24 research outputs found

    Perceptual learning transfer in an appetitive Pavlovian task

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    In two experiments, rats were given intermixed or blocked preexposure to two similar compound stimuli, AX and BX. Following preexposure, conditioning trials took place in which AX (Experiment 1) or a novel compound stimulus NX (Experiment 2) was paired with a food-unconditioned stimulus in an appetitive Pavlovian preparation. Animals that were given alternated preexposure showed lower generalization from AX to BX (Experiment 1) and from NX to a new compound, ZX (Experiment 2), than animals that were given blocked preexposure, a perceptual learning and a perceptual learning transfer effect, respectively

    Nicotine chronic tolerance development and withdrawal in the planaria (Schmidtea mediterranea).

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    Chronic nicotine exposure reduces sensitivity to the effects of nicotine, which then results in behavioural changes and tolerance development. In the planaria, a valuable first-stage preclinical model for addictive behaviour, acute nicotine administration has been shown to steadily alter the motility of the animals, a result that has been interpreted as evidence of tolerance and withdrawal effects; however, chronic exposure - typically regarded as a condition for the development of tolerance - and the role of the contextual cues have not been systematically assessed. The present study assessed the acute and chronic effects of nicotine on the motility of planarians (Schmidtea mediterranea). The animals in the experimental groups received long chronic exposure to nicotine (ten daily 30 min exposures); a control group was exposed to water in the same context but in the absence of the drug. The motility of the animals was closely monitored on every exposure. Following this phase, all the animals were subject to three different tests: in the presence of the exposure context (without the drug, Test 1); in the presence of nicotine in the exposure context (Test 2); and in the presence of the drug in a novel context (Test 3). Exposure to nicotine consistently reduced motility; the motility in the presence of nicotine increased with repeated exposures to the drug, an instance of tolerance development. Tolerance development was dependent on nicotinic receptor activation, because it was blocked by the co-administration of mecamylamine. However, this tolerance was found to be independent of the contextual cues where the effects of the drug had been experienced. The results are discussed by reference to the existent theories of tolerance development to drugs

    Evidence for feature and location learning in human visual perceptual learning

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    In Experiment 1, human participants were pre - exposed to two similar checkerboard grids (AX and X) in alternation, and to a third grid (BX) in a separate block of trials. In a subsequent test, the unique feature A was better detected than the feature B when they were presented in the same location during the pre - exposure and test phases. However, when the locations of the features were swapped during the test (A was tested in the location occupied by B during pre - exposure and vice versa ), B was detected bett er than A, suggesting that intermixed pre - exposure enhances the attention paid to the location of the unique features rather than the features themselves. In Experiment 2, participants were given intermixed or blocked pre - exposure to AX and X, and were the n required to detect the differences between pairs of stimuli containing either the pre - exposed unique feature A or a new feature, N, presented in a familiar location (used for pre - exposure) or a new location within the checkerboard grid. Participants that were given intermixed pre - exposure showed a facilitated capacity to detect A than N, and detected better the unique features in the familiar than in the new location. In contrast, participants in the blocked condition did not show any effect of feature or location. These results provide evidence that both location and feature learning processes take place during intermixed (but not blocked) pre - exposure. Aprendizaje perceptivo visual en humanos: Evidencia de aprendizaje de lugar y de contenido. En el Experimento 1, los participantes fueron expuestos a dos est铆mulos visuales muy similares (AX y X, donde X hace referencia al fondo visual y A se refiere a un elemento 煤nico que permite la discriminaci贸n entre AX y X) de forma alternada, y a un tercer estimulo (BX) en un bloque de ensayos separado. Durante una fase de prueba se puso de manifiesto que el elemento 煤nico A era m谩s f谩cilmente detectable que el B cuando se presentaban en la misma posici贸n que ocuparon durante la exposici贸n. Sin embargo, cu ando se cambiaron las posiciones (A se present贸 en la posici贸n ocupada por B durante la exposici贸n y viceversa ), B se detect贸 mejor que A. Este resultado sugiere que lo exposici贸n alternada a AX y X incrementa la atenci贸n que prestan los participantes a l a localizaci贸n y no al contenido (forma y color) del elemento 煤nico. En el Experimento 2, los participantes fueron expuestos a AX y X en alternancia o en bloques; en la prueba se les pidi贸 que detectaran las diferencias entre pares de est铆mulos que conten铆 an el elemento 煤nico A o un elemento nuevo, N, que pod铆an presentarse en la localizaci贸n familiar (usada durante la exposici贸n) o en un localizaci贸n novedosa. Los resultados mostraron que la exposici贸n alternada permite una mejor detecci贸n del elemento pre - expuesto A (aprendizaje de contenido); y que los dos elementos 煤nicos (A y N) se detectan m谩s f谩cilmente en la localizaci贸n familiar que en la localizaci贸n novedosa (aprendizaje de lugar). Por el contrario, los participantes del grupo de exposici贸n en bl oques no mostraron evidencia de aprendizaje de lugar ni de contenido. Los resultados sugieren que los participantes aprenden a atender tanto la localizaci贸n como el contenido del est铆mulo 煤nico durante la exposici贸n alternada, pero no durante la exposici贸n en bloques

    Dissociation of place preference and tolerance responses to sucrose using a dopamine antagonist in the planarian.

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    In rodents, sucrose has been found to elicit addictive-like behaviours like the development of tolerance and the association with cues present at the time of consumption. Furthermore, the neurochemical response to sucrose binges is equivalent to the one observed in response to the abuse of addictive substances like cocaine. The experiments reported here address the effects of sucrose on an invertebrate model, the Platyhelminth brown planarian. The animals exposed to a 10% sucrose solution in one context developed a conditioned place preference (CPP) which was subsequently extinguished in the absence of the rewarding agent. However, one exposure to sucrose per se sufficed to reinstate the CPP response, suggesting sucrose-induced CPP can be characterised as a standard Pavlovian response. The same training procedure led to the development of context-specific tolerance to the effects of sucrose. However, comparing animals treated with dopamine D1 antagonist (SCH-23390) with control animals showed that the establishment of CPP, but not the development of tolerance, is mediated by the dopamine reward system

    Mechanisms of perceptual learning: Prolonged intermixed preexposure reduces the effectiveness of the unique and the common elements.

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    In three experiments, rats were given intermixed or blocked preexposure to two similar compound stimuli, AX and BX. In Experiment 1, following preexposure, animals were given appetitive conditioning training with the compound AX. A subsequent generalization test showed better discrimination between AX and BX in the group given intermixed than in the one given blocked preexposure. Experiments 2 and 3 assessed the nature of the learning mechanisms underlying this instance of the perceptual learning effect. Experiment 2 assessed the associability of the common and unique elements (X and A); animals in the group given intermixed preexposure showed poorer conditioning with both the X and the A elements than those given blocked preexposure. Experiment 3 further assessed the perceptual effectiveness of the distinctive element A using a superimposition test (the capacity of A to interfere with the conditioned response commanded by an independent conditioned stimulus). The results showed, in line with the outcome of Experiment 2, that the unique element A is more salient following blocked than intermixed preexposure. These results are discussed by reference to current theories of perceptual learning. (PsycInfo Database Record (c) 2021 APA, all rights reserved

    Short- and Long-Term Habituation of Photonegative and Exploratory Responses in the Flatworm Planaria (Dugesia)

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    Two experiments address the habituation of photonegative and exploratory responses in the flatworm planaria (Dugesia). Planarians possess a well-documented photonegative response; Experiment 1 showed that repeated exposures to a bright light source with short inter trial intervals (ITIs) within one experimental session gradually weakens the unconditioned photonegative response. In addition, it was found that presentation of an unexpected arousal-increasing stimulus (dropped water or a shock) temporarily reestablishes the photonegative response. Experiment 2 addressed the development of long-term habituation; we recorded the locomotor activity of the animals exposed to an inescapable bright light. Experiments2A and 2Bshowed that planarians develop long-term habituation but only when they were trained in relatively novel contexts; when they were trained in familiar contexts (in surfaces similar to the ones in the home) the development of habituation was severely impaired. The results are discussed by reference to the theory of short-and long-term habituation put forward by Allan R. Wagner (Wagner, 1976), highlighting the impact that this theory has had in the research of invertebrate learning.</p

    Temozolomide toxicity.

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    <p>A) Relative growth rates (RGR) for tumor cell lines treated with TMZ. B) Relative growth rates for tumor cell lines before and after TMZ cycling treatment (B: basal cells; 1C: first TMZ cycle; 2C: second TMZ cycle). SF268 and SK-N-SH lines did not reveal any IC<sub>50</sub> variation, whereas A172 and LN229 showed a large increase in TMZ IC<sub>50</sub>. All data represent the mean value 卤 SD of triplicate cultures.</p

    Modulation of P-gp expression by TMZ treatment.

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    <p>A) Real-time PCR analysis of P-gp expression levels in tumor cell lines. The TMZ-resistant HCT15 cell line was used as a control. B) Modulation of P-gp expression by TMZ treatment in tumor cell lines. C) Relative growth rates after exposure to TMZ in tumor cell lines before and after verapamil (V) treatment. B: basal cells; 1C: first TMZ cycle; 2C: second TMZ cycle. All data represent the mean value 卤 SD of triplicate cultures.</p

    Analysis of MGMT promoter methylation and MGMT expression levels.

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    <p>A) Modulation of the MGMT promoter methylation percentage in tumor cell lines before and after TMZ treatment. B) Real-time PCR analysis of MGMT expression before and after TMZ treatment. Showing relative expression of MGMT compared with SK-N-H cell line. C) Western blot analysis of MGMT protein expression in tumor cell lines before and after TMZ treatment. Beta-actin expression was used as a control. The graphs on the right show the densitometry of the MGMT Western blot analysis in SF268 and SK-N-SH cell lines before and after TMZ treatment. B: basal cells; 1C: first TMZ cycle; 2C: second TMZ cycle. All data represent the mean value 卤 SD of triplicate cultures.</p

    Modulation of CD 133 expression by TMZ treatment.

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    <p>A) Flow cytometry analysis of percentages of CD133 positives in tumor cell lines using TMZ treatment B: basal cells, 1C: first TMZ cycle; 2C: second TMZ cycle. Data were calculated from three independent experiments. B) Representative flow cytometry data for CD133 expression. SSC: side-scattered light.</p
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