Activity increases quantal size at the frog neuromuscular junction

Summary Two h of nerve stimulation at 10 Hz or of elevated spontaneous release in hypertonic solution increased the size of miniature end-plate potentials (m.e.p.p.'s) and currents at the frog neuromuscular junction, probably by increasing the amount of acetylcholine in a quantum. Increases in quantal size may modulate synaptic transmission.Acknowledgments. Supported by grant 10320 from the NINCDS and by a grant from the MDA. We are grateful to Dr I.S. Cohen for participating in some of the experiments and for helpful criticism, and to Drs C. Clausen and G. Baldo for help with the computer. Some of the results were presented at a meeting of the Physiological Society.     

Malarial parasites complete sporogony in axenic mosquitoes

Summary To obtain sporogonic stages of malaria free from microbial contaminants for in vitro studies,Anopheles stephensi were reared under sterile conditions using a mosquito cell line as larval food. The adult females, kept in sterile humidified containers and allowed to engorge on parasitemic hamsters, supported the sporogonic development of the rodent malarial parasitePlasmodium berghei. In 10 experiments, the proportion of infected mosquitoes varied from 0 to 92%, and the geometric mean number of oocysts per female mosquito from 2.5 to 58,6, with a range of 1 to 548. The average number of salivary gland sporozoites per infected mosquito was determined by direct sporozoite counts in the pooled homogenate of the thoraces of all female mosquitoes. In five experiments, it varied from 2.7×10³ to 9.0×10³. The sterile sporozoites, harvested on day 19 or 20 after the infective blood meal, were as infective for rodents as nonsterile ones.Supported in part by Public Health Service research grant AI 18345 from the National Institute of Allergy and Infectious Diseases, by a grant from the Agency of International Development DSPE-5542-G-SS-3042-00, and by a Charles and Johanna Busch award.     

Microbial methylation of benzenethiols and release of methylthiobenzenes

Summary Three phylogenetically diverse microorganisms methylated several different chloro- and nitro-substituted benzenethiols to yield the corresponding methylthiobenzenes. These products were identified by gas chromatography-mass spectrometry. In several cases large percentages of the methylthio products were released by intact cells into the medium, suggesting that microbial methylation of xenobiotic thiols may be a significant biotransformation in many ecosystems.Acknowledgments. This investigation was supported by research grant ES 02639 from the National Institute for Environmental Health Sciences, and an equipment grant (RR07013) from the Biomedical Research Support grant program. Division of Research Resource, NIH. We thank Steve Hawthorne for assistance in performing GC-MS analyses.     

Interaction of polyamines or their precursors with the calcium-controlled secretion of peroxidase by sugarbeet cells

Summary Three polyamines tested (cadaverine, spermidine and spermine) and their 2 precursors (the amino acids arginine and ornithine) inhibit the Ca²⁺-mediated secretion of peroxidases by sugarbeet cells in suspension culture at concentrations ranging from 10^–15 to 10^–5M. In the absence of exogenous Ca²⁺, spermine added at higher concentrations mimics the activatory effect of Ca²⁺, the other polyamines being without effect.Supported by the Belgian FRFC (grant No. 2.9009.75 to T.G.) and the Swiss National Foundation for Scientific Research (grant No. 3.140-0.81 to C.P. and H.G.).     

Octopamine and proctolin mimic spontaneous membrane depolarisation inLucilia larvae

Summary Octopamine and proctolin at concentrations below 10^–8 M reversibly induce a spontaneous rhythmic depolarization which occurs in body-wall muscles ofLucilia larvae. The effect appears to be postsynaptic and mediated by receptors specific for each substance.This work was supported by NIEHS grant No. ES00814 and EPA grant No. R804345.     

Assay of aminoglycosides is influenced by tissue homogenization technique

Summary Recovery of neomycin from tissue homogenates was lower when glass/glass homogenizers were used due to the abrasion of glass which will bind to the drug. Glass homogenizers should be avoided for the determination of aminoglycoside levels in tissues.Acknowledgment. Supported by research grant NS-13792 and Program Project grant NS-05785 from the National Institutes of Health.     

The effect of postnatal undernourishment on epileptiform kindling of dorsal hippocampus

Summary Rats were undernourished postnatally from birth through 20 days of age. They were subsequently tested for susceptibility to motor seizures kindled in hippocampus in adulthood. Compared to littermate control animals the postnatally undernourished rats were more susceptible to the kindling treatment. We conclude that early postnatal undernourishment has a permanent effect on susceptibility of the hippocampus to electrically-induced seizures.This work was supported by Public Health Service grant NS 13799, National Science Foundation grant GB 35532, and by Hoffman-LaRoche, Inc.     

Oxytalan fibres in human dental pulp

Summary Scarce and randomly oriented oxytalan fibres are present in the connective tissue of dental pulp in both deciduous and permanent teeth.This investigation was supported by grant No.V-10/78 from the SIZ-V of S. R. Croatia.     

Effect of splenectomy on the in-vitro migration inhibition response to sheep erythrocytes in the lizard,Calotes versicolor

Summary Splenectomy completely erased the PFC response to SRBC in lizards. In contrast, it has very little effect on the degree of MI to all doses ranging from 10⁴ to 10⁹, excepting the lowest dose, 10³ SRBC.Supported by PL-480 (NIH) research grant, No. 01-077.Grateful to Madurai University for the award of Studentship during the tenure of the work and to Dr P. W. Askenase for the gift of capillaries used in this study.     

Tumorigenic activity of cloned polyoma virus DNA in newborn rats

Summary The proximal portion of the polyoma virus early region as well as the complete viral genome were cloned in pBR322. Recombinant plasmids induced tumors in newborn rats but only after linearization of the DNA by various restriction endonucleases.This work was financed by grant MA-6731 from the Medical Research Council and by a grant from the National Cancer Institute of Canada.     

Effects of sera and liver extracts from partially hepatectomized rats on liver slice DNA synthesis

Summary Sera from partially hepatectomized rats (PH) compared to sera from control rats (C) enhance liver slice DNA synthesis but depress kidney slice DNA synthesis. Alone, liver extracts from PH do not affect DNA synthesis; but adding sera to PH extracts stimulates, suggesting that sera and liver factors from PH may participate in compensatory growth.Acknowlegments. Supported by NIH, grant AM 15458, a grant from the Washington Heart Association, and Public Health Service, grant RR 5360 (Medical). The authors wish to express their appreciation to Angelina Vasques for technical assistance and Betty Mendelson, Patti Werr and Susan Dreux for secretarial help.     

Baroreceptor reflex sensitivity after acute blood volume expansion in anesthetized dogs

Summary Changes in heart rate resulting from mechanically induced changes in arterial blood pressure were used as a measure of baroreflex sensitivity. This sensitivity was shown to be decreased after volume expansion.This work was supported in part by PHS grant HL-23239 and a grant from the Central Ohio Heart Chapter of the American Heart Association.     

Response of murine spermatocytes to the metaphase-arresting effect of several mitotic arrestants

Summary Three mitotic arrestants, colchicine, Colcemid and vinblastine, were evaluated for their effects on producing meiotic arrest in the laboratory mouse. Colchicine is the most effective and its effect is both dose- and time-dependent. Treatment of mice with 40 mg/kg of colchicine for 3 h resulted in drastic improvement of the yield and quality of M-II figures. This treatment did not appear to increase the aneuploidy frequency in M-II's.Supported in part by research grant R-808582 from the US Environmental Protection Agency and research grant RR5511-21 from the National Institute of Health.     

Resolution of small G1 and G2 populations of L1210 leukemia by flow microfluorometric analysis aided by velocity sedimentation

Summary L1210 leukemic cells grown in vitro were subjected to kinetic analysis using a flow microfluorometer. A single broad peak was found for the DNA content distribution if unfractionated cells were used; prior fractionation using lg velocity sedimentation allowed the separation of small peaks with smaller (G₁) and larger (G₂) DNA contents from the dominant S phase peak with intermediate DNA content.This work was supported by grant number 5P01CA13053 awarded by the National Cancer Institute, DHEW USA, and by grant num ber RBI 76-1 from the Queen Wilhelmina Fund, The Netherlands.     

Course of development of isolated rat embryonic ectoderm as renal homograft

Summary When the isolated head-fold stage rat embryonic ectoderm is grafted under the kidney capsule, it gives rise to a new mesenchyme with the capacity to differentiate into mesodermal tissues.This investigation was supported by grant No. V-10/78 from the SIZ-V of S. R. Croatia.     

Ovarian response of pinealectomized and intact white-footed mice kept under naturally short photoperiods

Summary Pinealectomized and intact adult female white-footed mice were maintained outdoors from 28 November to 2 January. At the termination of the experiment, ovarian weight was significantly greater (p<0.02) in the pinealectomized group compared with that of the intact animals. Microscopic examination of the ovaries revealed that those of the intact animals had fewer and smaller follicles than those from animals which had had their pineal glands removed.Supported by NSF grant PCM 77-05734 and NIH grant HD 10202 through the Center for Research in Reproductive Biology Morphology Core.     

Lysozyme levels in tissues of iron-deficient rats

Summary Rats were fed either diets sufficient (300 ppm) or insufficient (5 ppm) in iron for 10 weeks. The iron-deficient animals had lowered hemoglobin and hematocrit levels and higher levels of kidney lysozyme activity than did control animals. There were no significant changes in serum and spleen lysozyme activity levels.Supported in part by grant HL18712-02, Heart and Lung Institute, NIH.     

Binding capacities of various analogues of S-adenosyl-L-homocysteine to protein methyltransferase II from human erythrocytes

Summary A series of analogues of S-adenosyl-L-homocysteine, modified mainly in the amino acid portion of the molecule, have been synthesized. All were found to be competitive inhibitors of protein methyltransferase II from human erythrocytes. S-adenosyl-L-homocysteine remains however by far the most effective inhibitor of the methylase.Acknowledgments. This work was supported by a grant of the Fonds National Belge de la Recherche Scientifique and by a grant of the Fonds Emile Defay.     

Effect of light adaptation on electrical responses of the retinas of four species of bats

Summary The levels of light adaptation at which the retinas of 4 species of microchiropteran bats became unable to generate electroretinograms were progressively ordered. The order correlated well with light preferences based on activity patterns of the 4 species. These results suggest that the ability of the retina to function in ambient light may govern some natural behaviors of these bats.This work was supported in part by grant No. EY 01228 from the U.S.P.H.S. and was facilitated by equipment provided by Bob Hope Fight for Sight Award No. G522 and a grant from Research to Prevent Blindness, Inc. Portions of this work were presented at the Fifth International Bat Research Conference, Albuquerque, New Mexico, USA, August, 1978.     

Evidence against cyclic GMP acting as a direct modulator of active sodium absorption in rat cecum

Summary Cyclic GMP concentrations were measured in rat cecum mucosa in vivo when the net absorption of sodium, chloride and fluid was stimulated by methylprednisolone (MP). Whereas Na–K-ATPase specific activity was increased by MP, suggesting enhanced active sodium transport, cyclic GMP levels remained unaffected.Acknowledgments. We thank Miss U. Kautz for engaged technical assistance and Dr G. Schultz for valuable discussions.Supported by Deutsche Forschungsgemeinschaft grant Lo 114/10.