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PubMed1990

Genetics of inbred Drosophila melanogaster. XXV. Simultaneous tests of I-inductivity and M-type.

From a branch of an inbred line of Drosophila melanogaster we introduced the genome into cytoplasms from various sources. Among a pair of sister-lines, which at first showed R-type in the I-R system, one line switched to I-type. From a branch of this I-type line, for several generations kept at 18 degrees C, we established sub-lines derived from four single females. They were propagated at 25 degrees C with 14 or 28-day generation interval, respectively. It was presumed that 14-day generation interval gave strong, and 28 days interval gave weak R-elements. Tests of the strength of the I-inductivity disclosed no relation to the assumed strength of the R-elements. By the same test technique, primary non-disjunction and chromosome loss, the M-type was studied in the eight sub-lines. There appeared diversities in the M-type, assumed to be related to chromosomal mutations. Both primary non-disjunction and chromosome loss were affected by the P-M reaction.

Animals↗

PubMed1989

Absence of synapsis during pachynema of the normal sized sex chromosomes of Microtus arvalis.

The pachytene behavior of the chromosomes of males of Microtus arvalis (Pall.) (Rodentia, Arvicolidae) was examined by electron microscopy in microspread preparations of spermatocytes. There was no synapsis between the axes of these two chromosomes during this period. Since synapsis is universally considered a prerequisite for crossing over and chiasmata formation, disjunction of the sex chromosomes in this species prerequisite for crossing over and chiasmata formation, disjunction of the sex chromosomes in this species must be presumed to be achiasmatic. Unlike previously examined species with no synapsis or crossing over between the X and Y, the sex chromosomes of M. arvalis are of normal size: the X chromosome is of an "original" X size and the Y is a small acrocentric. C-band studies of M. arvalis mitotic metaphase reveal no blocks of heterochromatin on the sex chromosomes. The implications of these findings are discussed.

Animals↗

PubMed2000

Investigation of a cluster of children with Down's syndrome born to mothers who had attended a school in Dundalk, Ireland.

OBJECTIVES: To investigate a reported cluster of Down's syndrome in offspring of former pupils of a girls' school in Ireland, to establish the prevalence of Down's syndrome among live births in the area around the school, and to review the literature on the possible causes of reported clusters of Down's syndrome. METHODS: Questionnaire survey of obstetric and personal histories of women who had attended the girls' school at Dundalk, County Louth, Republic of Ireland, at some time during 1956-7, and also of women who had attended another, nearby, girls' school during the same period. Comparison of observed numbers of cases of Down's syndrome identified by these surveys with maternal age adjusted expected numbers for the reported live births. Laboratory tests were conducted to verify and characterise the cases of Down's syndrome constituting the cluster. Retrospective collection and collation of data on Down's syndrome occurring among live births, and the compilation of maternal age specific incidences, in County Louth and in Newry and Mourne District in neighbouring Northern Ireland, during 1961-80. These rates were compared with reference rates and rates for other areas of Ireland. RESULTS: Six children with Down's syndrome were confirmed among 387 reported live births to women who had been pupils at the girls' school in Dundalk during 1956-7, compared with 0.69 expected (nominal p<10(-4)). Five of the affected births were to mothers under 30 years of age, against 0.15 expected (nominal p<10(-6)), although only four of these mothers were attending the school at any one time. The origin of the non-disjunction was found to be maternal first meiotic in four children, mitotic after fertilisation in another (with the youngest mother), and in the remaining one could not be determined. The marked excess of Down's syndrome in births to young mothers did not extend to offspring of former pupils of the other Dundalk girls' school surveyed, or to live births in County Louth generally or in adjacent Newry and Mourne District. CONCLUSION: A striking, highly localised, excess of Down's syndrome in births to young mothers who had attended a girls' school in Dundalk during 1956-57 has been confirmed. However, not all of the mothers of the affected children attended the school concurrently and the origin of non-disjunction in one child was an error occurring after conception. Some exposure essentially confined to girls attending the school at this time is a possible, although unlikely, explanation, but a review of potential risk factors does not suggest what this could be. Previous suggestions that an influenza epidemic or contamination from the Windscale nuclear reactor fire might be implicated, both of which occurred in October 1957, can be effectively dismissed because three of the women with affected offspring had left the school by then and had moved away from Dundalk, and Down's syndrome in the child of another mother originated in an error after fertilisation. Owing to the retrospective nature of the investigation and the characteristics of the cases, chance is the most likely explanation for the cluster.

Adult↗

PubMed1986

Neural control of vergence eye movements: neurons encoding vergence velocity.

Single-unit recordings were made from midbrain areas in monkeys trained to make both conjugate and disjunctive (vergence) eye movements. Previous work had identified cells with a firing rate proportional to the vergence angle, without regard to the direction of conjugate gaze. The present study describes the activity of neurons that burst for disjunctive eye movements. Convergence burst cells display a discrete burst of activity just before and during convergence eye movements. For most of these cells, the profile of the burst is correlated with instantaneous vergence velocity and the number of spikes in the burst is correlated with the size of the vergence movement. Some of these cells also have a tonic firing rate that is positively correlated with vergence angle (convergence burst-tonic cells). Divergence burst cells have similar properties, except that they fire for divergent and not convergent movements. Divergence burst cells are encountered far less often than convergence burst cells. Both convergence and divergence burst cells were found in an area of the mesencephalic reticular formation just dorsal and lateral to the oculomotor nucleus. Convergence burst cells were also recorded in another more dorsal mesencephalic region, rostral to the superior colliculus. Both of the areas also contain cells that encode vergence angle. Models of the vergence system derived from psychophysical data imply the existence of a vergence integrator, the output of which is vergence angle. Some models also suggest the presence of a parallel element that improves the frequency response of the vergence system, but has no effect on the steady-state behavior of the system. Vergence burst cells would be suitable inputs to a vergence integrator. By providing a vergence velocity signal to motoneurons, they may improve the dynamic response of the vergence system. The behavior of vergence burst cells during vergence movements is similar to that of the medium-lead burst cells during saccades. The proposed roles for vergence velocity cells are analogous to those of the saccadic burst cells. In this respect, the neural organization of the vergence system resembles that of the saccadic system, despite the distinct difference in the kinematics of these two types of eye movements.

Action Potentials↗

PubMed1992

Dynamics and efficacy of saccade-facilitated vergence eye movements in monkeys.

1. Four macaque monkeys were trained to fixate visual targets. Eye movements were recorded binocularly using the search coil technique. Saccades, vergence movements, and combinations of the two were elicited by training the monkeys to alternate the gaze between real visual targets that differed in viewing distance and eccentricity with respect to the monkeys' heads. 2. When they shifted the gaze between targets that were at different viewing distances, the monkeys made vergence eye movements. For targets placed along the midsagittal plane, the monkeys often made binocularly symmetric vergence movements. The peak speed of symmetric divergence movements increased linearly with vergence amplitude by 5.7 deg/s per degree of vergence. The peak speed of symmetric convergence movements increased linearly with vergence amplitude by 7.9 deg/s per degree of vergence. 3. For gaze shifts between targets placed eccentrically with respect to the midsagittal plane and at different viewing distances, the monkeys made saccades in combination with vergence eye movements. When a saccade occurred during a vergence movement, peak vergence eye speed increased abruptly and reached a peak that was proportional to the speed of the saccade. For four monkeys, peak divergence speed ranged from 242 to 315 deg/s and peak convergence speed ranged from 257 to 340 deg/s for 16-deg vergence and 20-deg saccadic eye movements. 4. For gaze shifts between far targets at the same viewing distance but different eccentricities, saccadic eye movements were transiently disjunctive even though there was no vergence requirement. Initially, the eyes diverged and then converged to restore fixation to the correct depth plane. Divergence was followed by convergence regardless of the direction of the saccade. 5. The presence of transient saccade-related disjunctive eye movements suggested that the abrupt increase in peak vergence speed during combined saccadic and vergence eye movements was produced by the linear addition of a vergence eye movement and the saccade-related transients. Consistent with this hypothesis, the rate of change in peak vergence speed during various-sized saccades between far targets (no vergence required) was similar to the rate of change in peak vergence speed during combined saccadic and vergence movements. However, the peak vergence speeds during the combined movements were higher than predicted by the linear addition hypothesis, suggesting the presence of an additional mechanism. 6. The saccade-related increase in peak vergence speed during combined saccades and vergences led to a significant decrease in the amount of time required to complete vergence movements.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed2004

Unique invasions and resolutions: DNA repair proteins in meiotic recombination in Drosophila melanogaster.

To ensure the accurate disjunction of homologous chromosomes during meiosis, most eukaryotes rely on physical connections called chiasmata, which form at sites of crossing over. In the absence of crossing over, homologs may segregate randomly, resulting in high frequencies of aneuploid gametes. The process of meiotic recombination poses unique problems for the cell that must be overcome to ensure normal disjunction of homologous chromosomes. How is it ensured that crossovers occur between homologous chromosomes, rather than between sister chromatids? What determines the number and location of crossovers? The functions of DNA repair proteins hold some of the answers to these questions. In this review, we discuss DNA repair proteins that function in meiotic recombination in Drosophila melanogaster. We emphasize the processes of strand invasion and Holliday junction resolution in order to shed light on the questions raised above. Also, we compare the variety of ways several eukaryotes perform these processes and the different proteins they require.

Animals↗

PubMed1985

Tactile cutaneous representation in cerebellar granule cell layer of the opossum, Didelphis virginiana.

Recent studies of the albino rat revealed extensive cutaneous somatosensory projections to the granule cell (GC) layer of the cerebellar hemispheres and the caudal vermis. These projections are organized asomatotopically in patchy mosaics. To determine whether similar projections exist in a marsupial, we explored the GC layer of the cerebellar cortex of anesthetized Virginia opossums using in-depth microelectrode micromapping and juxtathreshold cutaneous natural stimulation techniques. We found: Somatosensory projections to the GC layer exist throughout the mediolateral extent of the folia of the posterior lobe. The anterior lobe was not explored. The submodality of most receptive fields was 'gentle-touch' cutaneous, but some were located in muscle, joint, or other deep-lying structures. Peripheral projections to the GC layer are organized asomatotopically. Adjacent body parts project disjunctively to nonadjacent GC regions, and the overall pattern of peripheral projections forms a patchy columnar mosaic. Many body parts send projections to multiple loci. Ipsilateral projections predominate. Mechanoreceptors from face, snout, mouth and teeth activate the bulk of GC loci on crus I and crus II. The paramedian lobule receives projections from the entire ipsilateral body; the pyramis is activated from hindlimb and forelimb; the uvula from the upper arm and vibrissae. Different folia have different combinations and arrangements of disjunctive patchy peripheral projections. Individual differences in pattern of foliation and body representation occur. Except for differences in mosaic pattern and relative size of different projections, these findings are similar to those in rats and cats. These data suggest that somatosensory (especially cutaneous) inputs to the cerebellum are not only functionally significant, but that they exist widely among mammals.

Animals↗

PubMed1976

A mitotically unstable human dicentric Y chromosome in a male pseudohermaphrodite.

A patient with a mitotically unstable dic(Y)(p11) chromosome is reported. Physical examination revealed a small penis with severe hypospadia, undescended testes, rudimetary vagina, uterus, left fallopian tube, and no stigmata of Turner syndrome. Longitudinal chromosome studies over a four-year period, including blood, skin, foreskin, and testicular tissue, revealed 45,X/46,X,dic(Y)(p11)/46,X,del(dic Y) mosaicism. The proportions of these cells varied in the different tissues, and only 45,X and 46,X,del(dic Y) were major cell lines in testicular tissue. Additional minor cell lines were present mainly in peripheral blood: 47,X,dicY,dicY; 47,X,dicY,del(dicY); and 47,X,del(dicY),del(DICY). Premature disjunction of one of the centromeres in a high percentage of the dicentric Y chromosomes in metaphase was observed by Q- and C-banding. Lymphocytes at anaphase and telophase showed lagging Y chromosomes, fragments, and nondisjunction. These observations indicate a high degree of mitotic instability and thus raise the question of the effect of premature centromeric disjunction on mitotic instability of dicentric chromosomes.

Cell Line↗

PubMed1975

Mitotic activity and nuclear/cytoplasmatic ratio of the lachrymal and Harderian glands of the rat during postnatal life.

The authors performed a study of the mitotic activity and the nuclear/cytoplasmic (N/C) ratio during postnatal life of the lachrymal and Harderian glands of the rat. Based on the results, they concluded: (1) during the first days of postnatal life the development of lachrymal and Harderian glands was characterized by an intense mitotic activity and a low N/C ratio; (2) the period prior to eyelid disjunction was characterized by a diminished mitotic activity and a progressive and slow increase of the N/C ratio; (3) after eyelid disjunction, mitotic activity was reduced and an abrupt increase of the N/C ratio occurred, more evident in the Harderian gland; (4) during the final period of postnatal life studied mitotic activity was absent and the N/C ratio presented a higher, more constant level, which was always higher for the Harderian gland.

Age Factors↗

PubMed2005

Cognitive requirements for vestibular and ocular motor processing in healthy adults and patients with unilateral vestibular lesions.

This study investigated the role of cognition in the vestibulo-ocular reflex (VOR) and ocular pursuit using a dual-task paradigm in patients with unilateral peripheral vestibular loss and healthy adults. We hypothesized that cognitive resources are involved in successful processing and integration of vestibular and ocular motor sensory information, and this requirement would be greater in patients with vestibular dysfunction. Sixteen well-compensated patients with surgically confirmed absent unilateral peripheral vestibular function and 16 healthy age- and sex-matched controls underwent seven combinations of vestibular-only, visual-only, and visual-vestibular stimuli while performing three different information processing tasks. Visual-vestibular stimuli included a semicircular canal and an otolith stimulus provided through seated chair rotations; fixation on a laser target and sinusoidal smooth pursuit while still; and fixation on a head-fixed laser target during chair rotations. The information processing tasks were three different auditory reaction time (RT) tasks: (1) simple RT, (2) disjunctive RT, and (3) choice RT. Our results showed increases in RTs in both patients and controls under all vestibular-only stimulation conditions and during ocular pursuit. Patients showed greater increases in RTs during vestibular stimulation and the more complex disjunctive and choice RT tasks. No differences between the groups were found during the visual-only or visual-vestibular interaction conditions. These results reveal interference between vestibulo-ocular processing and a concurrent RT task, suggesting that the VOR and the ocular motor system are dependent upon cognitive resources to some extent, and thus, are not fully automatic systems. We speculate that this interference with cognition occurs as a result of the sensory integration required for resolving inputs from multiple sensory streams. The particularly large decrement in information processing task performance of the patients compared with controls during vestibular stimulation suggests that compensation for unilateral vestibular loss requires continued cognitive resources.

Acoustic Stimulation↗

PubMed2004

Dysregulation of arousal and amygdala-prefrontal systems in paranoid schizophrenia.

OBJECTIVE: The authors investigated impaired differentiation of limbic-prefrontal systems by autonomic arousal in schizophrenia. It was predicted that paranoid patients would be distinguished by a disjunction of hyperarousal but reduced amygdala and medial prefrontal activity relative to both healthy comparison subjects and patients with nonparanoid schizophrenia. METHOD: Pictures depicting facial expressions of fear were presented to 27 schizophrenia patients (13 paranoid, 14 nonparanoid) and 22 matched healthy comparison subjects in an implicit perception task to evoke limbic activity. Simultaneous functional magnetic resonance imaging and skin conductance arousal recordings were acquired during presentation of faces expressing fear or neutral emotion. Responses to fear stimuli were further examined by contrasting those that were associated with a skin conductance response ("with arousal") and those that were not ("without arousal"). RESULTS: In the comparison subjects, arousal dissociated amygdala/medial prefrontal ("visceral") networks and hippocampus/lateral prefrontal ("context") networks for fear perception. Excessive arousal responses were elicited in the schizophrenia subjects, but there was an associated reduction in amygdala/medial prefrontal activity. This disjunction was pronounced in paranoid patients relative to both healthy subjects and nonparanoid patients. Paranoid patients also showed a relatively greater prefrontal deficit for "without-arousal" responses. CONCLUSIONS: This is the first study to reveal a functional disconnection in autonomic and central systems for processing threat-related signals in patients with paranoid schizophrenia. Paranoid cognition may reflect an internally generated cycle of misattribution regarding incoming fear signals due to a breakdown in the regulation of these systems.

Adult↗

PubMed2004

Risk taking in adolescence: what changes, and why?

Extant studies of age differences in cognitive processes relevant to risk taking and decision making, such as risk perception and risk appraisal, indicate few significant age differences in factors that might explain why adolescents engage in more risk taking than adults. The present analysis suggests that the greater propensity of adolescents to take risks is not due to age differences in risk perception or appraisal, but to age differences in psychosocial factors that influence self-regulation. It is argued that adolescence is a period of heightened vulnerability to risk taking because of a disjunction between novelty and sensation seeking (both of which increase dramatically at puberty) and the development of self-regulatory competence (which does not fully mature until early adulthood). This disjunction is biologically driven, normative, and unlikely to be remedied through educational interventions designed to change adolescents' perception, appraisal, or understanding of risk. Interventions should begin from the premise that adolescents are inherently more likely than adults to take risks, and should focus on reducing the harm associated with risk-taking behavior.

Adolescent↗

PubMed2004

Modeling electronic discharge summaries as a simple temporal constraint satisfaction problem.

OBJECTIVE: To model the temporal information contained in medical narrative reports as a simple temporal constraint satisfaction problem. DESIGN: A constraint satisfaction problem is defined by time points and constraints (inequalities between points). A time interval comprises a pair of points and a constraint. Five complete electronic discharge summaries and paragraphs from 226 other discharge summaries were studied. Medical events were represented as intervals, and assertions about events were represented as constraints. Through a consensus process, a set of encoding procedures and a list of issues related to encoding were generated. MEASUREMENTS: Instances of temporal disjunction and contradiction and distribution of temporal constraints were used. RESULTS: An average of 95 medical events (range, 46-151) and 234 temporal assertions (range, 118-388) were identified per complete discharge summary. Nondefinitional assertions were explicit (36%) or implicit (64%) and absolute (17%), qualitative (72%), or metric (11%). Implicit assertions were based on domain knowledge and assumptions, e.g., the section of the report determined the ordering of events. Issues included linking events, intermittence, periodicity, granularity, vagueness, ambiguity, uncertainty, and plans. ions such as intermittence were not represented explicitly. The temporal network was sparse: Only 0.80% (range, 0.42%-1.38%) of possible constraints were instantiated. No instances of discontinuous temporal disjunction were found in the complete summaries or the 226 paragraphs. One instance of temporal contradiction was found (intrareport rate of 0.2 with a 95% confidence interval of 0.005-1.114). CONCLUSION: A simple temporal constraint satisfaction problem appears sufficient to represent most temporal assertions in discharge summaries and may be useful for encoding electronic medical records.

Algorithms↗

PubMed1991

Karyotypes and X chromosome inactivation in segregants of a murine X-autosome translocation, T(X;4)37H.

Karyotypes and X chromosome inactivation were studied in embryos obtained from female mice carrying T(X;4)37H translocation on day 6 to 8 of gestation by a BrdU-acridine orange method. A total of 18 different karyotypes were found in 477 embryos examined: 90.0% embryos were products expected from 2:2 alternate or adjacent 1 disjunction. 3:1 and adjacent 2 disjunctions accounted for approximately 8.0% and 0.7% conceptuses, respectively. In the embryo proper of balanced T37H/ + conceptuses, inactivation was random with respect to the normal X and the larger translocation X (4x) chromosome. In all the cells with the 4x inactive, the late replication apparently did not spread to the attached autosomal portion, although black/brown coat variegation implies spreading of inactivation into the autosomal region. The X chromosome segment deprived of the inactivation center remained active in all the cells examined and it exerted deleterious effects on embryonic or fetal development. Observation in embryos having two maternally derived X chromosomes showed that they were indeed resistant to inactivation in early extraembryonic cell lineages, and two copies of active X chromosomes in the trophectoderm fatally affected embryonic development due to inability to form the extraembryonic ectoderm and ectoplacental cone from the polar trophectoderm. In unbalanced X aneuploids the X chromosomes with the deletion were preferentially inactivated due to strong selection against nullisomy X.

Animals↗

PubMed1997

Gradual bone distraction in craniosynostosis. Preliminary results in seven cases.

Seven patients with craniosynostosis (mean age 8 years, Apert syndrome, n = 4, Crouzon's disease, n = 3) underwent lengthening of the skull by gradual bone distraction. Three patients (group A) were treated by coronal craniectomy reaching the orbital fissure and gradual bone distraction. The other four (group B) underwent monobloc craniofacial disjunction and gradual bone distraction. The patients' progress was monitored clinically as well as by radiographs and photographs. The results showed that craniofacial disjunction followed by gradual bone distraction produced complete correction of exophthalmus and an improvement in the functional and aesthetic aspects of the middle third of the face without the need for bone grafts.

Acrocephalosyndactylia↗

PubMed2001

Propositional reasoning: the differential contribution of "rules" to the difficulty of complex reasoning problems.

In Experiment 1, complex propositional reasoning problems were constructed as a combination of several types of logical inferences: modus ponens, modus tollens, disjunctive modus ponens, disjunctive syllogism, and conjunction. Rule theories of propositional reasoning can account for how one combines these inferences, but the difficulty of the problems can be accounted for only if a differential psychological cost is allowed for different basic rules. Experiment 2 ruled out some alternative explanations for these differences that did not refer to the intrinsic difficulty of the basic rules. It was also found that part of the results could be accounted for by the notion of representational cost, as it is used in the mental model theory of propositional reasoning. However, the number of models as a measure of representational cost seems to be too coarsely defined to capture all of the observed effects.

Adolescent↗

PubMed2001

Conjunctive bias in memory representations of logical connectives.

The paper presents the conjunctive bias in memory-a novel phenomenon that helps to clarify representations of logical connectives. The conjunctive bias is a tendency toward more accurate recall and recognition of conjunctive forms than of forms based on other logical connectives and a tendency to recall and recognize other logical forms as if they were conjunctions. Three experiments, in which participants' memory representations associated with different logical connectives were examined, were conducted to test the conjunctive bias hypothesis. In Experiment 1, participants learned picture-proposition pairs involving either conjunctions or disjunctions and then had to recall each proposition when cued with its picture. In Experiments 2 and 3, recognition memory for conjunctions, disjunctions, and conditionals was examined with an old/new recognition procedure. The findings of these experiments provide evidence for the conjunctive bias. Furthermore, the results of Experiment 3 suggest that corjunctive bias is not simply a pragmatically caused preference for conjunctions. The discussion focuses on the implications of these findings for current theories of deductive reasoning.

Adult↗

PubMed1996

[When a sense of justice hinders social efficiency: Pareto axiom revisited].

This study addressed people's judgments about desirability of various reward allocation under different task-rules aggregating individual inputs to a group outcome. The rules used in the study were additive, conjunctive, and disjunctive (Steiner, 1972), and subjects evaluated twelve cases of reward allocation reflecting different distributive principles, such as equality and equity. It was found that no one principle was favored under all three aggregation rules. Generally, a distributive principle was favored that was most beneficial for the member whose input 'determined' group success. Specifically, equality was endorsed most often under the conjunctive rule, and equity under the disjunctive rule. It was also found that the Pareto axiom was frequently violated. In pairwise comparison, more than 60% of the subjects endorsed an allocation scheme, that was, subjectively fairer but objectively inferior in terms of Pareto optimality, revealing their commitment to a specific distributive principle. The results suggest that the universal economic assumption of Pareto optimality for social policy-making be seriously questioned.

Adult↗