Duke Tanaka

The role of neurotoxic esterase (NTE) in the prevention and potentiation of organophosphorus-induced delayed neurotoxicity (OPIDN)

The first step in the initiation of organophosphorus-induced delayed neuropathy (OPIDN) is proposed to be the phosphorylation of an enzyme found in the nervous system called neurotoxic esterase (neuropathy target esterase, NTE). It has been known for over twenty years that non-neuropathic inhibitors of NTE exist and can actually prevent OPIDN when given before a neuropathic organophosphate (OP). Within the last three years it has become evident that another outcome is possible following in vivo interaction between neuropathic and nonneuropathic NTE inhibitors. When administered after OP exposure, nonneuropathic inhibitors can intensify or potentiate signs of OPIDN in adult chickens. Additionally, whereas developing chickens are typically resistant to the effects of neuropathic OPs, resistant age groups will develop OPIDN when exposure to a neuropathic OP is followed by the non-neuropathic NTE inhibitor phenylmethylsulfonyl fluoride. As in the case of prevention, studies of the potentiation of OPIDN may yield insight into mechanisms involved in the pathogenesis of delayed neurotoxicity. A brief review of current knowledge regarding the role of NTE in both the prevention and potentiation of OPIDN is presented.

Corticostriate projections from the primary motor cortex in the dog

Corticostriate projections from the hindlimb and forelimb areas of the primary motor cortex in the dog were traced using the autoradiographic technique. Injections of tritiated leucine into the hindlimb area resulted in discrete oval or semicircular patches of label confined to the dorsolateral corner of the head and body of the caudate nucleus. No label was found over the putamen. Injections into the forelimb area yielded irregularly shaped patches of label over the dorsolateral part of the head and body of the caudate nucleus as well as more diffuse label over the dorsal-most part of the putamen. In both instances diffuse terminal fields were noted in the dorsolateral part of the contralateral caudate nucleus. A comparison of results in the caudate nucleus indicates that projections from the forelimb area terminate somewhat more caudally and slightly more ventrally and medially than do projections from the hindlimb area. The results further suggest that although terminal fields from these areas may to some extent interdigitate with one another, they also overlap each other to a significant degree.

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.

Selective axonal and terminal degeneration in the chicken brainstem and cerebellum following exposure tobis(1-methylethyl)phosphorofluoridate (DFP)

Utilizing a variation of the Fink-Heimer method, we examined the extent and location of axonal and terminal degeneration within the chicken cervical spinal cord, brainstem and cerebellum resulting from a single subcutaneous dose of bis(1-methylethyl)phosphorofluoridate (DFP). The effects of DFP on the activities of whole-brain neuropathy target esterase (NTE) and cholinesterase (ChE) were also assessed as were the development and severity of clinical signs characteristic of organophosphorus-induced delayed neuropathy (OPIDN). Both whole brain NTE and ChE activities were maximally inhibited during the first 24 h post-exposure, showing gradual recovery over a period of 3 weeks. OPIDN clinical signs were not observed at 7 days post-DFP but progressed to severe ataxia by day 14 and paralysis by day 21. There was a relative absence of degeneration at 7 days, a dramatic increase in degeneration density at 14 days, and high density degeneration at both 21 and 28 days. Cervical spinal and medullary tracts containing axonal degeneration included the fasciculus gracilis, dorsal and ventral spinocerebellar tracts, spinal lemniscus, and the intramedullary portions of the glossopharyngeal and vagus nerves. Brainstem nuclei containing terminal degeneration included the lateral cervical, gracile-cuneate, external cuneate, and inferior olivary nuclei, the nucleus tractus solitarius, and the lateral and paragigantocellular lateral reticular nuclei. Mossy fiber degeneration was also present in cerebellar folia I-Vb. These results show that exposure to DFP causes axonal and terminal degeneration in ascending spinal tracts, brainstem nuclei and cerebellar folia associated with the transmission of somatic and visceral sensory information.

Exposure to triphenyl phosphite results in widespread degeneration in the mammalian central nervous system.

Previous studies in mammals have found that exposure to triphenyl phosphite results in cellular and axonal degeneration in the spinal cord and medulla. However, the nature of concomitant clinical signs suggested that other areas of the central nervous system might also be affected. In this study, the brains of ferrets receiving single subcutaneous injections of triphenyl phosphite were examined 8-12 days after dosing. Widespread areas of axonal, terminal, and somatic degeneration were seen in medullary, pontine, and thalamic nuclei. Extensive axonal and terminal degeneration were also noted in the cerebellar granule cell layer and in the cerebral cortical primary visual and sensorimotor areas. These data indicate that triphenyl phosphite exerts a potent neurotoxic effect, not only in the medulla and spinal cord, but also in the cerebellum, thalamus, and cerebral cortex.

The ventral lateral thalamic nucleus in the dog: Cytoarchitecture, acetylthiocholinesterase histochemistry, and cerebellar afferents

The canine ventral lateral nucleus was defined on the basis of Nissl cytoarchitecture, acetylthiocholinesterase (AChE) chemoarchitecture, and the distribution of cerebellar afferents. It consists of at least two subdivisions: a dorsal and rostral division (VLd) that stains intensely for AChE and contains densely packed cells, and a larger principal division (VL), located ventrocaudally, that stains moderately for AChE and contains a mixture of cells with moderate packing density. Results from autoradiographic, silver degeneration, and AChE material indicate that both divisions receive input from the deep cerebellar nuclei.

Corticostriate projections from reciprocally connected sectors of areas 4 and 5 in the dog

Injections of tritiated leucine were made into area 4 on the medial part of the posterior sigmoid gyrus and area 5 on the rostral part of the lateral gyrus. Both areas were found to project to each other as well as to an overlapping area in the caudate nucleus. These data suggest that areas 4 and 5 in the dog may relate to each other not only through direct reciprocal connections but also through overlapping projections to the neostriatum.

Delayed neurotoxic effects of tri-o-tolyl phosphate in the European ferret

The development of organophosphorus-induced delayed neurotoxicity (OPIDN) was studied in the European ferret (Mustela putorius furo). A single oral or dermal dose of 250, 500, or 1000 mg tri-o-tolyl phosphate (TOTP)/kg body weight was administered to adult male ferrets. Corn oil served as the vehicle in the oral test and 95% ethanol was the vehicle in the dermal test. At 48 h posttreatment, half the animals in each group were killed by cervical dislocation for assessment of whole-brain neuropathy target esterase (NTE) activity. The remaining 5 animals per group were observed and examined neurologically on a daily basis for a subsequent 54 d. All ferrets dosed dermally with 1000 mg TOTP/kg body weight developed clinical signs characteristic of OPIDN ranging from ataxia to partial paresis. Ferrets administered 250 and 500 mg TOTP/kg body weight via the dermal route displayed variable degrees of hind limb weakness and ataxia. Of the animals dosed orally, only those in the 1000 mg TOTP/kg body weight group showed clinical signs indicative of OPIDN. These signs did not progress beyond mild ataxia. Small amounts of axonal degeneration were noted in the dorsolateral part of the lateral funiculus and in the fasciculus gracilis of spinal cords in ferrets receiving dermal doses of 1000 mg TOTP/kg body weight. Whole-brain neuropathy target esterase activity was also maximally inhibited (46%) in animals receiving 1000 mg TOTP/kg dermally. These results suggest that the ferret is a species that is susceptible to OPIDN.

Contralateral corticothalamic projections from area 6 in the raccoon

Contralateral corticothalamic projections from cytoarchitectonic area 6 in the raccoon were studied using the autoradiographic tracing technique. Following injections of tritiated amino acids, accumulations of silver grains were present over both the ipsilateral and contralateral ventral medial, central lateral, paracentral, central medial, parafascicular and mediodorsal thalamic nuclei. These nuclei are also known to receive a number bilateral subcortical motor inputs. The additional presence of bilateral area 6 inputs suggests that these thalamic nuclei may be critically involved in the bilateral control of movement.

Neuropathological Effects of Triphenyl Phosphite on the Central Nervous System of the Hen (Gallus domesticus)

The neurotoxic effects of single subcutaneous injections of 1000 mg triphenyl phosphite (TPP)/kg body weight were investigated in White Leghorn hens. At 7 days postexposure, birds began to show signs of mild to moderate ataxia that progressed to severe ataxia and paralysis at 21 days. Inhibition of whole brain neuropathy target esterase was 85% at 48 hr and 73% by 21 days postexposure. After postexposure periods of 7, 14, and 21 days, hens were killed and their brains and spinal cords were examined for degenerating axons and terminals using the Fink-Heimer silver impregnation method. A small amount of degeneration was noted at 7 days. By 21 days, dense degeneration was noted in the spinal gray matter and funiculi. Degeneration was also present in the granular cell layer of cerebellar folia I-VI and in nuclei and fiber tracts of the medulla. Moderate to dense degeneration was also seen in several forebrain and midbrain areas including the paleostriatum, ansa lenticularis, the dorso-intermediate thalamic nucleus, lateral spiriform, pedunculopontine tegmental, and lateral mesencephalic nuclei and in the deeper layers of the optic tectum. These results indicate that, in addition to affecting the spinal cord and brainstem, exposure to TPP also damages higher order centers responsible for processing and integrating sensorimotor, visual, and auditory information.