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Pelagic amphipods belonging to the genus Phronima have four compound eyes; two lateral eyes and two large transparent medial eyes which comprise the entire top of the head. The eyes are structurally similar but the crystalline cones of the medial eyes are more than twenty times as long as those of the lateral eyes, reaching 5 mm in a large animal. The dioptric system of each ommatidium consists of an unfaceted cornea, a layer of hypodermal cells, two rudimentary cone cells, two cells which surround and form the crystalline cone, and the cone itself. The cone and its surrounding cells penetrate the layer of accessory pigment cells which surrounds the retina. The fused rhabdom is formed by the five retinula cells but is separated from them by an extracellular palisade which is crossed by bridges. The retinula cell nuclei lie proximal to the basement membrane. Further proximally the bundle of retinula cell axons is crossed by a second basement membrane, which surrounds each axon with a collar. Medial and lateral eyes on each side of the head share a common lamina. The medial eyes of Phronima appear to be a solution to the problem of remaining inconspicuous to predators while still maintaining sensitivity and resolution.
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To establish quantitative structure-activity relationships for the inhibition of trypsin, plasmin and thrombin by 4-amidinophenyl compounds with a keto group, attempts have been made to detect correlations between data on inhibition and substituent constants. The inhibitor activity of the derivatives is described by lipophilic or steric substituent constants using linear free energy relationships. To describe the action of beta-ketones, an additional sigma I term is necessary. The lipophilic or steric term stands for binding of the inhibitor side chain to a second hydrophobic binding site of the enzyme. The electronic term describing inductive influences on the keto group suggests the contribution of the beta-keto group to the enzyme inhibitor binding via a tetrahedral conformation of the carbonyl carbon.
Dynamical changes in the spleen of mice and rats were studied morphometrically and electron microscopically when the animals were given in drinking water radionucleotides in small concentrations (137Cs, 226Ra, 89Sr, 65Zn, Pb(NO3)2, BeCl2, hexamethyleniamine, methylmercurchloride) for 1-2 years. Total doses obtained for a year were 0.3-100 rad. Reactive reconstruction of the organ under radioactive and chemical effects was stated to proceed in three directions: a) hyperplasy of lymphoid tissue; b) enhanced plasmocytogenesis; c) hyperplasy of extramedullar hemopoiesis. Sequence in the appearance of these reactions and doses which produced them were different for every compound. In 1-2 years at large doses (160-200 rad) atrophy, amyloid degeneration of the spleen or signs of leukemia were observed. Disturbance of intercellular contacts and of intracellular regeneration was demonstrated electron microscopically.
The ultrastructure of the compound eyes of five species of mysids (Crustacea: Mysidacea), Praunus flexuosus, Siriella norvegica, Mysidopsis gibbosa, Neomysis integer and Erythrops serrata, is described. The ommatidia are constructed on a common plan, but there are considerable differences in detail. Common features include the arrangement of the cornea, crystalline cone and the basement membrane. The number of retinular cells differ: in Neomysis and Erythrops there are seven, whereas in the other species there are eight, the eighth cell forming a distal rhabdom, which consequently is lacking in the ommatidia of Neomysis and Erythrops. Another difference is the epirhabdom, which is lacking in Erythrops, but present in the other species. The epirhabdom is an extracellular structure, probably serving as a dioptric element. The pigment arrangement is similar in the first four species. The pigment shield consists of the distal pigment, distal reflecting pigment, proximal pigment (in the retinular cells) and the proximal reflecting pigment. The distal and proximal pigments are dark screening pigments. In addition to these, there are basal red pigment cells, which are mainly located below the basement membrane. In Erythrops there are three kinds of pigment cells: distal pigment cells, distal reflecting pigment cells and basal red pigment cells. Besides the basal red pigment cells, the distal pigment cells contain red pigment granules.
The influence of two drugs with antispermatogenic properties on steroid biosynthesis has been studied in rat testes in vitro with pregnenolone as the substrate. 20-438, an indenopyridine derivative increased the relative conversion of pregnenolone to progestins and estradiol, whilst decreasing the conversion of substrate to testosterone and androstenedione. PMHI, a pipecolinoindane derivative, reduced testosterone levels in the testes without altering the relative conversion of pregnenolone to various steroids. This suggests that the agent is partially inhibiting the biosynthesis of androgen precursors leading to a testosterone deficiency in testicular tissue which may result in reduced spermatogenesis.
Silybin significantly antagonises the lethal poisoning of mice with alpha-amanitine or phalloidine. In the same test, taxifolin, coniferyl alcohol, fisetin and (+)-catechin were not effective.
The effects of L-proline, D-proline, and L-azetidine-2-carboxylic acid (L-A.2.C., the lower homolog of L-proline) have been compared in two systems. L-Proline is more potent than either analog in causing amnesia of one-trial avoidance conditioning of the 2-day-old chick and in preventing mechanically induced spreading depression in the retina isolated from 2-3-week-old chicks. The results suggest that the L-configuration and the proper molecular size are essential for the effects of L-proline upon memory and upon spreading depression. This level of specificity is greater than that involved in protein synthesis because L-A.2.C. is incorporated into protein in place of L-proline, in several protein-synthesizing systems.
The compound eyes of the terrestrial isopod Porcellio scaber comprises about 20 ommatidia. The dioptric apparatus of each ommatidia includes a biconvex corneal lens and a spherical crystalline cone that is secreted by two cone cells. The closed rhabdom is formed by the microvillar extensions of seven pigmented retinula cells and one apical eccentric cell. All retinular axons exit the eye in one bundle. During dark-adaption pigment granules in the retinula cells rapidly withdrew from around the rhabdom and the cell periphery, and migrated basally. Rhabdoms thickened because of movement of the microvilli, and mitochondria moved medially and basally. During light adaption these processes were reversed. Multivesicular bodies became less numerous and rough endoplasmic reticulum and ribosomes proliferated during the initial stages of light adaption.
43 heteropolycyclic compounds belonging to a homologous series were investigated for mutagenicity. The results are compared with carcinogenicity data obtained with the same batches of compounds under conditions identical for all of them. Mutagenicity was tested in the Ames test with Salmonella typhimurium strains TA1535, TA1537 and TA100 in the presence and absence of liver 10 000 g supernatant from rats treated with Aroclor 1254. Carcinogenicity was tested by injection of the compounds into subcutaneous tissue of XVIInc/Z mice. 18 test compounds showed carcinogenic activity, some strongly, others only weakly. Of these, 17 were detected as mutagens: one weak carcinogen did not revert the Salmonella strains. No quantitative correlation was observed between the extents of the mutagenic and the carcinogenic effects. Of the 25 substances that did not produce tumours, 13 showed mutagenicity (12 in the presence, 2 in the absence, of the liver homogenate). The mutagenic effects of these compounds were quantitatively similar to those of the compounds that produced tumours. The most sensitive strain of Salmonella typhimurium was TA100. It detected all 30 mutagens. TA98 was mutated by 25 compounds, TA1537 by 16 compounds. No mutagenic effects were seen with TA1535. Possible reasons for the high percentage of apparently "false positives" in the Ames test and the lack of a quantitative correlation between the potency of the mutagenic and carcinogenic effects are discussed. It is suggested that the complexity of the metabolism of these heterocyclic compounds may lead to critical differences in metabolism in mouse subcutaneous tissue in vivo and in liver homogenates from rats treated with Aroclor. Therefore the present study will be extended to life-long oral and intrahepatic carcinogenicity tests leading to a higher proportion of metabolism in the liver.
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Explore the source record for details and available documents.
Explore the source record for details and available documents.
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