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Biomedical subjects

M H Johnson

Publications and source records attributed to M H Johnson.

At least 181 records · Page 10Linked to original sources
PubMed1991

CONSPEC and CONLERN: a two-process theory of infant face recognition.

Evidence from newborns leads to the conclusion that infants are born with some information about the structure of faces. This structural information, termed CONSPEC, guides the preference for facelike patterns found in newborn infants. CONSPEC is contrasted with a device termed CONLERN, which is responsible for learning about the visual characteristics of conspecifics. In the human infant, CONLERN does not influence looking behavior until 2 months of age. The distinction between these 2 independent mechanisms allows a reconciliation of the conflicting data on the development of face recognition in human infants. Finally, evidence from another species, the domestic chick, for which a similar 2-process theory has already been put forward, is discussed. The new nomenclature is applied to the chick and used as a basis for comparison with the infant.

Arousal↗
PubMed1991

Cryoprotection of human oocytes: inappropriate exposure to DMSO reduces fertilization rates.

Human oocytes were exposed to the cryoprotectant dimethyl-sulphoxide (DMSO) at either 4 or 37 degrees C. Subsequent fertilization of these oocytes showed that exposure to DMSO at 37 degrees C was associated with a greatly reduced fertilization rate when compared to untreated control oocytes, whereas no such reduction was seen in oocytes exposed to DMSO at 4 degrees C. The significance of these results for the potential cryopreservation of human oocytes is discussed.

Cryopreservation↗
PubMed1991

The incidence of abnormal morphology and nucleocytoplasmic ratios in 2-, 3- and 5-day human pre-embryos.

Human cleaving pre-embryos at 2 and 3 days and cavitated pre-embryos at 5 days post-insemination have been examined for cell number and the incidence of mononucleated cells. At least 60% of polynucleate or anucleate cells have been detected at all these stages and regardless of morphological grading at day 2. It is concluded that even by the time at which pre-embryo replacement would occur therapeutically, the majority of pre-embryos are unlikely to have full developmental potential. The possible origins of the abnormalities of nucleocytoplasmic ratios are discussed.

Blastocyst↗
PubMed1991

The origin of reactive oxygen species in mouse embryos cultured in vitro.

The increase in production of reactive oxygen species such as H2O2 at the G2/M phase of the second cell cycle may be related to the in vitro block to development of mouse 2-cell embryos. The occurrence of the H2O2 rise is independent of the activation of the embryonic genome and of passage through the S, G2 and M phases of the first cell cycle and G1 and M phases of the second cell cycle, but does require the activation of the unfertilized oocyte. The H2O2 is produced via dismutation of superoxide by the enzyme superoxide dismutase. Production of superoxide via mitochondrial, NADPH-oxidase and xanthine/xanthine oxidase systems has been investigated. The evidence suggests that superoxide, and thereby H2O2, is produced by the xanthine/xanthine oxidase system, but an involvement of the other superoxide generating systems has not been excluded. The relation between H2O2 and development in vitro is discussed.

Animals↗
PubMed1991

Progression of experimental infantile hydrocephalus and effects of ventriculoperitoneal shunts: an analysis correlating magnetic resonance imaging with gross morphology.

Although previous ultrasonographic studies did monitor ventricular enlargement successfully in experimentally-induced models of feline hydrocephalus, the resolution of neuroanatomic detail was relatively poor after placement of a ventriculoperitoneal (VP) shunt because the skull had ossified over the coronal sutures. Therefore, the present study employed magnetic resonance imaging to follow the progression of ventriculomegaly more accurately, as well as to evaluate the compensatory effects of VP shunting. Hydrocephalus was induced in kittens between 7 and 10 days old by injection of kaolin into the cisterna magna. Age-matched controls received similar injections of saline. At 9 to 14 days after the kaolin injection, the hydrocephalic animals received VP shunts. Anesthetized kittens were scanned at various intervals before and after shunt placement and were killed for morphological correlation. The features observed on the magnetic resonance imaging scans were consistent with the gross morphological changes that accompanied ventricular enlargement. The lateral ventricle began to enlarge as early as 1 day after the kaolin injection, and within 3 days, both the occipital and temporal horns, along with the 4th ventricle, showed signs of moderate dilatation. By 5 days, a bilateral communication had been established through the septum pellucidum. Continued expansion of the ventricular system occurred from 6 to 20 days after injection, to the point where the cerebral cortex was reduced to less than 25% of its original thickness. The internal capsule was stretched and edematous, the caudate nucleus was compressed ventrolaterally, and the cerebellar hemispheres were eroded and/or compressed. Animals in which shunts were successfully placed demonstrated a dramatic improvement in behavior, and a reduction of about 50% in the size of the lateral ventricles within 2 days. In some cases, the lateral ventricles became slit-like within 1 week. When they were killed, about half of the animals that received shunts exhibited mild to moderate ventriculomegaly. These results indicate that magnetic resonance imaging is an excellent method for visualizing the morphological changes associated with this animal model, that these alterations occur soon after the onset of hydrocephalus, and that VP shunting can successfully reduce ventriculomegaly.

Animals↗
PubMed1991

2-Hydroxydesipramine and desipramine plasma levels and electrocardiographic effects in depressed younger adults.

Desipramine was given to 34 outpatients aged 20 to 51 years who had primary major depressive disorder but who were otherwise in good health. Daily dosage at bedtime was constant for the final 3 weeks of the 5-week study (mean, [SD] 169.1 [46.1] mg). Electrocardiograms done predrug and after 5 weeks were read by a cardiologist blind to the order in which they were performed. Plasma samples drawn 14 hours after the final study dose were assayed by high performance liquid chromatography; mean (SD) levels were 140.2 (140.0) ng/ml for desipramine and 56.5 (29.4) ng/ml for 2-hydroxydesipramine (2-OH-DMI). Heart rate and PR, QRS and QTc intervals were significantly greater at the end of the study than at baseline, while QT intervals were significantly less. Changes in heart rate and PR, QT and QTc intervals were significantly negatively correlated with the value of the respective cardiac parameters at baseline. Changes in PR interval were significantly positively correlated with log desipramine, log 2-OH-DMI and log (desipramine + 2-OH-DMI). Stepwise multiple regression analyses showed that, for PR interval, each of the three plasma level variables showed a significant ability to improve R2 over that obtained from baseline PR alone. These findings suggest that both 2-OH-DMI and desipramine plasma levels predict a prolongation of intracardiac conduction in younger adults and that monitoring both levels may be useful in the clinical management of certain younger adult patients.

Adult↗
PubMed1990

Structural, functional, and subunit assembly properties of hemoglobin Attleboro [alpha 138 (H21) Ser----Pro], a variant possessing a site maturation at a critical C-terminal residue.

Hemoglobin Attleboro, a new alpha-chain variant with a substitution of proline for serine at position 138 (H21), was found to be a noncooperative high-affinity hemoglobin (P50 = 0.26 mmHg at pH 7 and 20 degrees C) which lacked an alkaline Bohr effect. Addition of 2,3-diphosphoglycerate (DPG) or inositol hexaphosphate (IHP) led to a decrease in oxygen affinity but to no alteration in either Bohr effect or cooperativity. Ligand binding kinetics studies revealed an overall rate of oxygen dissociation at pH 7.0 and 20 degrees C that was 2.7-fold slower than that for Hb A. At pH 8.5, the kinetic profile was identical with that at pH 7, confirming the absence of a Bohr effect for this variant hemoglobin. Measurement of the rate of oxygen dissociation with carbon monoxide replacement indicated a lack of cooperativity. Sedimentation velocity experiments yielded s20,w values of 2.8 and 4.3 for 65 microM solutions of oxyhemoglobins Attleboro and A, respectively (indicating an enhancement in the oxy dimer population of this variant). Studies of the carbon monoxide combination of this variant revealed an association rate 20-fold faster than that for Hb A; only in the presence of a 1000-fold molar excess of IHP was there a significant reduction in the overall rate. Rapid-scan and traditional stopped-flow experiments conducted in the Soret Soret region demonstrated an alteration in the structure and rate of assembly of the deoxy tetramer of Hb Attleboro relative to that of Hb A. The abnormal properties of this hemoglobin variant can be attributed to major perturbations in the C-terminal region.

Amino Acid Sequence↗
PubMed1990

Dimethylsulphoxide affects the organisation of microfilaments in the mouse oocyte.

The effect of dimethylsulphoxide (DMSO) on microfilament organisation has been studied in the mouse oocyte after staining with (NBD)-phallacidin. The cortical actin meshwork was disrupted by exposure of oocytes to 1.5 M DMSO at 37 degrees C, and this disruption was associated with changes in the cell surface, especially microvilli length and distribution, as observed by scanning electron microscopy. The irregular distribution of actin filaments observed also appears to lead to an irregular expansion of the cell after DMSO removal. However, when exposure to DMSO was combined with cooling, the effects on the microfilament system were much reduced. The reversibility of DMSO action is considered and the potential implications of microfilament disruption on the viability and functions of the oocyte discussed.

Actin Cytoskeleton↗
PubMed1990

Acid Tyrode's solution can stimulate parthenogenetic activation of human and mouse oocytes.

Fresh and aged (24 hours after ovulation) human oocytes and recently ovulated mouse oocytes may be activated by exposure to acidified Tyrode's solution. No activation of either type of human oocyte was observed after exposure to hyaluronidase or pronase, but significant numbers of fresh mouse oocytes were activated after exposure to pronase but not to chymotrypsin. The implications of these results for the manipulation of human and mouse eggs in vitro are discussed.

Animals↗
PubMed1990

Transient cooling to room temperature can cause irreversible disruption of the meiotic spindle in the human oocyte.

The effect on the microtubule system of human oocytes of cooling to room temperature for either 10 or 30 minutes has been investigated. Changes in spindle organization were found in all oocytes cooled for 30 minutes compared with control oocytes kept at 37 degrees C throughout. These changes included reduction in spindle size, disorganization of microtubules within the spindle itself, and sometimes a complete lack of microtubules. In some oocytes, chromosome dispersal from the metaphase plate was associated with these changes. Cooling the oocyte to room temperature for only 10 minutes produced a similar pattern of disruption to spindle structure in many cases. The spindles in oocytes that were cooled for either 10 or 30 minutes and then allowed to recover at 37 degrees C for either 1 or 4 hours were found to resemble those in noncooled control oocytes in less than one half of the cases examined, although in only a few cases did the chromosomes remain dispersed. The significance of these findings for the handling of oocytes during gamete intrafallopian transfer and in vitro fertilization procedures is discussed in relation to the levels of aneuploidy detected in early human embryos.

Chromosomes↗
PubMed1990

Dietary n-3 fatty acid supplementation reduces superoxide production and chemiluminescence in a monocyte-enriched preparation of leukocytes.

Consuming substantial quantities of n-3 fatty acids reduces atherogenesis in experimental models of atherosclerosis. The mechanisms of this beneficial effect remain uncertain. Monocyte-derived tissue macrophages are associated with atherogenesis, and inhibition of monocyte inflammatory activity could, hypothetically, be helpful in preventing atherosclerosis. We observed that stimulated human monocyte and/or macrophage production of superoxide and the occurrence of monocyte chemiluminescence, two indices of monocyte inflammatory activity, were significantly reduced by the ingestion of 6 g n-3 fatty acids/d for 6 wk. This effect was associated with a reduction of stearic and arachidonic acids whereas eicosapentaenoic and docosahexaenoic acid concentrations rose significantly. These results indicate that modest dietary n-3 fatty acid supplementation can reduce stimulated human-monocyte free-radical production and may impair the capability of macrophages derived from monocytes to promote oxidation of low-density-lipoprotein cholesterol and associated cellular toxicity.

Adult↗
PubMed1990

The effect of iron and iron chelators on the in-vitro block to development of the mouse preimplantation embryo: BAT6 a new medium for improved culture of mouse embryos in vitro.

The effect of iron and iron chelators on the development of the mouse embryo in vitro from the 1-cell stage to the blastocyst has been investigated. An adverse effect of iron was found. The high affinity iron chelator, desferal, also blocked development, whilst transferrin (whether as apoprotein or saturated with iron), DETAPAC and EDTA promoted development. The addition of transferrin permitted development to the blastocyst stage of embryos from stains normally exhibiting the 2-cell block. Under such circumstances both the rate of embryonic development and the proportion of embryos reaching the blastocyst stage approached levels found in vivo. Based on these results, a new medium, BAT6, is described for the optimal in-vitro culture of mouse embryos.

Animals↗
PubMed1990

Hydrogen peroxide levels in mouse oocytes and early cleavage stage embryos developed in vitro or in vivo.

We describe a fluorimetric method for measuring the level of H2O2 in individual mouse oocytes and early embryos. Levels of H2O2 are low but detectable in unfertilized oocytes recovered freshly from the female reproductive tract. The levels in early cleaving embryos (1-cell to 8-cell stages) immediately after recovery from the female tract seem to be slightly higher the later the stage examined. However, when embryos are cultured in vitro from the 1-cell or early 2-cell stage, H2O2 levels rise when the embryos reach the mid-2-cell stage and remain elevated until they enter the early 4-cell stage. No equivalent elevation of H2O2 is seen during the transition from 1-cell to 2-cell or from 4-cell to 8-cell stages. Embryos that are able to develop successfully in vitro, as well as those that show a developmental block at the 2-cell stage on culture in vitro, both show this rise in H2O2 levels after in vitro culture. The relationship between the rise in H2O2 and the '2-cell block' to development is discussed.

Animals↗
PubMed1990

The hardening effect of dimethylsulphoxide on the mouse zona pellucida requires the presence of an oocyte and is associated with a reduction in the number of cortical granules present.

When mouse ovulated oocytes were exposed to 1.5 M-dimethylsulphoxide (DMSO) the resultant hardening of the zona pellucida was not a direct effect but required the presence of an oocyte. The hardening of the zona pellucida when zonae used were aged in vitro was also dependent upon the presence of the oocyte. Protocols of DMSO exposure that induce zona-hardening also caused depletion of the numbers of cortical granules underlying the oocyte surface, whereas protocols without effect on the zona did not reduce significantly the cortical granule count. It is proposed that the effects of DMSO may be mediated by a release of cortical granule contents.

Animals↗