Placental/umbilical cord blood (PCB) stem cells for transplantation provide a potentially useful alternative for patients who do not have an HLA-matched family or unrelated bone marrow donor. Concerns regarding this source of stem cells include the limited number of stem cells in a PCB unit and the delayed time to platelet.engraftment. Because of the limited number of stem cells, there is a very clear cell dose effect for both success of engraftment and time to engraftment. As a result, many transplant centers will only consider PCB stem cells as a second choice for transplanting adults, despite the very favorable profile of post-transplant graft-versus-host disease (GvHD). This has resulted in considerable interest in the development of ex vivo stem cell expansion strategies. This review outlines the current status of PCB transplant outcomes as well as the status of our understanding of stem cell expansion with the currently available technologies. A stem cell dose-limiting effect on outcome will result in a narrower window of clinical indications for the use of this stem cell source, despite the acknowledged reduction in GvHD. The trade-offs between poor engraftment and reduction in fatal or severe chronic GvHD remain to be quantitated.

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Dimensional approaches have been used to describe the fundamental dimensions that underlie the entire domain of normal and pathological personality. We tested the five factor model of personality structure in a sample of Japanese twins, to clarify the contributions of genetic and envi-ronment. The revised NEO personality inventory (NEO-PI-R) was administered to 251 twin pairs, ranging in age from 15 to 27 years of age. The NEO-PI-R is a 240-item questionnaire which was developed to assess the dimensions of personality. Univariate genetic analysis showed that the AE model in which phenotypic covariances are explained only by additive genetic (A) and nonshared environment (E) is still a plausible model, and that the relative proportion of genetic influence was comparable to that reported by Loehlin (1992). Multivariate genetic analysis of the Japanese data suggested/revealed that the five factors are genetically dependent on each other and one common genetic factor mediates their interdependence. Previous studies have assumed that they are pheno-typically independent and robust. Although there are sampling biases in the present study, it is note-worthy that the results for all five factors depicted by the NEO-PI-R were comparable to those reported by Western researchers, and the genetic structure of the five-factor model is complex.

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A classic example of a complicated neurocomputation carried out by a relatively simple neuronal circuitry is that some mammalian retinal ganglion cells respond selectively to direction of motion. Search for the mechanisms of direction selectivity in the mammalian retina started some 35 years ago. It has been shown that direction selectivity is caused by an asymmetrical inhibition induced by GABA acting on GABAA receptors. However, the physical circuitry underling this computation is still not clear. A few recent breakthroughs provide important evidence for the sites where the compu-tation takes place.

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