Post-nodal mesoblast caudalizes the host axis and inhibits cell population growth, and induces new primitive streaks in chick embryos

Electrical stimulation of isolated retina with microwire glass electrodes

The development of high-resolution retinal prostheses fabricated from silicon wafers presents an interesting problem: how to electrically bridge the space between the flat silicon wafer and the curved retinal surface. One potential "bridge" is a microwire glass electrode. In this paper we present our results in evaluating microwire glass electrodes. We stimulated isolated rabbit retina (n = 5) with a 0.0256 cm(2) microwire electrode. The current and pulse duration were varied from 498 to 1660 microA and 0.1 to 3 ms, respectively. We found that short pulses produced more spikes per coulomb and longer pulses produced more spikes per milliamp. The optimal pulse duration range of 0.7-1 ms was identified as a compromise between the advantages of short and long pulses. Stimulation of isolated rabbit retina with microwire glass results in consistent neuronal spike formation at safe charge density, 20.7 +/- 4.3 microC/cm(2). We also examined the response of retinas (n = 6) to stimulation with a smaller microwire electrode, 0.0002 cm(2). We found that less current was required (15 microA versus 756 microA) for a 1 ms pulse, but at the expense of greater charge density (75 microC/cm(2) versus 29.5 microC/cm(2)). Nonetheless, a 128-fold reduction in area resulted in only a 2.7-fold increase in charge density required for a 1 ms pulse duration. The results presented here indicate that microwire glass can be used as a neural stimulating electrode to bridge the gap between flat microelectronic stimulator chips and curved neuronal tissue.

beta-Microseminoprotein-related molecules may participate in formation of the mesoderm in the chick embryo

It has previously been shown that human beta-microseminoprotein enhances development of mesodermal structures in the chick embryo. The present study was carried out to elucidate the mechanism of action of human beta-microseminoprotein in the chick embryo. beta-Microseminoprotein brought about significant modulation of expression of Brachyury in gastrulating embryos. In approximately 50% of the treated embryos, Brachyury expression was enhanced around the Hensen's node. These cells not only expressed higher levels of Brachyury, but also appeared to switch off Brachyury expression prematurely, postinvagination. The spatial modulation of Brachyury is not clearly reflected in the northern blots, indicating that beta-microseminoprotein treatment results in redistribution of available transcripts or that the upregulation is compensated for by early switching off of Brachyury postinvagination. Because higher levels of Brachyury during gastrulation are believed to result in early exit of cells from the primitive streak, beta-microseminoprotein treatment appeared to have stimulated morphogenetic movements by upregulating Brachyury around the Hensen's node. This deduction was confirmed by scanning electron microscopic analysis that showed that altered morphogenetic movements accompany modulation of Brachyury. The specific responses elicited by beta-microseminoprotein indicate presence of a structurally related molecule in the chick. By western blotting, similar molecules were indeed detected in the chicken seminal plasma and in chick embryos. These data strongly suggest that beta-microseminoprotein-related molecule(s) participates in mesoderm formation in the chick embryo.