Achromatopsia-Visual Cortex Stability and Plasticity in the Absence of Functional Cones.

Purpose: Achromatopsia is a rare inherited disorder rendering retinal cone photoreceptors nonfunctional. As a consequence, the sizable foveal representation in the visual cortex is congenitally deprived of visual input, which prompts a fundamental question: is the cortical representation of the central visual field in patients with achromatopsia remapped to take up processing of paracentral inputs? Such remapping might interfere with gene therapeutic treatments aimed at restoring cone function. Methods: We conducted a multicenter study to explore the nature and plasticity of vision in the absence of functional cones in a cohort of 17 individuals affected by autosomal recessive achromatopsia and confirmed biallelic disease-causing CNGA3 or CNGB3 mutations. Specifically, we tested the hypothesis of foveal remapping in human achromatopsia. For this purpose, we applied two independent functional magnetic resonance imaging (fMRI)-based mapping approaches, i.e. conventional phase-encoded eccentricity and population receptive field mapping, to separate data sets. Results: Both fMRI approaches produced the same result in the group comparison of achromatopsia versus healthy controls: sizable remapping of the representation of the central visual field in the primary visual cortex was not apparent. Conclusions: Remapping of the cortical representation of the central visual field is not a general feature in achromatopsia. It is concluded that plasticity of the human primary visual cortex is less pronounced than previously assumed. A pretherapeutic imaging workup is proposed to optimize interventions.

Redox Pioneer: Professor Valerian Kagan.

Professor Valerian Kagan (PhD, 1972, MV Lomonosov Moscow State University; DSci, 1981, USSR, Academy of Sciences, Moscow) is recognized as a Redox Pioneer because he has published 4 articles in the field of redox biology that have been cited >1000 times and 138 articles in this field have been cited between 100 and 924 times. The central and most important impact of Dr. Kagan's research is in the field of redox lipidomics-a term coined for the first time by Dr. Kagan in 2004-and consequently the definition of signaling pathways by oxidatively modified phospholipids; this acquires further significance considering that oxygenated phospholipids play multifunctional roles as essential signals coordinating metabolism and physiology. Some examples are the selective oxidation of cardiolipin (CL) by a cytochrome c peroxidase activity leading to the activation of the intrinsic apoptotic pathway; the hydroperoxy-arachidonoyl/adrenoyl phosphatidylethanolamine (PE) species, driven by 15-lipoxygenases (15-LOX), as death signals leading to ferroptotic cell death; the regulation of ferroptosis by iNOS/NO• in pro-inflammatory conditions by a novel mechanism (realized via interactions of 15-LOX reaction intermediates formed from arachidonoyl phosphatidylethanolamine [PE] species) and Ca2+-independent phospholipase A2 (iPLA2ß; via elimination of peroxidized PE); the involvement of oxygenated (phospho)lipids in immunosuppression by myeloid cells in the tumor microenvironment; hydrolysis of peroxidized CL by Ca2+-independent phospholipase A2 (iPLA2γ) leading to pro- and anti-inflammatory signals and lipid mediators. Kagan continues his investigations to decipher the roles of enzyme-linked oxygenated phospholipids. Antioxid. Redox Signal. 36, 813-823.

Amelanotic melanocytoma of the cervicomedullary junction.

A 64-year-old female with a 1-year history of gait difficulties and right-sided dysesthesias was found to have an intra-axial left-sided exophytic cervicomedullary enhancing mass. Microscopic, immunohistochemical, and ultrastructural findings demonstrated an amelanotic melanocytic neoplasm. Next-generation sequencing with a targeted exomic oncopanel identified a variant of functional significance in the GNA11 gene, thus confirming the diagnosis of a primary amelanotic melanocytoma. The crucial distinction from a melanoma was possible by correlating all of these studies that utilize different technologies.

Structural changes to primary visual cortex in the congenital absence of cone input in achromatopsia.

Autosomal recessive Achromatopsia (ACHM) is a rare inherited disorder associated with dysfunctional cone photoreceptors resulting in a congenital absence of cone input to visual cortex. This might lead to distinct changes in cortical architecture with a negative impact on the success of gene augmentation therapies. To investigate the status of the visual cortex in these patients, we performed a multi-centre study focusing on the cortical structure of regions that normally receive predominantly cone input. Using high-resolution T1-weighted MRI scans and surface-based morphometry, we compared cortical thickness, surface area and grey matter volume in foveal, parafoveal and paracentral representations of primary visual cortex in 15 individuals with ACHM and 42 normally sighted, healthy controls (HC). In ACHM, surface area was reduced in all tested representations, while thickening of the cortex was found highly localized to the most central representation. These results were comparable to more widespread changes in brain structure reported in congenitally blind individuals, suggesting similar developmental processes, i.e., irrespective of the underlying cause and extent of vision loss. The cortical differences we report here could limit the success of treatment of ACHM in adulthood. Interventions earlier in life when cortical structure is not different from normal would likely offer better visual outcomes for those with ACHM.

Structural Differences Across Multiple Visual Cortical Regions in the Absence of Cone Function in Congenital Achromatopsia.

Most individuals with congenital achromatopsia (ACHM) carry mutations that affect the retinal phototransduction pathway of cone photoreceptors, fundamental to both high acuity vision and colour perception. As the central fovea is occupied solely by cones, achromats have an absence of retinal input to the visual cortex and a small central area of blindness. Additionally, those with complete ACHM have no colour perception, and colour processing regions of the ventral cortex also lack typical chromatic signals from the cones. This study examined the cortical morphology (grey matter volume, cortical thickness, and cortical surface area) of multiple visual cortical regions in ACHM (n = 15) compared to normally sighted controls (n = 42) to determine the cortical changes that are associated with the retinal characteristics of ACHM. Surface-based morphometry was applied to T1-weighted MRI in atlas-defined early, ventral and dorsal visual regions of interest. Reduced grey matter volume in V1, V2, V3, and V4 was found in ACHM compared to controls, driven by a reduction in cortical surface area as there was no significant reduction in cortical thickness. Cortical surface area (but not thickness) was reduced in a wide range of areas (V1, V2, V3, TO1, V4, and LO1). Reduction in early visual areas with large foveal representations (V1, V2, and V3) suggests that the lack of foveal input to the visual cortex was a major driving factor in morphological changes in ACHM. However, the significant reduction in ventral area V4 coupled with the lack of difference in dorsal areas V3a and V3b suggest that deprivation of chromatic signals to visual cortex in ACHM may also contribute to changes in cortical morphology. This research shows that the congenital lack of cone input to the visual cortex can lead to widespread structural changes across multiple visual areas.

Atypical Tibial Fracture in a 63-Year-Old Woman With Intermittent Use of Bisphosphonate Unmasking Hypophosphatasia.

We report an unusual case of atypical proximal tibial stress fracture (APTF) associated with intermittent use of bisphosphonates (BPs) and persistently low serum alkaline phosphatase (ALP) levels. We describe the case of a 63-year-old white woman who had experienced an APTF after 4 years of intermittent exposure to alendronate given for recurrent metatarsal stress fractures. BP administration was stopped after the diagnosis of the APTF. A review of her previous serum ALP levels revealed they had been consistently low. Adult hypophosphatasia (HPP) was diagnosed by the low serum ALP activity and elevated urine phosphoethanolamine levels. She was treated conservatively with analgesics. Adult HPP is an underrecognized condition associated with atypical insufficiency fractures, and BP use compounds this risk. To the best of our knowledge, we report the first case of intermittent BP exposure preceding an APTF in an adult patient with HPP, highlighting the uncommon site of the proximal tibia for BP-associated atypical insufficiency fractures, the need to screen for HPP in those with persistently low ALP levels before they begin BP therapy, and the importance of avoiding BP use in those with HPP.

Hydrophilic polymer embolization after thoracic endovascular aortic repair.

Hydrophilic polymer embolization is a rare complication after endovascular procedures that is currently underappreciated. Present understanding on this phenomenon relies on sparse case reports with histologic evidence of foreign polymers in end-organ tissue. Here, we report two deaths associated with hydrophilic polymer embolization after complex thoracic endovascular aortic repair.

Iatrogenic embolization following cardiac intervention: postmortem analysis of 110 cases.

INTRODUCTION: Iatrogenic embolization following cardiac investigative procedures may result from hydrophilic polymer emboli (HPE) from catheter valve and vessel wall calcifications, and air embolism from open heart surgery. This retrospective clinical pathologic analysis was undertaken to ascertain the frequency and extent of these potentially fatal complications. METHODS: This retrospective clinical pathologic autopsy analysis with premortem diagnostic imaging correlation identified 110 individuals who had undergone endovascular procedures between 2010 and 2016 within 90 days of death and followed by hospital autopsy. Clinical outcomes, radiologic studies, and autopsy materials were reviewed. RESULTS: Iatrogenic emboli were assessed as causing death in 9/110 autopsy cases (8.2%) and 9/34 (26.5%) cases with proven iatrogenic emboli. Iatrogenic emboli caused strokes in 10/110 (9.1%) autopsy cases including calcified emboli (CE, n=6), HPE (n=2), cardiac valvular tissue (n=1), and air embolism (n=1). Seven cases of calcified emboli complicating endovascular procedures were identified: four of the CE were thought to be the cause of death due to fatal strokes (n=2) and fatal myocardial (n=1) and colonic infarction (n=1). The CE likely originated from calcified aortic valves and atherosclerotic aortic plaques. Histologic evidence of HPE was found in 23% (25/110) of cases; 54% (26/48) showed evidence of infarction in postprocedural imaging, with radiologic evidence of infarction in 32% (8/25) of cases with HPE histology. Endovascular aortic repair was associated with the greatest density/distribution of HPE. HPE material showed degradation with time and was often associated with an inflammatory response. HPE directly contributed to death in three cases. One fatal air embolism followed open heart surgery, and one cardiac tissue embolus resulted in a major stroke. CONCLUSIONS: We advocate for greater awareness of these underrecognized and occasionally fatal complications of endovascular procedures. Targeted postprocedural imaging has a role in the identification of iatrogenic embolic infarcts.

Thermodynamics of Tower-Block Infernos: Effects of Water on Aluminum Fires.

We review the thermodynamics of combustion reactions involved in aluminum fires in the light of the spate of recent high-profile tower-block disasters, such as the Grenfell fire in London 2017, the Dubai fires between 2010 and 2016, and the fires and explosions that resulted in the 9/11 collapse of the World Trade Center twin towers in New York. These fires are class B, i.e., burning metallic materials, yet water was applied in all cases as an extinguisher. Here, we highlight the scientific thermochemical reasons why water should never be used on aluminum fires, not least because a mixture of aluminum and water is a highly exothermic fuel. When the plastic materials initially catch fire and burn with limited oxygen (O2 in air) to carbon (C), which is seen as an aerosol (black smoke) and black residue, the heat of the reaction melts the aluminum (Al) and increases its fluidity and volatility. Hence, this process also increases its reactivity, whence it rapidly reacts with the carbon product of polymer combustion to form aluminum carbide (Al4C3). The heat of formation of Al4Cl3 is so great that it becomes white-hot sparks that are similar to fireworks. At very high temperatures, both molten Al and Al4C3 aerosol react violently with water to give alumina fine dust aerosol (Al2O3) + hydrogen (H2) gas and methane (CH4) gas, respectively, with white smoke and residues. These highly inflammable gases, with low spontaneous combustion temperatures, instantaneously react with the oxygen in the air, accelerating the fire out of control. Adding water to an aluminum fire is similar to adding "rocket fuel" to the existing flames. A CO2-foam/powder extinguisher, as deployed in the aircraft industry against aluminum and plastic fires by smothering, is required to contain aluminum fires at an early stage. Automatic sprinkler extinguisher systems should not be installed in tower blocks that are at risk of aluminum fires.

Rod- versus cone-driven ERGs at different stimulus sizes in normal subjects and retinitis pigmentosa patients.

PURPOSE: To study how rod- and cone-driven responses depend on stimulus size in normal subjects and patients with retinitis pigmentosa (RP), and to show that comparisons between responses to full-field (FF) and smaller stimuli can be useful in diagnosing and monitoring disorders of the peripheral retina without the need for lengthy dark adaptation periods. METHOD: The triple silent substitution technique was used to isolate L-cone-, M-cone- and rod-driven ERGs with 19, 18 and 33% photoreceptor contrasts, respectively, under identical mean luminance conditions. Experiments were conducted on five normal subjects and three RP patients. ERGs on control subjects were recorded at nine different temporal frequencies (between 2 and 60 Hz) for five different stimulus sizes: FF, 70°, 60°, 50° and 40° diameter circular stimuli. Experiments on RP patients involved rod- and L-cone-driven ERG measurements with FF and 40° stimuli at 8 and 48 Hz. Response amplitudes were defined as those of the first harmonic component after Fourier analysis. RESULTS: In normal subjects, rod-driven responses displayed a fundamentally different behavior than cone-driven responses, particularly at low temporal frequencies. At low and intermediate temporal frequencies (≤ 12 Hz), rod-driven signals increased by a factor of about four when measured with smaller stimuli. In contrast, L- and M-cone-driven responses in this frequency region did not change substantially with stimulus size. At high temporal frequencies (≥ 24 Hz), both rod- and cone-driven response amplitudes decreased with decreasing stimulus size. Signals obtained from rod-isolating stimuli under these conditions are likely artefactual. Interestingly, in RP patients, both rod-driven and L-cone-driven ERGs were similar using 40° and FF stimuli. CONCLUSION: The increased responses with smaller stimuli in normal subjects to rod-isolating stimuli indicate that a fundamentally different mechanism drives the ERGs in comparison with the cone-driven responses. We propose that the increased responses are caused by stray light stimulating the peripheral retina, thereby allowing peripheral rod-driven function to be studied using the triple silent substitution technique at photopic luminances. The method is effective in studying impaired peripheral rod- and cone- function in RP patients.

A Temporal White Noise Analysis for Extracting the Impulse Response Function of the Human Electroretinogram.

PURPOSE: We introduce a method for determining the impulse response function (IRF) of the ERG derived from responses to temporal white noise (TWN) stimuli. METHODS: This white noise ERG (wnERG) was recorded in participants with normal trichromatic vision to full-field (Ganzfeld) and 39.3° diameter focal stimuli at mesopic and photopic mean luminances and at different TWN contrasts. The IRF was obtained by cross-correlating the TWN stimulus with the wnERG. RESULTS: We show that wnERG recordings are highly repeatable, with good signal-to-noise ratio, and do not lead to blink artifacts. The wnERG resembles a flash ERG waveform with an initial negativity (N1) followed by a positivity (P1), with amplitudes that are linearly related to stimulus contrast. These N1 and N1-P1 components showed commonalties in implicit times with the a- and b-waves of flash ERGs. There was a clear transition from rod- to cone-driven wnERGs at ∼1 photopic cd.m-2. We infer that oscillatory potentials found with the flash ERG, but not the wnERG, may reflect retinal nonlinearities due to the compression of energy into a short time period during a stimulus flash. CONCLUSION: The wnERG provides a new approach to study the physiology of the retina using a stimulation method with adaptation and contrast conditions similar to natural scenes to allow for independent variation of stimulus strength and mean luminance, which is not possible with the conventional flash ERG. TRANSLATIONAL RELEVANCE: The white noise ERG methodology will be of benefit for clinical studies and animal models in the evaluation of hypotheses related to cellular redundancy to understand the effects of disease on specific visual pathways.

Elimination of the unnecessary: Intra- and extracellular signaling by anionic phospholipids.

High fidelity of biological systems is frequently achieved by duplication of the essential intracellular machineries or, removal of the entire cell, which becomes unnecessary or even harmful in altered physiological environments. Carefully controlled removal of these cells, without damaging normal cells, requires precise signaling, and is critical to maintaining homeostasis. This review describes how two anionic phospholipids - phosphatidylserine (PS) and cardiolipin (CL) - residing in distinct compartments of the cell, signal removal of "the unnecessary" using several uniform principles. One of these principles is realized by collapse of inherent transmembrane asymmetry and the externalization of the signal on the outer membrane surface - mitochondria for CL and the plasma membrane for PS - to trigger mitophagy and phagocytosis, respectively. Release from damaged cells of intracellular structures with externalized CL or externalized PS triggers their elimination by phagocytosis. Another of these principles is realized by oxidation of polyunsaturated species of CL and PS. Highly specific oxidation of CL by cytochrome c serves as a signal for mitochondria-dependent apoptosis, while oxidation of externalized PS improves its effectiveness to trigger phagocytosis of effete cells.

Known unknowns of cardiolipin signaling: The best is yet to come.

Since its discovery 75years ago, a wealth of knowledge has accumulated on the role of cardiolipin, the hallmark phospholipid of mitochondria, in bioenergetics and particularly on the structural organization of the inner mitochondrial membrane. A surge of interest in this anionic doubly-charged tetra-acylated lipid found in both prokaryotes and mitochondria has emerged based on its newly discovered signaling functions. Cardiolipin displays organ, tissue, cellular and transmembrane distribution asymmetries. A collapse of the membrane asymmetry represents a pro-mitophageal mechanism whereby externalized cardiolipin acts as an "eat-me" signal. Oxidation of cardiolipin's polyunsaturated acyl chains - catalyzed by cardiolipin complexes with cytochrome c. - is a pro-apoptotic signal. The messaging functions of myriads of cardiolipin species and their oxidation products are now being recognized as important intracellular and extracellular signals for innate and adaptive immune systems. This newly developing field of research exploring cardiolipin signaling is the main subject of this review. This article is part of a Special Issue entitled: Lipids of Mitochondria edited by Guenther Daum.

Rod Electroretinograms Elicited by Silent Substitution Stimuli from the Light-Adapted Human Eye.

PURPOSE: To demonstrate that silent substitution stimuli can be used to generate electroretinograms (ERGs) that effectively isolate rod photoreceptor function in humans without the need for dark adaptation, and that this approach constitutes a viable alternative to current clinical standard testing protocols. METHODS: Rod-isolating and non-isolating sinusoidal flicker stimuli were generated on a 4 primary light-emitting diode (LED) Ganzfeld stimulator to elicit ERGs from participants with normal and compromised rod function who had not undergone dark-adaptation. Responses were subjected to Fourier analysis, and the amplitude and phase of the fundamental were used to examine temporal frequency and retinal illuminance response characteristics. RESULTS: Electroretinograms elicited by rod-isolating silent substitution stimuli exhibit low-pass temporal frequency response characteristics with an upper response limit of 30 Hz. Responses are optimal between 5 and 8 Hz and between 10 and 100 photopic trolands (Td). There is a significant correlation between the response amplitudes obtained with the silent substitution method and current standard clinical protocols. Analysis of signal-to-noise ratios reveals significant differences between subjects with normal and compromised rod function. CONCLUSIONS: Silent substitution provides an effective method for the isolation of human rod photoreceptor function in subjects with normal as well as compromised rod function when stimuli are used within appropriate parameter ranges. TRANSLATIONAL RELEVANCE: This method of generating rod-mediated ERGs can be achieved without time-consuming periods of dark adaptation, provides improved isolation of rod- from cone-based activity, and will lead to the development of faster clinical electrophysiologic testing protocols with improved selectivity.

Failure to detect meaning in RSVP at 27 ms per picture.

The human visual system has the remarkable ability to rapidly detect meaning from visual stimuli. Potter, Wyble, Hagmann, and McCourt (Attention, Perception, & Psychophysics, 76, 270-279, 2014) tested the minimum viewing time required to obtain meaning from a stream of pictures shown in a rapid serial visual presentation (RSVP) sequence containing either six or 12 pictures. They reported that observers could detect the presence of a target picture specified by name (e.g., smiling couple) even when the pictures in the sequence were presented for just 13 ms each. Potter et al. claimed that this was insufficient time for feedback processing to occur, so feedforward processing alone must be able to generate conscious awareness of the target pictures. A potential confound in their study is that the pictures in the RSVP sequence sometime contained areas with no high-contrast edges, and so may not have adequately masked each other. Consequently, iconic memories of portions of the target pictures may have persisted in the visual system, thereby increasing the effective presentation time. Our study addressed this issue by redoing the Potter et al. study, but using four different types of masks. We found that when adequate masking was used, no evidence emerged that observers could detect the presence of a specific target picture, even when each picture in the RSVP sequence was presented for 27 ms. On the basis of these findings, we cannot rule out the possibility that feedback processing is necessary for individual pictures to be recognized.

Mitochondrial Redox Opto-Lipidomics Reveals Mono-Oxygenated Cardiolipins as Pro-Apoptotic Death Signals.

While opto-genetics has proven to have tremendous value in revealing the functions of the macromolecular machinery in cells, it is not amenable to exploration of small molecules such as phospholipids (PLs). Here, we describe a redox opto-lipidomics approach based on a combination of high affinity light-sensitive ligands to specific PLs in mitochondria with LC-MS based redox lipidomics/bioinformatics analysis for the characterization of pro-apoptotic lipid signals. We identified the formation of mono-oxygenated derivatives of C18:2-containing cardiolipins (CLs) in mitochondria after the exposure of 10-nonylacridine orange bromide (NAO)-loaded cells to light. We ascertained that these signals emerge as an immediate opto-lipidomics response, but they decay long before the commencement of apoptotic cell death. We found that a protonophoric uncoupler caused depolarization of mitochondria and prevented the mitochondrial accumulation of NAO, inhibited the formation of C18:2-CL oxidation product,s and protected cells from death. Redox opto-lipidomics extends the power of opto-biologic protocols to studies of small PL molecules resilient to opto-genetic manipulations.

Intracranial metastasis of adenocarcinoma of the prostate presenting with symptoms of spinal cord compression.

Spinal cord compression is a not uncommon complication of metastatic prostate cancer. Intracranial metastasis of prostatic adenocarcinoma is however unusual. We report a case of a 67-year-old man with metastatic prostate carcinoma, who presented with a 3-day history of lower limb weakness and collapse. Neurological assessment demonstrated increased tone and reduced power in both legs. As he had typical signs and symptoms of spinal cord compression, an MRI of the spine was performed; this demonstrated no evidence of cord compression. A subsequent CT of the brain demonstrated an extensive parafalcine metastasis. This revealed an extensive enhancing mass extending bilaterally along almost the entire length of the falx cerebri, measuring up to 3 cm in width and associated with marked white matter oedema in the adjacent brain bilaterally. Unfortunately, this man succumbed to his illness a few days later. The imaging findings are presented and highlight the importance of brain imaging in patients presenting with suspected cord compression due to prostatic metastatic disease when MR of the spine shows no evidence of cord compression.

The spatial properties of L- and M-cone inputs to electroretinograms that reflect different types of post-receptoral processing.

We studied the spatial arrangement of L- and M-cone driven electroretinograms (ERGs) reflecting the activity of magno- and parvocellular pathways. L- and M-cone isolating sine wave stimuli were created with a four primary LED stimulator using triple silent substitution paradigms. Temporal frequencies were 8 and 12 Hz, to reflect cone opponent activity, and 30, 36 and 48 Hz to reflect luminance activity. The responses were measured for full-field stimuli and for different circular and annular stimuli. The ERG data confirm the presence of two different mechanisms at intermediate and high temporal frequencies. The responses measured at high temporal frequencies strongly depended upon spatial stimulus configuration. In the full-field conditions, the L-cone driven responses were substantially larger than the full-field M-cone driven responses and also than the L-cone driven responses with smaller stimuli. The M-cone driven responses at full-field and with 70° diameter stimuli displayed similar amplitudes. The L- and M-cone driven responses measured at 8 and 12 Hz were of similar amplitude and approximately in counter-phase. The amplitudes were constant for most stimulus configurations. The results indicate that, when the ERG reflects luminance activity, it is positively correlated with stimulus size. Beyond 35° retinal eccentricity, the retina mainly contains L-cones. Small stimuli are sufficient to obtain maximal ERGs at low temporal frequencies where the ERGs are also sensitive to cone-opponent processing.