Foci of orientation plasticity in visual cortex

[Abstract] Cortical areas are generally assumed to be uniform in their capacity for adaptive changes or plasticity1, 2, 3, 4. Here we demonstrate, however, that neurons in the cat striate cortex (V1) show pronounced adaptation-induced short-term plasticity of orientation tuning primarily at specific foci. V1 neurons are clustered according to their orientation preference in iso-orientation domains5 that converge at singularities or pinwheel centres6, 7. Although neurons in pinwheel centres have similar orientation tuning and responses to those in iso-orientation domains, we find that they differ markedly in their capacity for adaptive changes. Adaptation with an oriented drifting grating stimulus alters responses of neurons located at and near pinwheel centres to a broad range of orientations, causing repulsive shifts in orientation preference and changes in response magnitude. In contrast, neurons located in iso-orientation domains show minimal changes in their tuning properties after adaptation. The anisotropy of adaptation-induced orientation plasticity is probably mediated by inhomogeneities in local intracortical interactions that are overlaid on the map of orientation preference in V1

The binding properties of some novel ruthenium (III) complexes with human serum transferrin

Aim. The transferrin cycle gained increased interest in recent years and it holds promise as an attractive system for strategies of drug targeting to tumors. Neoplasic cells exhibit a large demand of iron and therefore express highly transferrin receptors. As a consequence, transferrin conjugates can preferentially interact with cancer cells. This strategy is exploited nowadays for targeting novel anti-cancer drugs. Recent data showed that ruthenium (III) compounds possess antitumor and antimetastatic effects, due to their affinity for crucial biomolecules (like transferrin). Methods. The paper presents the transferrin-binding properties of some novel ruthenium (III) complexes with general formula RuL2 (DMSO) mCl3 ·nH2O ((Ru-nf) L: norfloxacin (nf), m = 1, n = 1; (Ru-cpx) L: ciprofloxacin (cpx), m = 2, n = 2; (Ru-oflo) L: ofloxacin (oflo), m = 1, n = 1; (Ru-levo) L: levofloxacin (Levo), m = 2, n = 8; (Ru-pip) L: pipemidic acid (pip), m = 1, n = 2, DMSO: dimethylsulfoxide). We investigated, in vitro, the interactions of these ligands with human transferrin through spectroscopic techniques, with the ultimate goal of preparing adducts with good selectivity for cancer cells. Results. All studied complexes interact with human serum transferrin; the molar ratio [complex]/[transferrin] strongly influences the binding affinity. Conclusions. The best interaction between the complexes studied and transferrin is achieved for a molar ratio of 8; the best interaction was registered for Ru-pip, followed by Ru-nf. Keywords: ruthenium (III) complexes, transferrin.Мета. Останніми роками трансфериновий цикл викликає по - силений інтерес як перспективна система цільової доставки протипухлинних препаратів безпосередньо в пухлину. Неопластичні клітини потребують багато заліза, через що експресують велику кількість трансферинових рецепторів. Внаслідок цього кон ’югати трансферину здатні насамперед взаємодіяти з раковими клітинами. Цю стратегію у наш час використовують для пошуку нових протиракових препаратів. Останні дані демонструють, що сполукам рутенію (III) притаманні протипухлинні і антиметастатичні ефекти завдяки їхній афінності до важливих біомолекул (таких як трансферин). Методи. У статті представлено трансферин-зв’язувальні властивості деяких нових комплексів рутенію (III) загальною формулою RuL2 (DMSO) mCl3 ×nH2O ((Ru-nf) L: норфлоксацин (nf), m = 1, n = = 1; (Ru-cpx) L: ципрофлоксацин (cpx), m = 2, n = 2; (Ru-of) L: офлоксацин (oflo), m = 1, n = 1; (Ru-levo) L: левофлоксацин (Levo), m = 2, n = 8; (Ru-pip) L: піпемідинова кислота (pip), m = = 1, n = 2, DMSO: диметилсульфоксид). Ми вивчали взаємодію in vitro цих лігандів з трансферином людини методом спектроскопії для одержання адуктів з високою селективністю до ракових клітин. Результати і висновки. Всі досліджувані комплекси взаємодіють з сироватковим трансферином людини, молярне співвідношення [комплекс]/[трансферин] значно впливає на зв’язувальні властивості. Найкращу взаємодію між аналізованими комплексами і трансферином відмічено при молярному співвідношенні 8:1, а також для Ru-pip і Ru-nf. Ключові слова: комплекси рутенію (III), трансферин.Цель. В последние годы трансферриновый цикл вызывает повышенный интерес как перспективная система целевой доставки противоопухолевых препаратов непосредственно в опухоль. Неопластические клетки испытывают высокую потребность в железе и, следовательно, экспрессируют много трансферриновых рецепторов. Вследствие этого конъюгаты трансферрина способны преимущественно взаимодействовать с раковыми клетками. Эту стратегию в настоящее время используют для поиска новых противораковых препаратов. Последние данные показывают, что соединения рутения (III) обладают противоопухолевым и антиметастатическим эффектами благодаря их аффинности к важным биомолекулам (таким как трансферрин). Методы. В статье представлены трансферрин-связывающие свойства некоторых новых комплексов рутения (III) с общей формулой RuL2 (DMSO) mCl3 ×nH2O ((Ru-nf) L: норфлоксацин (nf), m = 1, n = 1; (Ru-cpx) L: ципрофлоксацин (cpx), m = 2, n = 2; (Ru-of) L: офлоксацин (oflo), m = 1, n = 1; (Ru-levo) L: левофлоксацин (Levo), m = 2, n = 8; (Ru-pip) L: пипемидиновая кислота (pip), m = 1, n = 2, DMSO: диметилсульфоксид). Мы изучили взаимодействие in vitro этих лигандов с человеческим трансферрином методом спектроскопии для получения аддуктов, обладающих хорошей селективностью к раковым клеткам. Результаты и выводы. Все исследуемые комплексы взаимодействуют с человеческим сывороточным трансферрином, молярное соотношение [комплекс]/ [трансферрин] сильно влияет на связывающие свойства. Наилучшее взаимодействие между изучаемыми комплексами и трансферрином отмечено при молярном соотношении 8:1, а также для Ru-pip и Ru-nf. Ключевые слова: комплексы рутения (III), трансферрин

Visual Cells Remember Earlier Applied Target: Plasticity of Orientation Selectivity

BACKGROUND: A canonical proposition states that, in mature brain, neurons responsive to sensory stimuli are tuned to specific properties installed shortly after birth. It is amply demonstrated that that neurons in adult visual cortex of cats are orientation-selective that is they respond with the highest firing rates to preferred oriented stimuli. METHODOLOGY/PRINCIPAL FINDINGS: In anesthetized cats, prepared in a conventional fashion for single cell recordings, the present investigation shows that presenting a stimulus uninterruptedly at a non-preferred orientation for twelve minutes induces changes in orientation preference. Across all conditions orientation tuning curves were investigated using a trial by trial method. Contrary to what has been previously reported with shorter adaptation duration, twelve minutes of adaptation induces mostly attractive shifts, i.e. toward the adapter. After a recovery period allowing neurons to restore their original orientation tuning curves, we carried out a second adaptation which produced three major results: (1) more frequent attractive shifts, (2) an increase of their magnitude, and (3) an additional enhancement of responses at the new or acquired preferred orientation. Additionally, we also show that the direction of shifts depends on the duration of the adaptation: shorter adaptation in most cases produces repulsive shifts, whereas adaptation exceeding nine minutes results in attractive shifts, in the same unit. Consequently, shifts in preferred orientation depend on the duration of adaptation. CONCLUSION/SIGNIFICANCE: The supplementary response improvements indicate that neurons in area 17 keep a memory trace of the previous stimulus properties, thereby upgrading cellular performance. It also highlights the dynamic nature of basic neuronal properties in adult cortex since repeated adaptations modified both the orientation tuning selectivity and the response strength to the preferred orientation. These enhanced neuronal responses suggest that the range of neuronal plasticity available to the visual system is broader than anticipated

Invariant computations in local cortical networks with balanced excitation and inhibition

[Abstract] Cortical computations critically involve local neuronal circuits. The computations are often invariant across a cortical area yet are carried out by networks that can vary widely within an area according to its functional architecture. Here we demonstrate a mechanism by which orientation selectivity is computed invariantly in cat primary visual cortex across an orientation preference map that provides a wide diversity of local circuits. Visually evoked excitatory and inhibitory synaptic conductances are balanced exquisitely in cortical neurons and thus keep the spike response sharply tuned at all map locations. This functional balance derives from spatially isotropic local connectivity of both excitatory and inhibitory cells. Modeling results demonstrate that such covariation is a signature of recurrent rather than purely feed-forward processing and that the observed isotropic local circuit is sufficient to generate invariant spike tuning

Adaptive Filtering Enhances Information Transmission in Visual Cortex

Sensory neuroscience seeks to understand how the brain encodes natural environments. However, neural coding has largely been studied using simplified stimuli. In order to assess whether the brain's coding strategy depend on the stimulus ensemble, we apply a new information-theoretic method that allows unbiased calculation of neural filters (receptive fields) from responses to natural scenes or other complex signals with strong multipoint correlations. In the cat primary visual cortex we compare responses to natural inputs with those to noise inputs matched for luminance and contrast. We find that neural filters adaptively change with the input ensemble so as to increase the information carried by the neural response about the filtered stimulus. Adaptation affects the spatial frequency composition of the filter, enhancing sensitivity to under-represented frequencies in agreement with optimal encoding arguments. Adaptation occurs over 40 s to many minutes, longer than most previously reported forms of adaptation.Comment: 20 pages, 11 figures, includes supplementary informatio

Line orientation adaptation: local or global?

Prolonged exposure to an oriented line shifts the perceived orientation of a subsequently observed line in the opposite direction, a phenomenon known as the tilt aftereffect (TAE). Here we consider whether the TAE for line stimuli is mediated by a mechanism that integrates the local parts of the line into a single global entity prior to the site of adaptation, or the result of the sum of local TAEs acting separately on the parts of the line. To test between these two alternatives we used the fact the TAE transfers almost completely across luminance contrast polarity [1]. We measured the TAE using adaptor and test lines that (1) either alternated in luminance polarity or were of a single polarity, and (2) either alternated in local orientation or were of a single orientation. We reasoned that if the TAE was agnostic to luminance polarity and was parts-based, we should obtain large TAEs using alternating-polarity adaptors with single-polarity tests. However we found that (i) TAEs using one-alternating-polarity adaptors with all-white tests were relatively small, increased slightly for two-alternating-polarity adaptors, and were largest with all-white or all-black adaptors. (ii) however TAEs were relatively large when the test was one-alternating polarity, irrespective of the adaptor type. (iii) The results with orientation closely mirrored those obtained with polarity with the difference that the TAE transfer across orthogonal orientations was weak. Taken together, our results demonstrate that the TAE for lines is mediated by a global shape mechanism that integrates the parts of lines into whole prior to the site of orientation adaptation. The asymmetry in the magnitude of TAE depending on whether the alternating-polarity lines was the adaptor or test can be explained by an imbalance in the population of neurons sensitive to 1st-and 2nd-order lines, with the 2nd-order lines being encoded by a subset of the mechanisms sensitive to 1st-order lines

Reprogramming of orientation columns in visual cortex : a domino effect

Abstract : Cortical organization rests upon the fundamental principle that neurons sharing similar properties are co-located. In the visual cortex, neurons are organized into orientation columns. In a column, most neurons respond optimally to the same axis of an oriented edge, that is, the preferred orientation. This orientation selectivity is believed to be absolute in adulthood. However, in a fully mature brain, it has been established that neurons change their selectivity following sensory experience or visual adaptation. Here, we show that after applying an adapter away from the tested cells, neurons whose receptive fields were located remotely from the adapted site also exhibit a novel selectivity in spite of the fact that they were not adapted. These results indicate a robust reconfiguration and remapping of the orientation domains with respect to each other thus removing the possibility of an orientation hole in the new hypercolumn. These data suggest that orientation columns transcend anatomy, and are almost strictly functionally dynamic

Factor Varieties and Symbolic Computation

We propose an algebraization of classical and non-classical logics, based on factor varieties and decomposition operators. In particular, we provide a new method for determining whether a propositional formula is a tautology or a contradiction. This method can be autom-atized by defining a term rewriting system that enjoys confluence and strong normalization. This also suggests an original notion of logical gate and circuit, where propositional variables becomes logical gates and logical operations are implemented by substitution. Concerning formulas with quantifiers, we present a simple algorithm based on factor varieties for reducing first-order classical logic to equational logic. We achieve a completeness result for first-order classical logic without requiring any additional structure