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Sam Horng

Publications and source records attributed to Sam Horng.

5 recordsLinked to original sources
PubMed2006

Gene expression changes and molecular pathways mediating activity-dependent plasticity in visual cortex.

Two key models for examining activity-dependent development of primary visual cortex (V1) involve either reduction of activity in both eyes via dark-rearing (DR) or imbalance of activity between the two eyes via monocular deprivation (MD). Combining DNA microarray analysis with computational approaches, RT-PCR, immunohistochemistry and physiological imaging, we find that DR leads to (i) upregulation of genes subserving synaptic transmission and electrical activity, consistent with a coordinated response of cortical neurons to reduction of visual drive, and (ii) downregulation of parvalbumin expression, implicating parvalbumin-expressing interneurons as underlying the delay in cortical maturation after DR. MD partially activates homeostatic mechanisms but differentially upregulates molecular pathways related to growth factors and neuronal degeneration, consistent with reorganization of connections after MD. Expression of a binding protein of insulin-like growth factor-1 (IGF1) is highly upregulated after MD, and exogenous application of IGF1 prevents the physiological effects of MD on ocular dominance plasticity examined in vivo.

Animals↗
PubMed2003

Ethical framework for the use of sham procedures in clinical trials.

Ethical, professional, and financial considerations support the highest standards in demonstrating the safety and efficacy of new clinical interventions. Professional and regulatory mechanisms implemented to ensure that medical agents undergo a thorough process of systematic testing are lacking in the case of medical procedures. As a result, many procedures, including surgery, are rapidly introduced into the clinical setting without reliable evaluation of their efficacy. In many cases, a randomized, placebo-controlled procedure trial may be necessary to provide this data. We examine the major ethical objections to placebo-controlled procedure trials, including those involving sham surgery, and provide an ethical framework for assessing whether a placebo procedure is ethical to administer in the context of a clinical trial. A placebo-controlled trial of an invasive procedure can be ethically justified if: 1) there is a valuable, clinically relevant question to be answered by the research, 2) the placebo control is methodologically necessary to test the study hypothesis, 3) the risk of the placebo control itself has been minimized, 4) the risk of a placebo control does not exceed a threshold of acceptable research risk, 5) the risk of the placebo control is justified by valuable knowledge to be gained, and 6) the misleading involved in the administration of a placebo control is adequately disclosed and authorized during the informed consent process.

Ethics, Research↗
PubMed2002

Descriptions of benefits and risks in consent forms for phase 1 oncology trials.

BACKGROUND: Ethicists have suggested that written consent forms encourage participants in phase 1 cancer trials to expect benefit from the experimental agent and to overlook serious risks. METHODS: To evaluate the written description of direct benefit as well as risk, all consent forms for 1999 phase 1 cancer trials were compiled from 80 percent of the National Cancer Institute-designated cancer centers and from six of eight large pharmaceutical developers of anticancer drugs. In each case, we evaluated the characteristics of the trial, the descriptions of the purpose and procedures of the research, the promise of benefit, the description of risks, and the description of alternatives. RESULTS: Of 272 forms, 268 explicitly mentioned that the trial was research, and 249 stated that the purpose of the trial was testing for safety. Nearly all forms (269) mentioned the right to withdraw from the trial. Almost all forms (260) referred to the experimental agent as "treatment" or "therapy." Only one consent form promised direct benefit to subjects. Most forms (181) mentioned death as a risk, and very few (14) mentioned cure as even a possible benefit. Most (229) stated that there was unknown risk involved and indicated that severe or permanent harms were possible (224). CONCLUSIONS: Consent forms for phase 1 oncology studies almost never promise direct benefit to subjects, rarely mention cure, and usually communicate the seriousness and unpredictability of risk. Although there is room for improvement, the substance of these forms is unlikely to be the primary source of misunderstanding by subjects in phase 1 oncology trials.

Biomedical Research↗