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Insulin-like growth factors (IGF)-I and -II are bound to carrier or binding proteins in serum. There are at least two classes of binding protein: a high molecular weight complex and a low molecular weight species that is relatively unsaturated. Total binding capacity in serum generally is determined by incubating [125I]IGF with protein that has been stripped of IGF by acid gel filtration. We found that addition of NaCl to the assay increased binding to stripped guinea pig binding protein to about two to four times the level measured in the absence of salt. Stimulation by NaCl was optimal between concentrations of 0.6 and 1.4 M and also was observed when fetal calf or human sera were used as sources of stripped binding protein or when IGF-II was the ligand. Using chloride salts, the order of activity with respect to cations was Na+ greater than K+ greater than Li+. Na2HPO4 at 0.6 M was as stimulatory as 1.2 M NaCl but 0.6 M Na2SO4 was less effective. NH4HCO3 was as effective as NaCl at 0.6 M. Scatchard plots of data from competitive dilution experiments with [125I]IGF-I and unlabeled IGF-I showed that binding was heterogeneous in the absence of 0.6 M NaCl but linear in its presence. NaCl did not stimulate binding when whole serum was used, but after gel filtration of serum on Sephacryl 200 at pH 8, which does not dissociate IGFs from binding protein, binding to individual fractions was stimulated three- to fourfold by NaCl. Fractions stimulated included those containing the large complex or the unsaturated binding protein.(ABSTRACT TRUNCATED AT 250 WORDS)

The sensory neurons of the Drosophila wing differentiate during the initial stages of metamorphosis, appearing in the imaginal wing disc as it everts and flattens. These identifiable neurons arise in a stereotyped sequence, and lay down a specific pattern of axon bundles which travel proximally to the CNS. In several locations, the early arising "pioneer" neurons send axons in the direction of more proximal pioneer neurons, later joining with these to form continuous peripheral nerves. It is possible that distal neurons can contact more proximal neurons by random filopodial search, and use this information to guide axonal outgrowth. To test this "guidepost" hypothesis, everting wing discs were raised in vitro to allow surgical manipulation. Neural outgrowth was largely normal in vitro, though growth of the wing was stunted. If such discs were cut into proximodistal fragments before or at the time of initial axonogenesis, neural outgrowth remained normal: distal axons still grew in the direction of the now missing proximal neurons. Thus, proximal neurons are not necessary for the correct guidance of distal neurons in the developing wing.

Burtt and Catton suggested that insects can resolve striped patterns finer than the theoretical limit set by the small diameter (30 microns) of the ommatidial lenslets. Events at the edges of the window behind which the patterns are moved explain these experiments without transgressing diffraction limitations. This interpretation leads to successful quantitative predictions of the effects of changing the boundary conditions.