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At least 289 records · Page 16Linked to original sources
PubMed1991

Electron microscopy of 26 S complex containing 20 S proteasome.

A high molecular weight protease complex (26 S complex) involved in the intracellular protein degradation of ubiquitinated proteins was purified from rat liver and studied by electron microscopy. The most prevalent molecular species with best preserved symmetrical morphology had two large rectangular terminal structures attached to a thinner central one having four protein layers. We concluded that they were the closest representation of the 26 S complex so far reported. The central structure was identified as 20 S proteasome and the terminal one as recognition units for ubiquitinated proteins.

Animals↗
PubMed1969

Distributed representations for actin-myosin interaction in the oscillatory contraction of muscle.

In this paper we suggest and test a specific hypothesis relating the attachment-detachment cycle of cross bridges between actin (I) and myosin (A) filaments to the measured length-tension dynamics of active insect fibrillar flight muscle. It is first shown that if local A-filament strain perturbs the rate constants in the cross-bridge cycle appropriately, then exponentially delayed tension changes can follow imposed changes of length; the latter phenomenon is sufficient for the work-producing property of fibrillar muscle, as measured with small-signal forcing of length and at low Ca(2+) concentration, and possibly for related effects described recently in frog striated muscle. It is not clear a priori that the above explanation of work production by fibrillar muscle will remain tenable when the viscoelastic complexity of the heterogeneous sarcomere is taken into account. However, White's (1967) recent mechanical and electron microscope study of the passive dynamics of glycerinated fibrillar muscle has produced a model of the distributed viscoeleastic structure sufficiently explicit that alternative schemes for cross-bridge force generation in this muscle can now be tested more critically than previously. Therefore, we derive and solve third-order partial-differential equations which relate local interfilament shear forces associated with the perturbed cross-bridge cycles to the over-all length-tension dynamics of an idealized sarcomere. We then show (a) that the starting hypothesis can account approximately for the small-signal dynamics of glycerinated muscle in the work-producing state over two decades of frequency and (b) that the rate constants for cross-bridge formation and breakage, restricted solely by fitting of the model to the mechanical data, determine a cycling rate of cross bridges in the model compatible with recent measurements of ATP hydrolysis rate vs. stretch in this muscle. Finally, the formulation is extended tentatively to the large-signal nonlinear case, and shown to compare favorably with previous suggestions for the origin of the work-producing dynamics of fibrillar flight muscle.

Adenosine Triphosphate↗
PubMed2001

Fine-scale organization of SI (area 3b) in the squirrel monkey revealed with intrinsic optical imaging.

Optical imaging of intrinsic cortical activity was used to study the somatotopic map and the representation of pressure, flutter, and vibration in area 3b of the squirrel monkey (Saimiri sciureus) cortex under pentothal or isoflurane anesthesia. The representation of the fingerpads in primary somatosensory cortex was investigated by stimulating the glabrous skin of distal fingerpads (D1-D5) with Teflon probes (3-mm diam) attached through an armature to force feedback-controlled torque motors. Under pentothal anesthesia, intrinsic signal maps in area 3b obtained in response to stimulation (trapezoidal indentation) of individual fingerpads showed focal activations. These activations (ranging from 0.5 to 1.0 mm) were discrete and exhibited minimal overlap between adjacent fingerpad representations. Consistent with previously published maps, a somatotopic representation of the fingerpads was observed with an orderly medial to lateral progression from the D5 to D1 fingerpads. Under isoflurane anesthesia, general topography was still maintained, but the representation of fingerpads on adjacent fingers had higher degrees of overlap than with pentothal anesthesia. Multi- and single-unit recordings in the activation zones confirmed the somatotopic maps. To examine preferential inputs from slowly adapting type I (SA) and rapidly adapting type I (RA) and type II (PC) mechanoreceptors, we applied stimuli consisting of sinusoidal indentations that produce sensations of pressure (1 Hz), flutter (30 Hz), and vibration (200 Hz). Under pentothal anesthesia, activation patterns to these different stimuli were focal and coincided on the cortex. Under isoflurane, activation zones from pressure, flutter, and vibratory stimuli differed in size and shape and often contained multiple foci, although overall topography was maintained. Subtraction and vector maps revealed cortical areas (approximate 250-microm diam) that were preferentially activated by the sensations of pressure, flutter, and vibration. Multi- and single-unit recordings aided in the interpretation of the imaging maps. In conclusion, the cortical signals observed with intrinsic signal optical imaging delineated a somatotopic organization of area 3b and revealed different topographical cortical activation patterns for pressure, flutter, and vibratory stimuli. These patterns were dependent on anesthesia type. Possible relationships of these anesthesia effects to somatosensory cortical plasticity are discussed.

Anesthesia↗
PubMed2000

Acquisition of the algorithms of social life: a domain-based approach.

Proposing that the algorithms of social life are acquired as a domain-based process, the author offers distinctions between social domains preparing the individual for proximity-maintenance within a protective relationship (attachment domain), use and recognition of social dominance (hierarchical power domain), identification and maintenance of the lines dividing "us" and "them" (coalitional group domain), negotiation of matched benefits with functional equals (reciprocity domain), and selection and protection of access to sexual partners (mating domain). Flexibility in the implementation of domains occurs at 3 different levels: versatility at a bioecological level, variations in the cognitive representation of individual experience, and cultural and individual variations in the explicit management of social life. Empirical evidence for domain specificity was strongest for the attachment domain; supportive evidence was also found for the distinctiveness of the 4 other domains. Implications are considered at theoretical and applied levels.

Adolescent↗
PubMed2000

Effects of directionality in deductive reasoning: I. The comprehension of single relational premises.

Four experiments involving 123 university students tested directionality effects in the comprehension of spatial relations, quantified statements, and propositional connectives with a sentence-picture verification task. Presentation of the referents of terms in the statements was separated by 1 s, and presentation order was congruent or incongruent with the order of terms in the statement. Some relations showed faster verification times for congruent display order, others for incongruent display order, and still others showed no directionality effect. The authors proposed a 2-step process model for the construction of semantic representations of relational statements, in which a reference object is established first, and then the second object is attached in relation to it. This theory explains the various directionality effects as a general preference to process information about the reference object before information about the target object.

Adolescent↗
PubMed2001

The authority of complexity.

The assertion about the unique 'complexity' or the peculiarly intricate character of social phenomena has, at least within sociology, a long, venerable and virtually uncontested tradition. At the turn of the last century, classical social theorists, for example, Georg Simmel and Emile Durkheim, made prominent and repeated reference to this attribute of the subject matter of sociology and the degree to which it complicates, even inhibits the develop and application of social scientific knowledge. Our paper explores the origins, the basis and the consequences of this assertion and asks in particular whether the classic complexity assertion still deserves to be invoked in analyses that ask about the production and the utilization of social scientific knowledge in modern society. We present John Maynard Keynes' economic theory and its practical applications as an illustration. We conclude that the practical value of social scientific knowledge is not dependent on a faithful, in the sense of complete, representation of social reality. Instead, social scientific knowledge that wants to optimize its practicality has to attend and attach itself to elements of social situations that can be altered or are actionable.

Economics↗
PubMed2002

Contributions of the motor cortex to the control of the hindlimbs during locomotion in the cat.

Although the corticospinal tract is not essential for the production of the basic locomotor rhythm in cats, it does contribute to the regulation of locomotion, particularly in situations in which there is a requirement for precise control over paw placement or limb trajectory. Lesions of the dorsolateral funiculi at the low thoracic level (T(13)) that completely interrupted both the cortico- and rubrospinal pathways produced long-term deficits in locomotion on a level surface. These deficits included a paw-drag that was probably caused both by a loss of cortico- and rubrospinal input to motoneurones controlling distal muscles as well as by a change in the relative timing of muscles acting around the hip and knee. Smaller lesions produced similar deficits from which the cats recovered relatively quickly. Cats with the largest lesions of the dorsolateral funiculi were unable to modify their gait sufficiently to step over obstacles attached to the treadmill belt even 3-5 months postlesion. These results imply that the medial pathways, the reticulo- and vestibulospinal pathways, are unable to fully compensate for damage to the lateral pathways. Single unit recordings from identified pyramidal tract neurones (PTNs) within the hindlimb representation of the primary motor cortex (area 4) showed that a substantial proportion of neurones (67%) significantly increased their discharge frequency when the cats modified their gait to step over obstacles attached to the treadmill belt. Of those PTNs that showed increased activity during the swing phase, populations of neurones were activated at different times. A large proportion of PTNS discharged early in swing, in phase with knee flexors such as the semitendinosus. Others discharged slightly later, in phase with the activity of ankle flexors, such as tibialis anterior, while still others discharged at the end of swing, in phase with digit dorsiflexors, such as the extensor digitorum brevis. We suggest that different populations of cortical neurones may specifically modify the activity of selected groups of close synergistic muscles during different parts of the swing phase. We further suggest that these modifications are mediated, in part, by groups of interneurones that are involved in determining the base locomotor rhythm. This provides a means by which the changes specified by the descending signal from the motor cortex may be smoothly, and appropriately, incorporated into the locomotor cycle.

Animals↗
PubMed2005

Links among attachment-related cognitions and adolescent depressive symptoms.

We assessed the role of self-evaluative and support-seeking processes as mediators of the relation between maternal representations and depressive symptoms in a sample of 168 young adolescents. Representations of mother as unavailable, unresponsive, and unsupportive were associated with depressive symptoms measured by semistructured interview and self-report. Moderation tests revealed that the association between maternal representations and depressive symptoms varied as a function of stress level for self-reported symptoms only. Subsequent mediation analyses for higher and lower stress groups showed that support seeking functioned as a mediator in the higher, but not lower, stress group. When depressive symptoms were assessed via interview, results with the full sample indicated that self-worth contingencies mediated the association between maternal representations and symptoms. Findings are discussed in terms of the identification of proximal targets for intervention.

Adolescent↗
PubMedDate not supplied

The stability of attachment security from infancy to adolescence and early adulthood: general discussion.

For over three decades, critics of the developmental and psychometric paradigms have argued that individual differences are neither stable, coherent, nor clinically significant. The present studies extend a long line of research demonstrating the coherence of individual development in attachment security. They make it clear that attachment security can be stable from infancy through early adulthood and that change in attachment security is meaningfully related to changes in the family environment. The task now is to better understand the roles of cross-age consistency in caregiver behavior and the structure of mental representations of early experience in stability and change.

Adolescent↗
PubMed1989

Histological changes of the liver in experimental graft-versus-host disease across minor histocompatibility barriers. IV. A study of lymphocyte-endothelial interaction.

It has been reported in human hepatic graft-versus-host disease (GVHD) that an attachment of lymphocytes to vascular wall, the feature called "endothelialitis", is the most important predictive histologic sign of GVHD. However, its precise nature and significance in GVHD are still unknown. We developed experimental mouse GVHD across minor histocompatibility barriers and examined the lesion during a 14-month period after transplantation. The lesion was transiently found, appearing first at 4 days after transplantation, reaching a maximal level at 2 weeks and disappearing 5 weeks after transplantation. Electron microscopically, an intimate interaction between lymphocyte and endothelial cell was demonstrated. Lymphocytes showed irregular cytoplasmic processes and pseudopods and were in close contact with endothelial cells. Lymphocytes frequently penetrated in between and under the endothelial cells, and migrated into the perivascular spaces. Immunohistochemical analysis revealed that the vast majority of lymphocytes attached to the endothelial cells are helper/inducer T cells, indicating the cardinal role of helper/inducer T cell in lymphocyte-endothelial cell interactions. These results, together with previous evidence of the presence of Ia antigens and an antigen-presenting ability of vascular endothelial cells, suggest that the attachment of lymphocytes to the vascular endothelial cells in the early course of GVHD may represent an in situ morphologic representation of antigen presentation by endothelial cells to helper T cells.

Animals↗
PubMed1995

Social and emotional self-regulation.

In humans, frontal lesions result in deficits of social and emotional behavior that are often surprising in the presence of intact language and other cognitive skills. The connections between the motivation and memory functions of limbic cortex and the motor planning functions of frontal neocortex must be fundamental to meeting the daily challenges of self-regulation. The connectional architecture of limbic and neocortical networks suggests a model of function. The densely interconnected paralimbic cortices may serve to maintain a global motivational context within which specific actions are articulated and sequenced within frontal neocortical networks. The paralimbic networks represent the visceral and kinesthetic information that is integral to the representation of the bodily self. In a general sense, the implicit self-representation within paralimbic networks may shape the significance of perceptions and the motivational context for developing actions. The network architecture of the frontal lobe reflects the dual limbic origins of frontal cortex, in the dorsal archicortical and ventral paleocortical structures. In this paper, we speculated that these two limbic-cortical pathways apply different motivational biases to direct the frontal lobe representation of working memory. The dorsal limbic mechanisms projecting through the cingulate gyrus may be influenced by hedonic evaluations, social attachments, and they may initiate a mode of motor control that is holistic and impulsive. In contrast, the ventral limbic pathway from the amygdala to orbital frontal cortex may implement a tight, restricted mode of motor control that reflects adaptive constraints of self-preservation. In the human brain, hemispheric specialization appears to have led to asymmetric elaborations of the dorsal and ventral pathways. Understanding the inherent asymmetries of corticolimbic architecture may be important in interpreting the increasing evidence that the left and right frontal lobes contribute differently to normal and pathological forms of self-regulation.

Brain Diseases↗
PubMed1989

Social attachments in autistic children.

Social responses of young autistic children to separation from and reunion with their caregivers did not differ from the social responses to similar situations of young mentally retarded nonautistic children. Most autistic children directed more social behaviors to their caregivers than to strangers and increased their preferential behavior after separation. Individual differences in social responses were not associated with the level of representational skills shown by the autistic children.

Anxiety, Separation↗
PubMed1987

Adult psychosocial assets and depressive mood over time. Effects of internalized childhood attachments.

This paper discusses contrasting assumptions in psychiatric epidemiological research regarding the relative significance of childhood and adult social experiences as etiological factors in adult psychopathology. It delineates a set of hypotheses that relate internal parental representations to subsequent depressed mood and to psychosocial assets assumed to mediate the relationships between parental representations and mood states. These hypotheses were prospectively tested using a cohort of medical students surveyed at medical school entrance and 7 months later. The data show that earlier paternal affectivity perceived at time 1 is inversely predictive of time 2 depressed mood, holding time 1 mood constant, whereas earlier maternal and paternal overprotection perceived at time 1 are directly predictive of time 2 depressed mood, holding time 1 mood constant. In addition, parental representations at time 1 are significantly linked to particular personality characteristics at time 1 and 2. However, it is not clear whether these personality characteristics are antecedents or consequences of depressed mood. The paper concludes with a discussion of theoretical and methodological issues involved in the retrospective assessment of remote social experiences as etiological factors in adult psychopathology.

Child Development↗
PubMed2001

The human genome and the representational world: the role of early mother-infant interaction in creating an interpersonal interpretive mechanism.

The author discusses the interrelationship of genetic predisposition, experiences in the first 3 years of life, and psychological disturbance in later development. The current emphasis on genetic determinism has led to the popular misconception that early relationships with caregivers play a relatively minor role in the development of mental disorder. The author argues that early attachment relationships matter because the mental mechanism moderating the expression of individual genotypes is intrinsically linked to the relationship with the primary caregiver. Attachment in infancy has the primary evolutionary function of generating a mind capable of inferring things about other people's minds, their thoughts, ideas, motivations, and intentions. The child needs to be able to make these inferences to arrive at a representation of the self in terms of a set of stable and generalized intentional attributes. Awareness of others' thoughts and feelings is necessary to ensure social collaboration. This formulation underscores the vital importance of parent training for the normal emotional and cognitive development of a child and the prevention of major psychological disturbance.

Adolescent↗