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Summary form only given. In this paper we consider both theoretical and experimental aspects of adaptive wavefront phase distortion compensation using direct system performance metric optimization. A brief review of model free optimization techniques in adaptive optics, with an emphasis on gradient descent methods based on stochastic approximation of the true gradient is presented. The method is extended to include different requirements for wavefront control, as well as information from different wavefront sensor types. It is shown that both can be incorporated into a more general gradient descent optimization paradigm, giving rise to a variety of new control system architectures.

The extent of interaction between brachial muscles and foreign (thoracic) nerves of the chick embryo was determined during an extended period of development in ovo from the perspectives of innervation pattern, function (motility analyses), muscle growth (quantitative analyses of muscle volume) and fibre-type expression (myosin-ATPase profiles). Results indicated that according to all parameters analysed, initially a compatible union existed between the foreign nerves and their muscle targets. During subsequent stages of development, deterioration of the once compatible relationship emerged, until eventually denervation of muscles, i.e. an actual loss of intramuscular nerve branches, was observed. The process of denervation, which proceeded at a differential rate among individual muscles, however was restricted to brachial muscles derived from the premuscle masses of the wing bud. In contrast, brachial muscles of myotomal origin were spared the fate of wing-bud-derived muscles and maintained a successful union with the foreign nerves.

Intraspecific chick/chick chimaeras were prepared by transplanting thoracic somitic mesoderm from donor chick embryos with hereditary muscular dystrophy to replace extirpated brachial somites of normal host embryos at stage 13 (48–52 h in ovo). Since the wings of unoperated dystrophic embryos exhibit significantly reduced motility between day-10 in ovo (day-10E) to day-15E, this parameter was used as a marker both to verify the viability of the transplant and to assess if the dystrophic phenotype of impaired functional activity is preserved in the mutant wing muscles innervated by brachial nerves of normal embryos. Our motility analyses of the chimaeras confirmed that transplanted thoracic somitic mesoderm gives rise to brachial musculature and that the experimental muscles maintained the inherent dystrophic phenotype.

Current evidence favours the hypothesis that avian muscle fibre-type differentiation is intrinsically programmed during early embryogenesis and proceeds independent of neuronal influences (for review, Miller & Stockdale, 1987; Sanes, 1987). Previous interspecific (chick/quail) and intraspecific (chick/chick) chimaeric studies, involving the heterotopic transplantation of unsegmented somitic mesoderm, indicate that the ability of premyogenic cells to form specific limb muscles is determined by positional cues operative in the host embryo. To determine if similar influences are associated with embryonic fibre-type differentiation, the limb musculature of intraspecific (chick/chick) chimaeras was assessed using differential myosin-ATPase activity. The limb musculature analysed histochemically was derived from donor unsegmented thoracic somitic mesoderm transplanted to replace extirpated brachial somites of a host embryo at 48 –52 h in ovo. Our results demonstrated that (1) the donor tissue formed, on schedule, an appropriate brachial musculature and (2) the experimental muscles duplicated the fibre-type patterning characteristic of control muscles. Thus, our data suggest that an extramyogenic, non-neural factor(s) operative in the host limb-forming region is associated with both muscle pattern formation and muscle fibre-type pattern formation. Whether or not the same putative factor(s) influences both processes remains to be determined.

Previous analyses showed that following heterotopic transplantation of a thoracic neural tube segment into the region of the extirpated brachial neural tube in experimental (Thor-Br) chick embryos at embryonic day -2 (day -2E) the wings of hatched Thor-Br chicks are immotile. It was not known, however, if functional nerve-muscle interaction occurs during embryogenesis of Thor-Br embryos, although structural nerve-muscle connections do form in wing muscles during initial development of this experimental model. From day 8.5-9E onward, however, thoracic nerve-brachial muscle unions progressively uncouple in individual wing muscles. The present study explored the nature of initial nerve-muscle contacts and employed a well documented functional parameter, wing motility, to monitor daily the development of functional nerve-muscle interactions in wings of individual Thor-Br embryos. Control embryos were either unoperated (UC) or received a homotopic brachial neural tube transplant (Br-Br). The results demonstrated that Thor-Br embryos exhibited normal frequencies of wing movement up to day -8E; but the frequency of wing movement became greatly reduced from that of controls following this initial developmental period. The loss of wing motility in Thor-Br embryos coincided temporally with the withdrawal of intramuscular axons from individual wing muscles reported previously. Thus, foreign thoracic nerves did establish initial functional contacts with wing muscles, however, these connections were subsequently deemed inappropriate and nerve-muscle unions progressively uncoupled. To investigate factors responsible for the nerve-muscle uncoupling phenomenon observed in experimental (Thor-Br) embryos the development of heterotopically transplanted thoracic neural tubes was compared to that of neural tubes in control (Br-Br and UC) embryos. Parameters analysed include the pattern of peripheral nerve outgrowth, neural tube histogenesis, the source of motor innervation to individual wing muscles and the pattern of motoneuron death, growth and differentiation. The results showed that while the pattern of nerve outgrowth was controlled by local environmental signals, developmental events within the neural tube was governed autonomously, independent of the periphery. Thus, heterotopically transplanted thoracic neural tubes developed according to their site of origin. In addition to the heterotopic neural tube (Thor-Br) transplantation experiments a second series of surgically manipulated chick embryos (Thor-Br/som) was employed to determine if nerve-muscle incompatibility is limited to a thoracic nerve-brachial muscle combination. Experimental (Thor-Br/som) embryos were produced by transplanting thoracic somitic mesoderm into the site of extirpated brachial somites at day -2E. Daily wing motility analyses were performed to determine the extent of functional nerve-muscle interaction between in situ brachial nerves and wing muscles derived from heterotopically transplanted thoracic somitic mesoderm. The results demonstrated that functional nerve-muscle interaction did occur in wings of Thor-Br/som embryos and, in contrast to experimental (Thor-Br) embryos, wing motility was maintained in Thor-Br/som embryos throughout the developmental period analysed (day -6E through day -16E). Nerve-muscle uncoupling, therefore, dd not occur in heterotopic somitic mesoderm transplantation experiments. It was concluded that eventual nerve-muscle incompatibility observed following heterotopic neural tube (Thor-Br) transplantation is related to the rigidity of developmental processes within the spinal cord. Whereas heterotopically transplanted thoracic somitic mesoderm exhibited a high degree of plasticity and conformed to peripheral signals derived from the brachial environment, transplated thoracic neural tubes were unable to respond to environmental signals were eventually deemed inappropriate. Doctor of Philosophy (PhD)

Treatment of gravid hamsters with 60 mg/kg of retinoic acid on the 8th day of pregnancy resulted in facial skeletal defects in 100% of the survivors examined by alizarin staining at term. An investigation of the early stages in the development of these malformations indicated that the teratogen induced delayed and disorganized patterns of cranial neural crest cell migration as well as extensive death and damage of crest cells. The results demonstrate that retinoic acid provides a useful tool for studies in the pathogenesis of facial skeletal abnormalities in vivo. Moreover, the extensive defects seen in the teratogen-treated litters at term, together with the results of the microscopical analyses, support the hypothesis that cranial neural crest cells make an important contribution to the development of the mammalian facial skeleton.

During development ex ovo, the avian mutant with an hereditary form of muscular dystrophy demonstrates biochemical, histochemical, and physiological (functional) abnormalities which may result from impaired muscle-nerve interaction. To investigate if impaired functional activity also characterizes the dystrophic process during development in ovo, limb motility, an index of embryonic functional muscle-nerve interaction, was compared between normal and dystrophic embryos from day 6E through day 16E. A highly significant reduction in this parameter was exhibited by dystrophic wings from day 11E to day 14E inclusive. In contrast, genotypically dystrophic hind limbs demonstrated values equivalent to normal legs. Thus, in the dystrophic embryo, impaired muscle-nerve interaction characterized the brachial region exclusively during a specific period of embryogenesis.