When two small doses of ethanol were administered to pregnant mice during the gastrulation stage of embryogenesis, the embryos developed craniofacial malformations closely resembling those seen in the human fetal alcohol syndrome. Striking histological changes appeared in the developing brain (neuroectoderm) within 24 hours of exposure. Decreased development of the neural plate and its derivatives apparently accounts for the craniofacial malformations. The critical exposure period is equivalent to the third week in human pregnancy.

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BackgroundClimate has a long history in organizational studies, but few theoretical models integrate the complex effects of climate during innovation implementation. In 1996, a theoretical model was proposed that organizations could develop a positive climate for implementation by making use of various policies and practices that promote organizational members' means, motives, and opportunities for innovation use. The model proposes that implementation climate--or the extent to which organizational members perceive that innovation use is expected, supported, and rewarded--is positively associated with implementation effectiveness. The implementation climate construct holds significant promise for advancing scientific knowledge about the organizational determinants of innovation implementation. However, the construct has not received sufficient scholarly attention, despite numerous citations in the scientific literature. In this article, we clarify the meaning of implementation climate, discuss several measurement issues, and propose guidelines for empirical study.DiscussionImplementation climate differs from constructs such as organizational climate, culture, or context in two important respects: first, it has a strategic focus (implementation), and second, it is innovation-specific. Measuring implementation climate is challenging because the construct operates at the organizational level, but requires the collection of multi-dimensional perceptual data from many expected innovation users within an organization. In order to avoid problems with construct validity, assessments of within-group agreement of implementation climate measures must be carefully considered. Implementation climate implies a high degree of within-group agreement in climate perceptions. However, researchers might find it useful to distinguish implementation climate level (the average of implementation climate perceptions) from implementation climate strength (the variability of implementation climate perceptions). It is important to recognize that the implementation climate construct applies most readily to innovations that require collective, coordinated behavior change by many organizational members both for successful implementation and for realization of anticipated benefits. For innovations that do not possess these attributes, individual-level theories of behavior change could be more useful in explaining implementation effectiveness.SummaryThis construct has considerable value in implementation science, however, further debate and development is necessary to refine and distinguish the construct for empirical use.

The synthesis of (C 5 Me 5 ) 3 Ce and (C 5 Me 5 ) 3 Pr from [(C 5 Me 5 ) 2 Ln][(µ-Ph) 2 BPh 2 ] and KC 5 Me 5 completes the series of sterically crowded (C 5 Me 5 ) 3 Ln complexes for the larger lanthanides, La-Nd and Sm, and allows a comparison of structure and reactivity as a function of metal size. Synthesis of these new (C 5 Me 5 ) 3 Ln complexes required silylated glassware, which surprisingly was not necessary for the more sterically crowded analogues. (C 5 Me 5 ) 3 Ce and (C 5 Me 5 ) 3 Pr display longer Ln-C(C 5 Me 5 ) distances than any previously described Ce or Pr complexes containing the (C 5 Me 5 )ligand. The η 1 -C 5 Me 5 alkyl-like reactivity of the (C 5 Me 5 ) 3 Ln complexes was investigated with CO, ethylene, THF, and H 2 . The sterically induced reduction (SIR) reactivity of the (C 5 Me 5 ) 3 Ln complexes was examined with SedPPh 3 , AgBPh 4 , C 8 H 8 , and phenazine. All of these data indicate that (C 5 Me 5 ) 3 Ln reactivity increases with decreasing size of the metal and hence increased steric crowding. The reactivity of (C 5 Me 5 ) 3 Ln with CO 2 and with Et 3 NHBPh 4 was examined since each substrate could react by either η 1 -C 5 Me 5 alkyl or SIR pathways. In both cases, alkyl-like reactivity is observed: CO 2 forms the insertion product (C 5 Me 5 ) 2 Ln(O 2 CC 5 Me 5 ), containing a carboxylate with a pentamethylcyclopentadiene substituent, and Et 3 NHBPh 4 forms [(C 5 Me 5 ) 2 Ln][(µ-Ph) 2 BPh 2 ] and C 5 Me 5 H. The reactions of (C 5 Me 5 ) 3 Sm with aryl halides and primary alkyl halide radical clocks (RX) yield C 5 Me 5 R, C 5 Me 5 X, (C 5 Me 5 ) 2 , R-R, and [(C 5 Me 5 ) x SmX y ] z as products, which indicate that SIR is not the only reaction pathway with these substrates. The X-ray crystal structures of the (C 5 Me 5 ) 3 Ln reaction products [(C 5 Me 5 ) 2 La] 2 (µ-η 2 :η 2 -Se 2 ), [(C 5 Me 5 ) 2 (THF)La] 2 (µ-η 2 :η 2 -Se 2 ), [(C 5 Me 5 ) 2 La] 2 (µ-η 3 :η 3 -C 12 N 2 H 8 ), [(C 5 Me 5 ) 2 Sm(µ-I)] 3 , and (C 5 Me 5 ) 2 Sm(O 2 CC 5 Me 5 ) are described as well as a new synthesis of (C 5 Me 5 ) 3 Sm from (C 5 Me 5 ) 2 Sm and (C 5 Me 5 ) 2 .

The migration and fate of cranial neural fold cells of the chick embryo (White Leghorn strain) were followed radioautographically after replacing crestcontaining fold segments with comparable segments from donor embryos labeled with tritiated thymidine. The behavior of the neural crest cells was found to be remarkably similar to that of their amphibian counterparts. The movements of labeled crest cells into the upper facial region of the chick embryo, in conjunction with their proliferative activity, apparently gave rise to the embryonic facial (medial and lateral nasal, and maxillary) processes. As the cells moved into the visceral arches, they surrounded the core-like mesodermal muscle plates.In the upper face and visceral arch regions, labeled crest cells participated in the formation of cartilage. Judging from the distribution of these cells in the reniaining mesenchyme, it appears that the still undifferentiated skeletal and connective tissues of these regions are also of neural crest origin. Labeled crest cells were also found in the root ganglia of the VIIth and of the IXth and Xth nerves and the trigerninal and ciliary ganglia. While labeled neural crest contributed extensively to the formation of sheath cells, it made rather limited contributions to the meninges of the brain.