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Biomedical subjects

M H Johnson

Publications and source records attributed to M H Johnson.

At least 217 records · Page 12Linked to original sources
PubMed1988

The influence of cooling on the properties of the zona pellucida of the mouse oocyte.

Mouse oocytes were exposed to a variety of cooling regimes prior to insemination in vitro. Exposure to 4 degrees C, but not to 25 degrees C, was associated with a reduced fertilization rate, but development to the blastocyst stage of those oocytes that fertilized was not consistently different from that of non-cooled controls. The reduced fertilization rate seems to result from an effect of cooling on the zona pellucida, since it was not observed if the zona was removed prior to insemination, and since cooling rendered the zona pellucida resistant to the action of chymotrypsin. Using chymotrypsin resistance as an assay, the nature of the cooling-induced effect on the zona was investigated. It is suggested that rapid cooling to 4 degrees C may promote release of cortical granules and a premature zona reaction.

Animals↗
PubMed1988

Cytoskeletal organization in fresh, aged and spontaneously activated human oocytes.

The cytoskeleton of the human oocyte (microtubules and actin filaments) has been examined using fluorescence microscopy. In unfertilized oocytes in metaphase of the second meiotic division, microtubules were found exclusively within the spindle which was located at the periphery of the cell and oriented radially, with its long axis perpendicular to the surface membrane. The spindle was anastral and slightly pointed at each pole, the chromosomes being arranged on a metaphase plate at the equator. When treated with taxol, the oocyte spindle became astral and microtubules appeared in the cortex of the oocyte in the form of small strands or bundles. Polymerized actin was found to be present in a dense filamentous layer throughout the cortex of the unfertilized oocyte. Aged unfertilized oocytes displayed an increased incidence of disrupted or abnormal cytoskeletal organization. In parthenogenetically activated oocytes in anaphase and telophase, microtubules were again found predominantly in the spindle but in addition, cortical strands or bundles of microtubules were often present. Oocytes in late telophase sometimes showed the presence of a concentrated ring of actin in the cleavage furrow between the oocyte and the second polar body. Activated oocytes in early interphase contained a dense cortical mesh of microtubules and a midbody remnant between the oocyte and the polar body. The cytoskeletal organizations of mouse and human oocytes are compared.

Age Factors↗
PubMed1988

The clinical significance of thought disorder across time in psychiatric patients.

The occurrence and clinical significance of thought disorder, as measured by general abstraction ability and idiosyncratic abstractions, remains a complex and ambiguous area of inquiry. We studied 49 subjects in a longitudinal design in which the effects of general psychopathology and depression on abstraction function were assessed. Results indicate that a) depressive patients have a generalized abstraction dysfunction not limited to specific content areas, b) some depressive patients have a residual abstraction deficit on discharge from the hospital, c) idiosyncratic abstractions are a characteristic but not pathognomonic marker for schizophrenia, and d) across all subjects, abstraction difficulties represent a seemingly state-dependent "final common pathway" that significantly correlates with general psychopathological impairment rather than level of depression.

Depressive Disorder↗
PubMed1988

Cytocortical organization during natural and prolonged mitosis of mouse 8-cell blastomeres.

Late 8-cell blastomeres were harvested within the first 45 min after entering mitosis. Some mitotic cells were analysed within the ensuing 2 h for the organization of their surface in relation to their progress through mitosis. Whereas in most late interphase cells microvilli were restricted to a discrete polar region, in mitotic cells at all stages from early metaphase to immediately postcytokinesis microvilli were found to be present over more of the cell surface. Other mitotic cells were placed in nocodazole to arrest them in M-phase for up to 10 h. They were found to show an even more extensive distribution of microvilli over the whole surface, the longer periods of incubation yielding more extended coverage such that many cells no longer appeared to have any residual surface polarity. Removal from nocodazole at all time points from 1 to 10 h resulted in most cells completing mitosis to yield pairs of cells which, in most cases, resembled pairs derived from nonarrested blastomeres and in which a defined polar area of microvilli was restored. However, the percentage of differentiative divisions decreased after 6 h arrest. If, instead of removing cells from nocodazole, they were placed in both nocodazole and cytochalasin D (CCD) for periods of up to 3 h, most microvilli retracted to reveal a tight polar zone of CCD-resistant microvilli. This result suggests that a heterogeneity of cytocortical organization may still exist within the arrested mitotic cell. We propose a model to explain the origin of this heterogeneity of organization and its relationship to the generation of cell diversity.

Animals↗
PubMed1988

The influence of cell contact on the division of mouse 8-cell blastomeres.

The pattern of division of polarized 8-cell blastomeres with respect to the axis of cell polarity has been compared (i) for cells dividing alone with cells dividing in pairs, and (ii) for early and late dividing cells within a pair. Cell interactions do not seem to influence significantly the overall pattern of division within the population. The only significant difference found was that the second dividing cell in a pair tended to divide in the same way as its earlier dividing companion slightly more frequently than expected. These results suggest that cell interactions immediately prior to and during division do not influence strongly the orientation and position of the division plane. In contrast, interactions between the cells within an intact early 8-cell embryo, which is subsequently disaggregated to singletons or pairs, do influence the type of progeny generated at division to the 16-cell stage, and seem to do so via an effect on the size of the microvillous region generated at the cell apex.

Animals↗
PubMed1988

Simulation of genetic control of reproduction in beef cows. IV. Within-herd breeding value estimation with pasture mating.

Procedures for breeding value estimation for reproductive traits under pasture mating conditions were developed and tested using a computer simulation model of genetic control of bovine reproduction. The model generated annual calving rates (BCR) (0 or 1) and calving dates (CD) for each cow as a function of underlying genetic variation in two independent traits: single-service conception rate, which was indicative of the ability to conceive when estrus occurs, and postpartum interval (PPI) from calving to first estrus. Observed values for BCR and CD were shown to be complex, nonlinear functions of breeding values for ability to conceive (CRG) and for postpartum interval (PPIG) and of the previous CD. Effects of CRG on BCR and CD were small at high values of CRG, but these effects increased as CRG declined. Effects of PPIG on BCR and CD were small for cows that previously calved within the first 21 d of the calving season, but these effects increased for cows that calved after d 21. Previous CD had substantial nongenetic carryover effects on both BCR and CD. Unbiased estimates of CRG and PPIG could not be derived in the absence of breeding information. However, CD were reasonably highly correlated with breeding values for ability to conceive, provided information on open cows was included in the evaluation. Calving dates were only weakly associated with breeding values for PPI, in part because of the relatively short mean PPI (70 d) that was simulated.

Animals↗
PubMed1988

Evaluation of performance characteristics in a diallel among Simmental, Limousin, Polled Hereford and Brahman beef cattle. I. Growth, hip height and pelvic size.

Progeny of a diallel among Simmental, Limousin, Polled Hereford and Brahman breeds of cattle were evaluated over 5 yr for preweaning and postweaning growth, hip height and pelvic size. Calves from Brahman and Simmental dams had the highest preweaning gains and weaning weights, and those from Polled Hereford dams had the lowest (P less than .05). Differences in the availability of milk and postpartum compensatory gains in progeny of Brahman dams could have contributed to these results. However, calves from Simmental, Limousin and Polled Hereford dams had significantly greater feedlot daily gains than those from Brahman dams. Yearling hip height and pelvic area were lower for progeny of Polled Hereford dams, whereas calves from Simmental, Limousin and Brahman dams were not different for these traits. A series of linear comparisons among these four breeds using least-squares means to estimate general and specific combining ability and maternal effects found significant, negative maternal effects for Polled Hereford for preweaning gain and weaning weight. A positive maternal effect (P less than .05) for Limousin was found for feedlot gain. General combining ability and maternal estimates were significant and variable in most comparisons for yearling hip height and pelvic area. Heterosis estimates were positive and significant in all crosses with Brahman for preweaning gain, weaning weight, yearling weight, hip height and pelvic area. Significant, positive heterosis was also found in Polled Hereford crosses with Limousin and Simmental for preweaning gain, weaning weight and yearling weight.

Alleles↗
PubMed1988

Evaluation of performance characteristics in a diallel among Simmental, Limousin, Polled Hereford and Brahman beef cattle. II. Carcass traits.

Evaluations of steer and heifer progeny from a diallel mating design of Simmental, Limousin, Polled Hereford and Brahman beef cattle over 5 yr are presented. Traits evaluated included final weight, hot carcass weight, ribeye area, 12th rib fat thickness, marbling score, yield grade, dressing percentage and percentage of kidney, pelvic and heart fat. Progeny of Simmental sires were heavier at slaughter than those with Brahman sires (P less than .05), but no differences were found for carcass weight. Dressing percentage was higher for Limousin crosses compared with progeny of other sire breeds (P less than .05). Similar results were found for dam breeds, except that progeny of Limousin dams had heavier carcasses with a higher dressing percentage (P less than .05) than Brahman crosses. Crosses of Limousin and Simmental had larger ribeye areas (P less than .05) compared with calves of the other breeds. Progeny of Polled Hereford dams had higher marbling scores and were fatter than progeny of dams of other breeds (P less than .05). Heterosis estimates were significant for all Brahman crosses for final weight, carcass weight and ribeye area, but these contrasts were negligible for other traits. Estimates of general combining ability were positive and significant for Simmental for final weight, carcass weight, ribeye area and marbling score and were significant and negative for Limousin for final weight, fat thickness and yield grade. Maternal values were generally small.

Alleles↗
PubMed1988

The effects of hyperstriatal lesions on one-trial passive-avoidance learning in the chick.

The roles of different forebrain structures in memory formation in the chick were investigated using restricted radio-frequency lesions. Young chicks will spontaneously peck at a small bright bead. If the bead has been coated with a distasteful substance, the chicks learn not to peck a similar bead on subsequent presentation. Thus, in a single trial chicks learn not to peck at an aversive stimulus. Bilateral lesions of the intermediate part of the medial hyperstriatum ventrale (IMHV) prevented the acquisition of this 1-trial passive-avoidance learning task. However, neither bilateral lesions of the lateral cerebral area (LCA) nor sham operation affected learning. IMHV has previously been shown to be critically involved in the learning process of imprinting in the chick. The present experiment demonstrates that the role of IMHV in learning is not restricted to imprinting. The function of IMHV in imprinting has been suggested to be concerned with the recognition of objects. In the present study sham-operated and LCA-lesioned chicks recognized the visual characteristics of the training bead and did not avoid a bead of a different color in the test. We propose that IMHV-lesioned chicks fail to learn the task because they are unable to recognize the visual characteristics of the training bead and consequently cannot make the association between the bead and the unpleasant taste.

Animals↗
PubMed1987

The role of a restricted region of the chick forebrain in the recognition of individual conspecifics.

It has been proposed that there are two neural systems underlying filial preference behaviour in the domestic chick. Firstly, a predisposition which serves to orient the chick towards objects resembling adult fowl, and secondly a learning system which is engaged by particular objects, including the bird's own mother. Lesions to a particular region of the chick forebrain, the intermediate and medial part of the hyperstriatum ventrale (IMHV), impairs the learning system but not the predisposition. The present experiment was designed to test the hypothesis that the IMHV is involved in learning to recognise individual members of a species. Between 6 and 10 h after chicks had hatched, bilateral lesions were placed in the IMHV (n = 16), and the Wulst (n = 16). There were 52 sham-operated controls. Following recovery from surgery (20-28 h later), all chicks were exposed to one of two stuffed jungle fowl for 4 X 50 min. Two hours after the final training session all birds were given a preference test. This test involved the simultaneous presentation of the fowl to which the chicks had previously been exposed and the fowl which they had not previously seen. While both the sham-operated and the Wulst-lesioned groups had a significant mean preference for the fowl to which they had been exposed during training, the IMHV-lesioned birds had no preference. This result is consistent with the hypothesis that IMHV is involved in learning to recognise individual birds, as well as other conspicuous objects.

Animals↗
PubMed1987

The influence of cooling on the organization of the meiotic spindle of the mouse oocyte.

The effect of cooling on the organization of the microtubule system of the mouse oocyte has been investigated. Cooling to 25, 18 or 4 degrees C for varying periods of time resulted in a progressive disassembly of the spindle and the dispersal of the chromosomes. The extent of the changes observed was greater at lower temperatures and with longer periods of exposure. Transfer of oocytes from either 37 or 4 to 24 degrees C resulted in the rapid and transient appearance of polar asters and of multiple cytoplasmic asters associated with the pericentriolar material present at the spindle poles and in the cytocortex of the oocyte. This transient aster formation appeared to be driven by the elevated levels of free tubulin released during spindle disassembly. An apparent reversal of many of the changes induced by low temperature was observed in many but not all oocytes on their restoration to 37 degrees C for 1 h. These results have implications for our understanding of microtubule organization in the oocyte, and for the handling of oocytes during IVF and GIFT therapeutic procedures and during the cryopreservation of oocytes.

Animals↗
PubMed1987

Linoleic acid levels in white blood cells, platelets, and serum of multiple sclerosis patients.

We found a small but statistically significant reduction in the linoleic acid concentration of white blood cells and platelets in MS patients. The percent linoleic acid concentration (mean +/- S.D.) in the white blood cells if 24 MS patients was 8.8 +/- 1.8% as compared with 11.4 +/- 4.9 in 24 age and sex-matched controls (p less than 0.05). Platelet levels were 8.5 +/- 2.4% and 10.6 +/- 3.8% respectively (P less than 0.05). Serum linoleic acid levels were not significantly different in the two groups. The possible role of linoleic acid in the pathogenesis of MS has yet to be defined.

Adult↗
PubMed1987

Entoptic phenomena and reproducibility of corneal striae following contact lens wear.

Vertical corneal striae distributed across the posterior cornea are one of the objective signs of clinically unacceptable corneal swelling (greater than 6%) resulting from contact lens wear. This study reports that corneal striae are repeatable both in configuration and location with different levels of hypoxia. In most instances entoptic phenomena result from the presence of these lines. The results suggest that the healthy, avascular, transparent cornea has certain localised areas in its anatomical structure which may give rise to bundles of collagen fibres being made visible objectively and subjectively during conditions of corneal swelling.

Adult↗
PubMed1987

The establishment of the embryonic-abembryonic axis in the mouse embryo.

The influence of cell division order on the establishment of the embryonic-abembryonic axis (EA axis) of the mouse embryo was investigated. Aggregate embryos were constructed in which a labelled cell (or pair of cells) was combined with a group of unlabelled cells all of which were up to one cell cycle earlier or later in their progress through development to the blastocyst stage. The aggregates were cultured first to the nascent blastocyst stage and then to the expanded blastocyst stage. The positions of the progeny of the labelled cells in relation to the nascent blastocoel and to the orientation of the embryonic-abembryonic axis were recorded. It was concluded that cell division order does influence the establishment of the EA axis, early dividing cells tending to be associated with the nascent blastocoel and the site of the nascent blastocoel tending to mark the site of the abembryonic pole. However, the influence of division order was diminished by a requirement for intercellular cooperation during blastocoel formation and by a counteracting influence of division order arising from its effects on the allocation of cells to the inner cell mass.

Animals↗
PubMed1987

The effect of dimethylsulphoxide on the microtubular system of the mouse oocyte.

The effect of dimethylsulphoxide (DMSO) on the organization of the microtubular system of the mouse oocyte has been examined. Exposure to DMSO causes the immediate appearance of multiple, cold-resistant microtubular asters associated with the foci of pericentriolar material (PCM) normally present in the oocyte. More prolonged exposure to DMSO leads to progressive disassembly of the spindle, and as a result dispersal of the chromosomes and polar PCM foci occurs, and tubulin polymerization becomes confined to PCM-organized asters. Those astral microtubules located between the PCM foci and the cortex of the oocyte appear to be particularly stable, resulting in the development of lengthening radial bundles of microtubules between the PCM and the surface and the progressive movement of the PCM foci towards the centre of the cell. In contrast, after activation of the oocyte the microtubules generated in the presence of DMSO remain located in a cortical mesh. The effects of DMSO do not appear to be fully reversible in most oocytes. We discuss the implications of these results both for the cytoplasmic organization of the oocyte and zygote, and for the attempts at cryopreservation of human oocytes for therapeutic use in infertility programmes.

Animals↗
PubMed1987

When and how does cell division order influence cell allocation to the inner cell mass of the mouse blastocyst?

Aggregate 8-cell embryos were constructed from four 2/8 pairs of blastomeres, one of which was marked with a short-term cell lineage marker and was also either 4 h older (derived from an early-dividing 4-cell) or 4 h younger (derived from a late-dividing 4-cell) than the other three pairs. The aggregate embryos were cultured to the 16-cell stage, at which time a second marker was used to label the outside cell population. The embryos were then disaggregated and each cell was examined to determine its labelling pattern. From this analysis, we calculated the relative contributions to the inside cell population of the 16-cell embryo of older and younger cells. Older cells were found to contribute preferentially. However, if the construction of the aggregate 8-cell embryo was delayed until each of the contributing 2/8 cell pairs had undergone intercellular flattening and then had been exposed to medium low in calcium to reverse this flattening immediately prior to aggregation, the advantage possessed by the older cells was lost. These results support the suggestion that older cells derived from early-dividing 4-cell blastomeres contribute preferentially to the inner cell mass as a result of being early-flattening cells.

Animals↗