Non-visual environmental imaging and object detection through active electrolocation in weakly electric fish

Weakly electric fish orient at night by employing active electrolocation. South American and African species emit electric signals and perceive the consequences of these emissions with epidermal electroreceptors. Objects are detected by analyzing the electric images which they project onto the animal’s electroreceptive skin surface. Electric images depend on size, distance, shape, and material of objects and on the morphology of the electric organ and the fish’s body. It is proposed that the mormyrid Gnathonemus petersii possesses two electroreceptive “foveae” at its Schnauzenorgan and its nasal region, both of which resemble the visual fovea in the retina of many animals in design, function, and behavioral use. Behavioral experiments have shown that G. petersii can determine the resistive and capacitive components of an object’s complex impedance in order to identify prey items during foraging. In addition, fish can measure the distance and three-dimensional shape of objects. In order to determine object properties during active electrolocation, the fish have to determine at least four parameters of the local signal within an object’s electric image: peak amplitude, maximal slope, image width, and waveform distortions. A crucial parameter is the object distance, which is essential for unambiguous evaluation of object properties.     

Discrimination of objects through electrolocation in the weakly electric fish,Gnathonemus petersii

Summary Three weakly electric fish (Gnathonemus petersii) were force-choice trained in a two-alternative procedure to discriminate between objects differing in their electrical characteristics. The objects were carbon dipoles in plexiglass tubing (length 2.5 cm, diameter 0.6 cm). Their electrical characteristics could be changed by varying the impedance of an external circuit to which they were connected (Fig. 1). In one (the capacitance dipole) the resistance was very low(< 3 ) and the capcitance variable. In the other (the resistance dipole) the resistance was variable and the capacitance low (<50 pF).Capacitances from several hundred pF (lower thresholds, Fig. 2) to several hundred nF (upper thresholds, Fig. 3) could be discriminated from both insulators and good conductors. In all cases the reward-negative stimulus was the capacitance dipole, which was avoided by all fish spontaneously. Thresholds were defined at 70% correct choices.The fish were then tested for their ability to discriminate between one object with a given capacitance and another with resistances varying from 3 to 200 k. The capacitance dipole continued to be the negative stimulus throughout. All 3 fish avoided it in at least 80% of the trials at each stimulus combination (Fig. 4). This result suggests that Gnathonemus perceives the capacitance and the resistance of objects differentially.The effect of the dipole-objects as well as some natural objects on the local EOD was recorded differentially very close to the fish's skin (Fig. 5). The amplitude of the local EODs was affected by all types of objects as they approached the skin. However, the waveform was changed only by capacitance dipoles and some natural objects (Figs. 6 and 7). It appears that the fish perceive not only intensity changes in the local EOD but wave-form deformations as well and can thus distinguish objects of different complex impedances.Abbreviations EOD electric organ discharge - f _max maximal spectral frequency - GP Gnathonemus petersii - LFS local filtered signal - PMA probing motor act - S+ positive stimulus - S negative stimulus     

Responses of electrosensory neurons in the torus semicircularis of Eigenmannia to complex beat stimuli: testing hypotheses of temporal filtering

The weakly electric fish, Eigenmannia, changes its frequency of electric organ discharges (EODs) to increase the frequency difference between its EODs and those of a jamming neighbor. This jamming avoidance response is greatest for frequency differences (i.e., beat rates) of approximately 4 Hz and barely detectable at beat rates of 20 Hz. A neural correlate of this behavior is found in the torus semicircularis, where most neurons act as low-pass or band-pass filters over this range of beat rates.This study examines two mechanisms that could possibly underlie low-pass temporal filtering: 1) Inhibition by a high-pass interneuron. 2) Voltage and time-dependent conductances associated with ligand-gated channels. These mechanisms were tested by recording intracellularly while employing stimuli consisting of simultaneous low and high beat rates. A neuron's response to the low beat rate was not diminished by the addition of the higher frequency jamming signal (thereby superimposing a high rate of amplitude and phase modulation onto the lower rate), and the inhibitory interneuron hypothesis is, therefore, not supported. Also, the responses to the high beat rate were not facilitated during maintained depolarization in response to the low beat rate.In some cases, particularly band-pass neurons, accommodation processes appeared to contribute to the decline in the amplitude of psps at high beat rates.     

Electric fields affect the orientation of cortical microtubules and cell expansion in pea callus

Summary Cortical microtubules in callus derived fromPisum sativum roots form parallel arrays within cells but are randomly oriented across the tissue. These arrays align perpendicular to the direction of an applied electric field of 6 mV per cell. Application of a field of 6 mV per cell for 4 days resulted in the co-ordinated expansion of cells parallel to the field direction. Cortical microtubule arrays were still aligned perpendicular to the applied field 24 h after removal of the field. The imposition of a field to callus after the removal of cortical microtubules by oryzalin and in the presence of the herbicide resulted in the orientation of recovering microtubules perpendicular to the direction of the field, indicating that microtubules are not directly involved in the detection of the field.Abbreviations EGTA ethylene glycol-bis (-aminoethyl ether) N,N,N-tetraacetic acid - FITC fluorescein isothiocyanate - MSB microtubule stabilising buffer - PIPES piperazine-N,N-bis(2-ethanesulphonic acid) - oryzalin 3,5-dinitro-N⁴,N⁴ dipropylsulphanil-amide     

A single-image retrieval method for edge illumination X-ray phase-contrast imaging: Application and noise analysis

PurposeEdge illumination (EI) X-ray phase-contrast imaging (XPCI) has been under development at University College London in recent years, and has shown great potential for both laboratory and synchrotron applications. In this work, we propose a new acquisition and processing scheme. Contrary to existing retrieval methods for EI, which require as input two images acquired in different setup configurations, the proposed approach can retrieve an approximate map of the X-ray phase from a single image, thus significantly simplifying the acquisition procedure and reducing data collection times.MethodsThe retrieval method is analytically derived, based on the assumption of a quasi-homogeneous object, i.e. an object featuring a constant ratio between refractive index and absorption coefficient. The noise properties of the input and retrieved images are also theoretically analyzed under the developed formalism. The method is applied to experimental synchrotron images of a biological object.ResultsThe experimental results show that the method can provide high-quality images, where the “edge” signal typical of XPCI images is transformed to an “area” contrast that enables an easier interpretation of the sample geometry. Moreover, the retrieved images confirm that the method is highly stable against noise.ConclusionsWe anticipate that the developed approach will become the method of choice for a variety of applications of EI XPCI, thanks to its ability to simplify the acquisition procedure and reduce acquisitions time and dose to the sample. Future work will focus on the adaptation of the method to computed tomography and to polychromatic radiation from X-ray tubes.     

Three‐dimensional imaging technologies: a priority for the advancement of tissue engineering and a challenge for the imaging community

Tissue engineering/regenerative medicine (TERM) is an interdisciplinary field that applies the principle of engineering and life sciences to restore/replace damaged tissues/organs with in vitro artificially‐created ones. Research on TERM quickly moves forward. Today newest technologies and discoveries, such as 3D‐/bio‐printing, allow in vitro fabrication of ex‐novo made tissues/organs, opening the door to wide and probably never‐ending application possibilities, from organ transplant to drug discovery, high content screening and replacement of laboratory animals. Imaging techniques are fundamental tools for the characterization of tissue engineering (TE) products at any stage, from biomaterial/scaffold to construct/organ analysis. Indeed, tissue engineers need versatile imaging methods capable of monitoring not only morphological but also functional and molecular features, allowing three‐dimensional (3D) and time‐lapse in vivo analysis, in a non‐destructive, quantitative, multidimensional analysis of TE constructs, to analyze their pre‐implantation quality assessment and their fate after implantation. This review focuses on the newest developments in imaging technologies and applications in the context of requirements of the different steps of the TERM field, describing strengths and weaknesses of the current imaging approaches.

     

Mechanism of Alzheimer's disease: Arguments for a neurotransmitter-aluminium complex implication

The authors are convinced that in Alzheimer's disease, as in Down's syndrome and Guam-Parkinson dementia, one may find an alteration in blood brain barrier transfer and a resultant imbalance in mineral metabolism. Metals, such as aluminium, which in vivo yield stable complexes with aspartic and glutamic acids act as previously been clearly shown with glutamic acid; they cross the blood brain barrier, and are deposited in the brain. The authors explain how amyloid protein or neurofibrillary tangles could well be produced by aluminium complex formation. Whithin the brain, in the form precisely of aluminium complex,l-glutamic acid is consequently unable to detoxify ammonia from neurons and to produce L-glutamin. Accumulation of ammonia is subsequently responsible for the neuronal death, affecting each and every neurotransmitter system.     

Human topoisomerase I C-terminal domain fragment containing the active site tyrosine is a molten globule: implication for the formation of competent productive complex

Human topoisomerase I (topo I) is an essential cellular enzyme that relaxes DNA supercoiling. The 6.3 kDa C-terminal domain of topo I contains the active site tyrosine (Tyr723) but lacks enzymatic activity by itself. Activity can be fully reconstituted when the C-terminal domain is associated with the 56 kDa core domain. Even though several crystal structures of topo I/DNA complexes are available, crystal structures of the free topo I protein or its individual domain fragments have been difficult to obtain. In this report we analyze the human topo I C-terminal domain structure using a variety of biophysical methods. Our results indicate that this fragment protein (topo6.3) appears to be in a molten globule state. It appears to have a native-like tertiary fold that contains a large population of alpha-helix secondary structure and extensive surface hydrophobic regions. Topo6.3 is known to be readily activated with the association of the topo I core domain, and the molten globule state of topo6.3 is likely to be an energy-favorable conformation for the free topo I C-terminal domain protein. The structural fluctuation and plasticity may represent an efficient mechanism in the topo I functional pathway, where the flexibility aids in the complementary association with the core domain and in the formation of a fully productive topo I complex.     

Multiple functional linear model for association analysis of RNA-seq with imaging

Emerging integrative analysis of genomic and anatomical imaging data which has not been well developed, provides invaluable information for the holistic discovery of the genomic structure of disease and has the potential to open a new avenue for discovering novel disease susceptibility genes which cannot be identified if they are analyzed separately. A key issue to the success of imaging and genomic data analysis is how to reduce their dimensions. Most previous methods for imaging information extraction and RNA-seq data reduction do not explore imaging spatial information and often ignore gene expression variation at the genomic positional level. To overcome these limitations, we extend functional principle component analysis from one dimension to two dimensions (2DFPCA) for representing imaging data and develop a multiple functional linear model (MFLM) in which functional principal scores of images are taken as multiple quantitative traits and RNA-seq profile across a gene is taken as a function predictor for assessing the association of gene expression with images. The developed method has been applied to image and RNA-seq data of ovarian cancer and kidney renal clear cell carcinoma (KIRC) studies. We identified 24 and 84 genes whose expressions were associated with imaging variations in ovarian cancer and KIRC studies, respectively. Our results showed that many significantly associated genes with images were not differentially expressed, but revealed their morphological and metabolic functions. The results also demonstrated that the peaks of the estimated regression coefficient function in the MFLM often allowed the discovery of splicing sites and multiple isoforms of gene expressions.     

Electric organ discharges of the gymnotiform fishes: III. Brachyhypopomus

We measured and mapped the electric fields produced by three species of neotropical electric fish of the genus Brachyhypopomus (Gymnotiformes, Rham phichthyoidea, Hypopomidae), formerly Hypopomus. These species produce biphasic pulsed discharges from myogenic electric organs. Spatio-temporal false-color maps of the electric organ discharges measured on the skin show that the electric field is not a simple dipole in Brachyhypopomus. Instead, the dipole center moves rostro-caudally during the 1st phase (P1) of the electric organ discharge, and is stationary during the 2nd phase (P2). Except at the head and tip of tail, electric field lines rotate in the lateral and dorso-ventral planes. Rostro-caudal differences in field amplitude, field lines, and spatial stability suggest that different parts of the electric organ have undergone selection for different functions; the rostral portions seem specialized for electrosensory processing, whereas the caudal portions show adaptations for d.c. signal balancing and mate attraction as well. Computer animations of the electric field images described in this paper are available on web sites http://www.bbb.caltech.edu/ElectricFish or http://www.fiu.edu/∼stoddard/electricfish.html. Accepted: 22 September 1998     

Electrical and proton gradients in the sensory transduction of photophobic responses in the blue-green alga,Phormidium uncinatum

The gliding filaments of the blue-green alga Phormidium uncinatum stop their movement almost instantaneously when transfered from their growth pH of 7.2 into a buffer 4.5 or 12.5. A pH jump into the range between 5.6 and 12.0 induces no visible response while in the range between 4.9 and 5.5 the organisms reverse the direction of their movement. The pH jump is believed to simulate an early step during the sensory transduction chain of the photophobic response which eventually results in a reversal of movement.One of the subsequent steps is the inversion of an electric potential gradient existing between the front and rear ends of a filament which dictates the direction of movement. A similar reversal of the naturally existing potential gradient can be provoked by switching on an external do field when the filaments move towards the anode or switching it off when the filaments glide in the opposite direction. Implications of these results on the current model of sensory transduction of the photophobic response in Phormidium uncinatum are being discussed.     

Commissural neurons of the electrosensory lateral line lobe of Apteronotus leptorhynchus: morphological and physiological characteristics

Extracellular injections of horseradish peroxidase were used to label commissural cells connecting the electrosensory lateral line lobes of the weakly electric fish Apteronotus leptorhynchus. Multiple commissural pathways exist; a caudal commissure is made up of ovoid cell axons, and polymorphic cells' axons project via a rostral commissure. Intracellular recording and labeling showed that ovoid cells discharge spontaneously at high rates, fire at preferred phases to the electric organ discharge, and respond to increased receptor afferent input with short latency partially adapting excitation. Ovoid cell axons ramify extensively in the rostro-caudal direction but are otherwise restricted to a single ELL subdivision. Polymorphic cells are also spontaneously active, but their firing is unrelated to the electric organ discharge waveform. They respond to increased receptor afferent activity with reduced firing frequency and response latency is long. Electrical stimulation of the commissural axons alters the behavior of pyramidal cells in the contralateral ELL. Basilar pyramidal cells are hyperpolarized and nonbasilar pyramidal cells are depolarized by this type of stimulation. The physiological results indicate that the ovoid cells participate in common mode rejection mechanisms and also suggest that the ELLs may function in a differential mode in which spatially restricted electrosensory stimuli can evoke heightened responses.Abbreviations ccELL caudal commissure of the ELL - CE contralaterally excited - DML dorsal molecular layer - ELL electrosensory lateral line lobe - EOD electric organ discharge - HRP horseradish peroxidase - IE ipsilaterally excited - MTI mouth-tail inverted - MTN mouth-tail normal - rcELL rostral commissure of the ELL - TRI transverse inverted - TRN transverse normal     

MALDI imaging mass spectrometry for direct tissue analysis: a new frontier for molecular histology

Matrix-assisted laser desorption/ionization (MALDI) imaging mass spectrometry (IMS) is a powerful tool for investigating the distribution of proteins and small molecules within biological systems through the in situ analysis of tissue sections. MALDI-IMS can determine the distribution of hundreds of unknown compounds in a single measurement and enables the acquisition of cellular expression profiles while maintaining the cellular and molecular integrity. In recent years, a great many advances in the practice of imaging mass spectrometry have taken place, making the technique more sensitive, robust, and ultimately useful. In this review, we focus on the current state of the art of MALDI-IMS, describe basic technological developments for MALDI-IMS of animal and human tissues, and discuss some recent applications in basic research and in clinical settings.     

Bond‐selective imaging of deep tissue through the optical window between 1600 and 1850 nm

We report the employment of an optical window between 1600 nm and 1850 nm for bond‐selective deep tissue imaging through harmonic vibrational excitation and acoustic detection of resultant pressure waves. In this window where a local minimum of water absorption resides, we found a 5 times enhancement of photoacoustic signal by first overtone excitation of the methylene group CH₂ at 1730 nm, compared to the second overtone excitation at 1210 nm. The enhancement allows 3D mapping of intramuscular fat with improved contrast and of lipid deposition inside an atherosclerotic artery wall in the presence of blood. Moreover, lipid and protein are differentiated based on the first overtone absorption profiles of CH₂ and methyl group CH₃ in this window. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Revisiting excitation pattern design for magnetic resonance imaging through optimisation of the signal contrast efficiency

The design of excitation signals for Magnetic Resonance Imaging (MRI) is cast as an optimal control problem. Here, we demonstrate that signals other than pulse excitations, which are ubiquitous in MRI, can provide adequate excitation, thus challenging the optimality and ubiquity of pulsed signals. A class of on-resonance piecewise continuous amplitude modulated signals is introduced. It is shown that despite the bilinear nature of the Bloch equations, the spins system response is largely analytically tractable for this class of signals, using Galerkin approximation methods. To challenge the optimality of the pulse excitation, an appropriate cost criterion, the Signal Contrast Efficiency (SCE), is developed. It is to be optimised subject to dynamics expressed by the Bloch equations. To solve the problem the Bloch equation is transferred to the excitation dependent rotating frame of reference. The numerical solutions to the problem for different tissue types show that for a short period of time, pulse excitations provide the maximum signal contrast. However, the problem should be solved for longer periods of time which may result in a different answer than a pulse. For this purpose, the approximate analytic solution which is derived based on averaging the Bloch equation in the excitation dependent rotating frame of reference will be used to find the optimal excitation pattern. The solution to the optimisation problem is potentially useful for all forms of MRI including structural and functional imaging. The objective of this paper is to show that while classically transient response of pulses have been monitored so far, the optimal excitation pattern may be the steady state response of a non-pulse excitation.     

Electric pulses to prepare feeder cells for sustaining and culturing of undifferentiated embryonic stem cells

Current challenges in embryonic-stem cell (ESC) research include the inability of sustaining and culturing of undifferentiated ESCs over time. Growth-arrested feeder cells are essential to the culture and sustaining of undifferentiated ESCs, and they are currently prepared using gamma-radiation and chemical inactivation. Both techniques have severe limitations. In this study, we developed a new, simple and effective technique (pulsed electric fields, PEFs) to produce viable growth-arrested cells (RTS34st) and used them as high-quality feeder cells to culture and sustain undifferentiated zebrafish ESCs over time. The cells were exposed to 25 sequential 10-ns electric pulses (10nsEPs) of 25, 40 and 150 kV/cm with 1-s pulse interval, or 2 sequential 50-μs electric pulses (50μsEPs) of 2.83, 1.78 and 0.78 kV/cm with 5-s pulse interval, respectively. We found that the cellular effects of PEFs depended directly upon the duration, number and electric field strength of the pulses, showing the feasibility of tuning them to produce various types of growth-arrested cells for culturing undifferentiated ESCs. Both 10nsEPs of 40 kV/cm produced by a 10nsEP generator and 50μsEPs of 1.78 kV/cm provided by inexpensive and widely available conventional electroporators, generated high-quality growth-arrested feeder cells for proliferation of undifferentiated ESCs over time. PEFs can therefore be used to replace radiation and chemical inactivation methods for preparation of growth-arrested feeder cells for advancing ESC research.     

High resolution microanalysis for phosphorus in Golgi complex beads of insect fat body tissue by electron spectroscopic imaging

Golgi complex beads are 10 nm particles arranged in rings on the smooth forming face of the Golgi complex that stain specifically with bismuth in arthropod cells. In vitro experiments with biological molecules spotted on to cellulose acetate strips indicated that bismuth bound to the beads through phosphate groups. We could detect a weak phosphorus signal from the beads using a new technique called electron spectroscopic imaging that is capable of very high spatial resolution (0.3–0.5 nm) and sensitivity (50 atoms of phosphorus). Detection was not obscured by tissue staining with bismuth or uranyl acetate or by using an inorganic buffer (Na cacodylate). Localization of phosphorus was greatly improved by using colour-enhanced computer pictures of the electron spectroscopic images and quantitating the images. The results indicate that the phosphorus content of the beads is large enough to account for their bismuth reactivity.     

Self-assembly of molecular beacons through metal ion coordination for fluorescence imaging of miRNA in living cells

Fluorescence nanosensors based on functional nucleic acids have been explored as a powerful sensing platform for disease-relevant miRNAs. This work developed a new hybrid nanosensor (Zr-B) through coordination-driven self-assembly of Zr ions and beacons. The prepared nanosensor exhibited high loading efficiency of beacons and could achieve sensitive and specific detection for miRNAs. The hybrid nanosensor could transfer beacons into living cells efficiently and maintain high stability and biocompatibility in the biological environment, achieving effective miRNA fluorescence imaging in living cells. Therefore, the resultant nanosensor holds potential for applications in disease diagnostics.     

Potential use of exogenous RNAs for the analysis of the complex effects of biologically active substances

It has been established in rat experiments that RNA obtained from the liver and renal cortex of animals given hydrocortisone produces in recipients the rise of physical endurance evoked by the hormone. RNA obtained from other organs of these animals and from any test organs of control donors did not influence physical endurance. The key role of the liver and kidneys in the realization of the hydrocortisone effect is likely to be connected with activation of the synthesis of gluconeogenesis enzymes. RNA obtained from the organs of donors premedicated with hydrocortisone reproduced stimulation of gluconeogenesis with hydrocortisone. The use of exogenous RNA holds promise for analysis of complex effects of biologically active substances, since it permits studying separately the components of the effects determined by activation of protein synthesis in definite organs.