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61.
In two conditioned lick-suppression experiments with rats, the interaction of preexposure to a target stimulus and subsequent overshadowing of conditioned inhibition treatment was examined. Blaisdell, Bristol, Gunther, and Miller (1998) have demonstrated that stimulus preexposure and overshadowing counteract each other in their effects on Pavlovian excitation, producing strong excitatory responding to the target stimulus. In the present experiments, a conditioned inhibition analogue of this effect was examined. Overshadowing of conditioned inhibition (i.e., attenuation of inhibitory control of behavior by the target stimulus) was demonstrated when a more salient stimulus was compounded with the target inhibitor during conditioned inhibition training. However, the overshadowing deficit was attenuated by preexposing the target stimulus prior to overshadowing treatment. To account for this phenomenon, we contrast the comparator hypothesis (Miller & Matzel, 1988) with contemporary models that focus on associative acquisition. 相似文献
62.
Dielectrophoretic properties of DNA have been determined by measuring capacitance changes between planar microelectrodes. DNA sizes ranged from 100 bp to 48 kbp, DNA concentrations from below 0.1 to 70 μg∕ml. Dielectrophoretic spectra exhibited maximum response around 3 kHz and 3 MHz. The strongest response was found for very long DNA (above 10 kbp) and for short 100 bp fragments, which corresponds to the persistence length of DNA. The method allows for an uncomplicated, automatic acquisition of the dielectrophoretic properties of submicroscopical objects without the need for labeling protocols or optical accessibility. 相似文献
63.
Latent inhibition, which refers to attenuated responding to a conditioned stimulus (CS) after CS-unconditioned stimulus (CS-US) pairings as a result of CS-alone presentations prior to the pairings, is often attenuated if preexposure and conditioning occur in different contexts (i.e., it is context specific). Here we report two conditioned lick suppression experiments, using rat subjects, that examined whether manipulations known to attenuate the context specificity of extinction could also eliminate the context specificity of latent inhibition. Context specificity of latent inhibition was eliminated when the CS was preexposed in multiple contexts (Experiment 1) and when the CS was massively pre-exposed in the training context alone (Experiment 2). These results and their practical implications are discussed in the framework of contemporary theories of latent inhibition. 相似文献
64.
Lick suppression experiments with rats revealed that the magnitude of both second-order conditioning (Experiment 1) and sensory preconditioning (Experiment 2) was superior when that conditioning was based on backward (US→CS) relative to forward (CS→US) first-order pairings of a CS and US. The superiority of backward relative to forward first-order conditioning on suppression to the higher order cues can be understood by assuming that the magnitude of higher order conditioning was determined by a memory representation of the higher order cues that provided information about the expected temporal location of the US. The results suggest that temporal information such as order between paired CSs and USs was encoded, preserved, and integrated with memory for the higher order stimuli. The relevance of these findings to memory integration in Pavlovian learning, the temporal coding hypothesis (Barnet, Arnold, & Miller, 1991; Matzel, Held, & Miller, 1988), backward excitatory conditioning, and the associative structure that underlies second-order Pavlovian fear conditioning are discussed. 相似文献
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66.
Jaehoon Chung David Issadore Adeeti Ullal Kyungheon Lee Ralph Weissleder Hakho Lee 《Biomicrofluidics》2013,7(5)
We present a hybrid magnetic/size-sorting (HMSS) chip for isolation and molecular analyses of circulating tumor cells (CTCs). The chip employs both negative and positive cell selection in order to provide high throughput, unbiased CTC enrichment. Specifically, the system utilizes a self-assembled magnet to generate high magnetic forces and a weir-style structure for cell sorting. The resulting device thus can perform multiple functions, including magnetic depletion, size-selective cell capture, and on-chip molecular staining. With such capacities, the HMSS device allowed one-step CTC isolation and single cell detection from whole blood, tested with spiked cancer cells. The system further facilitated the study of individual CTCs for heterogeneity in molecular marker expression.Circulating tumor cells (CTCs) have emerged as an important biomarker in clinical practice as well as in fundamental research.1, 2 CTCs, shed from primary tumors, have been shown to be an early harbinger of tumor expansion and metastasis3 and have been used to predict disease progression, response to treatment, relapse, and overall survival.4, 5, 6 Recent work has shown that CTCs display distinct proteomic and genetic profiles; for example, CTCs in pancreatic cancer, have increased RNA expression of Wnt, implicating this pathway in metastasis.7 Proteomic characterization of proliferative markers such as Ki-67, and hormonal markers such as androgen receptor in prostate cancer, also have been shown to be predictive of treatment outcome.8, 9Despite such clinical potential of CTCs, their routine detection and characterization still remains a significant technical challenge.10 The task requires screening of a large number of cells (e.g., > 107 cells in 10 ml blood) and enrichment of heterogeneous targets against a complex biological background. Two main methods of CTC isolation are typically used: positive and negative selection. In positive selection, CTCs are directly isolated from blood via size-based filtration11, 12, 13, 14, 15, 16, 17, 18, 19, 20 or antibody-based capture.1, 8, 21 Negative depletion reduces abundant blood cells, often by immunomagnetic separation, for downstream CTC enrichment.22 Both approaches have been used for high throughput CTC isolation from whole blood (SI Table 1).23 Each method, however, has its own inherent limitations. Positive enrichment could be biased by its selection criteria (e.g., cell size and cell surface markers). Negative selection, albeit unbiased, often requires complex sample processing (e.g., multiple washing steps for CTC isolation) that could result in cell loss.We hypothesized that both positive and negative selection could be combined in a single platform to enable (1) highly efficient and unbiased CTC purification, and (2) in-situ molecular analyses of collected cells. As a proof-of-concept, we herein describe a hybrid magnetic/size-sorting (HMSS) system that integrates magnetic and size-based isolation into a compact microfluidic chip. The HMSS first uses a magnetic filter to deplete leukocytes through immunomagnetic capture. Samples then pass through a size-sorter region that traps individual cells at predefined locations. Since abundant leukocytes are removed by the magnetic filter, the size-sorter could have a low size cut-off (∼5 μm), which allows for the unbiased capture of even small cancer cells. Furthermore, molecular probes can be introduced to perform on-chip, multiplexed analyses at single-cell resolution. We evaluated the utility of the developed system by capturing and profiling tumor cells in whole blood. The HMSS offers the advantages of both negative and positive selection and thereby differs from the recently reported iChip system24 which can operate only in either a negative or a positive selection mode. 相似文献
67.
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69.
试论图书馆员国际交流项目及其评估——以四川大学和亚利桑那州立大学图书馆员交流项目为例 总被引:1,自引:0,他引:1
[目的/意义] 针对图书馆员国际交流项目缺乏评估研究的现状,提出一种有借鉴意义的测量工具来评估其实际效果和价值。[方法/过程] 以四川大学和亚利桑那州立大学图书馆员交流项目为例,参考D. Bachner和U. Zeutschel对国际青年交流项目的测量和评估方法确定评估标准,引入李克特五分量表,结合要求详细阐述的开放式问题,形成一个定性和定量相结合的评估工具。[结果/结论] 通过评估,对馆员交流项目进行全面审视,确定其在个人、机构、制度层面的影响和效果,发现项目决策、实施过程中的亮点与不足,提出促进馆员国际交流项目进一步发展的建议。 相似文献
70.
Separate groups of water-deprived rats had four trials with 15-min access to 0.0073 M saccharin, 0.3 M alanine, 0.3 M glucose,
0.1 M maltose, 0.3 M fructose, 0.06 M sucrose, or 0.03 M Polycose. Trials 1–3 were followed by injections of either 0.15 M
LiCl (1.33 ml/100 g b.w., i.p.) or saline; Trial 4 (Test) was CS only. Extinction included either 48-h access to water alone
or to the appropriate CS, both followed by a 24-h, two-bottle choice of CS and water. This 3-day cycle was repeated five to
six times. All rats acquired comparable conditioned taste aversions (CTAs), but extinction rates varied with the test and
the taste CS. No CTA extinguished during the two-bottle choices following 2 water days. During one-bottle CS exposure, all
CTAs extinguished, but the aversion continued longer in the probe two-bottle tests. Intake of glucose moieties recovered rapidly,
often in two cycles; the other CSs took four to six cycles. Thus, CTA extinction varies with the nature of the taste CS. 相似文献