Effect of selection cell density on the recovery of mutagen-induced 6-thioguanine-resistant cells (CHO/HGPRT system)

The relationship between the cell density utilized in the selection for 6-thioguaninine-resistant mutants induced by ethyl methanesulfonate and the recovery of mutant colonies was determined in Chinese hamster ovary cells. After an adequate phenotypic expression time of 9 days post mutagen treatment, cultures were plated in selection medium at cell densities ranging from 5 × 10⁴ to 2 × 10⁶ cells/100 mm dish (0.9 to 36.0 × 10³ cells/cm²). A decline in the frequency of mutant colonies was observed with increasing cell density, and analysis of the data showed that the loss was independent of the frequency of mutants in the cell population. This loss occurred in an exponential fashion, consistent with a random-target effect. Regression analysis of the data points yielded a best-fit line defined by the equation log(y) = 2.01 - 0.26(10^?6) x, where y = percentage recovery and × = selection cell density (cells per 100 mm dish). This study defines the cell densitydependent loss of mutants under selection conditions, and provides a basis for further study of the influence of agents on cell contact-mediated crossfeeding and possible effects on mutation induction determinations. These results also demonstrate the importance of the use of appropriate cell densities in mutant selections.     

Emotion expression in human punishment behavior

Evolutionary theory reveals that punishment is effective in promoting cooperation and maintaining social norms. Although it is accepted that emotions are connected to punishment decisions, there remains substantial debate over why humans use costly punishment. Here we show experimentally that constraints on emotion expression can increase the use of costly punishment. We report data from ultimatum games, where a proposer offers a division of a sum of money and a responder decides whether to accept the split, or reject and leave both players with nothing. Compared with the treatment in which expressing emotions directly to proposers is prohibited, rejection of unfair offers is significantly less frequent when responders can convey their feelings to the proposer concurrently with their decisions. These data support the view that costly punishment might itself be used to express negative emotions and suggest that future studies will benefit by recognizing that human demand for emotion expression can have significant behavioral consequences in social environments, including families, courts, companies, and markets.     

Transgenic overexpression of a dominant negative mutant of FADD that, although counterselected during tumor progression, cooperates in L-myc-induced tumorigenesis

Activation of the so-called death receptors, e.g., CD95/Fas/Apo-1, is a potent stimulus to trigger apoptosis. Overexpression of the C-terminal FADD deletion mutant FADD-DN blocks death receptor-induced apoptosis, but despite this antiapoptotic activity, lck FADD-DN transgenic mice do not develop lymphomas. To analyze whether functional inactivation of FADD cooperates with Myc overexpression in tumorigenesis, lck FADD-DN transgenic mice were crossed with Emicro L-myc transoncogenic animals. While no tumors were detected in single transgenic FADD-DN or L-myc mice within 15 months, 5 of 17 (29%) FADD-DN/L-myc double transgenic animals developed lymphomas with an average latency period of 47 weeks. Protein analysis of FADD-DN/L-myc tumors showed, however, undetectable levels of FADD-DN protein. FADD-DN protein expression was again lost in 16 of 17 FADD-DN/p53 k.o. T-cell lymphomas, though no significant acceleration of tumorigenesis in P53-deficient lck FADD-DN mice compared to p53 k.o. animals was observed. These data suggest a strong counterselection against the FADD-DN protein during tumor progression, which could be explained by the cell cycle inhibitory activity of FADD-DN. Such counterselection would have to be compensated for by other antiapoptotic mutations, and indeed, strong upregulation of the antiapoptotic Bcl-2 family member Bcl-xL was found in one of the tumors. This in vivo mouse model demonstrates that an antiapoptotic protein involved in the onset of tumorigenesis is selected against and consequently lost during tumor progression because of its additional antiproliferative activity.     

Enhanced mismatch negativity brain response after binaural word presentation

Abstract An oddball paradigm was used to investigate brain processes elicited by spoken words and pseudowords played monaurally, to the left or right ear, or simultaneously to both ears of human subjects instructed to ignore acoustic stimuli but watch a silent video film. The mismatch negativity (MMN), a neurophysiological index of the automatic activation of cortical memory traces, was calculated as the difference between the event-related potential elicited by an infrequent deviant stimulus and the event-related potential to the same item presented as a frequent standard stimulus. Consistent with earlier reports, the MMN to words was larger than that to pseudowords, possibly reflecting the existence of memory traces for spoken words. Bilateral redundant stimulus presentation led to a further increase of the MMN to words relative to both unilateral stimulation modes. This bilateral redundancy gain was absent for pseudowords. We interpret the neurophysiological manifestation of a word-specific bilateral redundancy gain as evidence for interhemispheric cooperation in the automatic access to memory traces for spoken words. Accordingly, word-related cortical networks distributed over both hemispheres allow summation of neural activity between and within hemispheres, thereby potentiating the word-related MMN.     

Modular biased-competition and cooperation: a candidate mechanism for selective working memory

Prefrontal cortex (PFC) has been suggested to play an important role in executive cognitive functions, participating in planning and controlling behaviour. The results of several recent electrophysiological studies indicate that PFC might be involved not only in the active maintenance of information but in doing so in a context- or task-dependent manner. In a delayed-match-to-sample paradigm, recordings from neurons in the PFC showed their ability to selectively represent information, which is needed for task completion, suggesting that task-irrelevant information does not access working memory. We present a neurodynamical computational model of a part of the PFC to account for the selective representation of information in working memory. We show that a network of biological realistic integrate-and-fire excitatory and inhibitory neurons, implementing the mechanisms of local or modular biased-competition, which is transmitted through cooperation to different subsets of neuronal pools, can explain the formation of selective context-dependent working memory. The modes of operation of the network are characterized and the corresponding parameter settings revealed. Modular competition and cooperation might constitute general mechanisms for implementing context-dependent formation of working memory.     

论大医院与中小医院合作双赢的现实措施

“看病难，看病贵”很大意义上指在大医院名医院就诊难治疗贵。通过大医院名医院与中小医院的合作，可以有效盘活并充分利用各自的优势卫生资源。大医院的高级医疗人力资源、先进医疗设备和管理理念可以有效提升中小医院的诊疗水平，同时常规诊疗和常见性疾病患者可以分流在中小医院，从而可以有效缓解大名医院患者“拥挤”中小医院“食不果腹”的现状。     

食管癌根治术的护理配合

目的探讨食管癌根治术的护理配合，以提高护理质量，为即将行该手术的患者提供相关信息，提高患者自我保护能力。方法通过对48例食管癌根治术患者的护理，了解其术前护理要求及最想了解的有关知识，按其需求调整护理措施。结果通过术前细致的护理，使患者了解了本病的相关知识，消除或明显减轻了恐惧心理。结论患者积极配合手术，保证了手术顺利进行，术中默契的配合，使手术顺利完成。