A model for the temporal organization of X- and Y-type receptive fields in the primate retina

A model is proposed for the temporal characteristics of X-and Y-type responses of ganglion cells in the primate retina. The main suggestions of the model are: (I) The X-type temporal response is determined primarily by the delay between center and surround contributions. (II) The Y-type response is generated in the inner plexiform layer by a derivativelike operation on the bipolar cell's input, followed by a rectification in the convergence of these inputs onto the Y-ganglion-cell. (III) The derivative-like operation is obtained by recurrent inhibition in the dyad synaptic structure.The X-and Y-type responses predicted by the model, for a variety of stimuli, were examined and compared with available electrophysiological recordings. Finally, certain predictions derived from the model are discussed.     

Schistosoma mansoni: Inhibition of glucosephosphate isomerase and glycolysis by sugar phosphates

Glucosephosphate isomerase (EC 5.3.1.9) of Schistosoma mansoni is inhibited competitively by a number of tetrose, pentose, and hexose phosphates with inhibitor constant (K_i) values in the range of 0.5 to 400 μM. The most potent inhibitor is 5-phospho-d-arabinonate which resembles the cis-enediolate transition state intermediate of the reaction. These analogs were also found to be effective inhibitors of the production of lactate from glucose by suitably supplemented worm homogenates. The rank order of potency of inhibition of glycolysis was inversely related to the magnitudes of the K_i values for glucosephosphate isomerase. These K_i values were similar to those previously reported for mammalian glucosephosphate isomerase, suggesting similarities in the steric and electronic characteristics of the active sites of these isofunctional enzymes. This conclusion was further supported by the observed pH dependence of the inhibition by 5-phospho-d-arabinonate. Although glucosephosphate isomerase is not a rate-limiting enzyme of glycolysis, in the conventional sense, its selective inhibition could be of chemotherapeutic importance, in part because of the accumulation in glycolyzing systems of glucose 6-phosphate which is a potent feedback inhibitor of hexokinase.     

Zur Ultrastruktur der seitlichen Sinnesorgane am Augenhügel vonAnoplodactylus pygmaeus (Pycnogonida)

Former light microscopic studies on the lateral sense organs of sea spiders yielded divergent results. Consequently, different authors ascribed different functions to these organs. The present ultrastructural study shows that each lateral sense organ ofA. pygmaeus consists of approximately 15 sensory cells of two different types, approximately 20 sheath cells with numerous long microvilli, and an outer cuticular covering. Essentially the same elements are characteristic features of arthropod sensilla. There are, however, differences between the sense organs described in this paper and the sense organs of other arthropods. The inner dendritic segments of sensory cells S₁ of theA. pygmaeus lateral sense organs are very short, the sensory cilia are invaginated, and the pericarya of the sensory cells contain electron lucent cytoplasmic regions with large granules (glycogen?). In addition, the lateral sense organs ofA. pygmaeus lack a marked receptor lymph cavity and junctions between the cells. The results of the present ultrastructural study clearly indicate that the lateral sense organs ofA. pygmaeus are not glands as was postulated for other sea spider species by earlier authors. Some investigators hypothesized that the lateral sense organs of other sea spider species were auditory organs or rudimentary eyes. The present results do not support such speculations. Some structural details of the sensory cells ofA. pygmaeus resemble those found in chemoreceptive or putative chemoreceptive organs of other arthropods. Accordingly, chemoreceptive or thermoreceptive functions should be taken into consideration for the lateral sense organs ofA. pygmaeus.     

Identification of a Cholinergic-Specific Antigen Chol-1 as a Ganglioside

Abstract: An antiserum specific for cholinergic terminals was used to identify an antigen conserved between Elasmobranchs and mammals. Immunohistochemistry and a cytotoxicity test were used to assay the binding of antibody to mammalian terminals. Torpedo electric organ gangliosides totally abolished antibody binding. The highest inhibitory activity was associated with a single polysialoganglioside band on TLC plates. Neuraminidase altered the migration of the inhibitory activity on TLC plates. Antibody binding was inhibited by ganglioside fractions derived from chicken and mammalian brains. A summary of those tissues in which the antigen has been detected is presented. The possible function of the antigen is discussed.     

In vitro degradation of guanosine 3′,5′-bis(diphosphate) [ppGpp] by the spoT gene product [ppGppase] from auxotrophic strains of Escherichia coli: Effects of various antibiotics and drugs

The enzyme specifically hydrolyzing guanosine 3,5-bis(diphosphate) [ppGpp] has been isolated from the ribosomal fraction of Escherichia coli; it released pyrophosphate from the 3-position of ppGpp. The effects of various drugs and antibiotics known to interfere with protein and/or RNA synthesis were investigated in the ppGpp degrading reaction. It was determined that tetracycline, chlorotetracycline, and thiostrepton strongly inhibited the reaction, whereas levallorphan gave a moderate inhibition. Only the tetracycline-mediated inhibition could be reversed by manganese ions. Oxytetracycline, rifampicin, fusidic acid, kirromycin, streptomycin, puromycin, chloramphenicol, and morphine did not inhibit the decay reaction.Abbreviations ppGpp guanosine 3,5-bis(diphosphate)     

Incorporation of the transmembrane hydrophobic domain of glycophorin into small unilamellar phospholipid vesicles Ion Flux studies

Human erythrocyte glycophorin is one of the best characterized integral membrane proteins. Reconstitution of the membrane-spanning hydrophobic segment of glycophorin (the tryptic insoluble peptide released when glycophorin is treated with trypsin) with liposomes results in the production of freeze-fracture intrabilayer particles of 80 Å diameter (Segrest, J.P., Gulik-Krzywicki, T. and Sardet, C. (1974) Proc. Natl. Acad. Sci. U.S.A. 71, 3294–3298), with particles appearing at or above a tryptic insoluble peptide concentration of 4 mmol per mol phosphatidylcholine. In the present study, increasing concentrations of tryptic insoluble peptide were added to sonicated small unilamellar egg phosphatidylcholine vesicles and the rate of efflux of ²²Na⁺ was examined by rapid (30 s) gel filtration on Sephadex G-50. Below a concentation of 3–5 mmol tryptic insoluble peptide/mol phosphatidylcholine, ²²Na⁺ efflux occurs at a constant slow rate at given tryptic insoluble peptide concentrations. Above a concentration of 3–5 mM, the rate of efflux is biphasic at given tryptic insoluble peptide concentrations, exhibiting both an initial fast and a subsequent slow component. On the basis of graphic and computer curve-fitting analysis, with increasing tryptic insoluble peptide concentration, the rate of the slow component reaches a plateau at a tryptic insoluble peptide concentration of 3–5 mM and remains essentially constant until much higher concentrations are reached; the fast component increases linearly with increasing tryptic insoluble peptide concentration well beyond 5 mM. The most consistent interpretation of this data is as follows. The slow ²²Na⁺ efflux component is due to perturbations of small unilamellar vesicle integrity by tryptic insoluble peptide monomers. At a tryptic insoluble peptide concentration of 3–5 mmol/mol, a critical concentration is reached following which there is intrabilayer tryptic insoluble peptide self-association. The fast ²²Na⁺ efflux component is due to the increasing presence of tryptic insoluble peptide self-associated multimers the 80-Å particles seen by freeze-fracture electron microscopy) which results in a significantly larger bilayer defect than do tryptic insoluble peptide monomers. The failure of complete saturation of efflux by the fast component is ascribed to the presence of two populations of small unilamellar vesicles, some of which contain tryptic insoluble peptide multimers and some of which do not.Addition of cholesterol to the tryptic insoluble peptide/phosphatidylcholine vesicles decreases the rate of ²²Na⁺ efflux by inhibiting primarily the fast component. Freeze-fracture electron microscopy indicates that the presence of cholesterol has no effect on the size, number or distribution of 80-Å intra-bilayer particles in the tryptic insoluble peptide/phosphatidylcholine vesicles. These results are consistent with a mechanism to explain the fast Na⁺ efflux component involving protein-lipid boundary perturbations.Efflux of ⁴⁵Ca²⁺ from phosphatidylcholine vesicles is also enhanced by incorporation of tryptic insoluble peptide, but only if divalent cations (Ca²⁺ or Mg²⁺) are present in the external bathing media as well as inside the sonicated vesicles. If monovalent Na⁺ only is present in the bathing media no ⁴⁵Ca²⁺ efflux is seen. Under conditions where ⁴⁵Ca²⁺ efflux is seen, both a fast and a slow component are present, although both appear lower than corresponding rate constants for ²²Na⁺ efflux. These results suggest a coordinated mechanism for ion efflux induced by tryptic insoluble peptide and, together with the ²²Na⁺ efflux studies, may have mechanistic implications for the transbilayer phospholipid exchange (flip-flop) suggesed to be induced at glycophorin/phospholipid interfaces (de Kruiff, B., van Zoelen, E.J.J. and van Deenen, L.L.M. (1978) Biochim. Biophys. Acta 509, 537–542).     

Bovine hypothalamic poly(A)-rich RNA-directed synthesis of a common precursor to the nonapeptide arginine vasopressin and neurophysin II. Immunological identification and tryptic peptide mapping

The common precursor to arginine vasopressin (AVP) and neurophysin II (NpII) has been synthesized in a reticulocyte lysate system directed by bovine hypothalamic poly(A)-rich RNA. The precursor, identified with antibodies raised against neurophysin II and arginine vasopressin, has an apparent Mr of 21 000 (21 k). The specificity of the immune reaction has been shown by competition experiments using excess amounts of a variety of unlabeled peptides. With anti Np II, but not with anti AVP, a second neurophysin precursor with an apparent Mr of 18 000 (18 k) has been identified. Comparison of the tryptic maps obtained from the 21 k and 18 k precursors shows that both products give rise to the four [35S]cysteine-labeled neurophysin II-peptide fragments; however, only the 21 k yields an AVP-like tryptic peptide, identified with antibodies raised against AVP. The possible implications of the two precursors, one consisting of AVP and Np II, the other of Np II only, are discussed.     

Temperature behavioral responses of the American eel,Anguilla rostrata (Lesueur), from Maryland

Acute temperature preference tests were conducted with American eels, Anguilla rostrata, collected from Maryland's eastern shore. Eels were acclimated to temperatures of 6, 12, 18, 24 and 30°C. Final temperature preferendum was 16.7°C. Data differ from the temperature responses of the majority of fishes tested to date in that acclimation temperature did not influence selected temperatures. Similar results were obtained for various other fishes (Oncorhynchus, Salmo, Salvelinus) by other investigators. Behavioral responses at various acclimation temperatures were observed.     

Hydroperoxide-induced loss of pyridine nucleotides and release of calcium from rat liver mitochondria

It has been previously reported (L?tscher, H. R., Winterhalter, K. H., Carafoli, E., and Richter, C. (1979) Proc. Natl. Acad. Sci. U. S. A. 76, 4340-4344) that in Ca2+-loaded mitochondria hydroperoxides induce a release of Ca2+ from mitochondria and an irreversible oxidation of mitochondrial pyridine nucleotides. Here we show that in the presence of Ca2+ oxidized mitochondrial pyridine nucleotides are hydrolyzed inside mitochondria and that nicotinamide is released from mitochondria. The extent of the hydrolysis of NAD(P)+ is dependent on the amount of both hydroperoxide and Ca2+. The hydrolysis is reversible in the presence of added nicotinamide. The release of Ca2+ from mitochondria is electroneutral, and is directly or indirectly dependent on oxidized mitochondrial pyridine nucleotides. By contrast, the uptake of Ca2+ most probably does not require the present of reduced pyridine nucleotides. Control experiments show that even under the most drastic conditions employed in this study (100 nmol of Ca2+ and 85 nmol of t-butylhydroperoxide/mg of protein) mitochondria retain a considerable degree of functional integrity.     

Replication of simian virus 40 chromatin in vitro depends on the amount of DNA polymerase alpha associated with replicating chromatin

Replication of simian virus 40 (SV40) chromatin in vitro is inhibited by chloride but stimulated by acetate anions even at physiological concentrations of 100-200 mM. In a similar fashion DNA polymerase alpha is affected with respect to the activity with activated DNA as primer template. Furthermore, at concentrations of 100-200 mM acetate DNA polymerase alpha remains associated with replicating chromatin, whereas association is strongly reduced when chloride anions are used at the corresponding concentrations. Thus the salt behaviour of DNA polymerase alpha explains the salt sensitivity of the replication system. Our results confirm the importance of this enzyme for DNA replication.