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Biomedical subjects

D C Anthony

Publications and source records attributed to D C Anthony.

At least 73 records · Page 4Linked to original sources
PubMed1993

Decreased levels of the high molecular weight subunit of neurofilaments and accelerated neurofilament transport during the recovery phase of 2,5-hexanedione exposure.

The neurotoxicant 2,5-hexanedione (HD) causes the accumulation of neurofilaments in the distal axon and an acceleration of neurofilament transport proximal to the site of their accumulation. It has been proposed that the acceleration of transport is due to the direct reaction of HD with neurofilament proteins and, conversely, that this acceleration is a secondary response to the axon to injury. The objective of this study was to determine whether the response of axons to HD intoxication includes acceleration of neurofilament transport. Pulse labelling was used to analyze neurofilament transport in age-matched rats exposed to HD or PBS. The animals receiving HD were exposed either throughout the period of radiolabel transport, or prior to the pulse labeling of neurofilament proteins. If acceleration of the rate of neurofilament transport was due to the direct reaction of HD with proteins, then neurofilaments synthesized after the exposure period should travel at control rates, since these proteins would not have been exposed to the toxicant. After 28 days of transport, optic nerve proteins were examined using SDS-PAGE, fluorography, and computerized densitometry. In both HD-treated groups, neurofilament transport was accelerated relative to age-matched control animals. In addition, the amount of NFH was decreased relative to other neurofilament subunits. The combination of accelerated transport and a diminished proportion of NFH is similar to the observations of neurofilament axonal transport during growth and development. These observations suggest that this persistent, secondary effect is a reparative response to injury that recapitulates axonal growth and development.

Animals↗
PubMed1993

Covalent cross-linking of erythrocyte spectrin by carbon disulfide in vivo.

Covalent cross-linking of proteins by CS2 has been demonstrated in vitro and represents a potential mechanism for the toxicity of this compound. In the present investigation the ability of CS2 to cross-link proteins covalently in vivo is demonstrated using denaturing polyacrylamide gel electrophoresis. Intraperitoneal injection of CS2 in rats at 2 or 5 mmol/kg for 21 or 42 days produced several high-molecular-weight (approximately 410 kDa) proteins eluted from erythrocyte membranes which were not present in control animals. Limited proteolysis of the high-molecular-weight protein bands, monomeric alpha spectrin, and monomeric beta spectrin using endoproteinase glu-C, followed by peptide mapping on denaturing polyacrylamide gels, showed the high-molecular-weight proteins to be alpha,beta heterodimers. The production of multiple heterodimers exhibiting different distances of migration was consistent with the existence of several preferred sites for cross-linking. Evidence for the presence of dithiocarbamate ester and thiourea cross-linking structures in spectrin dimers was obtained using selective base hydrolysis. No spectrin dimer was detected in control animals, and dimer formation demonstrated a cumulative dose response in CS2-treated rats. The longevity of red blood cells, the cumulative dose response, and the stability of the cross-linking structures endows spectrin cross-linking with the potential to serve as a biomarker of chronic low-level exposures to CS2 and may provide a means to correlate pathological changes with existing methods of CS2 exposure monitoring. The ability of CS2 to covalently cross-link erythrocyte spectrin suggests that CS2 may also cross-link other proteins in vivo and supports covalent cross-linking of proteins as a possible molecular mechanism through which CS2 manifests toxicity. If so, then spectrin cross-linking may parallel cross-linking reactions in the axon and provide a sensitive, preneurotoxic biomarker of this molecular event.

Animals↗
PubMed1992

The functional recovery of peripheral nerves following defined acute crush injuries.

This study evaluates the effect of crushing load on functional recovery of the sciatic nerve. Male Sprague-Dawley rats were divided into five groups: sham operation, resected sciatic nerve, and 100 g (13 mm Hg/mm2), 500 g (50 mm Hg/mm2), and 15,000 g (1,000 mm Hg/mm2) of sciatic crush load (groups 1-5). In groups 3-5, a 5-mm segment of sciatic nerve was crushed for 10 min using a specially designed crushing device. Motor functional recovery was assessed from hind-limb walking tracks by calculating a sciatic functional index. There was no detectable functional deficit in the group receiving sham operations, while the resected sciatic nerve group exhibited complete dysfunction for the full duration of the experiment. All groups subjected to crush exhibited an initial deficit that gradually recovered to normal by day 14 (100-g crush), day 39 (500-g crush), and day 53 (15,000-g crush). Histological changes were also related to the initial crushing load and the length of the recovery period. Results indicate that the crushing device described is able to administer an adjustable, defined crush injury to the rat sciatic nerve, and that the functional deficit resulting from such an injury can be easily monitored with a sciatic functional index. The rate of recovery of crushed nerves was directly related to the initial load. All crushed nerves recovered in this experiment, even after the application of a 15,000-g load for 10 min.

Animals↗
PubMed1992

Comparison of subchronic neurotoxicity of 2-hydroxyethyl acrylate and acrylamide in rats.

The comparative neurotoxicity of subchronic exposure to 2-hydroxyethyl acrylate (HEA) and acrylamide (ACR) was evaluated using a functional observational battery (FOB) and neuropathology. Three dose levels of each compound (HEA: 3, 20, 60 mg/kg; ACR: 1, 4, 12 mg/kg) were administered intraperitoneally to male and female Long-Evans rats (n = 10/sex/dose level), 5 days/week for 13 weeks. Two vehicle control groups were also included. The FOB, which includes home-cage and open-field observations and interactive tests of sensory, neuromuscular, and autonomic function, was administered before dosing, at monthly intervals, and on the day after the last dose. Subsets of rats (n = 6/sex/dose level) were then perfused and tissues from the brain, spinal cord, and peripheral nerve were prepared for light microscopic evaluation. There were clear differences between the effects of HEA and ACR. ACR produced time- and dose-related changes in FOB measures of muscle tone and equilibrium, and produced axonal degeneration in peripheral nerves and within long tracts of the spinal cord. HEA exposure was also associated with changes in muscular function on FOB testing, but the magnitude of the effects was not as great as with ACR and not dose related. In addition, no neuropathological changes were detected after HEA exposure. Thus, the effects of HEA did not resemble those of ACR. The FOB data were summarized in domains of neurobehavioral functions. Using a composite score analysis, ACR was shown to produce prominent effects in the neuromuscular domain whereas HEA was largely without effect. When the data are analyzed in this manner, the neurotoxic potential of HEA appears to be minimal.

Acrylamide↗
PubMed1992

Reversing nerve-graft polarity in a rat model: the effect on function.

To evaluate the effect of nerve-graft polarity on function, a 1-cm segment of sciatic nerve was excised and reoriented in three groups of 20 adult Sprague-Dawley rats. In one group, the nerve was cut and anastomosed in the original orientation to act as a control. In the second group, the nerve-graft polarity was reversed 180 degrees. The final group underwent reversal of polarity 180 degrees and was rotated 180 degrees, (i.e., the posterior tibial nerve fascicles proximally were opposite to the peroneal nerve fascicles distally). Functional recovery was evaluated using Bain's modification of de Medinaceli's sciatic functional index (SFI). Rat-track analysis was performed over a 120-day period. Histologic correlation was also performed at the time of sacrifice. From our study, we concluded that reversing nerve-graft polarity, with or without rotation, does not influence subsequent function in this model.

Anastomosis, Surgical↗
PubMed1992

The role of pyrrole formation in the alteration of neurofilament transport induced during exposure to 2,5-hexanedione.

Exposure to the gamma-diketone, 2,5-hexanedione (HD), results in the accumulation of neurofilaments within the distal axon and is associated with acceleration of neurofilament transport within the proximal axon. The epsilon-amino groups of lysyl residues react with HD forming pyrrole adducts, followed by pyrrole-mediated protein crosslinking. Both reaction steps have been proposed as mechanisms causing neurofilament accumulation and acceleration of transport. In order to assess the importance of these steps on neurofilament transport, we compared transport in the optic system of rats exposed to HD and 3-acetyl-2,5-hexanedione (AcHD), a non-toxic analog of HD which forms pyrroles but does not crosslink proteins. Control, HD-treated, and AcHD-treated rats received intraoptic injections of [35S]-methionine and were exposed to saline, HD, or AcHD by intraperitoneal injections before and during the period of neurofilament transport. Neurofilament triplet proteins in the optic nerve and tract were identified by polyacrylamide gel electrophoresis followed by fluorography. The rate of neurofilament transport was accelerated in HD-treated animals over that of controls. However, despite higher levels of protein-bound pyrroles in AcHD-treated animals, the rate of transport was indistinguishable from that of controls. These findings indicate that pyrrole formation alone is not sufficient to cause acceleration of neurofilament transport.

Animals↗
PubMed1992

Comparison of location, severity, and dose response of proximal axonal lesions induced by 3,3'-iminodipropionitrile and deuterium substituted analogs.

Administration of 3,3'-iminodipropionitrile (IDPN) to rats results in massive accumulation of tangled neurofilaments in the proximal axons of large neurons, such as in dorsal root ganglia (DRG) and ventral horns of the lumbar spinal cord (LSC). Clinically, rats develop hyperexcitability, circling, head bobbing, and retropulsion. The ultimate toxicant and the molecular mechanism are not known. In a study designed to explore potential activation and detoxification pathways, dose-related differences in location and severity of lesions were observed in rats treated with IDPN or deuterium substituted analogs, 2,2,2',2'-tetradeuterio-IDPN (2-d-IDPN) or 3,3,3',3'-tetradeuterio-IDPN (3-d-IDPN). The compounds or saline were administered intraperitoneally to three rats per group at dose levels of 3.0, 1.5, 1.0, and 0.0 mmole/kg/day for 3 days. One week after the initial dose, tissues from DRG and LSC were collected, prepared and evaluated histologically in zones extending from areas adjacent to the cell bodies, distally toward the DRG stalk or toward the lumbar spinal roots. In the low dose IDPN group, DRG and LSC lesions were most prominent in distal zones. As dosage increased, the lesions progressed in severity and in proximity to the cell bodies. At the high dose, lesions were prominent in all zones. The same general pattern occurred with both analogs, although 2-d-IDPN was less potent than IDPN and 3-d-IDPN was more potent than IDPN. The differences in potency from the secondary isotopic effect of deuterium suggest that the 3-position is important in detoxification while the 2-position is important in the bioactivation of IDPN.

Animals↗
PubMed1992

The effects of liver denervation on the regulation of hepatic biliary secretion.

Effects of liver denervation on bile formation were studied in eight dogs prepared with chronic biliary fistulas. The animals were studied in the basal state, after feeding, and during infusion of glucagon 50 ng/kg/min, secretin 2 U/kg/hr, or somatostatin 200 ng/kg/min. After this first set of experiments the animals underwent a total hepatic denervation that consisted of section of the hepatic ligaments and a careful dissection of the portal vein, hepatic artery, and common duct with stripping of all the surrounding connective tissue and topical application of phenol. The above experiments were then repeated. Denervation did not modify bile flow, or bile salts, cholesterol, or phospholipid concentration or output. Biliary response to glucagon and secretin was similar before and after denervation. Somatostatin had an anticholerectic effect in both intact and denervated animals, but significantly reduced bile salt output only in the intact dogs. Feeding had a choleretic effect pre- and postdenervation, and the infusion of somatostatin following feeding decreased bile flow to the same degree before and after denervation. In the intact animals the output of all three biliary lipids was reduced by somatostatin after feeding but they were unaffected by somatostatin after denervation. Moreover, cholesterol and phospholipid outputs were stable after feeding in intact animals, but significantly decreased after denervation. 14C-erythritol clearance studies indicated no change in the canalicular component of bile flow with denervation, except again during somatostatin suppression of feeding. These data indicate that basal bile flow is normal after denervation but that innervation may play an important role in the modulation of responses to somatostatin and more complex stimuli such as feeding.

Animals↗
PubMed1991

A case of myelinoclastic diffuse sclerosis in an adult.

We report a case of rapidly progressive cerebral demyelinating disease in a previously healthy 40-year-old woman. This case satisfies the diagnostic criteria for myelinoclastic diffuse sclerosis (MDS), but is unusual in the age of onset. This is the 1st case of MDS in an adult with full documentation of clinical, biochemical, radiographic, and pathologic features.

Adult↗
PubMed1990

Evaluation of selective liver denervation methods.

This study compares four methods of hepatic denervation and defines the rate and physiological significance of reinnervation. Five groups of rats were prepared: 10 underwent orthotopic liver transplantation. In nine rats a 90% aqueous phenol solution was applied circumferentially to the portal vein. Thirteen rats underwent microsurgical denervation; 28 received different doses of 6-hydroxydopamine (6-HODA) administered as a single intraportal injection [50 (n = 10), 75 (n = 6), and 100 mg/kg (n = 6)]. Twelve rats were studied as controls. Rats were killed 1, 4, and 8 wk after surgery to determine liver tissue content of norepinephrine (NE). Changes in mean arterial pressure (MAP) in response to hepatic nerve stimulation, which was supramaximum in intensity and frequency, were measured before rats were killed. NE content in controls ranged from 121 to 204 ng/g and MAP increased by 30-38 mmHg after electrical stimulation. At 1, 4, and 8 wk after treatment the liver NE content was less than 1, 2.3, and 20.2 ng/g in the transplant group; less than 1, 2.7, 4.1 ng/g in the phenol group; and 17.2, less than 1, and 3 ng/g in the surgically denervated group. In the 6-HODA group, values were 18.9, 47, and 61.5 ng/g (50 mg/kg); 5.7, 20.2, and 15 ng/g (75 mg/kg); and 7.7, 2.5, and 17.5 ng/g (100 mg/kg). When the level of NE was undetectable, MAP increase after stimulation was 0-18% that of controls. When NE content was 15-23% of normal, MAP increased 49-62% regardless of the denervation technique.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Sural nerve biopsy in chronic inflammatory demyelinating polyradiculoneuropathy.

We compared histologic features of sural nerve biopsies in 14 patients with chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) with those in other forms of neuropathy. In CIDP endoneurial pericapillary cellular infiltrates were found in 4 patients (29%), onion bulbs in 5 patients (36%), and predominant demyelination in 7 patients (50%). None of these abnormalities was specific, but cellular infiltrates and onion bulbs appear to be diagnostically useful when combined with clinical information. To detect macrophage infiltration of myelin, cell nuclei were counter-stained in 20 teased fiber preparations. Nine patients with CIDP had a significantly higher mean number of cells per centimeter of teased fiber than 11 patients with other neuropathies. Despite overlap, significant infiltration of myelin detected by this method suggests CIDP in an appropriate clinical setting.

Biopsy↗
PubMed1989

Neurofilament protein crosslinking in gamma-diketone neuropathy: in vitro and in vivo studies using the seaworm myxicola infundibulum.

Neurofilament (NF) protein crosslinking has been proposed as the ultimate pathogenetic mechanism underlying the neuropathies caused by the gamma-diketones 2,5-hexanedione (HD) and 3,4-dimethyl-2,5-hexanedione (DMHD). Mammalian models have been used to investigate this hypothesis, but alternative experimental models are needed. Myxicola infundibulum is a marine worm which is gaining popularity in neuroscience research because of its large syncytial axon. A model system using Myxicola has been developed to investigate NF crosslinking in worms exposed to neurotoxic agents whose putative mechanisms involve covalent crosslinking of NF proteins. In vitro studies using purified NF demonstrate that progressive alkylation of Myxicola NF with [2,5-14C]DMHD is accompanied by NF protein crosslinking. Rabbit anti-Myxicola NF antisera showed highly restricted activity for Myxicola axoplasm and NF and were employed for immunoblotting axoplasm from Myxicola treated in vivo with DMHD. A dramatic increase in high molecular weight material was demonstrated in the axoplasm of treated worms, as demonstrated by polyacrylamide gel electrophoresis, and the new high molecular weight bands stained with the anti-NF antisera, indicating the presence of anti-NF reactive material in the crosslinked protein. Further, there was progression of crosslinking after cessation of exposure in vivo, an observation which suggests oxidation of remaining pyrrolyl derivatives. These studies support previous observations which suggest that NF crosslinking is the molecular event which initiates NF aggregation in gamma-diketone neurotoxicity, and establish Myxicola infundibulum as a useful species in which to study certain neurotoxic compounds.

Alkylation↗
PubMed1988

Neuroimaging of scuba diving injuries to the CNS.

Diving accidents related to barotrauma constitute a unique subset of ischemic insults to the CNS. Victims may demonstrate components of arterial gas embolism, which has a propensity for cerebral involvement, and/or decompression sickness, with primarily spinal cord involvement. Fourteen patients with diving-related barotrauma were studied with MR imaging of the brain and spinal cord and with CT of the brain. In four patients with presumed cerebral gas embolism, cranial MR was abnormal in three patients while CT was abnormal in only one. Twelve patients had decompression sickness and spinal cord symptoms. MR documented spinal cord abnormalities in three patients. However, scans obtained early in our study were frequently limited by technical constraints. MR of the brain is more sensitive than conventional CT scanning techniques in detecting and characterizing foci of cerebral ischemia caused by embolic barotrauma to the CNS. Although spinal MR may be less successful in the localization of spinal cord lesions related to decompression sickness, these lesions were previously undetectable by other neuroimaging methods.

Adolescent↗
PubMed1987

Evidence that pyrrole formation is a pathogenetic step in gamma-diketone neuropathy.

Previous studies from this laboratory have demonstrated that the addition of methyl groups at the 3 and 4 positions of the 2,5-hexanedione (2,5-HD) molecule results both in more rapid pyrrole formation and in enhanced neurotoxicity. In order to define more clearly the relationship between rates of pyrrole formation and neurotoxicity, the dl and meso diastereomers of 3,4-dimethyl-2,5-hexanedione (DMHD), 3,4-diethyl-2,5-hexanedione (DEHD), and 3,4-diisopropyl-2,5-hexanedione (DiPHD) were synthesized and purified. The rates of pyrrole formation were compared with that of unsubstituted 2,5-HD, and rates of in vitro crosslinking were determined. Each of the compounds was administered to rats to determine relative neurotoxicity. Hindlimb paralysis was reached after a total administered dose of 1.6 mmol/kg of dl-DMHD, while 5.9 mmol/kg of meso-DMHD was required. Paralysis was not achieved with either diastereomer of DEHD or DiPHD, although both produced systemic toxicity. Histologic sections of spinal cords and anterior roots from rats treated with DMHD revealed large neurofilament-filled axonal swellings, while more distal sections contained axons undergoing Wallerian-type degeneration. Neither axonal swellings nor Wallerian-type degeneration were seen in sections from spinal cord or peripheral nerve of rats treated with DEHD or DiPHD. The rates of pyrrole formation were in the order dl-DMHD greater than meso-DMHD greater than 2,5-HD greater than dl-DEHD greater than meso-DEHD greater than dl-DiPHD greater than meso-DiPHD, while in vitro crosslinking rates were in the order dl-DMHD greater than meso-DMHD greater than dl-DEHD greater than meso-DEHD greater than 2,5-HD greater than dl-DiPHD greater than meso-DiPHD. Cyclic voltammetry showed that the autoxidation of pyrroles derived from DMHD, DEHD, and DiPHD occurred more readily than that derived from 2,5-HD. In addition, we report for the first time the segregation of axoplasmic organelles in animals treated with DMHD, providing further evidence that the neurofilamentous axonopathies caused by such compounds as beta,beta'-iminodipropionitrile (IDPN), 2,5-HD and CS2 share a common underlying mechanism. The strong correlations between rates of pyrrole formation, rates of in vitro crosslinking and relative neurotoxicity are seen as evidence that pyrrole formation is a step in the pathogenetic sequence of gamma-diketone neuropathy.

Animals↗
PubMed1987

dl- versus meso-3,4-dimethyl-2,5-hexanedione: a morphometric study of the proximo-distal distribution of axonal swellings in the anterior root of the rat.

The neurotoxicity of the dl and meso diastereomers of the gamma-diketone 3,4-dimethyl-2,5-hexanedione (DMHD) was studied to determine if the difference in rates of pyrrole derivatization would influence the clinical and morphological appearance of the neuropathy associated with these gamma-diketones. Two groups of rats received 0.2 mmol/kg/day intraperitoneal injections of their respective diastereomer, and two groups of control rats received comparable volumes of water. The dl-DMHD treated group reached the clinical end-point of hindlimb paralysis in a period of time threefold shorter than the meso-DMHD treated group, paralleling the in vitro kinetics of pyrrole formation with a model amine. A computerized morphometric analysis of cross-sectional axonal areas along the lengths of L4 and L5 anterior roots revealed that the dl-DMHD treated rats had axonal swellings more proximal and of smaller caliber than the meso-DMHD treated rats. 14C-labeled dl and meso diastereomers were synthesized and used to determine relative ability of the diastereomers to gain access to the nervous system. There was approximately 25% more dl-DMHD in the brain after 2 hr. The brain:serum ratios of the diastereomers, however, were equivalent. The more distal location of the neurofilament-filled swellings after meso-DMHD intoxication corroborates previous findings regarding toxicant potency and location of axonal swellings and suggests that the rate of neurofilament crosslinking determines the location of swellings along the length of the axon in the neurofilamentous axonopathies.

Animals↗
PubMed1987

Hyperbaric oxygen accelerates the neurotoxicity of 2,5-hexanedione.

The molecular pathogenesis of n-hexane neurotoxicity has been postulated to proceed as follows: The gamma-diketone metabolite, 2,5-hexanedione (HD), reacts with lysyl-amino groups on neurofilaments to form imines. The imines cyclize to form pyrroles. The pyrroles autoxidize, resulting in covalent protein-protein crosslinking within or between neurofilaments. A resultant impairment of neurofilament transport is proposed to lead to neurofilament-filled axonal swellings. This experiment was designed to test whether oxidation is a necessary pathogenetic step in vivo by comparing time of onset of paralysis of an HD treated group of rats to that of a group receiving HD plus oxygen under high pressure (OHP). The group of rats receiving the hyperbaric oxygen treatment reached the endpoint of hindlimb paralysis significantly sooner than the group receiving none. The fact that OHP does accelerate HD neuropathy points towards an oxidative step in the molecular pathogenesis of gamma-diketone neuropathy.

Animals↗