Differential expression of K4-AP currents and Kv3.1 potassium channel transcripts in cortical neurons that develop distinct firing phenotypes

Maturation of electrical excitability during early postnatal development is critical to formation of functional neural circuitry in the mammalian neocortex. Little is known, however, about the changes in gene expression underlying the development of firing properties that characterize different classes of cortical neurons. Here we describe the development of cortical neurons with two distinct firing phenotypes, regular-spiking (RS) and fast-spiking (FS), that appear to emerge from a population of immature multiple-spiking (IMS) neurons during the first two postnatal weeks, both in vivo (within layer IV) and in vitro. We report the expression of a slowly inactivating, 4-AP-sensitive potassium current (K4-AP) at significantly higher density in FS compared with RS neurons. The same current is expressed at intermediate levels in IMS neurons. The kinetic, voltage-dependent, and pharmacological properties of the K4-AP current are similar to those observed by heterologous expression of Kv3.1 potassium channel mRNA. Single-cell RT-PCR analysis demonstrates that PCR products representing Kv3.1 transcripts are amplified more frequently from FS than RS neurons, with an intermediate frequency of Kv3.1 detection in neurons with immature firing properties. Taken together, these data suggest that the Kv3.1 gene encodes the K4-AP current and that expression of this gene is regulated in a cell-specific manner during development. Analysis of the effects of 4-AP on firing properties suggests that the K4-AP current is important for rapid action potential repolarization, fast after-hyperpolarization, brief refractory period, and high firing frequency characteristic of FS GABAergic interneurons.

Widespread peroxynitrite-mediated damage in Alzheimer's disease

Increasing evidence suggests that oxidative damage to proteins and other macromolecules is a salient feature of the pathology of Alzheimer's disease. Establishing the source of oxidants is key to understanding what role they play in the pathogenesis of Alzheimer's disease, and one way to examine this issue is to determine which oxidants are involved in damage. In this study, we examine whether peroxynitrite, a powerful oxidant produced from the reaction of superoxide with nitric oxide, is involved in Alzheimer's disease. Peroxynitrite is a source of hydroxyl radical-like reactivity, and it directly oxidizes proteins and other macromolecules with resultant carbonyl formation from side-chain and peptide-bond cleavage. Although carbonyl formation is a major oxidative modification induced by peroxynitrite, nitration of tyrosine residues is an indicator of peroxynitrite involvement. In brain tissue from cases of Alzheimer's disease, we found increased protein nitration in neurons, including but certainly not restricted to those containing neurofibrillary tangles (NFTs). Conversely, nitrotyrosine was undetectable in the cerebral cortex of age-matched control brains. This distribution is essentially identical to that of free carbonyls. These findings provide strong evidence that peroxynitrite is involved in oxidative damage of Alzheimer's disease. Moreover, the widespread occurrence of nitrotyrosine in neurons suggests that oxidative damage is not restricted to long-lived polymers such as NFTs, but instead reflects a generalized oxidative stress that is important in disease pathogenesis.

Expression of a borage desaturase cDNA containing an N-terminal cytochrome b5 domain results in the accumulation of high levels of delta6-desaturated fatty acids in transgenic tobacco

gamma-Linolenic acid (GLA; C18:3 delta(6,9,12)) is a component of the seed oils of evening primrose (Oenothera spp.), borage (Borago officinalis L.), and some other plants. It is widely used as a dietary supplement and for treatment of various medical conditions. GLA is synthesized by a delta6-fatty acid desaturase using linoleic acid (C18:2 delta(9,12)) as a substrate. To enable the production of GLA in conventional oilseeds, we have isolated a cDNA encoding the delta6-fatty acid desaturase from developing seeds of borage and confirmed its function by expression in transgenic tobacco plants. Analysis of leaf lipids from a transformed plant demonstrated the accumulation of GLA and octadecatetraenoic acid (C18:4 delta(6,9,12,15)) to levels of 13.2% and 9.6% of the total fatty acids, respectively. The borage delta6-fatty acid desaturase differs from other desaturase enzymes, characterized from higher plants previously, by the presence of an N-terminal domain related to cytochrome b5.

A new method for measurement of anaesthetic partial pressure in blood

We have developed a simple, reliable method for rapid analysis of the partial pressure of volatile anaesthetic agents, based on a two-stage, head-space analysis. It is designed to solve the problems associated with reduced solubility of modern anaesthetics. After equilibration and analysis of a 2-ml sample of blood at 37 degrees C, 1 ml is transferred to another vial for a second equilibration. This ensures that there is no vapour in the headspace before the second equilibration. Measurements were performed on human blood samples equilibrated with 1% sevoflurane, 2.5% isoflurane or 3% desflurane in a tonometer. The mean error in the sample measurements was -2.3% of the tonometer reading and the 95% confidence interval for an individual measurement was +/- 8.5%. Blood samples may be stored overnight without any significant change in the results.

Ancient hematoma: a unifying concept for a post-traumatic lesion mimicking an aggressive soft tissue neoplasm

We describe the clinicopathologic features of four cases of ancient hematoma occurring in the tensor fascia lata and perifascial tissue that clinically and radiologically mimicked aggressive soft tissue neoplasms. The lesions arose in three men and one woman, aged between 31 and 61 years. In three cases, an injury to the affected site had been noted 18 months, 19 years, and 20 years beforehand, respectively. At presentation, these deep-seated and enlarging lesions were highly suggestive of soft tissue sarcomas. Three lesions were treated by excision of an intramuscular or perifascial mass; in one case, repeated incomplete excisions were performed. Grossly, in three cases a well-circumscribed, fusiform mass with a soft cystic center and a fibrous pseudocapsule was described. Histologically, blood clot, fibrin, and predominant amorphous debris were seen in the central cavities; in three cases, the fibrous pseudocapsule contained clumped, eosinophilic, amorphous debris surrounded by a prominent xanthogranulomatous inflammatory infiltrate with numerous, multinucleated, foreign body-type, giant cells. Additionally, cholesterol clefts, areas of hemorrhage and dystrophic calcification, hemosiderin deposits, and cellular scar tissue were seen. Follow-up information revealed no evidence of recurrence or secondary infection in the three cases treated by local or wide excision; in the case in which incomplete excision was performed, continuous symptomatic growth was noted. Pathologic features of ancient hematomas are similar, if not identical, to those hematomas described previously as calcific myonecrosis, chronic expanding hematoma or posttraumatic cyst of soft tissues; we propose instead the term ancient hematoma. The reason for the commonly very long delay between the initiating trauma and presentation is uncertain.

Reassessment of the carcinogenicity of polychlorinated biphenyls (PCBS)

The current policy for regulating polychlorinated biphenyls (PCBs) is based on one chronic bioassay that examined the carcinogenicity of a 60% chlorinated PCB (Norback & Weltman, 1985). All studies originally considered by the U.S. Environmental Protection Agency (EPA) for use in calculating a cancer slope factor (CSF) for PCBs were reevaluated and new CSFs calculated based on the results of a pathology reassessment (Moore et al., 1994). When studies of 60% chlorine PCBs from 3 different laboratories were compared, there was no scientific basis for selecting only 1 data set for deriving CSF estimates. Using a geometric mean to calculate a CSF based on all studies of PCBs with 60% chlorine replaces the current value of 7.7 (mg/kg/d)(-1) with a value of 1.9 (mg/kg/d)(-1). CSFs for PCBs containing less than 60% chlorine (54% and 42%) were less than 1.0 (mg/kg/d)(-1). Using a toxic equivalency factor (TEF) approach similar to that of 2,3,7,8-tetrachlorodibenzo-p-dioxin shows no correlation between toxic equivalent dose and CSFs, indicating that use of TEFs is not predictive of cancer potency for PCBs. Based on these findings, PCB cancer risk assessment policy would more closely reflect scientific data if (1) separate risk assessments were developed for each major PCB formulation and (2) all appropriate data were used when calculating cancer potency for PCB mixtures of 60% chlorine.

Collagen-induced arthritis is reduced in 5-lipoxygenase-activating protein-deficient mice

Collagen-induced arthritis in the DBA/1 mouse is an experimental model of human rheumatoid arthritis. To examine the role of leukotrienes in the pathogenesis of this disease, we have developed embryonic stem (ES) cells from this mouse strain. Here, we report that DBA/1 mice made deficient in 5-lipoxygenase-activating protein (FLAP) by gene targeting in ES cells develop and grow normally. Zymosan-stimulated leukotriene production in the peritoneal cavity of these mice is undetectable, whereas they produce substantial amounts of prostaglandins. The inflammatory response to zymosan is reduced in FLAP-deficient mice. The severity of collagen-induced arthritis in the FLAP-deficient mice was substantially reduced when compared with wild-type or heterozygous animals. This was not due to an immunosuppressive effect, because anti-collagen antibody levels were similar in wild-type and FLAP-deficient mice. These data demonstrate that leukotrienes play an essential role in both the acute and chronic inflammatory response in mice.

Lipofectin-facilitated transfer of cholecystokinin gene corrects behavioral abnormalities of rats with audiogenic seizures

To evaluate the potential for lipofectin-mediated central nervous system gene transfer, the plasmid coding for cholecystokinin was administered intracerebroventricularly to rats, which have congenital audiogenic seizures and high responses to peripheral electric stimulation-induced analgesia. Previous studies had shown that low brain cholecystokinin levels may be the neurochemical variable of rat's audiogenic seizure and high responses to the analgesia because cholecystokinin is an anticonvulsant and anti-opioid neuropeptide. Gene transfer of cholecystokinin corrected the increased susceptibility to audiogenic seizures and the high responses to analgesia for about one week. Similar administration of plasmid expressing beta-galactosidase indicated that the vector mainly transfected ependymal cells lining the ventricle and pia mater cells. The increased cholecystokinin messenger RNA and immunoreactivity in the hippocampus following stereotactic intrahippocampal administration of cholecystokinin plasmid was also demonstrated with in situ hybridization and immunohistochemistry techniques. These results suggest that lipofectin-mediated gene transfer will be useful for studies of brain function, the modification of behavior and gene therapy for central nervous system disorders.

Oxygen scavenging, NADH oxidase and metronidazole resistance in Helicobacter pylori

Failure of triple-therapy regimes to eradicate Helicobacter pylori from the stomach is thought to be due to the occurrence of a metronidazole-resistant bacterial population. Exposure of metronidazole-resistant (MtzR) strains of H. pylori to an anaerobic environment causes the activation of metronidazole and the loss of resistance. Using metronidazole-sensitive (MtzS) clinical isolates, we selected mutants conferring resistance to metronidazole, which were used to investigate the effect of bacterial cell density upon the activation of metronidazole. The addition of metronidazole, at a final concentration of 10 mg/L, to MtzR cultures of a bacterial cell density >1 x 10(6) cfu/mL, caused a loss in viability. No loss in viability, however, occurred upon addition of metronidazole to MtzR cultures of a cell density of <1 x 10(6) cfu/mL. MtzS cultures lost viability irrespective of the initial cell density, indicating that oxygen scavenging at the site of metronidazole reduction may occur in these cultures. The ability of MtzS wild types, MtzR isogenic mutants and MtzR wild types to scavenge oxygen from the intracellular environment was investigated. H. pylori cultures contained NADH and NADPH oxidase activity. NADPH oxidase activity was always more than double the NADH oxidase activity. MtzR mutants possessed approximately one-third the NADH oxidase activity found in their respective MtzS parent wild types. MtzR wild types possessed a low NADH oxidase level similar to that found in the MtzR mutants. We propose that metronidazole resistance may be mediated through an inability of MtzR strains to remove oxygen from the site of metronidazole reduction, thereby preventing metronidazole activation.

Simulation of two-dimensional tagged MRI

MR tagging is a recent imaging development that, in cardiac applications, makes possible the tracking of points in the myocardium during the cardiac cycle. Researchers have developed semiautomated, computer-based methods for analyzing tagged images, but the images are complex and present a challenge to automated tracking systems. Simulation can provide an inexhaustible supply of images for testing and validation of tag tracking software and preview the effect of parameter changes in acquisition. SIMTAG is an interactive computer program that simulates two-dimensional tagged-MR experiments. The mathematic model used in the simulation and algorithms for simulating image noise and object deformation are described. Examples of the use of simulated images in SPAMM parameter selection, a comparison of tag contrast in signal-averaged SPAMM and CSPAMM, and simulated images as test sets for tag-tracking software are presented.

The effect of arteriovenous fistulae in haemodialysis patients on whole body and segmental bioelectrical impedance

BACKGROUND

Bioelectrical impedance (BIA) is a potentially useful method for measuring body water and soft-tissue composition in patients with chronic renal failure. The majority of whole body impedance is derived from the limbs with only a small contribution from the trunk, and thus abnormalities of the limbs could have an exaggerated effect on estimates of total body impedance.

METHODS

This study investigated the effect of arteriovenous fistulae in the arm in haemodialysis patients on body composition measurement by whole body BIA. Body composition estimates from measurements on fistula and non-fistula sides of the body were compared and segmental impedance measurements of the arms were also performed.

RESULTS

Whole body resistance was markedly lower on the fistula side of the body compared with the nonfistula side at 517.1 (124.3) omega compared with 561.5 (121.2) omega, P < 0.0005. This difference was accounted for by differences in the arm segments. This was attributed to swelling of the fistula arm which had a greater mid-arm circumference at 28.5 (2.1) cm compared with the contralateral side at 27.5 (2.0) cm, P < 0.05. This resulted in greater estimates for total body water from the fistula side at 38.6 (10.0) kg compared with 36.6 (8.6) kg from the non-fistula side, P < 0.05 and fat-free mass at 51.1 (11.8) kg from the fistula side compared with 49.1 (11.2) kg from the non-fistula side, P < 0.005. Estimates of body fat from the fistula side, 13.1 (6.9) kg, were less than the nonfistula side, 15.0 (6.0), P < 0.005.

CONCLUSIONS

The presence of arteriovenous fistulae for vascular access in haemodialysis patients may have a significant effect on estimates of body composition by BIA.

Stroke rates during the 1980s. The Minnesota Stroke Survey

BACKGROUND AND PURPOSE

The decline in stroke mortality it the United States may have resulted from declining incidence improved survival of stroke patients, or both. We previously reported that stroke patients who were 30 to 74 years old and were treated in Minneapolis/St Paul hospitals in 1990 survived longer than did their counterparts in 1980. In the present study, we examined trends in the rate of hospitalized stroke in Minneapolis/ St Paul between 1980 and 1990.

METHODS

For 1980, 1985, and 1990, we obtained lists of discharge codes (International Classification of Diseases, 9th revision) from Minneapolis/St Paul hospitals, identified hospitalizations for acute cerebrovascular disease, and randomly selected 50% of the cases for medical record abstraction. We counted stroke events in five different ways, which were based on discharge codes as well as diagnostic criteria, and computed age adjusted stroke rates for each year. Stroke mortality in the population was computed for 1960 through 1994.

RESULTS

Among men, all five measures of hospitalized stroke attack rate indicated a decline between 1980 and 1985, which ranged from 5% to > 20%. Among women, there was a sharp contrast between trends that relied on discharge codes and trends that relied on diagnostic criteria: the former indicated a decline (4% to 19%), whereas the latter indicated some increase. For the second half of the 1980s, most measures of stroke attack rate in men, all measures of stroke attack rate in women, and measures of stroke incidence in both sexes did not indicate a decline in stroke occurrence in the population. Mortality from stroke among 30- to 74-year-old residents of Minneapolis/St Paul, which declined rapidly during the 1970s and early 1980s, declined slowly, if at all, during the second half of the 1980s and early 1990s.

CONCLUSIONS

The incidence of stroke may have declined among 30- to 74-year-old residents of Minneapolis/St Paul in the early 1980s. However, we found little indication of such a trend between 1985 and 1990, a period of slow decline or no decline in stroke mortality in that population.

The molecular pathogenesis of treatment-induced (secondary) leukemias: foundations for treatment and prevention

Acute myeloid leukemia (AML) developing after exposure to genotoxic agents has been recognized as a distinctive entity for more than 40 years. Secondary, or therapy-related, AML accounts for 10% to 20% of all AML cases. The basic and clinical investigation of these complex malignancies can be approached from four major vantage points: (I) dissection of the molecular structure of the induced genetic lesions and identification of the functional consequences of these changes, thereby providing clues to the pathogenesis of secondary AML and potentially serving as a basis for innovative therapeutic interventions; (2) identification and characterization of mechanisms of DNA damage and the orderly repair of such damage; (3) identification and application of accurate biomarkers of leukemogenesis for the purpose of risk prediction and quantification, potentially allowing recognition of patients especially susceptible to the leukemogenic effects of chemotherapy (for genetic or acquired reasons) and allowing their treatment for cancer to be modified based on this susceptibility; and (4) design and implementation of longitudinal clinical and genetic monitoring of high-risk populations (ie, individuals undergoing cytotoxic therapies for primary malignancies). In this article, we build on these themes, and attempt to integrate these seemingly disparate areas of research so that they can be more effectively used together to address the problem of secondary AML. Ultimately, the evaluation of these areas will inform our understanding of de novo leukemia and serve as a springboard for the development of new concepts of therapy and prevention.

Differences in macronutrient selections in users and nonusers of an oral contraceptive

One of the problems inherent in using women in clinical research is the effect that oral contraceptive (OC) use might have on physical indexes. Although weight gain is frequently reported as a side effect of OC use, there is little empirical evidence that such weight gain actually occurs. The current study investigated differences in energy balance [ie, dietary intake, resting energy expenditure (REE), and physical activity] between groups of users and nonusers of OCs. Each group completed a protocol that covered one menstrual cycle and consisted of daily recording of dietary intake, measurement of REE once during each phase of the menstrual cycle, and reporting of physical activity over the entire cycle. Comparisons indicate that there was a marginal interaction (P = 0.06) of OC use with total energy intake, indicating a different pattern of intake for the two groups. There were qualitative between-group differences such that the OC group consumed a greater percentage of energy as fat (P = 0.02) and a lesser percentage of energy as carbohydrate (P = 0.008). No group differences were found in the percentage of energy consumed as protein, but both groups consumed significantly less protein during menses (P = 0.008). There were no significant differences in REE. Both groups of women reported marginally more activity (P = 0.09) during menses than during the luteal phase.

Treatment of experimental methicillin-resistant Staphylococcus epidermidis endophthalmitis with intravitreal vancomycin and intravitreal dexamethasone

The use of intravitreal steroids to treat bacterial endophthalmitis remains controversial. The efficacy of intravitreal vancomycin alone (group 1), intravitreal dexamethasone alone (group 2), and a combination of intravitreal vancomycin and dexamethasone (group 3) in the treatment of experimental methicillin-resistant Staphylococcus epidermidis endophthalmitis was evaluated in a rabbit model: 24 h after bacterial inoculation of all eyes, right eyes were treated and left eyes served as infected controls. Vitreal aspirations and grading of vitreal inflammatory reaction were done regularly until sacrifice. Group 2 eyes demonstrated more inflammation histologically than control eyes. Vitreal aspirations demonstrated no growth by 5 days from groups 1 and 3 eyes. Although the clinical appearance was not significantly different between groups 1 and 3, the histologic appearance of group 3 eyes showed less intense intraocular inflammation. Treatment with dexamethasone in the absence of appropriate antibiotics was more harmful than no treatment at all (P < .05). Therapy with both intravitreal vancomycin and dexamethasone results in less inflammation than intravitreal vancomycin alone in this model.

Amygdala-kindled seizures increase the expression of corticotropin-releasing factor (CRF) and CRF-binding protein in GABAergic interneurons of the dentate hilus

Kindling, a model of temporal lobe epilepsy, induces a number of neuropeptides including corticotropin-releasing factor (CRF). CRF itself can produce limbic seizures which resemble kindling in some aspects. However, tolerance to the convulsant effects of CRF develops rapidly. Hypothetically, this could be explained should seizures also induce the CRF-binding protein (CRF-BP), which has been postulated to restrict the actions of CRF. Therefore, in the present study, we used in situ hybridization to examine the effects of amygdala-kindled seizures on the mRNA levels of CRF and CRF-BP. Kindled seizures markedly elevated CRF and CRF-BP in the dentate gyrus of rats. CRF and CRF-BP were induced almost exclusively in GABAergic interneurons of the dentate hilus. The CRF and CRF-BP interneurons also expressed neuropeptide Y but not cholecystokinin. CRF appeared to have an excitatory role in the dentate gyrus as it decreased the afterhyperpolarization of dentate granule neurons. These results suggest that CRF may contribute to the development of amygdala kindling. However, the compensatory induction of CRF-BP may serve to limit the excitatory effects of CRF in the dentate gyrus.

Preliminary experience with medical applications of rapid prototyping by selective laser sintering

Rapid prototyping techniques, originally developed for building components from computer aided designs in the motor industry, are now being applied in medicine to build models of human anatomy from high resolution multiplanar imaging data such a computed tomography (CT). The established technique of stereolithography and the more recent selective laser sintering (SLS), both build up an object layer by layer. Models have applications in surgical planning, for the design of customised implants and for training. Preliminary experience of using the SLS technique for medical applications is described, addressing questions regarding image processing, data transfer and manufacture. Pilot models, built from nylon, included two skills (a child with craniosynoslosis and an adult with hypertetorism) and a normal femur which was modelled for use in a bioengineering test of an artificial hip. The dimensions of the models were found to be in good agreement with the CT data from which they were built-for the child's skull the difference between the model and the CT data was less than 1.0 +/- 0.5 mm in each direction. Our experience showed that, with care, a combination of existing software packages may be used for data conversion. Ideally, image data of high spatial resolution should be used. The pilot models generated sufficient clinical interest for the technique to be pursued in the orthopaedic field.

Assessment of renal osteodystrophy in dialysis patients: use of bone alkaline phosphatase, bone mineral density and parathyroid ultrasound in comparison with bone histology

Bone biopsies were studied in 73 patients to determine if a two-site radioimmunometric assay for serum bone alkaline phosphatase (BAP), total serum alkaline phosphatase (ALP), serum intact parathyroid hormone (iPTH), hand X-rays, regional bone mineral density (BMD) measurements and parathyroid enlargement detected by ultrasonography could accurately predict renal osteodystrophy. In the patients studied 57 had hyperparathyroid bone disease, 4 mixed renal osteodystrophy, 3 adynamic bone disease, 1 osteomalacia and 8 normal histology. Serum BAP, ALP and iPTH correlated positively with mineral apposition rate, osteoblastic, osteoid and eroded surface. In the diagnosis of hyperparathyroid bone disease serum iPTH was the most sensitive investigation, detecting 81% of patients at a level > 100 pg/ml but with a specificity of only 66%. Serum BAP was more sensitive, 70% at a level of > 10 ng/ml, than serum total ALP, 30% at a level of 300 IU/l, with similar specificities, 92 and 100%, respectively. Ultrasound detection of an enlarged parathyroid gland had a sensitivity of 64% and a specificity of 100% for the diagnosis of hyperparathyroid bone disease. Hand X-rays had a poor sensitivity, 47%, but a high specificity, 92%, for the detection of hyperparathyroid bone disease. The majority of patients had regional BMD values within the normal reference range and this test was of poor discriminatory value. The non-invasive markers were unable to distinguish between patients with low turnover, mild hyperparathyroidism and patients with normal histology. In conclusion the measurement of serum iPTH is a useful screening tool for the detection of hyperparathyroid bone disease which can be confirmed by the finding of a raised serum BAP or parathyroid enlargement. For definitive diagnosis, however, the gold standard remains bone biopsy and at present one cannot recommend any non-invasive method as an adequate substitute.

Introduction of fast MR imaging in the assessment of hepatic steatosis

We determined the utility of fast gradient echo techniques (modified Dixon method) in the assessment of hepatic fat content. Fast spoiled gradient echo was performed on bovine liver/corn oil homogenates with known fat fractions (FFE) to assess the accuracy of fat quantitation (FFMRI). The pulse sequence was manipulated via alterations in TE (echo time), TR (repetition time), and alpha (flip angle). In vivo studies were then performed using breath-holding maneuvers on normal adult volunteers and subjects at risk to develop hepatic steatosis, with cystic fibrosis or morbid obesity. At out-of-phase, TE, TR, and alpha were 2.1 ms, 7.3 ms, and 30-50 degrees and in-phase TE, TR, and alpha were 4.2 ms, 9.3 ms, and 30-50 degrees; FFMRI correlated well with FFE. An elevated fat fraction was observed in a high percentage of subjects with cystic fibrosis and morbid obesity. Fast gradient echo techniques were used successfully in the assessment of hepatic steatosis. The reduced acquisition times permitted in vivo analysis on adults and children using breath hold maneuvers.

Measurement of total body water and urea kinetic modelling in peritoneal dialysis

Studies of the effect of Kt/V (urea) on prediction of outcome in patients on peritoneal dialysis have shown conflicting results. We performed this study to examine the effects of the measurement of V by varying techniques on the calculation of Kt/V, using body water estimated by deuterium oxide dilution (D2O dilution) as the criterion method for estimation of V. Studies were performed in 20 peritoneal dialysis patients. Kt was calculated from 24-hour dialysate and urine collections and V estimated by D2O dilution, Watson formulae, 58% of body weight, bioelectrical impedance (BIA) and 73% of fat-free mass estimated by DEXA. V was also measured in 35 healthy controls. Hydration, expressed as body water by D2O dilution as a percentage of fat-free mass estimated by DEXA did not differ between peritoneal dialysis patients 71.0 (4.9)% and a healthy control group 71.1 (5.0)%. Mean Kt/V using D2O dilution was 2.14 (0.36). The other techniques resulted in a significantly lower Kt/V; Watson equations 2.01 (0.35), p < 0.005, BIA 1.93 (0.31), p < 0.0001, DEXA 2.06 (0.28), p < 0.05, 58% body weight 1.83 (0.38), p < 0.0001. Limits of agreement of Kt/V by the simpler techniques compared with D2O dilution [mean difference of (other techniques -D2O dilution) as % of mean values +/- 95% limits of agreement] were Watson equation -5.9 +/- 15.3%, BIA -10.1 +/- 15.5%, DEXA -3.4 +/- 13.5% and 58% body weight -9.9 +/- 23.5%. Differences in Kt/V from estimates using D2O dilution were significantly negatively correlated with body fat for 58% body weight (r = -0.80, p < 0.0001) and the Watson formulae (r = -0.49, p < 0.05) but not for BIA or DEXA. We conclude that clinically significant variation in Kt/V may occur due to the estimation of V and may account for the uncertainty of the value of Kt/V as a predictor of outcome in peritoneal dialysis patients. Estimating V by BIA and DEXA did not have any benefit over the Watson formulae in terms of agreement with D2O dilution, though did avoid systematic errors related to body fat. Estimation of V as a fixed proportion of body weight is clearly inferior to the other techniques.

Four-component model of body composition in chronic renal failure comprising dual-energy X-ray absorptiometry and measurement of total body water by deuterium oxide dilution

1. Assessment of nutrition in patients with chronic renal failure by body composition measurement techniques may be affected by variable hydration. 2. This study aimed to derive a four-component model of body composition (consisting of fat, protein, total body water and body mineral) from a combination of dual-energy X-ray absorptiometry and total body water measured by deuterium oxide dilution, allowing assessment of body protein stores without the effect of variation in hydration. Patients with chronic renal failure on haemodialysis, peritoneal dialysis and conservative treatment and a control group were studied. Patients with chronic renal failure were at an 'ideal' state of hydration on clinical assessment. 3. Hydration was defined by total body water as a percentage of fat-free mass measured by dual-energy X-ray absorptiometry, and no differences were found between chronic renal failure subgroups and control subjects (except in the female undialysed chronic renal failure subgroup). Hydration was significantly correlated with percentage total body fat in the control groups but not in patients with chronic renal failure. 4. Lean tissue measured by dual-energy X-ray absorptiometry was significantly reduced in three of the six chronic renal failure groups compared with control subjects (male and female patients on haemodialysis and female patients on peritoneal dialysis). Protein estimated from the four-component model failed to detect these abnormalities. 5. Lean tissue measured by dual-energy X-ray absorptiometry in normal subjects strongly correlated with fat-free mass measured by total body potassium in normal subjects (male r = 0.91; female r = 0.89, both P < 0.0001). The correlation of protein estimated from the four-component model with fat-free mass measured by total body potassium was far weaker in male control subjects (r = 0.51, P < 0.05) and not significant in female control subjects (r = 0.38, P not significant). In the normal subjects protein estimated from the four-component model showed a much greater variation from protein estimated by total body potassium than did protein estimated simply as 27% of dual-energy X-ray absorptiometry fat-free mass minus total body mineral. 6. Hydration in patients with chronic renal failure in whom fluid balance is believed to be normal on clinical criteria does not differ from that in normal subjects. The combined model of dual-energy X-ray absorptiometry and total body water is not a useful method for the measurement of body protein.

Single-cell analysis of gene expression in the nervous system. Measurements at the edge of chaos

The characteristic functions of tissues and organs result from the integrated activity of individual cells. Nowhere is this more evident than in the nervous system, where the activities of single neurons communicating via electrical and chemical signals mediate complex functions, such as learning and memory. The past decade has seen an explosion in the identification of genes encoding proteins, such as voltage-gated channels and neurotransmitter receptors, responsible for neuronal excitability. These studies have highlighted the fact that even within a neuroanatomically defined region, the coexistence of multiple cell types makes it difficult, if not impossible, to correlate patterns of gene expression with function. The recent development of techniques sensitive enough to study gene expression at the single-cell level promises to break this bottleneck to our further understanding. Using examples taken from our own laboratories and the work of others, we review these techniques, their application, and discuss some of the difficulties associated with the interpretation of the data.