Stimulus-evoked slow potential shifts and changes in [K+]0 of the frog optic tectum

Summary In 17 frogs (Rana esculenta var ridibunda) immobilised with succinyl choline the optic tectal surface was stimulated by trains of electrical pulses or by a flash to the contralateral eye. Sustained potential shifts (SPSs) and changes in extracellular potassium concentration ( [K⁺]₀) were simultaneously recorded.In response to electrical stimulation SPSs of maximal amplitudes (1.19±0.1 mV) were recorded between 50 and 200 m in depth and maximal [K⁺]₀ (0.69 ±0.08 mM) between 100 and 350 m. The changes of SPS and [K⁺]₀ showed a close similarity in experiments with changes in voltage, pulse duration and frequency of stimuli within a train. The induced SPS had a duration of 28±1.54 s, the [K⁺]₀ of 32±1.23 s.The flash stimulus induced an SPS and [K⁺]₀ of maximal amplitudes between 50 and 200 m in depth with values of 0.57±0.1 mV and 0.29±0.03 mM respectively. An additional wave with a latency of ca 1 s and a duration of ca 3 s arose on the background of the SPS to a flash stimulus, associated with an additional increase in [K⁺]₀.It is considered that the accumulation of K⁺ in extra-cellular space, with neuronal activity, results in depolarization of radial processes of ependymal glia. This is reflected in the neuropil of the upper layers of the optic tectum as an SPS.We would like to dedicate this article to the memory of Alexander Roitbak who died as a result of a tragic accident while this paper was in press. He will be remembered fondly especially for his contributions to understanding of the functions of Neuroglia. E.V.O., P.R.L., T.A.R.     

Cytogenetics of human oocytes,zygotes, and embryos after in vitro fertilization

Summary Chromosome errors, inherited or arising de novo during gametogenesis and transmitted at fertilization to the conceptus, may be a major cause of embryonic mortality. The in vitro fertilization and embryo transfer (IVF/ET) procedure provides extra material — oo-cytes, zygotes, and embryos — to investigate the contribution of chromosomal abnormality to implantation failure. This paper reviews the results of cytogenetic studies on such material. Estimates from a total of 1120 oocytes from 11 studies give an overall proportion of chromosomal abnormality of 35%. Single and multiple nullisomies and disomies are found, involving nonrandom chromosome gain or loss. Hypohaploid complements are more frequent than hyperhaploid complements. The higher rate of chromosome loss of hypohaploid karyotypes was found to be largely artifactual. The estimated overall frequency of aneuploidy is 13%. In embryos the level of chromosomal abnormality is 23%–40%. Errors of fertilization are responsible for a substantial number of triploid embryos, many of which develop into mosaics. Factors extrinsic to the conceptus, such as infertility, advanced maternal age, and ovarian hyperstimulation, may increase the level of chromosomal abnormality. More refined methods for accurately recognizing and selecting chromosomally normal embryos for transfer are needed to improve the success rate of this reproductive technology.     

A multi-recombination model for the mtDNA rearrangements seen in maize cmsT regenerated plants

Regeneration of plants from maize cytoplasmic male sterile type T (cmsT) callus tissue culture promotes, in some instances, genetic variability in their mitochondrial genomes. These mutations have been analyzed in various cmsT regenerated plants that have or have not regained the male fertile phenotype. A unique multi-recombination model explains the various mitochondrial genome rearrangements. First, recombination involving two different sets of direct repeats gives rise to subgenomic recombinant circles. Second, intermolecular recombination between some selected subgenomes gives rise to a new rearranged master chromosome. The consequence of these events is the formation of a new master chromosome containing sequence deletions and duplications when compared to the progenitor. This new mitochondrial genome seems stable, although it does not contain the entire genetic complexity of the progenitor.     

Parthenogenesis in Tubificidae

The ability of tubificids to reproduce parthenogenetically following or in place of bisexual reproduction has been proved. During parthenogenesis the spermatogenesis ceases at an early stage of sexual cell development, which, together with some peculiarities of the structure of the sexual system, rules out the possibility of self-fertilization in the worms. For two years of cultivation the life cycles of 3 parthenogenetic generations in Tubifex tubifex and 2 in Limnodrilus hoffmeisteri were traced.     

Rates and outcome of pregnancies achieved in the first 4 years of an in-vitro fertilization program.

Between Feb. 1, 1984, and Dec. 31, 1987, 578 couples were treated in the in-vitro fertilization (IVF) program at University Hospital, London, Ont. The 160 confirmed pregnancies resulted in 86 deliveries and the birth of 108 babies. There were 20 spontaneous abortions, 12 ectopic pregnancies, 11 presumptive pregnancies, 4 neonatal deaths and 1 stillbirth. At the time of writing, 41 pregnancies of 20 weeks'' gestation or more were in progress. Except for a high cesarean section rate the obstetric outcome of pregnancies achieved with IVF does not appear to be different from that expected for a group of infertile couples treated with conventional therapies. The pregnancy rates varied according to the denominator used.     

Family networks in prenatal and postnatal health

This paper examines the effects of kin access on prenatal health practices, birth outcome, and postnatal health practice for infants born to black and white mothers ages 21 to 28 in the U.S. during 1984-86. The data used for this research were compiled from three sources: (1) The National Longitudinal Survey of Youth; (2) The Children of the National Longitudinal Survey of Youth; (3) special kin access data files, which were created specifically for this study. Logistic regression procedures are used to assess the effects of kin proximity, maternal grandmother proximity, and presence of the child's father on health practices (N = 1,030) and birth outcome (N = 1,385), controlling for the mother's educational attainment, work experience, poverty, presence of the child's father, and birth order of the child. We find no evidence supporting the notion that kin access positively affects the prenatal and postnatal health practices of young mothers. The results suggest that young mothers who reside with their mothers or other adult kin, and those who are in close proximity to them, are no more likely to seek prenatal care during the first trimester, or to avoid smoking or drinking during pregnancy. Mothers who live with a sexual partner or husband are, however, somewhat more likely to seek prenatal care and to avoid alcohol use during pregnancy. Closer kin access is associated with a lower probability of breastfeeding. These results suggest that it will not be adequate to rely on kin networks or kin assistance to improve the prospect of healthy birth outcomes.     

Human immunodeficiency virus protein gp120 interferes with β-adrenergic receptor-mediated protein phosphorylation in cultured rat cortical astrocytes

Summary 1. We have previously shown that acute exposure to the HIV coat protein gp120 interferes with the -adrenergic regulation of astroglial and microglial cells (Leviet al., 1993). In particular, exposure to 100 pM gp120 for 30 min depressed the phosphorylation of vimentin and glial fibrillary acidic protein (GFAP) induced by isoproterenol in rat cortical astrocyte cultures. In the present study we have extended our analysis on the effects of gp120 on astroglial protein phosphorylation.2. We found that chronic (3-day) treatment of the cells with 100 pM gp120 before exposure to isoproterenol was substantially more effective than acute treatment in depressing the stimulatory effect of the -adrenergic agonist on vimentin and GFAP phosphorylation.3. Even after chronic treatment with gp120, no differences were found in the levels and solubility of these proteins.4. Besides stimulating the phosphorylation of intermediate filament proteins, isoproterenol inhibited the incorporation of³²P into a soluble acidic protein of 80,000M _r , which was only minimally present in Triton X-100-insoluble extracts.5. Treatment of astrocytes with a phorbol ester or exposure to³H-myristic acid indicated that the acidic 80,000M _r protein is a substrate for protein kinase C (PKC) and is myristoylated, thus suggesting that it is related to the MARCKS family of PKC substrates.6. Acute (30-min) treatment with 100 pM gp120 totally prevented the inhibitory effect of isoproterenol on the phorphorylation of the 80,000M _r MARCKS-like protein.7. Our studies corroborate the hypothesis that viral components may contribute to the neuropathological changes observed in AIDS through the alteration of signal transduction systems in glial cells.