Axon growth from limb motorneurons in the locust embryo: the effect of target limb removal on the pattern of axon branching in the periphery

Metathoracic limb buds have been unilaterally ablated from locust embryos at 25 to 30% of embryonic development and the effect of this operation on the axon morphology of the motorneuron fast extensor tibiae (FETi) observed at later embryonic stages. In control embryos this neuron sends a single axon out the main leg nerve, nerve 5, to the extensor tibiae muscle in the femur. In limb ablated embryos the axon of FETi is found in a wide variety of aberrant peripheral nerve pathways and projects to a wide range of foreign muscles. There is a degree of apparent selectivity, but no rigid hierarchy, in the choice of pathway and muscle made by FETi. A high degree of variability is found between one embryo and another in the extent and pattern of axon branching. The axon of FETi is generally found in pathways that correspond to nerves in control embryos but on occasion grows along novel routes. An anteriorly directed dendritic branch, seldom seen in control FETi neurons, is frequently seen in experimental FETis. These findings are discussed in terms of the rules for specific axon growth in normal development.     

The coxal glands of geophilomorpha (chilopoda): Organs of osmoregulation

Summary The organs terminating at the coxal pores of the tug-legs of Geophilomorpha are not repugnatorial glands, but possess typical transport epithelia with deep apical and basal infoldings of the cell membranes, between which numerous large mitochondria are located. Many transport vesicles are found in the basal region but fewer in the apical cytoplasm. The apex is characterized by bundles of longitudinally oriented microtubules, sparse endoplasmic reticulum and free ribosomes. Single neurosecretory axons with synaptoid areas are scattered among the cells. It is suggested that the coxal organs have a diuretic function in moist habitats and an antidiuretic effect in arid environments. The switch-over is evidently controlled by a neuroendocrine mechanism.     

Synaptic vesicles from hog brain—their isolation and the coupling between synthesis and uptake of γ-aminobutyrate by glutamate decarboxylase

Purified synaptic vesicles were isolated from hog cerebral cortex by a rapid procedure consisting of homogenization of cerebral cortex slices in iso-osmotic sucrose, differential centrifugation and sucrose density-gradient centrifugation. The purity of the vesicles was evaluated both biochemically and morphologically. The vesicles contained high amounts of γ-aminobutyrate (GABA) and acetylcholine at specific concentrations of 390 nmol/mg protein and 7.2 nmol/mg protein respectively.

Glutamate decarboxylase, the enzyme which catalyses GABA formation, binds to the synaptic vesicles in a calcium-dependent manner. The percentage of glutamate decarboxylase bound to the vesicles increases from about 5% without calcium, reaching a plateau of about 60% at 4 mM Ca²⁺. Magnesium in concentrations 0.2–10 mM has no significant effect on glutamate decarboxylase binding. Also in phospholipid vesicles (small unilamellar phosphatidylserine-phosphatidylcholine. 2:1 liposomes) Ca²⁺, but not Mg²⁺, induced the binding of glutamate decarboxylase, reaching a plateau of 50% at 2 mM Ca²⁺. Both in synaptic vesicles and in phospholipid vesicles the calcium-dependent glutamate decarboxylase binding seems to be specific, and not caused by unspecific association of proteins, since the specific binding (bound enzyme activity/mg bound protein) increases 3-fold from 0 to 4 mM Ca²⁺.

The functional role of this binding was studied in GAD containing vesicles by measuring the relationship between the accumulation of [³H]GABA, newly synthetized from [³H]glutamate, and the uptake of added [¹⁴C]GABA. No significant uptake of [¹⁴C]GABA was found under the experimental conditions used, whereas large amounts of [³H]GABA were found within the vesicles. It appears that the [³H]GABA accumulation process is functionally linked to [³H]GABA synthesis and is mediated by the membrane-bound glutamate decarboxylase. This synthesis-coupled uptake of GABA into synaptic vesicles possibly serves to bring about a plasticity effect in previously stimulated GABAergic nerve endings.     

The hemocytes of the centipedeLithobius forficatus (Chilopoda,Lithobiomorpha)

Summary Five different types of hemocytes are found within the hemolymph ofLithobius forficatus: (1) small prohemocytes, (2) very actively spreading plasmatocytes, (3) granulocytes which have a lower spreading ability but tend to agglutinate, (4) spherulocytes which are filled with spherules, and (5) presumably, a coagulocyte, characterized by instant disintegration. Cystocytes as described forL. forficatus in the literature are preparation artifacts. Cell types are characterized by electron microscopy and in vitro and vital staining techniques at the light microscopic level. Results are discussed with reference to different nomenclatures and functions of hemocytes in other arthropods.     

Effects of Detergents, Proteins, and Lipids on 2'':3''-Cyclic-Nucleotide 3''-Phosphodiesterase Activity

The myelin marker 2':3'-cyclic-nucleotide 34'-phosphodiesterase (CNPase) was isolated to a lipid- and phosphate-free stage. The effects of exogenously added lipids were tested on this preparation and compared to the known stimulation of the enzyme by detergents and proteins. CNPase could be stimulated 2-3 fold by these various agents which appeared to be additive in their effect. Enzyme-protein and enzyme-lipid interactions and possible medical use of the improved assay conditions for CNPase employed in the study are discussed.     

Development of cell surface saccharides on embryonic pancreatic cells

Using a battery of seven lectin-ferritin conjugates as probes for cell surface glycoconjugates, we have studied the pattern of plasmalemmal differentiation of cells in the embryonic rat pancreas from day 15 in utero to the early postpartum stage. Our results indicate that differentiation of plasmalemmal glycoconjugates on acinar, endocrine, and centroacinar cells is temporally correlated with development and is unique for each cell type, as indicated by lectin-ferritin binding. Specifically, (a) expression of adult cell surface saccharide phenotype can be detected on presumptive acinar cells as early as 15 d in utero, as indicated by soybean agglutinin binding, and precedes development of intracellular organelles characteristic of mature acinar cells; (b) maturation of the plasmalemma of acinar cells is reached after intracellular cytodifferentiation is completed, as indicated by appearance of Con A and fucoselectin binding sites only at day 19 of development; conversely, maturation of the endocrine cell plasmalemma is accompanied by "loss" (masking) of ricinus communis II agglutinin receptors; and (c) binding sites for fucose lectins and for soybean agglutinin are absent on endocrine and centroacinar cells at all stages examined. We conclude that acinar, centroacinar, and endocrine cells develop from a common progenitor cell(s) whose plasmalemmal carbohydrate composition resembles most closely that of the adult centroacinar cell. Finally, appearance of acinar lumina beginning at approximately 17 d in utero is accompanied by differenetiation of apical and basolateral plasmalemmal domains of epithelial cells, as indicated by enhanced binding of several lectin-ferritin conjugates to the apical plasmalemmal, a pattern that persists from this stage through adult life.     

The effect of sodium chloride on the structure of ribonucleoprotein particles from rat liver nuclei.

38S (monoparticles) and greater than 50--200S ribonucleoprotein particles (polyparticles) from rat liver nuclei were treated with increasing concentrations of sodium chloride. Treatment of 38S or greater than 50--200S particles, with 0.14, 0.25, 0.5, 1.0, and 2.0M NaCl resulted in a decrease of protein to RNA ratios from 8 to 3.1 for 38S particles and from 4.0 to 1.5 for greater than 20--200S particles. Correspondingly the densities in CsCl increased. Whereas the maximum of the sedimentation profile of polyparticles decreased from 90S to 50S after treatment with increasing NaCl concentrations, a discontinuous change was found in the case of monoparticles. It was shown by sodium dodecyl sulfate-polyacrylamide gel electrophoresis that the proteins which were dissociated by NaCl were in the molecular weight range of 30--45 000. Four of the 5 small molecular weight RNAs in the range of 4.5 to 8S remained tightly associated even after treatment of polyparticles with 2.0M NaCl. When 38S or 70--200S nRNP particles were exposed to increasing concentrations of NaCl (0.25, 0.5, 1.0, 2.0M), the molar ellipticity at 264 nm increased progressively to about 40%. Upon NaCl treatment of polyparticles and successive removal of the dissociated proteins by centrifugation the increase in the positive CD band at 264 nm was only 15%.     

Polysaccharide and protein degradation,germination, and virulence against mosquitoes in the entomopathogenic fungus Metarhizium anisopliae

From a genetically uniform wild-type strain of Metarhizium anisopliae pathogenic to mosquitoes, mutants were selected which were altered in the ability to degrade starch, gelatin, or milk. The mutants with enhanced starch degradation (dep), when grown on starch-containing media, proved hypervirulent toward the mosquito Culex pipiens pipiens in standard laboratory tests. Alterations in protein (gelatin or milk) degradation did not correlate with changes in virulence. The dep mutants appear to belong to the same class as mutants selected previously as hypervirulent and characterized by early spore germination. The relationship among polysaccharide degradation, early germination, and virulence is discussed.