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Self-polycondensation of AB-type monomers is an advantageous route to produce high-molecular-weight polymers without considerable adjustment in the mole ratio of the functionalities. Furthermore, the resulting polymers incorporate two different functional groups at the chain ends that enable the preparation of AB- and ABC-type block copolymers. In this study, poly(ether sulfone)s (PESs) were prepared via self-polycondensation of four AB-type monomers. The reactivity of the AB-type monomers was systematically investigated through model reactions and nuclear magnetic resonance measurements, which suggested that the novel AB-type monomers, 4-chloro-4'-(hydroxyphenyloxy)diphenylsulfone (monomer C) and 4-fluoro-4'-(hydroxyphenyloxy)diphenylsulfone (monomer D), are highly susceptible to nucleophilic aromatic substitution (SNAr) reactions. High-molecular-weight PESs (Mw>110?000) were obtained via the self-polycondensation of monomers C and D. The resulting PESs exhibited excellent thermal properties comparable with PESs prepared from A2- and B2-type monomers.

Abstract: The real-time observation of cell movement in brain slice preparations reveals that in the developing brain, postmitotic neurons alter their shape concomitantly with changes in the mode, direction, tempo, and rate of migration as they traverse different cortical layers. Although it has been hypothesized that orchestrated activities of multiple external cues and cell-cell contact are essential for controlling the cortical-layer-specific changes in cell migration, signaling mechanisms and external guidance cues related to the alteration of neuronal cell migration remain to be determined. In this article, we will first review recent studies on position-specific changes in granule cell behavior through different migratory terrains of the developing cerebellar cortex. We will then present possible roles for the coordinated activity of Ca2+ channels, NMDA type of glutamate receptors, and intracellular Ca2+ fluctuations in controlling cerebellar granule cell movement. Furthermore, we will discuss the crucial roles of brain-derived neurotrophic factor (BDNF), neuregulin (NRG), stromal cell-derived factor 1α (SDF-1α), ephrin-B2, and EphB2 receptor in providing directional cues promoting granule cell migration from the external granular layer (EGL) to the internal granular layer (IGL). Finally, we will demonstrate that endogenous somatostatin controls the migration of granule cells in a cortical layer-specific manner: Endogenous somatostatin accelerates granule cell movement near the birthplace within the EGL, but significantly slows down the movement near their final destination within the IGL.

Abstract:  We used optical methods to examine the spatial gradient of intrinsic rhythmicity in early-stage multiple-heart chick embryos. The latter were induced experimentally in whole-embryo culture. The embryos were cut microsurgically through the tissue of the anterior intestinal portal at the 5- to early 7-somite developmental stage. Spontaneous electrical activity in 4 to 6 segmented hearts, during the 7- to 10-somite stages of development, were monitored simultaneously by means of multiple-site optical recordings of membrane potential activity, using a voltage-sensitive merocyanine-rhodanine dye (NK2761). Each segment of the heart exhibited its own inherent rhythmicity. In quadruple hearts, the order of the rhythmicity was often left-caudal segment>right-caudal segment>left-cephalic segment>right-cephalic segment; the heart rate in the left-caudal segment was often faster than that in the other segments. An atypical pattern of ”bursting” rhythm was observed in the cephalic segments suggesting that, in these segments, the development of rhythmicity is relatively poor. These findings strongly emphasize the concept that, in the early phases of cardiogenesis, the formation of a regional gradient of pacemaker activity (i.e. a spatial gradient of intrinsic rhythmicity) results in the functional self-organization of the pacemaking area.

The real-time observation of cell movement in acute cerebellar slices reveals that granule cells alter their shape concomitantly with changes in the mode and rate of migration as they traverse different cortical layers. Although the origin of local environmental cues responsible for these position-specific changes in migratory behavior remains unclear, several signaling mechanisms involved in controlling granule cell movement have emerged. The onset of one such mechanism is marked by the expression of voltage-gated ion channels and neurotransmitter receptors in postmitotic cells prior to the initiation of their migration. Granule cells start their radial migration after the expression of N-type Ca²⁺ channels and the N-methyl-D-aspartate subtype of glutamate receptors on the plasmalemmal surface. Blockade of the channel or receptor activity significantly decreases the rate of cell movement, indicating that the activation of these membrane constituents provides an essential signal for the translocation of granule cells. Another signal that controls the rate of cell migration is embedded in the combined amplitude and frequency components of Ca²⁺ fluctuations in the somata of migrating granule cells. Interestingly, each phase of Ca²⁺ fluctuation controls a separate phase of saltatory movement in the granule cells: The cells move forward during the phase of transient Ca²⁺ elevation and remain stationary during the troughs. Consequently, the changes in the amplitude and frequency components of Ca²⁺ fluctuations directly affect granule cell movement: Reducing the amplitude or frequency of Ca²⁺ fluctuations slows down the speed of cell movement, while the enhancement of these components accelerates migration. These findings suggest that signaling molecules present in the local cellular milieu encountered on the migratory route control the shape and motility of granule cells by modifying Ca²⁺ fluctuations in the soma through the activation of specific ion channels and neurotransmitter receptors. © 1998 John Wiley & Sons, Inc. J Neurobiol 37: 110–130, 1998