Fulminant endocarditis and disseminated infection caused by carbapenem-resistant Acinetobacter baumannii in a renal-pancreas transplant recipient.

Acinetobacter baumannii is an important cause of healthcare-associated infections, and is particularly problematic among patients who undergo organ transplantation. We describe a case of fulminant sepsis caused by carbapenem-resistant A. baumannii harboring the blaOXA-23 carbapenemase gene and belonging to international clone II. This isolate led to the death of a patient 6 days after simultaneous kidney-pancreas transplantation. Autopsy findings revealed acute mitral valve endocarditis, myocarditis, splenic and renal emboli, peritonitis, and pneumonia. This case highlights the severe nature of certain A. baumannii infections and the vulnerability of transplanted patients to the increasingly intractable "high-risk" clones of multidrug-resistant organisms.

Visual adaptations in a diurnal rodent, Octodon degus.

The degu (Octodon degus) is a diurnal rodent, native to Chile. Basic features of vision and visual organization in this species were examined in a series of anatomical, electrophysiological and behavioral experiments. The lens of the degu eye selectively absorbs short-wavelength light and shows a progressive increase in optical density as a function of age. Electroretinograms recorded using a flicker-photometric procedure reveal three spectral mechanisms: a rod with peak sensitivity of about 500 nm and two types of cone having respective spectral peaks of about 362 nm and 507 nm. Opsin antibody labeling was used to determine the retinal distributions of the three receptor types. A total of about one-third of the approximately 9 million photoreceptors of the degu retina are cones with the two types (507 nm/362 nm) represented in a ratio of about 13:1. The contributions to vision of all three receptor types were examined in a series of behavioral experiments. A consistent feature of both the electrophysiological and behavioral results is that relatively high levels of light adaptation are required to effect the full transition from rod-based to cone-based vision. In behavioral tests degus were shown to be able to make color discriminations between ultraviolet and visible lights.

Cone-based vision of rats for ultraviolet and visible lights.

Rats (Rattus norvegicus) have two classes of cone, one containing an ultraviolet (UV)-sensitive photopigment and the other housing a pigment maximally sensitive in the middle (M) wavelengths of the visible spectrum. The manner in which signals from these two cone types contribute to rat vision was investigated through recordings of a gross electrical potential (the electroretinogram, ERG) and behavioral discrimination tests. Spectral sensitivity functions obtained from both types of measurement indicate clear contributions from each of the cone classes, but there is a marked enhancement of the relative sensitivity to UV light in the behavioral index; for instance, under some photopic test conditions, rats are approximately equally sensitive to middle-wavelength and UV lights. In adaptation tests, thresholds for UV and M lights were found to be differentially elevated in the presence of chromatic adapting backgrounds, thus providing the possibility that signals from the two cones could be used by the rat visual system to support color discriminations. Evidence of dichromatic color vision in the rat was subsequently obtained from tests of wavelength discrimination.

Photopigments and colour vision in New World monkeys from the family Atelidae.

Most New World monkeys have an X-chromosome opsin gene polymorphism that produces a variety of different colour vision phenotypes. Howler monkeys (Alouatta), one of the four genera in the family Atelidae lack this polymorphism. Instead, they have acquired uniform trichromatic colour vision similar to that of Old World monkeys, apes and people through opsin gene duplication. In order to determine whether closely related monkeys share this arrangement, spectral sensitivity functions that allow inferences about cone pigments were measured for 56 monkeys from two other Atelid genera, spider monkeys (Ateles) and woolly monkeys (Lagothrix). Unlike howler monkeys, both spider and woolly monkeys are polymorphic for their middle- and long-wavelength cone photopigments. However, they also differ from other polymorphic New World monkeys in having two rather than three possible types of middle- and long-wavelength cone pigments. This feature directly influences the relative numbers of dichromatic and trichromatic monkeys.

The genetics of primary vesico-ureteric reflux.

INTRODUCTION: Vesico-ureteric reflux (VUR), reflux of urine from the bladder into the ureter and towards the kidney, is an important cause of end-stage renal failure in both children and adults. Primary VUR is considered to be a result of a disruption of the normal anti-reflux mechanism of the ureterovesical junction (UVJ). VUR is common, occurring in approximately 1% to 2% of newborns in Caucasian populations. The aetiology of VUR is thought to involve a substantial genetic component, supported by the observation that VUR frequently occurs in multiple members of the same family. The purpose of this article is to review the literature supporting a genetic cause of VUR, and to draw together observations and make suggestions regarding differential diagnosis of VUR, which might help in future studies on the genetic aetiology of VUR. RESULTS: A common theme arising was the notion that VUR may be caused by multiple genes in the population. However, any one individual with VUR may carry a single dominant mutant allele. Overall, progress has been made in mapping putative VUR loci in both humans and mice, although the mode(s) of inheritance and the exact nature of the underlying defect are still poorly understood. CONCLUSIONS: It is likely that over the next few years VUR genes will be mapped and, once identified, the challenge will be to understand how changes in the expression of these genes lead to the underlying defect in VUR.

Functional consequences of the relative numbers of L and M cones.

Direct imaging of the retina by adaptive optics allows assessment of the relative number of long-wavelength-sensitive (L) and middle-wavelength-sensitive (M) cones in living human eyes. We examine the functional consequences of variation in the relative numbers of L and M cones (L/M cone ratio) for two observers whose ratios were measured by direct imaging. The L/M cone ratio for the two observers varied considerably, taking on values of 1.15 and 3.79. Two sets of functional data were collected: spectral sensitivity measured with the flicker electroretinogram (ERG) and the wavelength of unique yellow. A genetic analysis was used to determine L and M cone spectra appropriate for each observer. Rayleigh matches confirmed the use of these spectra. We determined the relative strength of L and M cone contributions to ERG spectral sensitivity by fitting the data with a weighted sum of L and M cone spectra. The relative strengths so determined (1.06 and 3.38) were close to the cone ratios established by direct imaging. Thus variation in L/M cone ratio is preserved at the sites tapped by the flicker ERG. The wavelength of unique yellow varied only slightly between the two observers (576.8 and 574.7 nm). This small variation indicates that neural factors play an important role in stabilizing unique yellow against variation in the L/M cone ratio.

Transterm: a database of messenger RNA components and signals.

Transterm facilitates studies of messenger RNAs and translational control signals. Each messenger RNA (mRNA) from GenBank is extracted and broken into its functional components, its coding sequence, initiation context, termination context, flanking sequence representing its 5' UTR (untranslated region), 3' UTR and translational signals. In addition, numerical parameters characterising each coding region in Transterm, including codon and GC bias, are available. For each species in Transterm, the initiation and termination regions are aligned by their start or stop codons and presented as base frequency matrices and tables of the information content of the bases in the alignments. Users can obtain summaries of characteristics of the mRNAs for species of their choice and search for translational signals both in the Transterm database and in their own sequence. The current release contains data from over 10 000 species, including the complete genomes of 20 prokaryotes and three eukaryotes. Both flat-file and relational database forms of Transterm are accessible via the WWW at http://biochem.otago.ac.nz/Transterm/

Uniformity of colour vision in Old World monkeys.

It is often assumed that all Old World monkeys share the same trichromatic colour vision, but the evidence in support of this conclusion is sparse as only a small fraction of all Old World monkey species have been tested. To address this issue, spectral sensitivity functions were measured in animals from eight species of Old World monkey (five cercopithecine species and three colobine species) using a non-invasive electrophysiological technique. Each of the 25 animals examined had spectrally well-separated middle- and long-wavelength cone pigments. Cone pigments maximally sensitive to short wavelengths were also detected, implying the presence of trichromatic colour vision. Direct comparisons of the spectral sensitivity functions of Old World monkeys suggest there are no significant variations in the spectral positions of the cone pigments underlying the trichromatic colour vision of Old World monkeys.

MR imaging-guided radio-frequency thermal ablation in the pancreas in a porcine model with a modified clinical C-arm system.

PURPOSE: To test the hypotheses that (a) magnetic resonance (MR) imaging-guided radio-frequency (RF) thermal ablation in the pancreas is safe and feasible in a porcine model and (b) induced thermal lesion size can be predicted with MR imaging monitoring. MATERIALS AND METHODS: MR imaging-guided RF ablation was performed in the pancreas of six pigs. A 17-gauge monopolar RF probe was inserted into the pancreas with MR imaging guidance, and RF was applied for 10 minutes. After postprocedural imaging (T2-weighted, short inversion time inversion-recovery [STIR], and T1-weighted imaging before and after intravenous administration of gadodiamide), the pigs were observed for 7 days and follow-up MR images were acquired. The pigs were sacrificed, and pathologic examination was performed. RESULTS: Successful RF probe placement was accomplished in all pigs; the interventional procedure took 46-80 minutes. Thermal lesions were 12-15 mm perpendicular to the probe track and were best seen on STIR and contrast material-enhanced T1-weighted images with a radiologic and/or pathologic mean difference in RF lesion diameter of 1.7 mm +/- 1.0 (SD) and 0.8 mm +/- 1.2, respectively. Diarrhea was the only side effect during the 1-week follow-up; no clinical signs of pancreatitis occurred. CONCLUSION: MR imaging-guided RF thermal ablation in the pancreas is feasible and safe. Induced thermal lesion size can best be monitored with STIR and contrast-enhanced T1-weighted images. In the future, RF ablation may offer an alternative treatment option for pancreatic cancer.

Flicker ERG responses to stimuli parametrically modulated in color space.

PURPOSE: To develop methods for recording human electroretinogram (ERG) responses to stimuli that modulate different classes of cones in various ratios, to draw inferences about the combination of cone signal in early retinal processing. METHODS: Subjects viewed large-field temporal modulations presented on a computer-controlled color monitor. A flicker photometric paradigm was used to equate the ERG response elicited by interleaved reference and test modulations. Test modulations were chosen to stimulate the L- and M-cones in various ratios. Results were obtained from color-normal subjects, dichromats, and an anomalous trichromat. RESULTS: Reliable signals were obtained from all subjects to both L- and M-cone-isolating modulations and to intermediate modulations. Signals from color-defective subjects were predominantly determined by the modulation seen by only one cone type, whereas signals from color-normal subjects were sensitive to both L- and M-cone modulations. For most color-normal subjects, the recorded signal was a linear function of the contrasts seen by the L- and M-cones. There was individual variability in how strongly each cone type contributed to the overall signal. CONCLUSIONS: It is straightforward to record signals to color modulations presented on a CRT by using the flicker photometric ERG. For most observers, signals from L- and M-cones combine linearly. The relative contribution of the two cone classes varies across observers, probably because of individual differences in the relative numbers of L- and M-cones.

MR-guided RF thermal ablation of the kidney in a porcine model.

OBJECTIVE: The purpose of the study was to evaluate the ability of MR imaging to reveal RF interstitial thermotherapy in the porcine kidney, as a model for future human trials, and to provide guidance for RF probe insertion. SUBJECTS AND METHODS: Ten MR-guided RF ablations were performed in the kidneys of three pigs. A 17-gauge monopolar RF probe electrode was inserted into the renal cortex using MR guidance, and RF was applied for 10 min. After postprocedure imaging (T2-weighted, turbo short inversion time inversion recovery [STIR], and T1-weighted sequences), the kidneys were harvested for pathologic examination. RESULTS: Successful RF probe placement was accomplished in all cases; the interventional procedure time for probe insertion ranged from 4 to 15 min. The thermal lesion size varied from 7 to 14 mm perpendicular to the probe track and was best seen on turbo STIR images. Turbo STIR had the highest renal cortex-to-RF thermal lesion contrast-to-noise ratio with an average of 4.4 +/- 3.5. Turbo STIR imaging never overestimated pathologic lesion diameter with a mean difference of 1.5 +/- 1.4 mm. Three subcapsular hematomas occurred. which could be detected immediately on postprocedure imaging. CONCLUSION: MR-guided RF thermal ablation in the porcine kidney was found to be feasible, but minor complications occurred. Induced thermal lesion size was best monitored using turbo STIR images. In the future, RF ablation may offer an alternative treatment option for renal cancer.

Effects of superparamagnetic iron oxide on radio-frequency-induced temperature distribution: in vitro measurements in polyacrylamide phantoms and in vivo results in a rabbit liver model.

PURPOSE: To determine whether contrast medium containing superparamagnetic iron oxide (SPIO) alters radio-frequency (RF)-related temperature distribution in acrylamide phantoms and in an in vivo model. MATERIALS AND METHODS: In nine acrylamide phantoms with increasing SPIO content, RF was applied with simultaneous measurement of temperature profile along the probe track. Additionally, magnetic resonance imaging-guided RF ablation was performed in the liver of six rabbits after the intravenous administration of SPIO (0.05 mL per kilogram of body weight) 40 minutes prior to ablation (SPIO group) and in another six rabbits without prior SPIO administration (control group). Coagulation diameter was evaluated on the basis of postprocedural imaging and subsequent gross pathologic findings. Statistical analysis was performed with the Student t test. RESULTS: In the phantoms, progressive increases in iron content resulted in higher temperatures along the RF electrode track (P < .05). In the in vivo model, however, SPIO at physiologic concentrations did not significantly increase the diameter of coagulation on the basis of either postprocedural imaging or subsequent gross pathologic findings. Additionally, no significant differences were seen in other RF-related parameters including impedance, voltage, current, and grounding pad temperature. CONCLUSION: Administration of SPIO in conjunction with RF ablation of focal liver lesions is feasible and safe, but no significant difference in the extent of induced coagulation can be expected.

MRI-guided radiofrequency thermal ablation of implanted VX2 liver tumors in a rabbit model: demonstration of feasibility at 0.2 T.

Successful radiofrequency (RF) thermal ablation was performed on VX2 tumors implanted in 23 rabbit livers under magnetic resonance (MR) guidance using a C-arm-shaped low-field 0.2 T system. RF application and immediate postprocedure MRI of all animals was performed [T2-weighted, turbo short tau inversion recovery (STIR), T1-weighted before and after gadopentetate dimeglumine administration). Follow-up MRI with a superparamagnetic iron oxide (SPIO) contrast medium was performed in nine rabbits at 2 weeks and in four rabbits at 1 month post RF ablation. All livers were harvested for pathologic examination. T2-weighted and turbo-STIR images demonstrated the highest tumor-to-RF-thermal lesion contrast-to-noise ratios (CNRs; means 4.5 and 3.8, respectively) on postprocedure images; this was redemonstrated at 2- and 4-week follow-up imaging. T2-weighted imaging never overestimated pathologic lesion size by more than 2 mm, and the radiologic-pathologic correlation coefficient was not less than 0.90. In conclusion, MRI-guided RF thermal ablation in implanted liver tumor is feasible using a C-arm-shaped low-field 0.2 T system. The thermal lesion size can be most accurately monitored with T2-weighted and turbo-STIR images.

Prospects for trichromatic color vision in male Cebus monkeys.

Polymorphic color vision is characteristic of many species of New World monkey. A fundamental feature of the polymorphism is that male monkeys are routinely dichromatic. A recent paper describes an experiment in which Cebus monkeys were required to discriminate between pairs of Munsell color chips (Pessoa VF, Tavares MCH, Aguiar L, Gomes UR, Tomaz C. Color vision discrimination in the capuchin monkey Cebus apella: evidence for trichromaticity. Behav Brain Res 1997;89:285-288). The results were interpreted as demonstrating trichromatic color vision in male Cebus monkeys. An examination of the literature on Cebus. monkey photopigments and results from a replication of the discrimination experiment conducted with dichromatic human subjects cast doubt on this claim.

Modelling the mosaic organization of rod and cone photoreceptors with a minimal-spacing rule.

The mosaic of photoreceptors is regarded as a prime example of the precise control of cellular positioning in the vertebrate nervous system. This study was undertaken with the idea that understanding the intrinsic geometrical features of photoreceptor mosaics is a necessary step to unveil the biological mechanisms governing their formation. We show in the retina of the ground squirrel that the arrays of both the rods and S cones are non-random, but that nothing more than a simple minimal-spacing rule constraining receptor positioning is sufficient to account for the spatial organization of both mosaics. The size of this 'exclusion zone' is an intrinsic characteristic of each cell type, and it is simply the difference in the size of this domain that accounts for the regularity of the S cone array and the irregularity of the rod array at identical density. Consequently, regularity in receptor mosaics is produced by two independent biological events, one embodying the exclusion zone, and another specifying the local density of a given receptor type.

Human cone pigment expressed in transgenic mice yields altered vision.

Genetically driven alterations in the complement of retinal photopigments are fundamental steps in the evolution of vision. We sought to determine how a newly added photopigment might impact vision by studying a transgenic mouse that expresses a human cone photopigment. Electroretinogram (ERG) measurements indicate that the added pigment works well, significantly changing spectral sensitivity without deleteriously affecting the operation of the native cone pigments. Visual capacities of the transgenic mice were established in behavioral tests. The new pigment was found to provide a significant expansion of the spectral range over which mice can perceive light, thus underlining the immediate utility of acquiring a new photopigment. The transgenic mouse also has the receptor basis for a novel color vision capacity, but tests show that potential was not realized. This failure likely reflects limitations in the organizational arrangement of the mouse retina.

Cone receptor variations and their functional consequences in two species of hamster.

Results from earlier experiments indicate that different species of rodent vary both in the number of cone types found in their retinas and in the spectral sensitivities of the cone pigments. These features have now been examined in two types of hamster commonly used for research purposes: Syrian golden hamsters (Mesocricetus auratus) and Siberian dwarf hamsters (Phodopus sungorus). Electroretinogram (ERG) flicker photometry, behavioral discrimination tasks, and opsin antibody labeling were used to investigate hamster photoreceptors and their visual consequences. Results from the three approaches support the following conclusions: (1) The retinas of both species have an abundant population of rods containing a photopigment with peak sensitivity of about 498-500 nm; (2) Siberian dwarf hamsters have two classes of cone: one with maximum sensitivity in the ultraviolet (c. 360 nm), the other with peak sensitivity closely similar to that of its rod; and (3) Syrian golden hamsters have a class of cone with peak sensitivity at about 506 nm, but they lack a second cone type. Implications of these alternative arrangements are discussed.

Resolution of hepatitis B viremia in a renal transplant recipient treated with alpha-2b interferon.

A renal transplant patient developed symptomatic hepatitis after withdrawal from corticosteroids. Tests for hepatitis B e antigen and hepatitis B viral DNA were both positive prior to treatment with 1 million units alpha interferon three times weekly for 3 weeks followed by an increase to 3 million units alpha interferon three times weekly for a total of 16 weeks. At the end of treatment, hepatitis had clinically resolved with conversion to a hepatitis B e antibody positive and hepatitis B e antigen and viral DNA negative state. The renal allograft function remained excellent throughout the course of therapy with interferon.