Peculiarities of Ca<Superscript>2+</Superscript>-regulation of functional activity of myocardium of frog <Emphasis Type="Italic">Rana temporaria</Emphasis>

To elucidate role of intra- and extracellular Ca²⁺ in regulation of rhythm and strength of frog heart contractions, there were studied ECC and isometric contraction of myocardium preparations in response to verapamil, adrenaline, and blockers of α- and β-adrenoreceptors. It has been shown that after an intramuscular injection of verapamil (6 mg/kg), bradycardia develops, the heart rate (HR) decreasing by 50–70%. Further, the cardiac arrest occurred; however, administration to the animals of adrenaline (100 mg/kg) restored the cardiac rhythm for a short while. After an intramuscular injection of adrenaline at doses of 0.1–10 mg/kg, no essential changes were observed in the potential action amplitude and HR; an increase of the administered adrenalin concentration to 100 mg/kg was not accompanied by the cardiac rhythm stimulation, as this takes place in homoiothermal animals and human; on the contrary, an essential HR deceleration was revealed. Phentolamine (5 mg/kg) gradually decelerated HR rhythm by 32–45%. The potential amplitude changed insignificantly. A subsequent intracardiac injection of adrenaline (100 mg/kg) on the background of block of α-adrenoreceptors produced acceleration of the rhythm (by 15–21%) and fall of the electrogram amplitude. These results can indicate that in the frog heart phentolamine interacts predominantly with α 1-adrenoreceptors. An intracardial administration of propranolol (1 mg/kg) to frogs promoted inhibition of β-adrenergic receptors and produced a gradual cardiac rhythm deceleration. In experiments on assessment of verapamil effect on the character of contractions this preparation at a concentration of 150 μM was established to produce a significant dose-dependent decrease of the contraction strength. A rise of verapamil concentration in the sample to 200 μM led to a decrease of the amplitude, on average, by 68–70% and in individual preparations—by 80–85%; however, administration into the sample of adrenaline (10 μM) restored the cardiac contraction strength. Adrenaline (1 nM–100 μM) increased markedly the contraction amplitude. Phentolamine (10 μM) did not inhibit transmission of contractile signal to cardiomyocytes; this was manifested in that the contraction amplitude after addition of adrenaline (10 μM) into the sample was approximately the same as in the sample containing no phentolamine. Propranolol (10 μM) eliminated the stimulatory action of adrenaline (10 μM). The results of these experiments indicate that in the frog ventricular cardiomyocytes the main adrenaline acceptors are β-adrenoreceptors.     

ADP-Inhibition of H<Superscript>+</Superscript>-F<Subscript>O</Subscript>F<Subscript>1</Subscript>-ATP Synthase

H⁺-F_OF₁-ATP synthase (F-ATPase, F-type ATPase, F_OF₁ complex) catalyzes ATP synthesis from ADP and inorganic phosphate in eubacteria, mitochondria, chloroplasts, and some archaea. ATP synthesis is powered by the transmembrane proton transport driven by the proton motive force (PMF) generated by the respiratory or photosynthetic electron transport chains. When the PMF is decreased or absent, ATP synthase catalyzes the reverse reaction, working as an ATP-dependent proton pump. The ATPase activity of the enzyme is regulated by several mechanisms, of which the most conserved is the non-competitive inhibition by the MgADP complex (ADP-inhibition). When ADP binds to the catalytic site without phosphate, the enzyme may undergo conformational changes that lock bound ADP, resulting in enzyme inactivation. PMF can induce release of inhibitory ADP and reactivate ATP synthase; the threshold PMF value required for enzyme reactivation might exceed the PMF for ATP synthesis. Moreover, membrane energization increases the catalytic site affinity to phosphate, thereby reducing the probability of ADP binding without phosphate and preventing enzyme transition to the ADP-inhibited state. Besides phosphate, oxyanions (e.g., sulfite and bicarbonate), alcohols, lauryldimethylamine oxide, and a number of other detergents can weaken ADP-inhibition and increase ATPase activity of the enzyme. In this paper, we review the data on ADP-inhibition of ATP synthases from different organisms and discuss the in vivo role of this phenomenon and its relationship with other regulatory mechanisms, such as ATPase activity inhibition by subunit ε and nucleotide binding in the noncatalytic sites of the enzyme. It should be noted that in Escherichia coli enzyme, ADP-inhibition is relatively weak and rather enhanced than prevented by phosphate.     

Molecular characterisation of the <Emphasis Type="Italic">STRUBBELIG-RECEPTOR FAMILY</Emphasis> of genes encoding putative leucine-rich repeat receptor-like kinases in <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis>

Background  

Receptor-like kinases are a prominent class of surface receptors that regulate many aspects of the plant life cycle. Despite recent advances the function of most receptor-like kinases remains elusive. Therefore, it is paramount to investigate these receptors. The task is complicated by the fact that receptor-like kinases belong to a large monophyletic family with many sub-clades. In general, functional analysis of gene family members by reverse genetics is often obscured by several issues, such as redundancy, subtle or difficult to detect phenotypes in mutants, or by decision problems regarding suitable biological and biochemical assays. Therefore, in many cases additional strategies have to be employed to allow inference of hypotheses regarding gene function.     

The presence of <Emphasis Type="Italic">Zygina</Emphasis> sp. and <Emphasis Type="Italic">Puccinia myrsiphylli</Emphasis> reduces survival and influences oviposition of <Emphasis Type="Italic">Crioceris</Emphasis> sp.

A leaf beetle, Crioceris sp. (Coleoptera: Chrysomelidae), was introduced into Australia as a biological control agent of bridal creeper (Asparagus asparagoides L. Druce) during October 2002. Rearing of Crioceris sp. is labour intensive therefore all releases of Crioceris sp. have been under 1000 individuals, which may be too low to ensure establishment if high mortality and high competition with other agents occurs. The aim of this study is to understand how the presence of two well-established biocontrol agents, a rust fungus (Puccinia myrsiphylli (Thuem) Wint [Basidiomycota: Uredinales]) and a leafhopper (Zygina sp. [Hemiptera: Cicadellidae]), might influence Crioceris sp. establishment. Crioceris sp. neonate larvae were placed on bridal creeper plants with or without the leafhopper and/or rust. The number of larvae that pupated was reduced by 38 and 65% in the presence of the rust fungus and leafhopper, respectively and by 45% in the presence of both agents. As the area infected by the rust increased the area damaged by the leafhopper decreased. The rust appeared to be negatively impacted by the presence of the leafhopper. In a second experiment, female Crioceris sp. adults were given a choice between uninfested bridal creeper plants and those infested with the rust or the leafhopper. The females preferred to lay their eggs on plants without leafhoppers but did not seem to be deterred by the presence of the rust. Consequently, the performance and impact of Crioceris sp. on bridal creeper may be reduced if populations overlap with the other biocontrol agents in the field.     

<Emphasis Type="Italic">Clavispora lusitaniae</Emphasis> and <Emphasis Type="Italic">Chaetomium atrobrunneum</Emphasis> as Rare Agents of Cutaneous Infection

We describe the first case of cutaneous infection caused by Chaetomium atrobrunneum and Clavispora lusitaniae in a one-and-a-half-year-old boy with acute and severe inflammation around his left eyelid. He presented to our outpatient center with a 6-day history and previously ineffective antibacterial therapy. Scanning electron microscopy (SEM) revealed hyphae and spores were on the surface of the crusty exudates and also penetrated into it, and the microbiology study further showed their characteristic cultural features. Fungal isolates were identified by the amplification and sequencing of the 26S RNA gene and of the ITS region, as C. lusitaniae and C. atrobrunneum. Up until now, most known clinical records of these rare species have shown them as agents of deep mycosis. Due to the emergency situation, medications were administered promptly and confirmed by subsequent fungal identification and successful therapeutic outcome. This article illustrates the importance of recognizing fungal infections, especially those caused by uncommon pathogens. Limitations in the routine identification procedures and therapeutic options of this emerging opportunistic agent are also discussed in this report.     

Physiological aspects of tolerance in <Emphasis Type="Italic">Atriplex</Emphasis><Emphasis Type="Italic">halimus</Emphasis> L. to NaCl and drought

Forty-day-old seedlings of Atriplex halimus were treated either with NaCl (50, 300 and 550 mM) for the subsequent 30 days or with 15% PEG for the subsequent 10 days. As much as 50 mM of NaCl significantly increased shoot fresh and dry weight and height; nevertheless, 300 or 550 mM NaCl seemed to have no effect. On the other hand, these growth parameters were not affected by drought after 3 or 6 days, but were reduced after 10 days. The gas exchange parameters (photosynthetic rate, stomatal conductance and transpiration rate) were increased by 50 mM NaCl, but decreased by 300 and 550 mM. These parameters were decreased in response to drought only after 10 days of withholding water. In contrast to Na⁺, K⁺ was significantly decreased by NaCl but not by drought. The time course effect revealed that phosphoenol pyruvate carboxylase (PEPC) protein was doubled in response to NaCl after 1 and 5 h and continued thereafter, higher than control, while drought had no significant effect. Rubisco seemed unchanged by NaCl or drought. It could be concluded that the decrease in fresh weight might be attributed to the decrease in water content. Moreover, the decrease in photosynthesis could result from a decrease in stomatal conductance, a protective mechanism against water loss to improve water use efficiency. These findings indicate that Atriplex halimus tolerates NaCl and drought through decreasing growth, reducing gas exchange parameters to improve water use efficiency, uptake Na⁺ and saving, if any, the photosynthetic enzyme particularly PEPC.     

Les séries silicoclastiques miocènes du Nord-Est au Sud-Ouest de la Tunisie : une mise au point

During the Miocene time, the Atlas-pelagian block, which is limited northward by the atlasic-alpin chain of North Africa-Sicily, southward by the Gafsa-Jeffara-Azizia fault and eastward by the Malta escarpment, resulted from the extension-compression regime, mainly controlled by the subduction-collision processes. This regime induced the opening of many Miocene microbasins, which have been infilled by silicoclastic materials showing lateral and vertical facies variations and several hiatus associated to tectonic and stratigraphic unconformities. Excepting the very local transgressive regimes, such as those of Langhian and Messinian periods, most of the Miocene deposits took place on internal platforms, especially at the NE part of the country. The fluviodeltaic and alluvial sediments are, in fact, lateral equivalents which infilled the valley and depression enclosed systems towards the SW. In this context (rapid facies variations in time and space, superposition of tectonic and eustatic unconformities, climatic variations, rare or absent stratigraphic markers…), some controversies remain as regards the correlation and dating of these series. This work consists of a study of the lateral and vertical facies and thickness variations, coupled to the identification of the main unconformities. It is also a study of significance of the main sedimentological mechanisms and an inventory of the different palynological and paleontological content of the sediments. The aim of this work is to propose a new vision on the Miocene deposits in Tunisia along a NE-SW axis. Then, using these data, we have correlated the different lithological formations, discuss their age and, finally, proposed paleogeographical drafts for them.     

Computational synthesis of hydrogenated fullerenes from C<Subscript>60</Subscript> to C<Subscript>60</Subscript>H<Subscript>60</Subscript>

Hydrogenation from C₆₀ to C₆₀H₆₀ was studied by an unrestricted broken spin symmetry Hartree–Fock approach implemented in semiempirical codes based on the AM1 technique. The calculations focused on the successive addition of hydrogen molecules to the fullerene cage following the identification of the cage target atoms by calculating the highest atomic chemical susceptibility at each step. The results obtained are analyzed from energy, symmetry, and composition perspectives.     

Proteolysis of <Emphasis Type="Italic">α</Emphasis>-amylase from <Emphasis Type="Italic">Saccharomycopsis fibuligera</Emphasis>: characterization of digestion products

α-Amylase from Saccharomycopsis fibuligera R-64 was successfully purified by butyl Toyopearl hydrophobic interaction chromatography, followed by Sephadex G-25 size exclusion and DEAE Toyopearl anion exchange chromatography. The enzyme has a molecular mass of 54 kDa, as judged by SDS PAGE analysis. Upon tryptic digestion, two major fragments with relative molecular masses of 39 kDa and 10 kDa, which resemble the A/B and C-terminal domains in the homologous Taka-amylase, were obtained and were successfully separated with the Sephadex G-50 size exclusion column. The 39-kDa fragment demonstrated a similar amylolytic activity to that of the undigested enzyme. However, it was found that the K _m value of the 39-kDa fragment was about two-times higher than that of the undigested enzyme. Moreover, thermostability studies showed a lower half-life time for the 39-kDa fragment. These findings suggest that the 39-kDa fragment is the catalytic domain, while the 10-kDa fragment is the C-terminal one, which plays a role in thermostability and starch binding. Although the undigested enzyme is able to act on raw starches at room temperature, with maize starches as the best substrate, neither the undigested enzyme nor the fragments adsorb the tested raw starches. These results propose Saccharomycopsis fibuligera α-amylase as a raw starch-digesting but not adsorbing amylase, with a similar domain organization to that of Taka-amylase A.     

Le groupe des « bisons adossés » de Lascaux. Étude de la technique de l'artiste par analyse des pigments

The painting matter of the “back to back bison's panel” of Lascaux was examined and analysed by electron microscopy in order to understand the know-how of Magdalenian artists. The observation of several samples coming from specific areas of the two bisons give an access to the nature of the used pigments, to the preparation mode used to obtain various colours and also to the application mode. Thanks to this physicochemical approach, we can make hypotheses about the mind and the gestures of the artists.     

<Emphasis Type="Italic">RAD18</Emphasis> gene product of yeast <Emphasis Type="Italic">Saccharomyces cerevisiae</Emphasis> controls mutagenesis induced by hydrogen peroxide

Within eukaryotes, tolerance to DNA damage is determined primarily by the repair pathway controlled by the members of the RAD6 epistasis group. Genetic studies on a yeast Saccharomyces cerevisiae model showed that the initial stage of postreplication repair (PRR), i.e., initiation of replication through DNA damage, is controlled by Rad6–Rad18 ubiquitin-conjugating enzyme complex. Mutants of these genes are highly sensitive to various genotoxic agents and reduce the level of induced mutagenesis. In this case, the efficiency of mutagenesis suppression depends on the type of damage. In this study we showed that DNA damage induced by hydrogen peroxide at the same mutagen doses causes significantly more mutations and lethal events in the rad18 mutant cells compared to control wild-type cells.     

Mutagenicity and antimutagenicity of <Emphasis Type="Italic">Croton cajucara</Emphasis>

Croton cajucara Benth. (‘sacaca’) is a tree of the Euphorbiaceae family, native to the Amazon region in northern Brazil, where it is widely used in the popular treatment of various diseases. Its active principle, the terpenoid trans-dehydrocrotonin, has been credited with a variety of medical properties, including antiulcer, antiinflammatory, antitumor, antimutagenic and hypoglycemic activity. In this investigation, possible mutagenic and antimutagenic effects were evaluated in treatments using methanol extract of this plant on Swiss Albino mice by examining their peripheral blood cells for micronuclei. In these tests, the material obtained by methanol extraction of C. cajucara tree bark was administered to the mice by gavage. None of the doses evaluated in this study presented mutagenicity. Analysis of the results obtained from studies evaluating antimutagenicity revealed protection against the chemotherapeutic agent cyclophosphamide for the two highest doses used.     

Characterization and functional analysis of hsp21.8b: An orthologous small heat shock protein gene in Tribolium castaneum

Small heat shock proteins (sHSPs) act as molecular chaperones and are widely distributed in all kinds of organisms. Comparative analysis revealed that an orthologous shsp was present during insect evolution. Here, hsp21.8b, one insect orthologous shsp, had been identified in Tribolium castaneum. Quantitative real‐time PCR illustrated that Tchsp21.8b was expressed in all developmental stages, along with the lowest expression at early embryonic stage and relative high expression at other stages especially in late eggs and late pupae. In the adult period, Tchsp21.8b exhibited the highest expression level in central nervous system and followed in elytron, epidermis, ovary and fat body. Moreover, it was upregulated 3.39‐fold in response to enhanced heat stress (45°C) for 4 hr but not to cold stress (4°C) and was upregulated by 1.73‐ to 1.94‐fold under ultraviolet (UV) exposure during 4–6 hr. It was also downregulated by 20.8%–41.8% under starvation in 3 days and had a “down‐up‐down” trend under the pathogen stresses. Larval RNA interference of Tchsp21.8b caused 40.6% insects mortality and reduced the oviposition amount by 66.0% and only 21.0% of the ds‐Tchsp21.8b eggs could hatch into larvae. These results suggested that as an orthologous shsp, Tchsp21.8b not only plays important roles in the growth, development and fecundity of T. castaneum but with the competence to resist the environment stresses, although the response is relatively weak compared to other hsps. Results from this study also uncovered the functions of the orthologous shsp in the development and anti‐stresses ability of T. castanuem. It provided more scientific evidence for revealing the physiological mechanisms of shsps of the insects and enhanced the capabilities to control different pests.     

Effect of Isoxanthopterin on the Activity of Transforming DNA in <Emphasis Type="Italic">Bacillus subtilis</Emphasis>

WHEN an aqueous solution of the pteridine, isoxanthopterin, is incubated with salmon sperm DNA, an unstable association of the pteridine with the DNA can be demonstrated by chromatography on “Sephadex”¹. One interesting property of the complex is that the fluorescence of isoxanthopterin is enhanced ten-fold, a phenomenon which has been ascribed, in other cases, to intercalation of a planar heterocycle between base pairs in the DNA double helix². If such an intimate positioning occurred, it might be possible to disrupt the structure of DNA by using radiant energy of a wavelength (345 nm) which would be absorbed by the pteridine but not by the DNA. In a living organism the result would be expressed as a mutational event, or in the extreme case, cell death. We have tested this hypothesis using a sensitive biological indicator—bacterial transformation—to observe effects at specific gene loci. For experimental convenience, changes in DNA were detected by changes in transforming ability of wild type DNA.     

<Superscript>1</Superscript>H, <Superscript>15</Superscript>N and <Superscript>13</Superscript>C resonance assignments of the J-domain of co-chaperone Sis1 from <Emphasis Type="Italic">Saccharomyces cerevisiae</Emphasis>

Protein folding in the cell is usually aided by molecular chaperones, from which the Hsp70 (Hsp?=?heat shock protein) family has many important roles, such as aiding nascent folding and participating in translocation. Hsp70 has ATPase activity which is stimulated by binding to the J-domain present in co-chaperones from the Hsp40 family. Hsp40s have many functions, as for instance the binding to partially folded proteins to be delivered to Hsp70. However, the presence of the J-domain characterizes Hsp40s or, by this reason, as J-proteins. The J-domain alone can stimulate Hsp70 ATPase activity. Apparently, it also maintains the same conformation as in the whole protein although structural information on full J-proteins is still missing. This work reports the ¹H, ¹⁵N and ¹³C resonance assignments of the J-domain of a Hsp40 from Saccharomyces cerevisiae, named Sis1. Secondary structure and order parameter prediction from chemical shifts are also reported. Altogether, the data show that Sis1 J-domain is highly structured and predominantly formed by α-helices, results that are in very good agreement with those previously reported for the crystallographic structure.     

Ndst1, a heparan sulfate modification enzyme, regulates neuroectodermal patterning by enhancing Wnt signaling in Xenopus

Neural tissue is derived from three precursor regions: neural plate, neural crest, and preplacodal ectoderm. These regions are determined by morphogen-mediated signaling. Morphogen distribution is generally regulated by binding to an extracellular matrix component, heparan sulfate (HS) proteoglycan. HS is modified by many enzymes, such as N-deacetyl sulfotransferase 1 (Ndst1), which is highly expressed in early development. However, functions of HS modifications in ectodermal patterning are largely unknown. In this study, we analyzed the role of Ndst1 using Xenopus embryos. We found that ndst1 was expressed in anterior neural plate and the trigeminal region at the neurula stage. ndst1 overexpression expanded the neural crest (NC) region, whereas translational inhibition reduced not only the trigeminal region, but also the adjacent NC region, especially the anterior part. At a later stage, ndst1 knocked-down embryos showed defects in cranial ganglion formation. We also found that Ndst1 activates Wnt signaling pathway at the neurula stage. Taken together, our results suggest that N-sulfonated HS accumulates Wnt ligand and activates Wnt signaling in ndst1-expressing cells, but that it inhibits signaling in non-ndst1-expressing cells, leading to proper neuroectodermal patterning.     

Expression in <Emphasis Type="Italic">Escherichia coli</Emphasis> of the gene encoding ascorbate peroxidase from <Emphasis Type="Italic">Brassica napus</Emphasis> enhances salt tolerance of bacterial cells

Ascorbate peroxidase (APX) is an important enzyme to scavenge the reactive oxygen species (ROS), which are often caused by the salt stress. Here, APX cDNA from Brassica napus was amplified by RT-PCR and cloned into the prokaryotic expression vector pGEX-6p-1 to express BnAPX as a glutathione S-transferase (GST) fusion protein. The recombinant expression plasmid was then transformed into Escherichia coli BL21 (DE3) and induced with 0.2 mM IPTG at 28°C. The enzyme activity analysis of the induced protein showed the GST-APX protein had the similar enzyme activity with the other found APXs, which decompose H₂O₂. Moreover, the GST-APX fusion protein was purified by affinity chromatography using the glutathione-Sepharose 4B column. The purified GST-APX protein was then used to immunize rabbits to obtain the anti-BnAPX serum, which was suitable to recognize both the recombinant exogenous BnAPX and the endogenous BnAPX in vivo by western blotting and the immunohistochemical experiment. Furthermore, the immuno-fluorescent microscopy observation revealed that BnAPX was expressed in the chloroplasts. Finally, the bacteria expressing BnAPX grew much faster in the presence of 3% NaCl than the control cells, indicating that the transformant expressing BnAPX acquired resistance to salt stress.     

Venom volatiles of the paper wasp social parasite <Emphasis Type="Italic">Polistes sulcifer</Emphasis> elicit intra-colonial aggression on the nest of the host species <Emphasis Type="Italic">Polistes dominulus</Emphasis>

Insect social parasites rely on host workers to rear and protect their own brood. To conquer a host colony, a parasite must overcome the defensive mechanisms of the host, often by exploiting its chemical communication system. A widespread strategy involves the production of specific allomones (the so-called “propaganda pheromones”) to facilitate the usurpation process by manipulating the defensive behavior of the host. Polistes sulcifer is the obligate and permanent social parasite of the congeneric paper wasp Polistes dominulus. In this study, we investigated if the venom volatiles, well known to be alarm pheromones in the host species, could be used by the parasite to manipulate the host defense. We thus performed laboratory bioassays, to evaluate the possible effect of the venom volatile compounds of the parasite on the host. Our results show that host colony members reacted to the venom volatiles extract of the parasite with an increase in intra-colonial aggression compared to the reaction induced by the venom volatiles extract of the host foundress. Besides, a re-analysis of previously published chemical data showed that the parasite venom volatiles profile differs from that of the host: the spiroacetals are absent, whilst the amides are very abundant in the parasite venom when compared with that of the host. Similar to other insect social parasites, Polistes wasp parasites might be able to increase their invasion success by using venom volatile pheromones to distract the host defenders.     

微流控芯片技术用于精子与上皮细胞分离的研究

为研究建立使用微流控芯片技术分离精子与阴道上皮细胞的方法,选用制作工艺简单的玻璃-PDMS芯片,对混合样本进行分离。加样前分别在进、出口池中加入7此和lO此缓冲液,然后在进样口加入2此混合样本。至少静置8nlin后,从出口池中取出3此形成重力驱动的微流体后开始分离,每隔5min在进样口补加1此缓冲液。达到理想分离效果时,用移液器从出口池取出分离出的精子,核酸酶去除游离DNA,经过提取、扩增和电泳分离脸测等步骤得到精子的分型结果。结果显示,使用基于重力驱动微流体原理的微流控芯片可在30min内分离出精子,不会有上皮细胞进入分离通道;通过核酸酶对分离出的精子液的去游DNA处理,可得到单一、完整的精子分型。与传统的差异裂解法相比,这种方法在很大程度上节省了检验时间,在性侵案件中具有一定的法医物证分析价值。     

Active electrolocation of polarized objects by a pulse-discharging electric fish, <Emphasis Type="Italic">Gnathonemus </Emphasis><Emphasis Type="Italic">petersii</Emphasis>

Weakly electric fish react to resistance and capacitance of objects that locally amplify and distort their self-generated Electric Organ Discharge (EOD) received by their skin receptors. The successive-layer structure of tissues gives certain biological materials a kind of electrical anisotropy. A polarized object, for instance, will conduct current differently in one versus the other direction. This diode-like electric anisotropy should make a significant difference to a Mormyrid who emits a directional, biphasic EOD and whose receptors are sensitive to EOD amplitude and distortion changes. The ability of Gnathonemus petersii (Mormyridae) to discriminate polarity was investigated on a virtual object by manipulating changes in a circuit comprised of diodes combined in various ways. The “novelty response,” an increase in the discharge rate in response to perceived changes, was used to assess the fish’s sensitivity. Indeed, G. petersii detects polarized objects and discriminates between polarity directions. However, the diode-like anisotropy entails a voltage threshold. Because voltage decreases with distance, and the EOD comprises opposite phases of different amplitudes, the active spaces of detection and discrimination are different and depend on the object orientation. Electric polarity thus extends the “palette” of dielectric properties used by this fish to evaluate object quality, direction, and distance.