Effect of natural organic matter on iron uptake by the freshwater cyanobacterium Microcystis aeruginosa.

The mode of Fe uptake by the cyanobacterium Microcystis aeruginosa cultured in Fraquil* (pH 8) containing Suwannee River fulvic acid (SRFA) was examined using short-term radiolabeled (55)Fe uptake assays and a kinetic model that describes extracellular Fe transformations. Both Fe(II) and Fe(III) uptake rates decreased substantially with increasing SRFA concentration as the availability of unchelated Fe decreased due to complexation by SRFA. Fe uptake rates under illuminated conditions were comparable to or slightly higher than those observed in the dark at the same Fe:SRFA concentration ratio, in contrast to results for systems containing ethylenediaminetetraacetic acid where Fe uptake rates were much greater under illumination than in the dark. The limited effect of light principally resulted from the relatively high rates of thermal dissociation and dark reduction of Fe(III) bound to SRFA and complexation of photogenerated Fe(II) by SRFA. Our findings imply that Fe uptake by M. aeruginosa at a fixed total Fe concentration of 200 nM is close to saturation when fulvic acid is present at concentrations near those typically found in natural waters (< ∼5 mg·L(-1)), with cellular growth likely to be limited by Fe availability only when natural organic matter is present at very high concentrations (>25 mg·L(-1)).

Characteristics of the freshwater cyanobacterium Microcystis aeruginosa grown in iron-limited continuous culture.

A continuous culturing system (chemostat) made of metal-free materials was successfully developed and used to maintain Fe-limited cultures of Microcystis aeruginosa PCC7806 at nanomolar iron (Fe) concentrations (20 to 50 nM total Fe). EDTA was used to maintain Fe in solution, with bioavailable Fe controlled by absorption of light by the ferric EDTA complex and resultant reduction of Fe(III) to Fe(II). A kinetic model describing Fe transformations and biological uptake was applied to determine the biologically available form of Fe (i.e., unchelated ferrous iron) that is produced by photoreductive dissociation of the ferric EDTA complex. Prediction by chemostat theory modified to account for the light-mediated formation of bioavailable Fe rather than total Fe was in good agreement with growth characteristics of M. aeruginosa under Fe limitation. The cellular Fe quota increased with increasing dilution rates in a manner consistent with the Droop theory. Short-term Fe uptake assays using cells maintained at steady state indicated that M. aeruginosa cells vary their maximum Fe uptake rate (ρ(max)) depending on the degree of Fe stress. The rate of Fe uptake was lower for cells grown under conditions of lower Fe availability (i.e., lower dilution rate), suggesting that cells in the continuous cultures adjusted to Fe limitation by decreasing ρ(max) while maintaining a constant affinity for Fe.

Effect of light on iron uptake by the freshwater cyanobacterium Microcystis aeruginosa.

Visible light was observed to induce reductive dissociation of organically complexed Fe and dramatically increase the short-term uptake rate of radiolabeled Fe by Microcystis aeruginosa PCC7806 in Fraquil* medium buffered by a single metal chelator, ethylenediaminetetraacetic acid (EDTA). Only wavelengths <500 nm activated Fe uptake indicating that Fe photochemistry rather than biological factors is responsible for the facilitated uptake. The measured rate of photochemical Fe(II) production combined with a significant decrease in (55)Fe uptake rate in the presence of ferrozine (a strong ferrous iron chelator) confirmed that photogenerated unchelated Fe(II) was the major form of Fe taken up by M. aeruginosa under the conditions examined. Mathematical modeling based on unchelated Fe(II) uptake by concentration gradient dependent passive diffusion of Fe(II) through nonspecific transmembrane channels (porins) could account for the magnitude of Fe uptake and a variety of other observations such as the effect of competing ligands on Fe uptake. Steady-state uptake rates indicated that M. aeruginosa acquires Fe predominantly during the light cycle. This study confirms that Fe photochemistry has a dominant impact on Fe acquisition and growth by M. aeruginosa in EDTA-buffered culture medium.

The effects of combined androgen blockade on cognitive function during the first cycle of intermittent androgen suppression in patients with prostate cancer.

PURPOSE: Men with prostate specific antigen (PSA) only relapse of prostate cancer after primary therapy are generally fully functional and asymptomatic with a life expectancy of up to 10 or more years. These patients are often treated with androgen suppression. We evaluate the effects of androgen suppression on cognitive function. MATERIALS AND METHODS: Hormone naïve patients without evidence of metastases with an increasing PSA were treated with intermittent androgen suppression consisting of 9 months of leuprolide and flutamide followed by an off treatment period determined by the increase in PSA. Cognitive function tests were administered at baseline, after 9 months of androgen suppression and after 3 months off treatment. Cognitive tests measured spatial abilities, spatial memory, verbal fluency, verbal memory and selective attention. A total of 19 patients 52 to 76 years old completed the intermittent androgen suppression study along with 15 healthy community dwelling control participants. RESULTS: Combined androgen blockade reduced PSA and testosterone in all patients compared to baseline. Patients did not significantly change on measures of verbal and spatial memory, executive functions or language. Patients declined on a measure of spatial rotation and improved on a measure of verbal memory during treatment which continued during the off treatment period. CONCLUSIONS: Although preliminary, these findings demonstrate that 9 months of combined androgen blockade resulted in a beneficial effect on verbal memory but adversely affected a measure of spatial ability. Intermittent androgen suppression for a period of 9 months in otherwise healthy men with prostate cancer may have beneficial and adverse effects on cognition that are selective.

The assessment of cognitive procedural learning in amnesia: why the tower of Hanoi has fallen down.

The Tower of Hanoi has been widely accepted as an evaluation of cognitive procedural learning in amnesia but inconsistent findings have raised questions about the nature of the learning process involved in this task. This article presents the performance of a hippocampal amnesic, MS, who, showing poor learning across daily sessions of a formal evaluation, subsequently solved the puzzle through spontaneous use of a declarative-level strategy (the odd-even rule), suggesting that his primary approach to the task was the deployment of declarative solution-searching strategies. The presented data suggest normal learning within daily sessions, but subnormal learning across daily sessions due to the forgetting of acquired declarative information. It is suggested that tasks that are potentially solvable by an algorithm or rule, as is the Tower of Hanoi, be regarded as inappropriate for use in cognitive procedural assessments.

Chemiluminescence of luminol in the presence of iron(II) and oxygen: oxidation mechanism and implications for its analytical use.

The validity of chemiluminescence-based methods relies upon the uniqueness of the relationship between the concentration of the analyte and the intensity of chemiluminescence produced. We have examined the chemiluminescence of luminol (5-amino-2,3-dihydro-1,4-phthalazinedione) in the presence of O2, without added H202, to measure nanomolar concentrations of total Fe(II) (both inorganically and organically complexed) in aqueous samples. To test the validity of the method, we have developed a kinetic model that describes the two-step oxidation of luminol by superoxide and hydroxyl (or hydroxyl-like) radicals produced from the oxidation of Fe-(II) by O2 by synthesis of existing published data. This model was coupled with a model for Fe(II) oxidation by O2 in the presence and absence of the naturally occurring Suwannee River fulvic acid (SRFA). The production of chemiluminescence depended upon the concentrations of free radicals in both the sample and luminol reagent and the pH at which the reactions were performed. The relationship between Fe(II) concentration and chemiluminescence intensity was found to be unique at Fe(II) concentrations from 1 nM to 1 microM without organic complexation and from 1 to 32 nM in the presence of SRFA despite strong signal quenching in the latter case. This type of behavior will likely ensure a similarly unique relationship in the presence of a wide range of organic compounds; however, when other systems are being investigated, the technique should be carefully evaluated.

Clinical, pathologic, and neurochemical studies of an unusual case of neuronal storage disease with lamellar cytoplasmic inclusions: a new genetic disorder?

A child of first-cousin Puerto Rican parents had global developmental delay, failure to thrive, and hypotonia since early infancy. At 1 1/2 years of age, she developed clinical and electrophysiologic evidence of progressive motor and sensory neuropathy. At 2 1/2 years, she developed visual impairment and optic atrophy followed by gradual involvement of the 7th, 9th, 10th, and 12th cranial nerves. Uncontrollable myoclonic seizures began at 4 years and she died at 6 years of age. Motor nerve conduction velocities were initially normal and later became markedly slowed. Sensory distal latency responses were absent. Lysosomal enzyme activities in leukocytes and fibroblasts were normal. Sural nerve and two muscle biopsies showed only nondiagnostic abnormalities. Electron microscopy of lymphocytes, skin, and fibroblasts showed cytoplasmic inclusions. Light microscopy of frontal cortex biopsy showed neuronal storage material staining positively with Luxol fast blue, and electron microscopy showed cytoplasmic membranous bodies in neurons, suggesting an accumulation of a ganglioside. At autopsy, all organs were small but otherwise normal and without abnormal storage cells in the liver, spleen, or bone marrow. Anterior spinal nerve roots showed loss of large myelinated axons. The brain was small and atrophic; cortical neurons showed widespread accumulation of storage material, most marked in the pyramidal cell layer of the hippocampus. Subcortical white matter was gliotic with loss of axons and myelin sheaths. In cortical gray matter there was a 35% elevation of total gangliosides, with a 16-fold increase in GM3, a three- to four-fold increase in GM2 gangliosides, and a 15-fold elevation of lactosyl ceramide. GM3 sialidase activity was normal in gray matter at 3.1 nmols/mg protein per hour and lactosyl ceraminidase I and II activities were 70% to 80% of normal. In white matter, total myelin was reduced by 50% but its composition was normal. Phospholipid distribution and sphingomyelin content were normal in gray matter, white matter, and in the liver. These biochemical findings were interpreted as nonspecific abnormalities. The nature of the neuronal storage substance remains to be determined.

First African-American child with juvenile neuronal ceroid lipofuscinosis.

The neuronal ceroid lipofuscinoses are among the most common forms of progressive neurodegenerative disease of childhood. They appear to be panethnic, but there is a special predilection of the infantile subtype in Finland. In the United States, the Batten disease registry of 731 cases shows that juvenile neuronal ceroid lipofuscinosis (JNCL) is the most common form. Here, we report on the first known African-American child with JNCL. Genetic study showed the 1.02-kb deletion typically seen in JNCL cases.

Severe anterograde amnesia with onset in childhood as a result of anoxic encephalopathy.

Our patient (M.S.) had an abrupt onset of amnesia due to a respiratory arrest at the age of 8 years and has been followed by one of us (A.L.R.) for 19 years. A specially designed MRI study indicated that the neuroanatomical localization of his lesion is restricted to the hippocampal formation bilaterally. Comparison of M.S.'s present IQ and academic scores with earlier scores revealed that his literacy skills, certain basic language functions and vocabulary development were arrested by his memory disorder. In contrast, development of mathematical skill was less curtailed, and verbal and nonverbal logical abilities developed to adult levels. Neuropsychological examination at the age of 27 years elicited a pattern of memory deficits similar to those found in a case (H.M.) of known mesial temporal lobe damage in adulthood. The neuropsychological pattern revealed those aspects of cognitive development that do, and those that do not, require intact memory. The limitations to intellectual development imposed by severe amnesia in childhood are not pervasive, but rather, are limited to specific types of abilities.

Pediatric AIDS. Neuroradiologic and neurodevelopmental findings.

A group of 23 pediatric patients seropositive for HIV antibody were studied by computed tomography and evaluated neurodevelopmentally. Significant neurodevelopmental delays were found in over 95% of the patients studied. CT findings in six patients were normal and thirteen of 23 (57%) had prominence of the CSF spaces. Less frequent findings included calcifications in the basal ganglia and white matter. Cerebral mass lesions included one case of lymphoma and one case of hemorrhage. The CT findings in the pediatric age group differs from the adult population in that contrast enhancing inflammatory mass lesions are uncommon.

Hexachlorophene retinopathy in suckling rats. A light- and electron-microscopic study of short-term and long-term effect of hexachlorophene intoxication on the retina of young rats.

Hexachlorophene (HCP) in very large doses has a toxic effect on the retina of adult rats. The present study examined the sensitivity of the developing retina to smaller doses and its ability to recover from neurotoxic damage. Suckling rats were intoxicated with HCP added to the mothers' diet. The retinae of the pups were examined by light and electron microscopy for early and late effects. All dose levels above 100 ppm caused vacuolar degeneration of the outer segments of photoreceptor cells within 14 days of intoxication, followed by degeneration of the inner segments after 28 days. The cell bodies of photoreceptor cells and all other retinal layers remained normal. Suckling intoxicated with HCP (100 - 500 ppm) added to the mothers' diet for 28 days and then withdrawn, showed no recovery of the outer or inner segments o photoreceptors when examined up to 150 days later. In addition, extensive degeneration and loss of photoreceptor cell occurred after withdrawal of HCP and the degenerative process extended to involve the inner nuclear layer. The rate of appearance of pathological changes was proportional to the total amount of ingested HCP. This study showed that photoreceptor cells in newborn rats are highly sensitive to HCP. The retinal lesions were irreversibly an continued to progress by continued trans-synaptic degeneration after withdrawal of the toxic agents.

Postvaccinal encephalomyelitis without cutaneous vaccination reaction.

A 5-year-old girl developed a progressive febrile neurological illness consisting of right focal seizures, right hemiparesis, and stupor evolving over a period of six weeks. During the month preceding the onset of her illness she had received two apparently unsuccessful smallpox vaccinations without a skin lesion. Elevation of cerebrospinal fluid gamma globulin and findings on brain biopsy were consistent with postinfectious encephalitis, and a simultaneous increase in serum vaccinia antibody titer suggested that the illness was postvaccinial encephalitis. Clinically, the child developed a severe extrapyramidal movement disorder during the acute phase followed by nine months of stuporous unresponsiveness, yet subsequently made a substantial recovery.

Seasonal variations in urinary excretion of calcium and oxalate in normal subjects in patients with idiopathic hyperclaciuria.

A longitudinal 9-year retrospective study of 24-hour urinary calcium values has been made in a metabolic stone clinic amongst patients with idiopathic hypercalciuria. No seasonal variations could be observed in contrast ot a previous study from Leeds, A prospective longitudinal study was made of 24-hour urinary calcium values in a small group of normal subjects. No seasonal variation could be ovserved. In the prospective study no seasonal variations in urinary oxalate could be observed. In a 2-year longitudinal study of stone patients with idiopathic hypercalciuria, urinary oxalate was found to be higher in the summer than in the winter. This was attributed to the combination of a higher intake of oxalate-rich foods in the summer, and the low calcium diet with which they were treated.

Biochemical and pathological studies of myelin in hexachlorophene intoxication.

Adult female rats were fed a diet containing 500 ppm hexachlorophene (HCP). Morphological study of brains from these animals showed vacuolation of the myelin sheaths due to separation of myelin lamellae at the minor dense line. However, myelin could be isolated from the brains of these animals in normal yield. The myelin isolated from HCP-fed animals had normal lipid and protein compositions as shown by analyses of the individual lipids and by disc gel electrophoresis of the proteins. Assay of the myelin-specific enzyme, 2',3'-cyclic nucleotide-3'-phosphohydrolase, showed normal specific activity in myelin obtained from HCP-fed rats. Brains of HCP-fed rats showed an increase in wet weight and a decrease in dry weight, with the chloroform-methanol insoluble fraction showing the greatest weight loss. During isolation of myelin from HCP-fed rats material was found floating over 0.32 M sucrose. This "floating fraction" contained a higher ratio of lipid to protein but the same relative proportions of the individual lipids as are found in myelin. The yield of "floating fraction" from each HCP-fed rat was less than 10 percent of the yield of myelin. Disc gel electrophoresis demonstrated the presence of the usual myelin proteins in this fraction, but with a slight increase in the relative amount of the low molecular weight basic protein. The data were compared to reports on the biochemistry of triethyltin poisoning, and it was concluded that vacuolation of myelin in HCP poisoning is probably due to increased permeability of myelin lamellae to water and electrolytes.

Neurotoxicity of hexachlorophene: new pathological and biochemical observations.

Twenty female rats with nursing litters were fed a diet containing 500 p.p.m. of hexachlorophene (HCP). The blood concentrations of hexachlorophene in mother rats were 4.7-6.0 mug/ml and in infant rats 2.0-2.5 mug/ml. Fifty percent of mother rats and 75% of infant rats died. Most of the surviving animals were asymptomatic apart from imparied visual function. Ten adult and 20 infant rats were killed by perfusion. Light- and electron-microscopic studies showed vacuolation of myelin in the central and peripheral nervous system and axonal degeneration which was especially severe in the optic nerves. After withdrawal of HCP hydrocephalus ex vacuo was present in the chronically intoxicated infant rats and the optic nerves showed marked atrophy and gliosis. Studies with liver mitochondria prepared from lactating hexachlorophene-fed rats showed a 50-75% inhibition of respiration with succinate as substrate.