Traditional approaches to teacher education are increasingly critiqued for their limited relationship to student teachers' needs and for their meager impact on practice. Many pleas are heard for a radical new and effective pedagogy of teacher education in which theory and practice are linked effectively. Although various attempts to restructure teacher education have been published, no coherent body of knowledge exists about central principles underlying teacher education programs that are responsive to the expectations, needs and practices of student teachers. By analyzing effective features of programs in Australia, Canada, and the Netherlands, this study contributes an initial framework of seven fundamental principles to guide the development of responsive teacher education programs that make a difference.

ABSTRACT

Axons are traditionally considered stable transmission cables, but evidence of the regulation of action potential propagation demonstrates that axons may have more important roles. However, their small diameters render intracellular recordings challenging, and low-magnitude extracellular signals are difficult to detect and assign. Better experimental access to axonal function would help to advance this field. Here we report methods to electrically visualize action potential propagation and network topology in cortical neurons grown over custom arrays, which contain 11,011 microelectrodes and are fabricated using complementary metal oxide semiconductor technology. Any neuron lying on the array can be recorded at high spatio-temporal resolution, and simultaneously precisely stimulated with little artifact. We find substantial velocity differences occurring locally within single axons, suggesting that the temporal control of a neuron's output may contribute to neuronal information processing.

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When the right hand washes the left, the right hand comes clean too.

Mouse embryonic stem (ES) cells can proliferate indefinitely in an undifferentiated state in the presence of leukemia inhibitory factor (LIF), or differentiate into all three germ layers upon removal of this factor. To determine cellular factors associated with self-renewal of undifferentiated ES cells, we used polymerase chain reaction-assisted cDNA subtraction to screen genes that are expressed in undifferentiated ES cells and down-regulated after incubating these cells in a differentiation medium without LIF for 48 h. The mRNA expression of a tetraspanin transmembrane protein, CD9, was high in undifferentiated ES cells and decreased shortly after cell differentiation. An immunohistochemical analysis confirmed that plasma membrane-associated CD9 was expressed in undifferentiated ES cells but low in the differentiated cells. Addition of LIF to differentiating ES cells reinduced mRNA expression of CD9, and CD9 expression was accompanied with a reappearance of undifferentiated ES cells. Furthermore, activation of STAT3 induced the expression of CD9, indicating the LIF/STAT3 pathway is critical for maintaining CD9 expression. Finally, addition of anti-CD9 antibody blocked ES cell colony formation and reduced cell viability. These results indicate that CD9 may play a role in LIF-mediated maintenance of undifferentiated ES cells. INTRODUCTIONMouse embryonic stem (ES) cells, which originally derived from inner cell mass of an early embryo named blastocyst, are able to sustain their pluripotency in in vitro cell culture (Evans and Kaufman, 1981;Martin, 1981). Undifferentiated mouse ES cells can be maintained for a long time in media containing the cytokine leukemia inhibitory factor (LIF) (Smith et al., 1988;Williams et al., 1988). Pluripotency of such cultured ES cells has been demonstrated in both in vivo and in vitro experiments. When injected into blastocysts, ES cells participate in embryonic development involving all three germ layers producing chimeric mice (Bradley et al., 1984). ES cells also form teratomas containing various mature tissues when injected into immunocompromised mice (Evans and Kaufman, 1981;Martin, 1981). In vitro, mouse ES cells start to differentiate to every possible lineage upon removal of LIF from the culture medium. The mechanism by which LIF maintains ES cells in undifferentiated state is not completely understood. The transcription factor STAT3 is a downstream target of LIF and its receptor interaction Matsuda et al., 1999). It has been shown that the activity of STAT3 is necessary and sufficient for LIF-induced self-renewal of mouse ES cells (Matsuda et al., 1999). It remains unclear, however, which genes are regulated by the STAT3 transcription factor in mouse ES cells and play actual roles in the maintenance of stem cells. Indeed, there is no generally accepted mechanism by which stem cells are maintained as undifferentiated cells. Human ES cell cultures have been recently established using mouse fibroblasts as feeder cells (Shamblott et al., 1998;Thomson et al., 1998). In contrast ...

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We studied the circuitry that underlies the behavior of the local edge detector (LED) retinal ganglion cell in rabbit by measuring the spatial and temporal properties of excitatory and inhibitory currents under whole cell voltage clamp. Previous work showed that LED excitation is suppressed by activity in the surround. However, the contributions of outer and inner retina to this characteristic and the neurotransmitters used are currently unknown. Blockage of retinal inhibitory pathways (GABA(A), GABA(C), and glycine) eliminated edge selectivity. Inverting gratings in the surround with 50-microm stripe sizes did not stimulate horizontal cells, but suppressed on and off excitation by roughly 60%, indicating inhibition of bipolar terminals (feedback inhibition). On pharmacologic blockage, we showed that feedback inhibition used both GABA(A) and GABA(C) receptors, but not glycine. Glycinergic inhibition suppressed GABAergic feedback inhibition in the center, enabling larger excitatory currents in response to luminance changes. Excitation, feedback inhibition, and direct (feedforward) inhibition responded to luminance-neutral flipping gratings of 20- to 50-microm widths, showing they are driven by independent subunits within their receptive fields, which confers sensitivity to borders between areas of texture and nontexture. Feedforward inhibition was glycinergic, its rise time was faster than decay time, and did not function to delay spiking at the onset of a stimulus. Both the on and off phases could be triggered by luminance shifts as short in duration as 33 ms and could be triggered during scenes that already produced a high baseline level of feedforward inhibition. Our results show how LED circuitry can use subreceptive field sensitivity to detect visual edges via the interaction between excitation and feedback inhibition and also respond to rapid luminance shifts within a rapidly changing scene by producing feedforward inhibition.