Compositional analysis of mixed-cation-anion III-V semiconductor interfaces using phase retrieval high-resolution transmission electron microscopy.

Employing exit-plane wave function (EPWF) reconstruction in high-resolution transmission electron microscopy (HRTEM), we have developed an approach to atomic scale compositional analysis of III-V semiconductor interfaces, especially suitable for analyzing quaternary heterostructures with intermixing in both cation and anion sub-lattices. Specifically, we use the focal-series reconstruction technique, which retrieves the complex-valued EPWF from a thru-focus series of HRTEM images. A study of interfaces in Al(0.4)Ga(0.6)As-GaAs and In(0.25)Ga(0.75)Sb-InAs heterostructures using focal-series reconstruction shows that change in chemical composition along individual atomic columns across an interface is discernible in the phase image of the reconstructed EPWF. To extract the interface composition profiles along the cation and anion sub-lattices, quantitative analysis of the phase image is performed using factorial analysis of correspondence. This enabled independent quantification of changes in the In-Ga and As-Sb contents across ultra-thin interfacial regions (approximately 0.6 nm wide) with true atomic resolution, in the In(0.25)Ga(0.75)Sb-InAs heterostructure. The validity of the method is demonstrated by analyzing simulated HRTEM images of an InAs-GaSb-InAs model structure with abrupt and graded interfaces. Our approach is general, permitting atomic-level compositional analysis of heterostructures with two species per sub-lattice, hitherto unfeasible with existing HRTEM methods.

Effect of aminoguanidine on the frequency of neuroaxonal dystrophy in the superior mesenteric sympathetic autonomic ganglia of rats with streptozocin-induced diabetes.

Aminoguanidine, which prevents formation of advanced glycation end products and is a relatively selective potent inhibitor of the inducible (versus constitutive) isoform(s) of nitric oxide synthase, has been reported to ameliorate structural and functional abnormalities in peripheral somatic nerves in rats with streptozocin (STZ)-induced diabetes. In the present studies, the effects of aminoguanidine treatment on ultrastructural changes in the autonomic nervous system of rats with STZ-induced diabetes were examined. The frequency of neuroaxonal dystrophy, the neuropathological hallmark of sympathetic autonomic neuropathy in diabetic rats, increased 9- to 11-fold in the superior mesenteric ganglia of 7- and 10-month STZ-diabetic rats compared with that in age-matched controls. Administration of aminoguanidine continuously from the time of induction of diabetes at a dose equal to or in excess of that providing a salutary effect in the diabetic somatic peripheral nervous system did not alter the severity of diabetes as assessed by plasma glucose level, 24-h urine volume, and levels of glycated hemoglobin. Chronic aminoguanidine therapy did not diminish the frequency or affect the ultrastructural appearance of neuroaxonal dystrophy in diabetic or age-matched control rat sympathetic ganglia after 7 or 10 months of continuous administration. Our findings (under these experimental conditions) do not support a role for aminoguanidine-sensitive processes in the development of sympathetic neuroaxonal dystrophy in diabetic rats. Glycation-linked aminoguanidine-insensitive processes, however, such as the formation of early glucose adducts (Schiff bases and Amadori products) with intracellular and/or extracellular proteins and amine-containing lipids, superoxide anion generation during subsequent autoxidation of these glucose adducts, and non-glycative processes, remain potential pathogenetic mechanisms for diabetic autonomic neuropathy.

Effect of NGF and neurotrophin-3 treatment on experimental diabetic autonomic neuropathy.

Peripheral neuropathy is a significant complication of diabetes resulting in increased patient morbidity and mortality. Deficiencies of neurotrophic substances (e.g. NGE NT-3, and IGF-I) have been proposed as pathogenetic mechanisms in the development of distal symmetrical sensory diabetic polyneuropathy, and salutary effects of exogenous NGF administration have been reported in animal models. In comparison, relatively little is known concerning the effect of NGF on experimental diabetic sympathetic autonomic neuropathy. We have developed an experimental animal model of diabetic autonomic neuropathy characterized by the regular occurrence of pathologically distinctive dystrophic axons in prevertebral sympathetic ganglia and ileal mesenteric nerves of rats with chronic streptozotocin (STZ)-induced diabetes. Treatment of STZ-diabetic rats for 2-3 months with pharmacologic doses of NGF or NT-3, neurotrophic substances with known effects on the adult sympathetic nervous system, did not normalize established neuroaxonal dystrophy (NAD) in diabetic rats in the prevertebral superior mesenteric ganglia (SMG) and ileal mesenteric nerves as had pancreatic islet transplantation and IGF-I in earlier experiments. NGF treatment of control animals actually increased the frequency of NAD in the SMG. New data suggests that, in adult sympathetic ganglia. NGF may contribute to the pathogenesis of NAD rather than its amelioration, perhaps as the result of inducing intraganglionic axonal sprouts in which dystrophic changes are superimposed. NT-3 administration did not alter the frequency of NAD in diabetic animals, although it resulted in a significant decrease in NAD in control SMG. Although deficiencies of neurotrophic substances may represent the underlying pathogenesis of a variety of experimental neuropathies, delivery of excessive levels of selected substances may produce untoward effects.

Neurotrophin sensitivity of prevertebral and paravertebral rat sympathetic autonomic ganglia.

Prevertebral and paravertebral sympathetic autonomic ganglia respond differently to a large number of experimental and clinical insults. The selective involvement of subpopulations of sympathetic neurons may reflect differences in their response to neurotrophic substances. To test this hypothesis, we investigated the response of prevertebral and paravertebral rat sympathetic ganglia to selected neurotrophic substances in vivo and in vitro and identified the ganglionic distribution of neurons expressing high affinity neurotrophin receptor mRNAs. Dissociated cultures of embryonic prevertebral and paravertebral ganglionic neurons showed comparable responses to NGF deprivation and only small differences in their response to rescue with other trophic substances. In situ hybridization studies of adult rat sympathetic ganglia using probes specific for the high-affinity neurotrophin receptor transcripts trks A, B, and C demonstrated that neurons in both prevertebral and paravertebral sympathetic ganglia express predominantly trkA receptors in vivo. In addition, increased tyrosine hydroxylase (TOH) activity was induced only by doses of neurotrophic substances that activate trkA and showed only small differences between neonatal prevertebral and paravertebral ganglia. Although small differences in the sensitivity of pre- and paravertebral sympathetic neurons to various neurotrophins have been identified in our studies, they are unlikely, in isolation, to explain major differences in the sensitivity of these ganglia to neuropathologic processes.

Dystrophic axonal swellings develop as a function of age and diabetes in human dorsal root ganglia.

Neuroaxonal dystrophy, characterized by swollen axon terminals and, to a lesser degree, enlarged initial segments of axons or perikaryal projections, develops in human dorsal root sensory ganglia as a function of aging and diabetes. Lesions are typically located within the satellite cell capsule and are intimately applied to sensory neuronal perikarya, which are compressed and distorted but are otherwise normal. Swollen axons contain large numbers of neurofilaments that are immunoreactive with antisera to highly phosphorylated neurofilament epitopes but fail to stain with antisera directed against hypophosphorylated neurofilament epitopes. Other dystrophic swellings contain collections of tubulovesicular profiles admixed with neurotransmitter granules. Neuroaxonal dystrophy involves subpopulations of intraganglionic axons and apparent terminals, notably those containing CGRP, while apparently sparing others, including noradrenergic sympathetic axons. Diabetic subjects develop lesions prematurely and in greater numbers than in aged subjects. Individual dystrophic axons in diabetics and aged human subjects are identical in their light microscopic, immunohistochemical and ultrastructural appearance, suggesting the possibility of shared pathogenetic mechanisms.

Effect of sorbitol dehydrogenase inhibition on experimental diabetic autonomic neuropathy.

The polyol pathway and its dependent biochemical pathways are thought to play a role in the pathogenesis of diabetic neuropathy. We have developed an animal model of diabetic autonomic neuropathy characterized by neuroaxonal dystrophy involving ileal mesenteric nerves and prevertebral sympathetic superior mesenteric ganglia (SMG) in chronic streptozocin-diabetic rats. Our previous studies have shown a salutary effect of aldose reductase inhibitors on experimental autonomic neuropathy, suggesting a role for the polyol pathway in its pathogenesis. In the current studies we have examined the effect of the sorbitol dehydrogenase inhibitor (SDI) CP-166,572, which interrupts the conversion of sorbitol to fructose (and reactions dependent on the second step of the polyol pathway) resulting in markedly increased levels of sorbitol in peripheral nerve. Fourteen weeks of treatment with CP-166,572 resulted in a dramatically increased frequency of neuroaxonal dystrophy in ileal mesenteric nerves and SMG. Although lesions developed prematurely and in greater numbers in SDI-treated diabetics than untreated diabetics did, their anatomic distribution and ultrastructural appearance were identical to that previously reported in long-term untreated diabetics. CP-166,572 treatment did not produce neuroaxonal dystrophy in control animals despite the fact that sciatic nerve sorbitol levels were markedly increased, reaching the same levels as untreated diabetic animals. Treatment of diabetic rats for 14 weeks with the aldose reductase inhibitor zopolrestat resulted in a significant decrease in the frequency of neuroaxonal dystrophy compared with untreated diabetics.

Inhibition of sorbitol dehydrogenase exacerbates autonomic neuropathy in rats with streptozotocin-induced diabetes.

We have developed an animal model of diabetic autonomic neuropathy that is characterized by neuroaxonal dystrophy (NAD) involving ileal mesenteric nerves and prevertebral sympathetic superior mesenteric ganglia (SMG) in chronic streptozotocin (STZ)-diabetic rats. Studies with the sorbitol dehydrogenase inhibitor SDI-158, which interrupts the conversion of sorbitol to fructose (and reactions dependent on the second step of the sorbitol pathway), have shown a dramatically increased frequency of NAD in ileal mesenteric nerves and SMG of SDI-treated versus untreated diabetics. Although lesions developed prematurely and in greater numbers in SDI-treated diabetics, their distinctive ultrastructural appearance was identical to that previously reported in long-term untreated diabetics. An SDI effect was first demonstrated in the SMG of rats that were diabetic for as little as 5 wk and was maintained for at least 7.5 months. As in untreated diabetic rats, rats treated with SDI i) showed involvement of lengthy ileal, but not shorter, jejunal mesenteric nerves; ii) demonstrated NAD in paravascular mesenteric nerves distributed to myenteric ganglia while sparing adjacent perivascular axons ramifying within the vascular adventitia; and, iii) failed to develop NAD in the superior cervical ganglia (SCG). After only 2 months of SDI-treatment, tyrosine hydroxylase immunolocalization demonstrated marked dilatation of postganglionic noradrenergic axons in paravascular ileal mesenteric nerves and within the gut wall versus those innervating extramural mesenteric vasculature. The effect of SDI on diabetic NAD in SMG was completely prevented by concomitant administration of the aldose reductase inhibitor Sorbinil. Treatment of diabetic rats with Sorbinil also prevented NAD in diabetic rats not treated with SDI. These findings indicate that sorbitol pathway-linked metabolic imbalances play a critical role in the development of NAD in this model of diabetic sympathetic autonomic neuropathy.

PET and P300 relationships in early Alzheimer's disease.

The P300 (P3) wave of the auditory brain event-related potential was investigated in patients with probable Alzheimer's disease to determine whether P300 latency discriminated these patients from controls and whether prolonged P300 latency correlated with rates of brain glucose metabolism as measured by Positron Emission Tomography. P300 latency was prolonged by more than 1.5 standard deviations from age expectancy in 14 of 18 patients, but none of 17 controls. In these subjects P300 latency was shown to be inversely correlated with relative metabolic rates of parietal and, to a lesser extent, temporal and frontal association areas, but not with subcortical areas.

Memory self-appraisal in middle-aged and older adults with the apolipoprotein E-4 allele.

OBJECTIVE: Because subjective memory complaints may indicate subtle functional brain abnormalities, the authors studied the influence of the major genetic risk for Alzheimer's disease, the apolipoprotein E-4 (APOE-4) allele, on self-reports of memory performance in middle-aged and older adults. METHOD: Subjective and objective assessments of memory performance were compared in relation to the presence or absence of the APOE-4 allele in 39 cognitively intact persons with mild memory complaints. RESULTS: Subjects with the APOE-4 allele had lower scores on objective verbal memory and on the subjective memory measure for retrospective functioning. Among the subjects in the age range where APOE-4 has its greatest influence on the risk of Alzheimer's disease (55-74 years), the APOE-4 group had lower scores on the subjective memory measure for frequency of forgetting. Moreover, the standardized difference in retrospective functioning scores between the two genetic risk groups increased when the mid-age-range group was examined rather than the whole study group. CONCLUSIONS: The APOE-4 allele is associated with increased subjective memory impairment in middle-aged and older adults. Longitudinal studies of age-related memory loss should include genetic risk and subjective memory measures as potential predictors of decline.

Value of intraoperative left ventricular microbubbles detected by transesophageal two-dimensional echocardiography in predicting neurologic outcome after cardiac operations.

To determine whether the presence or absence of left ventricular (LV) intracavitary microbubbles during cardiac surgery predicts neurologic sequelae, 82 patients undergoing cardiac surgery were studied using transesophageal 2-dimensional (2-D) echocardiography. Cross-sectional images were recorded just before and immediately after cardiopulmonary bypass and stop frames were reviewed for the presence of microbubbles, rated as: 0 = absent, 1 = fewer than 5/frame, 2 = 10 to 25/frame, 3 = too numerous to count. Microbubbles were detected after cardiopulmonary bypass in 34 patients (41%) and found more often in valvular or other intracardiac manipulations than in coronary revascularization, 30 of 40 vs 4 of 42, respectively (p less than 0.001). When grade 2 or 3 microbubbles were identified (22 of 34 patients), mechanical attempts to eradicate them were not successful. Postoperative follow-up in all patients revealed no new focal neurologic deficits. Prolonged encephalopathy (confusional state more than 72 hours) occurred in 4 of 48 patients with no detectable microbubbles and in 3 of 34 patients with microbubbles (difference not significant). Thus, intracavitary left ventricular microbubbles are often detected during cardiac operations, particularly during valve replacement, but are not predictive of postoperative neurologic complications. This is true even if microbubbles are densely concentrated; attempts to eradicate microbubbles are unsuccessful and may be unnecessary.

Laboratory studies of transovarial transmission of trivittatus virus by Aedes trivittatus.

Aedes trivittatus were experimentally exposed through a membrane to a concentration of trivittatus (TVT) virus in dog defibrinated blood of 10(3.4)-10(3.5) SMICLD 50/0.025 ml. Transovarial and transstadial transmission was demonstrated. Fifty-five percent of the infected mosquitoes tested transovarially transmitted TVT virus. TVT virus was isolated from 16% of the F1 generation progeny examined, including 19% of the larvae, 23% of adult females, and 10% of adult males.

Trivittatus virus infections in wild mammals and sentinel rabbits in central Iowa.

A serological survey was conducted in Iowa to determine the prevalence rate of California group virus antibodies in sera of several vertebrate species. Serum specimens were assayed for infectivity-neutralizing antibody in a microneutralization system with baby hamster kidney cell culture. Of 77 sera assayed, 21 (27%) neutralized trivittatus (TVT) virus infectivity. The antibody prevalence rate was highest for eastern cottontail rabbits inasmuch as 46% (10/22) of the serum specimens form this species possessed neutralizing activity. Other vertebrate species having TVT virus antibody included the fox squirrel, 29% (7/24), opossum, 12% (3/25), and raccoon, 17% (1/6). One cottontail rabbit serum neutralized both TVT virus and Jamestown Canyon (JC) virus infectivity, and one opossum serum specimen neutralized JC virus. None of the vertebrate sera neutralized La Crosse, St. Louis encephalitis, or western equine encephalomyelitis virus infectivity. Trivittatus virus neutralizing antibody was detected in the sera of sentinel rabbits, and TVT virus was isolated from the blood collected from one of these sentinels shortly after the first population peak of adult Aedes trivittatus mosquitoes in 1973. The implications of these data and the possibility of trans-ovarial transmission of TVT virus in A. trivittatus are discussed.

The significance of western equine encephalomyelitis viral infections in Aedes trivittatus (Diptera: Culicidae) in Iowa. I. Variation in susceptibility of Aedes trivittatus to experimental infection with three strains of western equine encephalomyelitis virus.

F1 pregnancy obtained from field-collected Aedes trivittatus were evaluated for susceptibility to infection with western equine encephalomyelitis (WEE) virus by intrathoracic inoculation and by oral imbibition of virus-blood suspensions through a membrane. Mosquitoes were uniformly susceptible to infection by intrathoracic inoculation of three strains of WEE virus, but minimum infective doses varied as much as 2,000 to 12,000-fold between strains by membrane feeding. Dose-response data obtained by membrane feeding also indicated that field strains of A. trivittatus were quite heterogeneous in their susceptibility to WEE virus since some individual mosquitoes could be infected by ingestion of low virus concentrations while others could not be infected by a 20,000-fold increase in virus concentration. Moreover, A. trivittatus showed a greater affinity for a WEE viral strain isolated from this species than for a WEE viral strain isolated from Culex tarsalis, even though the site, date of collection, and passage history of these isolates were identical. Field strains of A. trivittatus were relatively refractory to oral infection with WEE virus.

Immunohistochemical characterization of NPY and substance P containing nerve terminals in aged and diabetic human sympathetic ganglia.

To compare the neuropeptide specificity of dystrophic axon formation in aging versus diabetic human sympathetic ganglia we have immunohistochemically characterized neuropeptide Y (NPY) and substance P containing intraganglionic nerve terminals. Prevertebral superior mesenteric but not paravertebral superior cervical ganglia developed markedly swollen NPY containing axonal termini with both aging and diabetes. Substance P containing nerve terminals failed to develop dystrophic changes. Selective loss of classes of nerve terminals may result in discrete functional sequellae.

Axonal cytoskeletal pathology in aged and diabetic human sympathetic autonomic ganglia.

Prevertebral sympathetic ganglia develop markedly enlarged argyrophilic neurites as a function of age, gender and diabetes. Immunolocalization studies demonstrate their preferential labeling with antisera to highly phosphorylated 200 kDa neurofilament (NF-H) epitopes, NPY, peripherin and synapsin I, but not to hypophosphorylated NF-M and NF-H or MAP-2. The immunophenotype of dystrophic neurites in conjunction with the results of histochemical and ultrastructural studies are consistent with the terminal axonal and/or synaptic origin of neuritic dystrophy in the sympathetic ganglia of aged and diabetic human subjects.

Characterization of NADPH diaphorase activity in rat sympathetic autonomic ganglia--effect of diabetes and aging.

NADPH-diaphorase histochemistry, which identifies neural sites of nitric oxide production, demonstrated intensely stained nerve terminals surrounding the cell bodies of a subpopulation of neurons in rat prevertebral celiac and superior mesenteric sympathetic ganglia but failed to comparably label terminals in paravertebral superior cervical ganglia or perikarya in any sympathetic ganglion. The superior mesenteric ganglia of aged and diabetic rats, in which synaptic dysplasia (neuroaxonal dystrophy) is prominent, failed to show involvement of diaphorase containing nerve terminals.

Effect of streptozotocin-induced diabetes on NGF, P75(NTR) and TrkA content of prevertebral and paravertebral rat sympathetic ganglia.

Diabetic autonomic neuropathy results in significant morbidity and mortality. Both diabetic humans and experimental animals show neuroaxonal dystrophy of autonomic nerve terminals, particularly in the prevertebral superior mesenteric ganglia (SMG) and celiac ganglia (CG) which innervate the hyperplastic/hypertrophic diabetic small intestine. Previously, investigators suggested that disturbances in ganglionic nerve growth factor (NGF) content or transport might play a pathogenetic role in diabetic autonomic pathology. To test this hypothesis, we measured NGF content and NGF receptor expression, p75(NTR) (low affinity neurotrophin receptor) and trkA (high affinity NGF receptor), in control and diabetic rat SMG, CG and superior cervical ganglia (SCG). Surprisingly, rather than a decrease, we observed an approximate doubling of NGF content in the diabetic SMG and CG, a result which reflects increased NGF content in the hyperplastic diabetic alimentary tract. No change in NGF content was detected in the diabetic SCG which is relatively spared in experimental diabetic autonomic neuropathy. NGF receptor expression was not consistently altered in any of the autonomic ganglia. These observations suggest that increased NGF content in sympathetic ganglia innervating the diabetic alimentary tract coupled with intact receptor expression may produce aberrant axonal sprouting and neuroaxonal dystrophy.

Vacuolar neuritic dystrophy in aged mouse superior cervical sympathetic ganglia is strain-specific.

We have developed a model of autonomic nervous system aging using the mouse superior cervical sympathetic ganglion (SCG) which is characterized by the reproducible development of distinctive, markedly-enlarged neuritic swellings (vacuolar neuritic dystrophy, VND). These structures contained an admixture of lucent vacuoles and subcellular organelles, and involved both presynaptic and postsynaptic ganglionic elements. Quantitation of the frequency of VND was accomplished at the light microscopic level and validated by ultrastructural examination. VND lesions were 30-100-fold more frequent in the aged mouse paravertebral SCG than in the prevertebral celiac/superior mesenteric (C/SMG) sympathetic ganglia. Although VND was identified in all ages of mice examined, the number of lesions increased significantly with age. The frequency of VND was a function of the strain of mouse examined with a 40-fold difference in VND frequency between C57BL6 mice, the least involved strain, and the DBA/2J strain, which was most affected and began to develop significant numbers of lesions at an early age. As in our human studies of aging in the sympathetic nervous system, there was a prominent gender effect with males developing twofold greater numbers of VND lesions than females. Mice maintained on a significant calorie restricted diet for 30 months developed 70% fewer lesions than ad libitum-fed, age and sex matched controls. The aging mouse SCG, therefore, represents a robust animal model with reproducible, quantifiable and unambiguous neuropathology. Insights into pathogenetic mechanisms gained in the subsequent analysis of this relatively simple peripheral sympathetic nervous system model may contribute to the understanding of some of the most complex and significant problems involving higher brain function.

Effect of IGF-I and neurotrophin-3 on gracile neuroaxonal dystrophy in diabetic and aging rats.

Neuroaxonal dystrophy (NAD), a distinctive axonopathy characterized by dramatic swelling of preterminal axons and nerve terminals by the accumulation of a variety of subcellular organelles, develops in the central projections of sensory neurons to medullary gracile nuclei in aged animals and man, and in a number of diseases and experimental conditions. Although its pathogenesis is unknown, proposed mechanisms include abnormalities of axonal regeneration, collateral sprouting and synaptic plasticity which may reflect alteration in neurotrophic support. In the current study, we have demonstrated quantitatively that aging causes the expected marked increase in the frequency of gracile NAD; however, substantial numbers of dystrophic axons develop between 6 and 10 months of age, earlier than expected. Although diabetes has been reported to increase the frequency of NAD in the central processes of sensory neurons in the gracile fasciculus of genetically diabetic BB rats, we have found that 8-10 months of streptozotocin-induced diabetes results in fewer dystrophic axons in the gracile nucleus than in age-matched controls. Administration of neurotrophin-3 (NT-3) and insulin-like growth factor-I (IGF-I), which have been shown to affect synaptic plasticity (implicated in the pathogenesis of NAD), for the last two months before sacrifice did not affect the frequency of gracile NAD in controls or diabetics. The sensory terminals in the gracile nuclei provide a simple, well-characterized experimental system in which questions of pathogenesis and prevention of neuroaxonal dystrophy can be addressed.

Correlation of GAP-43 immunoreactivity with subpopulations of chromaffin cells in rat adrenal medulla.

The neuronal growth-associated protein (GAP-43) is widely expressed during embryonic growth and axonal regeneration and has been thought to contribute to synaptic plasticity in adult animals. In contrast to the exclusively presynaptic pattern of GAP-43 immunoreactivity in sympathetic ganglia, GAP-43 intensely and selectively labeled the noradrenergic subpopulation of adult rat adrenal medullary chromaffin cell bodies, a pattern which persisted with adrenal denervation. Adjacent adrenergic islands containing neuropeptide Y and phenylethanolamine-N-methyl transferase immunoreactivity failed to express GAP-43. The immunohistochemical appearance of GAP-43 was qualitatively unchanged in the adrenal medulla of aged and diabetic rats, conditions in which the sympathoadrenal axis is thought to be dysfunctional.