Peripheral and Central Determinants of a Nociceptive Reaction: An Approach to Psychophysics in the Rat

BACKGROUND: The quantitative end-point for many behavioral tests of nociception is the reaction time, i.e. the time lapse between the beginning of the application of a stimulus, e.g. heat, and the evoked response. Since it is technically impossible to heat the skin instantaneously by conventional means, the question of the significance of the reaction time to radiant heat remains open. We developed a theoretical framework, a related experimental paradigm and a model to analyze in psychophysical terms the "tail-flick" responses of rats to random variations of noxious radiant heat. METHODOLOGY/PRINCIPAL FINDINGS: A CO(2) laser was used to avoid the drawbacks associated with standard methods of thermal stimulation. Heating of the skin was recorded with an infrared camera and was stopped by the reaction of the animal. For the first time, we define and determine two key descriptors of the behavioral response, namely the behavioral threshold (Tbeta) and the behavioral latency (Lbeta). By employing more than one site of stimulation, the paradigm allows determination of the conduction velocity of the peripheral fibers that trigger the response (V) and an estimation of the latency (Ld) of the central decision-making process. Ld (approximately 130 ms) is unaffected by ambient or skin temperature changes that affect the behavioral threshold (approximately 42.2-44.9 degrees C in the 20-30 degrees C range), behavioral latency (<500 ms), and the conduction velocity of the peripheral fibers that trigger the response (approximately 0.35-0.76 m/s in the 20-30 degrees C range). We propose a simple model that is verified experimentally and that computes the variations in the so-called "tail-flick latency" (TFL) caused by changes in either the power of the radiant heat source, the initial temperature of the skin, or the site of stimulation along the tail. CONCLUSIONS/SIGNIFICANCE: This approach enables the behavioral determinations of latent psychophysical (Tbeta, Lbeta, Ld) and neurophysiological (V) variables that have been previously inaccessible with conventional methods. Such an approach satisfies the repeated requests for improving nociceptive tests and offers a potentially heuristic progress for studying nociceptive behavior on more firm physiological and psychophysical grounds. The validity of using a reaction time of a behavioral response to an increasing heat stimulus as a "pain index" is challenged. This is illustrated by the predicted temperature-dependent variations of the behavioral TFL elicited by spontaneous variations of the temperature of the tail for thermoregulation

Colorectal Cancer with Multiple Metastases: Is Palliative Surgery Needed?

In patients with symptomatic incurable metastatic colorectal cancer (mCRC), the goal of resection of the primary lesion is to palliate cancer-related morbidity, including obstruction, bleeding, or perforation. In patients with asymptomatic primary tumors and incurable metastatic disease, however, the necessity of primary tumor resection is less clear. Although several retrospective analyses suggest survival benefit in patients who undergo resection of the primary tumor, applying this older evidence to modern patients is out of date for several reasons. Modern chemotherapy regimens incorporating the novel cytotoxic agents oxaliplatin and irinotecan, as well as the target agents bevacizumab and cetuximab, have improved median survival from less than 1 year with the only available single-agent 5-fluorouracil until the mid-1990s to over 2 years. In addition to significant prolongation of overall survival, combinations of novel chemotherapeutic and target agents have allowed improved local and distant tumor control, decreasing the likelihood of local tumor-related complications requiring surgical resection. Resection of an asymptomatic primary tumor risks surgical complications and may postpone the administration of chemotherapy that may offer both systemic and local control. In conclusion, the morbidity and the mortality of unnecessary surgery or surgery that does not improve quality of life or survival in patients with mCRC of a limited life expectancy should be carefully evaluated. With the availability of effective combinations of chemotherapy and target agents, systemic therapy for the treatment of life-threatening metastases would be a preferable treatment strategy for unresectable asymptomatic patients with mCRC

Confidence-based Reasoning in Stochastic Constraint Programming

In this work we introduce a novel approach, based on sampling, for finding assignments that are likely to be solutions to stochastic constraint satisfaction problems and constraint optimisation problems. Our approach reduces the size of the original problem being analysed; by solving this reduced problem, with a given confidence probability, we obtain assignments that satisfy the chance constraints in the original model within prescribed error tolerance thresholds. To achieve this, we blend concepts from stochastic constraint programming and statistics. We discuss both exact and approximate variants of our method. The framework we introduce can be immediately employed in concert with existing approaches for solving stochastic constraint programs. A thorough computational study on a number of stochastic combinatorial optimisation problems demonstrates the effectiveness of our approach.Comment: 53 pages, working draf

Sustainable livelihoods to adaptive capabilities: a global learning journey in a small state, Zanzibar

This thesis takes global learning out of the formal setting of a Northern classroom to a rural community setting in the Global South as a social learning process. It begins with a critical reflection of a large EU project to develop a global learning programme as a Global North South initiative. The focus narrows to Zanzibar, a small island state, to critically reflect on the delivery of the programme. And then further to focus on the global social learning and change that occurred in a rural community setting in the north of the island. Through participatory action research, I investigate the relevance of global learning as a social learning process, how norms and rules are shaped within a community setting and how these enable social change towards sustainable livelihoods. The thesis splices the intersection between critical and social theories of learning and engagement, to include critical social theories of Habermas (1984) and Wals (2007); critical race theories of Giroux (1997) and Said (1994) and distributive justice and entitlements theories of Sen (1997) and Moser (1998). It demonstrates the importance of dissonance and a safe space for deliberative dialogue, to be able to consider the global pressures and forces on local realities as the precursor to social change towards sustainability. I conclude by relating the learning from this small island state to the wider world and the current discourse on quality of education in a community development context

Role of Primary Tumor Resection Among Chemotherapy-Treated Patients with Synchronous Stage IV Colorectal Cancer: A Survival Analysis

INTRODUCTION: The benefit of an operation to remove the primary tumor among patients with synchronous stage IV colorectal cancer is controversial. This study analyzed the survival benefits associated with primary tumor resection among chemotherapy-treated stage IV colorectal cancer patients. METHODS: The study analyzed 11,716 chemotherapy-treated stage IV colorectal cancer patients in the California Cancer Registry between 1996 and 2007, with follow-up through 2009. Patients were stratified into operation and non-operation groups. Estimates of median overall and colorectal cancer-specific survival were generated. RESULTS: Patients undergoing operation compared to those who are not had higher median overall and colorectal cancer-specific survival, 21 versus 10 months (p <0.0001) and 22 versus 12 months (p <0.0001), respectively. Patients who were offered surgery but refused had decreased median overall and colorectal cancer-specific survival when compared to patients who underwent resection, 8 versus 21 months (p <0.001) and 7 versus 22 months (p <0.001), respectively. In multivariate regression models, patients who underwent resection of primary tumor had improved overall (hazard ratio (HR), 0.42; 95 % confidence interval (CI) 0.40–0.44, p <0.0001) and colorectal cancer-specific survival (HR, 0.43; 95 % CI, 0.41–0.45; p <0.0001). CONCLUSION: Primary tumor resection is associated with improved survival among stage IV chemotherapy-treated colorectal cancer patients