function were performed on the day of the 10th injection (day 0) and 7, 21 and 35 days thereafter. In untreated animals tetanic conditioning evoked stimulus-bound repetition (SBR) in 85% of soleus alpha-motoneurones. Following administration of acrylamide, the percent of axons elaborating SBR were: day 0 -- 79%, day 7 -- 71%, day 21 -- 31%, day 35 -- 22%. The response of soleus muscle to SBR is normally a post-tetanic potentiation (PTP) of contractile tension which is proportional to the tetanic conditioning frequency; during the development of the neuropathy, PTP in response to all tetanic frequencies progressively declined, concomitant with and as a result of the declining incidence of SBR. These data indicate that initial functional alterations in motor nerves during acrylamide neuropathy occurs at the level of the nerve terminal, preceding alterations in conduction velocities in the axons. However, the motor nerve deficit is not adequate, in either time to onset or severity, to account for the clinical manifestations of the neuropathy. The possible contribution to clinical signs of the neuropathy made by lesions to other peripheral nerves is discussed.