Putative neuropathological interactions in MSA: focus in the rostral ventrolateral medulla.

We used double immunocytochemistry for α-synuclein and markers of sympathoexcitatory neurons, oligodendrocytes, iron metabolism, and autophagy to study putative neuropathological interactions in multiple system atrophy. We focused in the rostral ventrolateral medulla as a prototype vulnerable region. We found that loss of C1 neurons and oligodendrocytes related to glial cytoplasmic inclusion accumulation, downregulation of iron transport, and upregulation of autophagy and ferritin expression in these area.

TDP-43 pathology occurs infrequently in multiple system atrophy.

AIMS AND METHODS: The α-synucleinopathy multiple system atrophy (MSA) and diseases defined by pathological 43-kDa transactive response DNA-binding protein (TDP-43) or fused in sarcoma (FUS) aggregates such as amyotrophic lateral sclerosis and frontotemporal lobar degeneration show overlapping clinico-pathological features. Consequently, we examined MSA for evidence of TDP-43 or FUS pathology utilizing immunohistochemical studies in autopsy material from 29 MSA patients. RESULTS: TDP-43 pathology was generally rare, and there were no FUS lesions. The TDP-43 lesions were located predominantly in medio-temporal lobe and subcortical brain areas and were comprised mainly of dystrophic processes and perivascular (and subpial) lesions. CONCLUSIONS: The multisystem clinical symptoms and signs of MSA, and in particular the neurobehavioural/cognitive and pyramidal features, appear not to result from concomitant TDP-43 or FUS pathology, but rather from widespread white matter α-synuclein positive glial cytoplasmic inclusions and neurodegeneration in keeping with a primary α-synuclein-mediated oligodendrogliopathy. The gliodegenerative disease MSA evidently results from different pathogenetic mechanisms than neurodegenerative diseases linked to pathological TDP-43.

Effects of glucagon-like peptide-1 and sympathetic stimulation on gastric accommodation in humans.

In humans, glucagon-like peptide-1 (GLP-1) delays gastric emptying by inhibiting vagal activity and also increases gastric volumes, by unclear mechanisms. Because GLP-1 inhibits intestinal motility by stimulating the sympathetic nervous system in rats, we assessed the effects of a GLP-1 agonist and yohimbine, an alpha(2)-adrenergic antagonist, on gastric volumes in humans. In this double-blind study, 32 healthy volunteers were randomized to placebo, a GLP-1 agonist, yohimbine or GLP-1 and yohimbine. Gastric volumes (fasting predrug and postdrug, and postprandial postdrug) were measured by (99m)Tc single photon emission computed tomography imaging. Plasma catecholamines and haemodynamic parameters were assessed. Compared with placebo, GLP-1 increased (P = 0.03) but yohimbine did not affect fasting gastric volume. However, GLP-1 plus yohimbine increased (P < 0.001) postprandial gastric accommodation vs placebo and vs GLP-1 alone [postprandial volume change = 542 +/- 29 mL (mean +/- SEM, placebo), 605 +/- 31 mL (GLP-1), 652 +/- 54 mL (yohimbine) and 810 +/- 37 mL (GLP-1 and yohimbine)]. Plasma noradrenaline and dihydroxyphenylglycol concentrations were higher for yohimbine vs placebo and for GLP-1 and yohimbine vs GLP-1. Yohimbine stimulates central sympathetic activity and in combination with GLP-1, augments postprandial accommodation in humans.

Progression of dysautonomia in multiple system atrophy: a prospective study of self-perceived impairment.

To assess severity and progression of self-perceived dysautonomia and their impact on health-related quality of life (Hr-QoL) in multiple system atrophy (MSA), twenty-seven patients were recruited by the European MSA Study Group (EMSA-SG). At baseline, all patients completed the Composite Autonomic Symptom Scale (COMPASS) and the 36 item Short Form Health Survey (SF-36), and they were assessed using the 3-point global disease severity scale (SS-3) and the Unified MSA Rating Scale (UMSARS). After 6 months follow-up, the self completed COMPASS Change Scale (CCS), the SF-36, SS-3, and UMSARS were obtained. MSA patients showed marked self-perceived dysautonomia at baseline visit and pronounced worsening of dysautonomia severity on the CCS at follow-up. Severity and progression of dysautonomia did not correlate with age, disease duration, motor impairment and overall disease severity at baseline. There were no significant differences between genders and motor subtypes. Baseline COMPASS scores were, however, inversely correlated with SF-36 scores. Progression of self-perceived dysautonomia did not correlate with global disease progression. Hr-QoL scores were stable during follow-up. This is the first study to investigate self-perceived dysautonomia severity in MSA and its evolution over time. Our data suggest that dysautonomia should be recognized as a key target for therapeutic intervention in MSA.

Effects of hemin on heme oxygenase-1, gastric emptying, and symptoms in diabetic gastroparesis.

BACKGROUND: Therapeutic options for management of diabetic gastroparesis are limited. Failure to maintain upregulation of heme oxygenase (HO1) leads to loss of interstitial cells of Cajal and delayed gastric emptying (GE) in non-obese diabetic mice. Our hypothesis was that hemin upregulation of HO1 would restore normal GE in humans with gastroparesis. AIMS: To compare effects of hemin and placebo infusions on HO1 activity and protein, GE, autonomic function, and gastrointestinal symptoms in diabetic gastroparesis. METHODS: In a single-center, double-blind, placebo-controlled, randomized clinical trial, we compared intravenous hemin, prepared in albumin, or albumin alone (placebo) in 20 patients, aged 41 ± 5 (SEM) years with diabetic gastroparesis. After infusions on days 1, 3, and 7, weekly infusions were administered for 7 additional weeks. Assessments included blood tests for HO1 protein and enzyme activity levels, GE with 13 C-spirulina breath test, autonomic functions (baseline and end), and gastrointestinal symptoms every 2 weeks. KEY RESULTS: Nine of 11 patients randomized to hemin completed all study procedures. Compared to placebo, hemin increased HO1 protein on days 3 (p = 0.0002) and 7 (p = 0.008) and HO1 activity on day 3 (p = 0.0003) but not after. Gastric emptying, autonomic functions, and symptoms did not differ significantly in the hemin group relative to placebo. CONCLUSIONS & INFERENCES: Hemin failed to sustain increased HO1 levels beyond a week and did not improve GE or symptoms in diabetic gastroparesis. Further studies are necessary to ascertain whether more frequent hemin infusions or other drugs would have a more sustained effect on HO1 and improve GE.

Structural specificity in demyelination induced by lysophospholipids.

The demyelinating activity of lysophosphatidylcholine (lysoPC) and various structural analogs in rat sciatic nerve was evaluated by following electrophysiologic changes within the first hour and 1 week after intraneural injection. The lysophospholipids tested included 1-O-hexadecanoyl-sn-glycero-3-phosphocholine (1-acyl-GPC), 3-O-hexadecanoyl-sn-glycero-1-phosphocholine (3-acyl-GPC), 1-O-hexadecanoylpropanediol-3-phosphocholine (acyl-PPC), 1-O-hexadecylpropanediol-3-phosphocholine (alkyl-PPC) and 1-acyl-sn-glycero-3-phosphoethanolamine (1-acyl-GPE). Changes in conduction velocity, width, amplitude and time integral percentage were measured. Within 1 hour, the highest demyelinating activity was observed for alkyl-PPC, followed by 3-acyl-GPC, 1-acyl-GPC and acyl-PPC. Hydrolysis products of lysoPC (glycerophosphocholine, fatty acid), lysophosphatidylethanolamine (1-acyl-GPE), biradyl choline phospholipids (1,2-di-O-alkyl-rac-glycero-3-phosphocholine, dialkyl-GPC) or sodium deoxycholate proved ineffective in these short-term experiments. One week after intraneural injection, all lysophospholipids tested caused severe electrophysiologic changes, although dialkyl-GPC and sodium deoxycholate did not. Our data suggest (i) that differences in early demyelinating activity by the choline lysophospholipids are related to their rate of turnover, as highest activity was associated with the agents that are not metabolized by lysophospholipase (e.g., alkyl-PPC) or lysolecithin acyltransferase (e.g., 3-acyl-GPC), (ii) that the lysoPC molecule as such and not its products of catabolism causes demyelination, and (iii) that demyelinating activity is not due to the general detergent action of lysoPC, but rather that specific interactions appear to trigger the processes of demyelination induced by lysophospholipids.

Oxygen free radical effects in sciatic nerve in experimental diabetes.

We previously reported the presence of endoneurial hypoxia, ischemia, impairment of the blood-nerve barrier, and reduction of norepinephrine and 6-ketoprostaglandin F1 alpha in chronic streptozocin-induced diabetic neuropathy (SDN) and interpreted these findings as suggesting the involvement of oxygen free radicals (OFRs) but did not directly measure indices of OFR activity. In this study, we report on sciatic nerve conjugated dienes, hydroperoxides, norepinephrine, and malondialdehyde in SDN at 1, 4, and 12 mo in male Sprague-Dawley rats. Severe hyperglycemia was present throughout in diabetic rats. Conjugated dienes were consistently increased at all time points, hydroperoxides were consistently reduced, and malondialdehyde was not significantly different in diabetes compared with controls. These findings are consistent with increased OFR activity in experimental diabetes. It is necessary to monitor several indices of OFR activity in a metabolically active tissue such as the peripheral nerve.

The roles of oxidative stress and antioxidant treatment in experimental diabetic neuropathy.

Oxidative stress is present in the diabetic state. Our work has focused on its presence in peripheral nerves. Antioxidant enzymes are reduced in peripheral nerves and are further reduced in diabetic nerves. That lipid peroxidation will cause neuropathy is supported by evidence of the development of neuropathy de novo when normal nerves are rendered alpha-tocopherol deficient and by the augmentation of the conduction deficit in diabetic nerves subjected to this insult. Oxidative stress appears to be primarily due to the processes of nerve ischemia and hyperglycemia auto-oxidation. The indexes of oxidative stress include an increase in nerve, dorsal root, and sympathetic ganglia lipid hydroperoxides and conjugated dienes. The most reliable and sensitive index, however, is a reduction in reduced glutathione. Experimental diabetic neuropathy results in myelinopathy of dorsal roots and a vacuolar neuropathy of dorsal root ganglion. The vacuoles are mitochondrial; we posit that lipid peroxidation causes mitochondrial DNA mutations that increase reduced oxygen species, causing further damage to mitochondrial respiratory chain and function and resulting in a sensory neuropathy. Alpha-lipoic acid is a potent antioxidant that prevents lipid peroxidation in vitro and in vivo. We evaluated the efficacy of the drug in doses of 20, 50, and 100 mg/kg administered intraperitoneally in preventing the biochemical, electrophysiological, and nerve blood flow deficits in the peripheral nerves of experimental diabetic neuropathy. Alpha-lipoic acid dose- and time-dependently prevented the deficits in nerve conduction and nerve blood flow and biochemical abnormalities (reductions in reduced glutathione and lipid peroxidation). The nerve blood flow deficit was 50% (P < 0.001). Supplementation dose-dependently prevented the deficit; at the highest concentration, nerve blood flow was not different from that of control nerves. Digital nerve conduction underwent a dose-dependent improvement at 1 month (P < 0.05). By 3 months, all treated groups had lost their deficit. The antioxidant drug is potentially efficacious for human diabetic sensory neuropathy.

Alpha-lipoic acid: effect on glucose uptake, sorbitol pathway, and energy metabolism in experimental diabetic neuropathy.

The peripheral nerve of experimental diabetic neuropathy (EDN) is reported to be ischemic and hypoxic, with an increased dependence on anaerobic metabolism, requiring increased energy substrate stores. When glucose stores become reduced, fiber degeneration has been reported. We evaluated glucose uptake, nerve energy metabolism, the polyol pathway, and protein kinase C (PKC) activity in EDN induced by streptozotocin. Control and diabetic rats received lipoic acid (0, 10, 25, 50, 100 mg/kg). Duration of diabetes was 1 month, and alpha-lipoic acid was administered intraperitoneally 5 times per week for the final week of the experiment. Nerve glucose uptake was reduced to 60, s 37, and 30% of control values in the sciatic nerve, L5 dorsal root ganglion, and superior cervical ganglion (SCG), respectively, in rats with EDN. Alpha-lipoic acid supplementation had no effect on glucose uptake in normal nerves at any dose, but reversed the deficit in EDN, with a threshold between 10 and 25 mg/kg. Endoneurial glucose, fructose, sorbitol, and myo-inositol were measured in sciatic nerve. Alpha-lipoic acid had no significant effect on either energy metabolism or polyol pathway of normal nerves. In EDN, endoneurial glucose, fructose, and sorbitol were significantly increased, while myo-inositol was significantly reduced. Alpha-lipoic acid had a biphasic effect: it dose-dependently increased fructose, glucose, and sorbitol, peaking at 25 mg/kg, and then fell beyond that dose, and it dose-dependently increased myo-inositol. Sciatic nerve cytosolic PKC was increased in EDN. ATP, creatine phosphate, and lactate were measured in sciatic nerve and SCG. Alpha-lipoic acid prevented the reduction in SCG creatine phosphate. We conclude that glucose uptake is reduced in EDN and that this deficit is dose-dependently reversed by alpha-lipoic acid, a change associated with an improvement in peripheral nerve function.

Distinct hemodynamic profiles in patients with vasovagal syncope: a heterogeneous population.

OBJECTIVE: The objective was to investigate mechanisms of vasovagal syncope by identifying laboratory techniques that characterize cardiovascular profiles in patients with vasovagal syncope. BACKGROUND: The triggering mechanisms of vasovagal syncope are complex. The patient population is likely heterogeneous. We hypothesized that distinct hemodynamic profiles are definable with provocative maneuvers. METHODS: Three groups of subjects were matched for age and gender: 16 patients with a history of syncope and an inducible vasovagal response during passive tilt table testing (70 degrees, 45 min, group I), 16 with a history of syncope, negative passive tilt table testing but positive isoproterenol tilt table testing (0.05 microg/kg per min, 70 degrees, 10 min, group II), and 16 control subjects. Beat-to-beat hemodynamic functions were determined noninvasively by photo-plethysmography and impedance cardiography. RESULTS: At baseline, hemodynamic functions were not different among the three groups (supine). In response to tilt before any symptoms developed, total peripheral resistance decreased 9% +/- 14% in group I from baseline supine to tilt position but increased 27% +/- 18% in group II and 28% +/- 17% in controls (p < 0.001). Responses to isoproterenol were not significantly different between group II and controls in supine position. In response to tilt during isoproterenol infusion before any symptoms developed, total peripheral resistance decreased 24% +/- 20% in group II and increased 20% +/- 48% in controls (p = 0.002). CONCLUSIONS: Group I patients may have impaired ability to increase vascular resistance during orthostatic stress. The inability to overcome isoproterenol-induced vasodilatation during tilt is important in triggering a vasovagal response in group II patients. These data suggest that the population with vasovagal response is heterogeneous. Distinct hemodynamic profiles in response to various provocative maneuvers are definable with noninvasive, continuous monitoring techniques.

Adenosine: potential modulator for vasovagal syncope.

OBJECTIVES: This study examined the hypothesis that adenosine could provoke a vasovagal response in susceptible patients. Mechanisms of the vasovagal response were further explored by studying the adenosine-mediated reactions. BACKGROUND: Increased sympathetic activity is frequently observed before vasovagal syncope. Recent studies have demonstrated that adenosine, in addition to its direct bradycardiac and vasodilatory effects, can increase sympathetic discharge by activating cardiovascular afferent nerves. METHODS: The effects of adenosine and head-up tilt-table testing with or without isoproterenol were prospectively evaluated in 85 patients examined for syncope after negative results of electrophysiologic testing (51 men and 34 women, mean [+/- SD] age 61 +/- 17 years). Adenosine bolus injections of 6 mg and 12 mg were sequentially administered to patients in the upright position. The same protocol was implemented in 14 normal control subjects (7 men and 7 women, mean [+/- SD] age 38 +/- 10 years). RESULTS: Transient hypertension or tachycardia was observed in 57 (67%) and 20 (24%) patients after administration of 6 mg and 12 mg of adenosine, respectively, during the immediate phase (first 15 s), suggesting direct sympathetic activation. Hypotension and reflex tachycardia were observed in all patients during the delayed phase (15 to 60 s after adenosine injection), suggesting baroreceptor unloading. A vasovagal response was induced in 22 (26%) and 29 (34%) patients after adenosine administration and during tilt-table testing. Inducibility of a vasovagal response by these two methods was comparable (p = 0.12). Of the control subjects, one (7%) had a vasovagal response after adenosine administration and one (7%) had a positive response during tilt-table testing. CONCLUSIONS: These observations support the idea that adenosine is an endogenous modulator of the cardiac excitatory afferent nerves. Sympathetic activation by adenosine can be direct (i.e., cardiac excitatory afferent nerves) and indirect (i.e., vasodilation and reflex sympathetic activation). Adenosine could be an important modulator in triggering a vasovagal response in susceptible patients during examination for syncope.

Lipoic acid improves nerve blood flow, reduces oxidative stress, and improves distal nerve conduction in experimental diabetic neuropathy.

OBJECTIVE: To determine whether lipoic acid (LA) will reduce oxidative stress in diabetic peripheral nerves and improve neuropathy. RESEARCH DESIGN AND METHODS: We used the model of streptozotocin-induced diabetic neuropathy (SDN) and evaluated the efficacy of LA supplementation in improving nerve blood flow (NBF), electrophysiology, and indexes of oxidative stress in peripheral nerves affected by SDN, at 1 month after onset of diabetes and in age-matched control rats. LA, in doses of 20, 50, and 100 mg/kg, was administered intraperitoneally five times per week after onset of diabetes. RESULTS: NBF in SDN was reduced by 50%; LA did not affect the NBF of normal nerves but improved that of SDN in a dose-dependent manner. After 1 month of treatment, LA-supplemented rats (100 mg/kg) exhibited normal NBF. The most sensitive and reliable indicator of oxidative stress was reduction in reduced glutathione, which was significantly reduced in streptozotocin-induced diabetic and alpha-tocopherol-deficient nerves; it was improved in a dose-dependent manner in LA-supplemented rats. The conduction velocity of the digital nerve was reduced in SDN and was significantly improved by LA. CONCLUSIONS: These studies suggest that LA improves SDN, in significant part by reducing the effects of oxidative stress. The drug may have potential in the treatment of human diabetic neuropathy.

Disturbances of gastrointestinal transit and autonomic functions in postural orthostatic tachycardia syndrome.

BACKGROUND: Gastrointestinal symptoms are common in the postural orthostatic tachycardia syndrome (POTS). However, few studies have evaluated gastrointestinal transit in POTS. Our primary objectives were to evaluate gastrointestinal emptying and the relationship with autonomic dysfunctions in POTS. METHODS: We reviewed the complete medical records of all patients aged 18 years and older with POTS diagnosed by a standardized autonomic reflex screen who also had a scintigraphic assessment of gastrointestinal transit at Mayo Clinic Rochester between 1998 and 2012. Associations between specific gastric emptying and autonomic (i.e., cardiovagal, adrenergic, and sudomotor) disturbances were evaluated. KEY RESULTS: Among 163 patients (140 women, mean [± SEM] age 30 [± 1] years), 55 (34%) had normal, 30 (18%) had delayed, and 78 (48%) had rapid gastric emptying. Fifty-eight patients (36%) had clinical features of physical deconditioning, which was associated (p = 0.02) with rapid gastric emptying. Associations with delayed gastric emptying included vomiting, which was more common (p < 0.003), and anxiety or depression, which was less common (p = 0.02). The tilt-associated increase in heart rate and reduction in systolic BP at 1 min was associated (p < 0.05), being greater in patients with delayed gastric emptying. CONCLUSIONS & INFERENCES: Two-thirds of patients with POTS and GI symptoms had abnormal, most frequently rapid gastric emptying. Except for more severe adrenergic impairment in patients with delayed gastric emptying, the pattern of autonomic dysfunction did not discriminate among gastric emptying groups. Further studies are necessary to ascertain whether extravascular volume depletion and/or deconditioning contribute to POTS in patients with gastrointestinal symptoms.

Effect of neostigmine on gastroduodenal motility in patients with suspected gastrointestinal motility disorders.

BACKGROUND: Acetylcholinesterase inhibitors (ACIs), e.g., neostigmine, are known to increase upper and lower gastrointestinal (GI) motility and are used to treat acute colonic pseudoobstruction. However, their effects on gastroduodenal motility in humans are poorly understood. Our hypotheses were that, in patients with suspected GI motility disorders, neostigmine increases gastric and small intestinal motor activity, and these effects are greater in patients with cardiovagal neuropathy, reflecting denervation sensitivity. METHODS: In this open label study, the effects of neostigmine (1 mg intravenously) on gastroduodenal motor activity recorded with manometry were assessed in 28 patients with a suspected GI motility disorder. Cardiovagal function was assessed with the heart rate response to deep breathing and GI transit by scintigraphy. KEY RESULTS: The final diagnoses were gastroparesis (6 patients), gastroparesis with intestinal neuropathy (3 patients), intestinal neuropathy or pseudoobstruction (5 patients), functional dyspepsia (6 patients), chronic abdominal pain (3 patients), mechanical small intestinal obstruction (3 patients), and pelvic floor dysfunction (2 patients). Neostigmine increased both antral and intestinal phasic pressure activity (p < 0.001). Neostigmine increased antral and intestinal pressure activity in 81% and 50% of patients with reduced postprandial antral and intestinal contractile responses to meal, respectively. The antroduodenal pressure response to neostigmine was not higher in patients with cardiovagal dysfunction. CONCLUSIONS & INFERENCES: Neostigmine increased antral and intestinal motor activity in patients with hypomotility, including intestinal dysmotility. These responses to neostigmine were not greater in patients with cardiovagal dysfunction. The use of longer-acting ACIs for treating antroduodenal dysmotility warrant further study.

Splanchnic preganglionic neurons in man. III. Morphometry of myelinated fibers of rami communicantes.

The myelinated fiber (MF) composition of T6-T8 Rami Communicantes were obtained in 9 healthy persons of various ages. The textbook picture that distal rami (DR) contain all of the myelinated fibers and therefore are white, while proximal rami (PR) contain none of them and therefore are grey must be modified. We found that DR usually contained abundant MFs and that PR concordance was found between segmental numbers of intermediolateral nuclei cytons, ventral root small myelinated fibers (SMFs), and rami total small MFs to suggest that both rami probably contain the distal myelinated axons of preganglionic autonomic fibers. Finally, there was an attrition of total MFs of rami with age, similar to what we had previously found for ILC cytons and for root SMFs. The decrease in number of pre-ganglionic autonomic neurons with age is thought to be of sufficient magnitude to account for the dysautonomia of the elderly.

The number and sizes of reconstructed peripheral autonomic, sensory and motor neurons in a case or dysautonomia.

Motor, spinal ganglion, intermediolateral and sympathetic trunk neurons were reconstructed by morphometric sampling of their cell bodies at L5 and T7 segments and at various levels of spinal roots and peripheral nerves in a 31-year-old patient with dysautonomia and compared to reference cases. The patient had strikingly fewer intermediate motoneuron column neurons and intermediate ventral root axons (probably gamma motoneurons), spinal ganglion neurons, preganglionic autonomic neurons and sympathetic trunk neurons that did controls (approximately 10--30% of reference values). The striking agreement between selective absence of intermediate-diameter cytons (Ci) and of intermediate diameter myelinated fibers (Ai), which are thought to be gamma efferent, of L5 motoneuron columns provides further confirmation to our previous suggestion that the Ci peak of motoneuron columns are somas of gamma efferent neurons. The number and size of alpha motoneuron cell bodies and their proximal axons were like those of controls but their distal axons were probably atrophic. This finding probably explains the small reduction in maximum conduction velocity of motor nerve fibers found in this disorder. The brunt of the pathologic process in this disorder has been borne by intermediate and small neurons preferentially.

Effect of serum hyperosmolality on morphometry of healthy human sural nerve.

Fascicles of human sural nerve, fixed by immersion in isosmolar 2.5% glutaraldehyde solution and in isosmolar osmium tetroxide and embedded in epoxy, undergo a 10% shrinkage in area when compared with cryostal sections. By contrast, fascicles fixed in hyperosmolar solutions (whether 5.6% glutaraldehyde solution or 2.5% glutaraldehyde raised to the same level of hyperosmolality with sucrose) undergo a 43% shrinkage in area. Axis cylinders of myelinated fibers undergo a selective and severe shrinkage and assume noncircular shapes, the shapes allowing the transverse area to decrease when the perimeter remains unchanged. These studies raise the intriguing question of whether interstitial hyperosmolality in metabolic diseases, such as diabetes mellitus, or in uremia may cause osmotic axonal shrinkage, altered transverse fiber shape, and abnormality of function and structure of nerve.

Axonal caliber and neurofilaments are proportionately decreased in galactose neuropathy.

Feeding galactose to rats induces nerve conduction abnormalities, increased levels of nerve galactitol, endoneurial edema, elevated pressure and hypoxia of endoneurial fluid, and pathological abnormalities of nerve fibers. To investigate the cellular mechanisms of the fiber lesions and their possible relationship to alterations in the nerve microenvironment, rat peroneal nerves were morphometrically evaluated eight months after the commencement of galactose feeding. Whereas the density of neurofilaments (NF/micron2) in the transverse axonal area of myelinated fibers was not significantly different between the nerves of galactose-fed and control rats, axonal areas and the number of NF/axon, when related to myelin spiral length, were significantly less in nerves of galactose-fed rats. Myelin alterations, characteristic of axonal atrophy, were also significantly increased. The present data provide evidence of a proportionate decrease in axonal caliber and the number of NF/axon in myelinated fibers in experimental galactose neuropathy, suggesting that galactose induces fibers in experimental galactose neuropathy, suggesting that galactose induces either decreased NF synthesis, assembly or transport. The possible role of microenvironmental alterations, including endoneurial hypoxia and hyperosmolarity, in the production of this axonal atrophy is discussed.

Blood nerve barrier in rat and cellular mechanisms of lead-induced segmental demyelination.

Feeding of lead carbonate to rats causes widespread and reproducible segmental de- and remyelination of myelinated fibers (MFs) of peripheral nerve. Such segmental demyelination might be explained by increased permeability of endoneurial capillaries to serum containing protein-bound lead. The perineurium of control and lead nerves was impermeable to fluorescein-labeled bovine albumin (FBA) and to horseradish peroxidase (HRP). Epineurial capillaries in both conditions allowed HRP to pass freely between and, to a lesser extent, through endothelial cells. Confirming earlier work, endoneurial capillaries of control rats did not appear to allow HRP to pass between endothelial cells, but allowed some to pass by pinocytosis through endothelial cells where it was taken up by macrophages. Contrary to expectation, flooding of the endoneurium with HRP was seen in only 1 of 36 tissue blocks of lead nerves from rats fed 4% lead carbonate for 7 1/2 and 12 weeks. Abundant HRP reaction product was seen in the epineurium in more than half of these tissue blocks. HRP was not generally found in endoneurial fluid, even in lead nerves with marked edema and widespread segmental de- and remyelination. These findings are against a massive breakdown of the blood nerve barrier, so that HRP passes freely into the endoneurium between endoneurial endothelial cells. It was our impression that HRP reaction product was slightly increased in endoneurial endothelial cells and macrophages of lead nerves as compared to control nerves. These studies suggest that there may be an increased transfer of HRP through endoneurial cells in lead neuropathy. The studies do not provide additional evidence that an altered blood nerve barrier is involved in the development of segmental demyelination in lead neuropathy.