Changes in size of motor axons in hereditary canine spinal muscular atrophy

Hereditary canine spinal muscular atrophy (HCSMA), a dominantly inherited disorder of motor neurons, has three phenotypes: accelerated, intermediate, and chronic. In the accelerated and intermediate phenotypes, axonal sizes in ventral roots were smaller than in controls. Reductions in axonal size occurred primarily in large axons, and the frequency of small-caliber axons was increased. In HCSMA, nerve fiber shape, i.e., circularity, was reduced, and the relative thickness of the myelin sheath as a function of axonal caliber was decreased. The density of fibers in motor nerves was increased, making it unlikely that a selective loss of large-caliber axons explained the increased frequency of small-caliber axons. These observations suggest that, in HCSMA, changes in axonal size in motor nerves are associated with both growth arrest and axonal atrophy.

Axotomy-like electrophysiological alterations in spinal motoneurons in beta,beta'-iminodipropionitrile neuropathy

Motoneurons (MNs) exhibit characteristic electrophysiological alterations following axotomy which are concomitants of perikaryal remodeling induced by the axonal injury. beta,beta'-Iminodipropionitrile (IDPN) neurotoxicity, which produces proximal axonal swellings in the first internodes of motor fibers, was studied as a model of perikaryal electrophysiological properties in axonal pathologies without axonal degeneration. Similarities between parameters of MN excitability (delayed depolarizations, repetitive discharge, and the afterhyperpolarization potential, AHP) known to occur in axotomized MN and those in IDPN neuropathy were examined in type-identified spinal MN of cats during the evolution (7 to 35 days) of proximal axonal swellings. Delayed depolarization potentials were observed frequently in fast MN types throughout the neuropathy but only at 35 days in slow MN types. Similarly, repetitive firing occurred most prominently in fast MNs early in the neuropathy. Concomitantly, AHP duration decreased as early as 7 days in all MN types and was significantly shortened in types FF, FR, and S motoneurons. AHP peak amplitude and current declined continuously from 7 to 35 days of the neuropathy and were significantly (p less than 0.05) decreased at 35 days in types FF and S MNs. These results suggest that not only are fast MN types vulnerable early in IDPN neuropathy, but also that all MN types exhibit electrophysiological changes strikingly similar to those following mechanical axotomy. The possibility is raised that IDPN may initiate electrophysiological changes, analogous to perikaryal remodeling, by mechanism(s) unrelated to axonal degeneration.

Neurofilament antigens in acrylamide neuropathy

After repeated exposure, acrylamide (AC) produces degeneration of distal axons. Because neurons whose axons have been injured (e.g. by axotomy) show alterations in their structural and chemical properties, the present study was designed to differentiate the direct effects of AC intoxication from neuronal responses secondary to axonal injury caused by AC. Rats were given AC as either a single high dose (75 mg/kg), or as daily intraperitoneal injections (30 mg/kg, six days per week for four weeks). Dorsal root ganglia of the fifth lumbar level, L5, were examined using a variety of monoclonal antibodies directed against nonphosphorylated (2-135) and phosphorylated (03-44, 06-17, 07-05) epitopes of 145 and 200 kilodalton neurofilament proteins. In control rats, antibody 2-135 stained axons and neuronal cell bodies; antibodies against phosphorylated epitopes of neurofilaments stained only axons distal to the glomerulus. Following chronic AC intoxication, all three antibodies directed against phosphorylated epitopes of neurofilaments (particularly 07-05) demonstrated intense immunoreactivity in 20-30% of neuronal cell bodies. In addition, the glomerular region of these axons was stained. Electron microscopy revealed many chromatolytic cells containing few neurofilaments. In contrast, a single high dose of AC produced no abnormal staining of neuronal cell bodies at a time when slow axonal transport was impaired. Our findings are compared to those observed following axotomy and to those occurring in aluminum-intoxicated rabbits, two experimental disorders in which altered distributions of phosphorylated filaments have been documented.

The pathophysiology of proximal neurofilamentous giant axonal swellings: implications for the pathogenesis of amyotrophic lateral sclerosis

Neurofilamentous giant axonal swellings are observed in a number of human disorders, although they can manifest at different locations (i.e. proximal or distal) along the axon. Recent advances in understanding the pathogenesis of these changes has resulted from correlations of ultrastructural changes with abnormalities in the axonal transport of neurofilament proteins in experimental models produced by toxic chemicals. Using single, high doses of either acrylamide or 2,5-hexanedione, a reduction in neurofilament transport has been shown in the rat sciatic nerve. In contrast to the distal axonal swellings observed upon repeated exposures to these agents, modest proximal axonal swellings containing increased neurofilament content are found following high dose exposures. Thus, regardless of the location of swelling production, a defect in slow transport appears to underlie swelling formation. beta,beta'-Iminodipropionitrile (IDPN) produces proximal neurofilamentous giant axonal swellings which are indistinguishable from those observed in some patients with amyotrophic lateral sclerosis (ALS). Although not a model for ALS, IDPN provides a means to study the functional consequences of proximal giant axonal swellings. Intracellular recordings from IDPN-intoxicated cats reveal a number of abnormalities which may have electrophysiological counterparts in ALS, suggesting that the swellings may be important in the expression of the disease. Although axonal degeneration is rarely observed in the cat, perikaryal recordings reveal a number of alterations which are strikingly similar to those obtained from chromatolytic motor neurons following nerve transection. A perturbation of "trophic" signals from the periphery may be involved in the generation of axotomy-like changes in IDPN-intoxicated cats.

Cross talk between intraspinal elements during progression of IDPN neuropathy

Unusual electrical interactions between neuronal elements of cat spinal cord were examined during the evolution (7-70 days) of proximal paranodally demyelinated axonal enlargements in alpha motor axons induced by beta, beta'-iminodipropionitrile (IDPN) treatment, 50 mg/kg ip, once weekly for up to 5 weeks. The electrical cross talk was observed as early as 7 days of the neuropathy, at which time it occurred in 17.0% of all motoneuron perikaryal recordings. The incidence was greater at 14 (39.1%) and 35 (26.1%) days, without preferential involvement of any motoneuron type. The frequency of recordings from axonal swellings increased from 7 to 35 days but without an increase in cross talk per recording. At 70 days of the neuropathy, L7 ventral root was stimulated repetitively to examine a possible influence of potassium on cross talk. Subsequently, action potentials could be elicited in motoneurons by stimulation of additional other ventral root filaments. These studies are in agreement with the lack of direct electrical apposition between excitable membranes in IDPN neuropathy but suggest support for a role for an accumulation of extracellular potassium, due to paranodal demyelination as the axon enlarges, in the pathogenesis of these aberrant electrical interactions.

Distribution of neurofilament antigens after axonal injury

Phosphorylated and nonphosphorylated epitopes of neurofilament (NF) proteins are distributed in different regions of individual neurons. Immunocytochemical methods, with monoclonal antibodies directed against phosphorylated and nonphosphorylated NF, demonstrated nonphosphorylated NF in perikarya and proximal axonal segments of neurons in dorsal root ganglia, while phosphorylated NF proteins were present in axons of these cells. The distribution of these epitopes of NF were examined at various times following injury of axons in the rat sciatic nerve. Between one and 21 days after crush of the proximal nerve, phosphorylated NF were present in neuronal perikarya. We have compared patterns of perikaryal immunoreactivity at one time point (three weeks) following a more distal crush or complete transection of the sciatic nerve. At this time period, following transection/ligation, phosphorylated NF immunoreactivity was not present in perikarya, but abnormal staining was observed after nerve crush. These altered distributions of phosphorylated epitopes of NF are of interest because several recent reports have indicated that similar, but not identical, abnormal staining patterns occur in human neurological diseases, including Alzheimer's disease and Parkinson's disease. In accord with previous studies, this investigation indicates that one response of neurons to injury, or to disease, is an abnormal distribution of phosphorylated epitopes of NF proteins.

Schwann cell proliferation and migration during paranodal demyelination

This study examined Schwann cell behavior during paranodal demyelination induced by beta,beta'-iminodipropionitrile (IDPN). The stimuli for Schwann cell proliferation, extensively studied in vitro, are less well understood in vivo. Most in vivo systems previously used to examine Schwann cell proliferation in disease are dominated by loss of internodal myelin sheaths. As used in this study, IDPN administration produces neurofilamentous axonal swellings and paranodal demyelination, without segmental demyelination or fiber degeneration. We asked whether Schwann cells would proliferate following the restricted paranodal demyelination that accompanies the axonal swellings, and if so what the sources and distributions of new Schwann cells might be. IDPN was given as a single large dose (2 ml/kg) to 21-d-old rats. Neurofilamentous axonal swellings formed in the proximal regions of motor axons, reaching their greatest enlargement in the root exit zone 8 d after IDPN administration. These swellings subsequently migrated distally down the nerves at rates approaching 1 mm/d. The axonal enlargement was consistently associated with displacement of the myelin sheath attachment sites into internodal regions, and consequent paranodal demyelination. This stage was associated with perikaryal changes, including nucleolar enlargement, "girdling" of the perikaryon, and formation of attenuated stalks separating the perinuclear region from the external cytoplasmic collar. Schwann cells proliferated abundantly during this stage. Daughter Schwann cells migrated within the endoneurial space (outside the nerve fiber basal laminae) to overlie the demyelinated paranodes of swollen nerve fibers. In these regions, local proliferation of Schwann cells continued, resulting in large paranodal clusters of Schwann cells. As the axonal calibers subsequently returned to normal, the outermost myelin lamellae of the original internodes returned to their paranodal attachment sites and the supernumerary Schwann cells disappeared. Formation of short internodes, segmental demyelination, and nerve fiber loss were rare phenomena. These results indicate that paranodal demyelination is a sufficient stimulus to excite abundant Schwann cell proliferation; neither internodal demyelination nor myelin breakdown is a necessary stimulus for mitosis. The 3H-thymidine incorporation studies indicated that the sources of new Schwann cells included markedly increased division of the Schwann cells of unmyelinated fibers and, as they formed, supernumerary Schwann cells. In addition, there were rare examples of 3H-thymidine incorporation by Schwann cells associated with myelinated nerve fibers.(ABSTRACT TRUNCATED AT 400 WORDS)

Sulbactam/ampicillin vs. chloramphenicol/ampicillin for the treatment of meningitis in infants and children

Eighty-one patients ages one month to 14 years with meningitis were randomized to receive either sulbactam (50 mg/kg per day) and ampicillin (400 mg/kg per day; 41 patients) or chloramphenicol and ampicillin (40 patients). The groups were comparable in terms of sex and degree of illness; however, more patients treated with chloramphenicol/ampicillin than patients treated with sulbactam/ampicillin were younger than 12 months of age (78% vs. 56%). Pathogens were isolated from the cerebrospinal fluid (CSF) of 65 (80%) of the 81 patients. In the sulbactam/ampicillin group, there were 18 Haemophilus influenzae isolates (one resistant to ampicillin), five Streptococcus pneumoniae, five Neisseria meningitidis, one Klebsiella pneumoniae, one Pseudomonas aeruginosa, and one Listeria. In the chloramphenicol/ampicillin group, there were 19 H. influenzae isolates, 10 S. pneumoniae, three N. meningitidis, one Haemophilus parainfluenzae, and one Citrobacter. Of 63 patients with assessable CSF pathogens, one (3%) of 29 treated with sulbactam/ampicillin died (S. pneumoniae) and six (18%) of 34 treated with chloramphenicol/ampicillin died (two, H. influenzae; three, S. pneumoniae; and one, Citrobacter). Twelve percent in the sulbactam/ampicillin group and 18% in the chloramphenicol/ampicillin group had neurologic sequelae. No clinically significant reactions or toxicities were noted. Sulbactam/ampicillin was as effective as chloramphenicol/ampicillin in the treatment of meningitis.

Ceftazidime vs. standard therapy for pediatric meningitis: therapeutic, pharmacologic and epidemiologic observations

One hundred patients ages 1 month to 15 years received either ceftazidime (CZ) at a dose of 150 mg/kg/day divided every 8 hours or conventional treatment with chloramphenicol and ampicillin (CA). Seventy-eight had isolates recovered from the cerebrospinal fluid: 40 (51%) were Haemophilus influenzae (all ampicillin-susceptible); 16 (21%) were Streptococcus pneumoniae; 14 (18%) were Neisseria meningitidis; 3 (4%) were salmonellae; 1 (2%) was Pseudomonas; and 1 (2%) was Group B Streptococcus. Six patients with negative cerebrospinal fluid culture had positive latex agglutination (two H. influenzae, three N. meningitidis, one S. pneumoniae). Sixty-one patients had positive blood cultures. CZ inhibited 100% of H. influenzae at 0.78 micrograms/ml, S. pneumoniae at 0.39, N. meningitidis at 0.04 and salmonellae at 0.39 micrograms/ml. The mean peak serum concentration of CZ was 36.4 micrograms/ml with a mean cerebrospinal fluid level of 7.4 micrograms/ml. If one eliminates from the statistics those patients who died less than or equal to 24 hours after admission, five (10%) of 49 patients treated with CZ died, one (2%) improved and 43 (88%) were cured. Overall 29 patients died, 12 receiving CZ (20%) and 8 receiving CA (21%). There were no significant CZ-related toxicities. Gross neurologic sequelae were noted in 5% of 38 CZ patients and 4% of 28 CA patients. CZ compared favorably to CA for treatment of meningitis.

Structural correlates of physiological abnormalities in beta, beta'-iminodipropionitrile

beta, beta'-Iminodipropionitrile (IDPN) produces neurofilamentous giant axonal swellings in proximal internodes of large myelinated axons. Secondary demyelinative changes result from the production of these axonal enlargements. Electrophysiological studies have demonstrated profound alterations in the electrical properties of motor neurons (MN) within the spinal cord. On the basis of intracellular recordings, it has been suggested that electrical contacts may exist between swollen axons and neighboring MN. In addition, the possibility remained that synaptic contacts develop on demyelinated axonal swellings. In the present study, we report the lack of either synapses on demyelinated axonal swellings or direct electrical contacts between neighboring MN. Axonal swellings are surrounded by attenuated processes of glial cells (probably fibrillary astrocytes), a finding discussed in terms of its possible role in the production of ephaptic transmission. There was considerable variation in the degree of axonal enlargements and in the extent of secondary (passive and active) demyelination. It is suggested that these morphological changes may represent structural correlates of some electrophysiological alterations observed in IDPN neuropathy.

Slowing of neurofilament transport and the radial growth of developing nerve fibers

Several lines of evidence indicate that neurofilaments are major intrinsic determinants of axonal caliber in myelinated nerve fibers, and that the delivery of neurofilaments by slow axonal transport is an important mechanism by which neurons regulate axonal caliber. To further clarify the relationship between neurofilament transport and axonal caliber, we examined transport in developing motor fibers of rat sciatic nerve. In 3-, 10-, 12-, and 20-week-old rats, lumbar motor neurons were labeled by the intraspinal injection of radioactive amino acids, and the distributions of labeled cytoskeletal proteins within the sciatic nerve were analyzed at various times afterwards using sodium dodecyl sulfate-polyacrylamide gel electrophoresis, gel fluorography, and liquid scintillation spectroscopy. There was a progressive decline in the velocity of neurofilament transport with increasing distance along axons undergoing radial growth. By examining transport in different regions of the nerve in animals of the same age, we separated age-dependent reductions in velocity from those related to position along the nerve. The cross-sectional areas of these motor axons (in the L5 ventral root) increased linearly between 3 and 18 weeks of age. Quantitative electron microscopic analysis at 3 and 10 weeks of age revealed that neurofilament density was comparable in fibers of all calibers, indicating that the radial growth of these myelinated nerve fibers correlates with a proportional increase in neurofilament content. We propose that progressive reduction in the velocity of neurofilament transport along the nerve provides for radial growth during development.

Slow axonal transport in acrylamide neuropathy: different abnormalities produced by single-dose and continuous administration

Alterations in axonal caliber and neurofilament content have been associated with altered neurofilament transport in several models of neurofibrillary degeneration. Acrylamide intoxication provides a prototype of distal axonal degeneration, the most frequent pattern of axonal pathology in human and experimental neurotoxic injury. Neurofibrillary changes are a variable and often minor aspect of the early pathological changes observed in acrylamide intoxication, and previous studies of slow axonal transport have produced conflicting results. In this study, we have correlated slow axonal transport, specifically neurofilament transport, with structural changes in the sciatic nerve complex of rats exposed to acrylamide. To study direct toxic effects of acrylamide, young rats were given a single dose of acrylamide (75 mg/kg, i.p.). A second group received daily injections of acrylamide at a lower dose (30 mg/kg, i.p.) in order to study animals with established acrylamide neuropathy. The slow component of axonal transport was labeled by intraspinal injections of [35S] methionine. Transport of individual slow component polypeptides was compared to profiles obtained from age-matched controls. Similarly intoxicated rats were perfused for morphometric and morphological studies. Results demonstrate that two different abnormalities of the slow component of axonal transport arise at different stages during the development of experimental acrylamide neuropathy. Both patterns of altered transport have structural correlates which reflect the changes in neurofilament transport. Following a single high dose, there was a modest retardation of the leading edge of the slow component. At this time, neurofilaments accumulated in proximal axons with formation of axonal swellings. During chronic administration, when distal axonal degeneration was present, the proportion of neurofilaments in the slow component was markedly reduced, and there was prominent loss of caliber in proximal axons. We suggest that these early changes represent a direct toxic effect of acrylamide on slow transport, whereas the later changes reflect reordering of slow transport as a neuronal response to toxin-induced axonal injury. This latter effect is of sufficient magnitude to obscure the acrylamide-induced retardation of slow transport.

Electrophysiological investigation of beta,beta'-iminodipropionitrile neuropathy: intracellular recordings in spinal cord

beta,beta'-Iminodipropionitrile (IDPN) was given to cats (50 mg/kg/week for 5 weeks) to induce giant axonal swellings in the proximal internodes of motor axons. Conventional intracellular recording techniques were used to investigate the influence of the axon swellings on axonal impulse conduction and generation of action potentials in unidentified lumbosacral motoneurons (MN). Action potentials recorded from axon swellings, verified by lack of orthodromically or antidromically elicited EPSPs or IPSPs, afterhyperpolarization potentials or initial segment-somaldendritic (IS-SD) inflections, were variable in shape. Some were indistinguishable from recordings in normal axons. Component or extra potentials occurred in 45% of recordings from axon swellings; their position on the action potential depended on the direction of impulse invasion into the swelling. Many action potentials were broad, with amplitudes less than 30 mV. Impulse conduction was estimated to be blocked in 19% of motor axons tested. Action potentials recorded in MN of IDPN treated cats resembled in many aspects those recorded in chromatolytic MN, with increased latencies upon antidromic stimulation and decreased IS conduction times and SD thresholds; other parameters did not differ significantly. The minimal interval between two stimuli which each evoked action potentials increased from 3.3 +/- 0.1 to 5.8 +/- 0.5 ms.(ABSTRACT TRUNCATED AT 250 WORDS)

IDPN neuropathy in the cat: coexistence of proximal and distal axonal swellings

Administration of beta,beta'-iminodipropionitrile (IDPN) to rodents has previously been shown to produce neurofilament-filled axonal swellings in the proximal regions of motor and sensory nerve fibers. Because of the distinctive distribution of these swellings, IDPN has been classed as a proximal axonopathy and thereby distinguished from other disorders in which similar axonal swellings occur in the distal parts of the axon (distal axonopathies). This report describes the pathology in the peripheral nerves of cats which received intermittent injections of IDPN and calls attention to two previously undescribed pathological changes. First, in addition to the typical proximal swellings associated with IDPN, these animals developed numerous axonal swellings within the distal branches of the sciatic nerve. Distal swellings were present as early as 23 days after initiation of intoxication, indicating that they formed locally (rather than developing in the proximal axon and undergoing transport into the distal regions). The second finding was Wallerian-like degeneration within the affected nerve branches. These changes in the distal sciatic nerve and its branches closely resembled the pathology of the distal axonopathies produced by agents such as the neurotoxic hexacarbons and carbon disulfide. The pathological similarities suggest that IDPN may share with these agents pathogenetic mechanisms to an extent not previously suspected.

Haemophilus influenzae biotype III infections in children and report of three unusual cases

Three hundred thirty seven Haemophilus influenza isolates from infections in children were studied to determine the relationship between H. influenza, biotype III, and specimen source. Eighteen per cent (60) of the isolates were H. influenza biotype III. Of these, 70% were from the eye, 18% from the respiratory tract, 7% from the ear and 2% from blood. Although conjunctivitis was the most common clinical condition associated with H. influenza biotype III, three cases of systemic infection with this organism are presented: a 10-month-old female with pneumonia, a 17-year-old male with sepsis, and a 7-year-old male with endophthalmitis. This organism may be a significant pathogen depending on the clinical setting. Increased awareness of its importance will lead to more reports of its isolation.