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We have analyzed the distribution of neural crest-derived precursors and the expression of catecholaminergic and neuronal markers in developing adrenal tissue of chick embryos. Undifferentiated neural crest cells are found in presumptive adrenal regions from embryonic day 3 (E3) onward. An increasing proportion of cells expressing tyrosine hydroxylase (TH) mRNA indicates catecholaminergic differentiation of precursors not only in primary sympathetic ganglia, but also in presumptive adrenal regions. Whereas precursors and differentiating cells show mesenchymal distribution until E5, discrete adrenal anlagen form during E6. Even during E5, catecholaminergic cells with low or undetectable neurofilament M (NF-M) mRNA expression prevail in positions at which adrenal anlagen become distinct during E6. The predominance of TH-positive and NF-M-negative cells is maintained throughout embryogenesis in adrenal tissue. RNA encoding SCG10, a pan-neuronal marker like NF-M, is strongly expressed throughout adrenal anlagen during E6 but is found at reduced levels in chromaffin cells compared with neuronal cells at E15. Two additional neuronal markers, synaptotagmin 1 and neurexin 1, are expressed at low to undetectable levels in developing chromaffin cells throughout embryogenesis. The developmental regulation of neuronal markers shows at least three different patterns among the four mRNAs analyzed. Importantly, there is no generalized downregulation of neuronal markers in developing adrenal anlagen. Thus, our observations question the classical concept of chromaffin differentiation from a common sympathoadrenal progenitor expressing neuronal properties and suggest alternative models with changing instructive signals or separate progenitor populations for sympathetic neuronal and chromaffin endocrine cells.

The reuse of soda-lime-silica scrap or waste glasses as additives for traditional ceramics has been investigated extensively in the literature. Although interesting, this solution does not generally allow large quantities of glass to be recycled. This study reports a novel high glass recycle approach that replaces, in the formulation of porcelain stoneware, the feldspar flux with finely powdered glass derived from the melting of different waste products, e.g. lime from fume abatement systems, feldspar mining residues, and scrap soda-lime glass. At an optimized glass/clay ratio, the ''glass-ceramic stoneware'' samples sinter at 10001C. The ''glass-ceramic stoneware'' has a bending strength approaching 90 MPa and a fracture toughness exceeding 2.0 MPa . m 0.5 , similar to those of conventional porcelain stoneware, which requires sintering at higher temperatures. The high strength and fracture toughness are attributed to the interaction between the glass and clay residues upon sintering, which allows the development of several different crystalline phases.C. Jantzen-contributing editor