Individual neuronal subtypes control initial myelin sheath growth and stabilization

Background In the developing central nervous system, pre-myelinating oligodendrocytes sample candidate nerve axons by extending and retracting process extensions. Some contacts stabilize, leading to the initiation of axon wrapping, nascent myelin sheath formation, concentric wrapping and sheath elongation, and sheath stabilization or pruning by oligodendrocytes. Although axonal signals influence the overall process of myelination, the precise oligodendrocyte behaviors that require signaling from axons are not completely understood. In this study, we investigated whether oligodendrocyte behaviors during the early events of myelination are mediated by an oligodendrocyte-intrinsic myelination program or are over-ridden by axonal factors. Methods To address this, we utilized in vivo time-lapse imaging in embryonic and larval zebrafish spinal cord during the initial hours and days of axon wrapping and myelination. Transgenic reporter lines marked individual axon subtypes or oligodendrocyte membranes. Results In the larval zebrafish spinal cord, individual axon subtypes supported distinct nascent sheath growth rates and stabilization frequencies. Oligodendrocytes ensheathed individual axon subtypes at different rates during a two-day period after initial axon wrapping. When descending reticulospinal axons were ablated, local spinal axons supported a constant ensheathment rate despite the increased ratio of oligodendrocytes to target axons. Conclusion We conclude that properties of individual axon subtypes instruct oligodendrocyte behaviors during initial stages of myelination by differentially controlling nascent sheath growth and stabilization.

Individual neuronal subtypes control initial myelin sheath growth and stabilization

BackgroundIn the developing central nervous system, pre-myelinating oligodendrocytes sample candidate nerve axons by extending and retracting process extensions. Some contacts stabilize, leading to the initiation of axon wrapping, nascent myelin sheath formation, concentric wrapping and sheath elongation, and sheath stabilization or pruning by oligodendrocytes. Although axonal signals influence the overall process of myelination, the precise oligodendrocyte behaviors that require signaling from axons are not completely understood. In this study, we investigated whether oligodendrocyte behaviors during the early events of myelination are mediated by an oligodendrocyte-intrinsic myelination program or are over-ridden by axonal factors.MethodsTo address this, we utilized in vivo time-lapse imaging in embryonic and larval zebrafish spinal cord during the initial hours and days of axon wrapping and myelination. Transgenic reporter lines marked individual axon subtypes or oligodendrocyte membranes.ResultsIn the larval zebrafish spinal cord, individual axon subtypes supported distinct nascent sheath growth rates and stabilization frequencies. Oligodendrocytes ensheathed individual axon subtypes at different rates during a two-day period after initial axon wrapping. When descending reticulospinal axons were ablated, local spinal axons supported a constant ensheathment rate despite the increased ratio of oligodendrocytes to target axons.ConclusionWe conclude that properties of individual axon subtypes instruct oligodendrocyte behaviors during initial stages of myelination by differentially controlling nascent sheath growth and stabilization.

Flourishing and its Associations with Affective Reactivity and Recovery to Daily Stress

There are marked individual differences in the impact of daily stress on health. We use trait measures of well-being, here quantified as flourishing, and daily reports of stress and negative mood to test (i) the moderating effects of flourishing on affective reactivity and recovery in response to increases in daily stress. To examine whether high curiosity acts as a resource to diminish stress effects, we additionally test (ii) the association between flourishing and curiosity and (iii) the associations between day’s curiosity and both affective reactivity and recovery. We then test for (iv) prospective associations between affective reactivity and recovery and change in flourishing over 3 months. People high in flourishing show lower affective reactivity and augmented recovery. Participants high in flourishing exhibit more frequent days of high curiosity and high curiosity buffers the effects of stress on day’s mood. Finally, greater affective reactivity is associated with longitudinal decreases in flourishing.

Tracking snacking in real time: Time to look at individualised patterns of behaviour

Background: Identifying when and where people overeat is important for intervention design, yet little is known about how unhealthy behaviours unfold in real life. Aim: To track the activities, social contexts and locations that co-occur with unhealthy snacking. Methods: Sixty-four adults (49F, mean age = 38.6 years) used electronic diaries to record snacking, location, social context and current activity every waking hour over 7 days. The proportion of snacking episodes that co-occurred with each location/activity/context was calculated by group and individual. Results: Over the group, snacking was most frequent whilst socialising (19.9% of hours spent socialising) or using the TV/computer (19.7%), when with friends (16.7%) and when at home (15.3%). All intra-class correlation statistics for cued behaviour were low, indicating the importance of within-person variability. There were marked individual differences between people in what constituted a ‘typical’ context for snacking. Conclusions: People show substantial differences in the contexts in which they snack. Tailoring interventions to these individual patterns of behaviour may improve intervention efficacy.

Morphological variation of the Long-tailed Reed Finch Donacospiza albifrons (Vieillot, 1817) (Aves: Thraupidae)

The Long-tailed Reed Finch Donacospiza albifrons of south-central South America is patchily distributed in a variety of open habitats, usually near water. I present a detailed study of morphological variation based on 141 specimens, describing its plumage sequence and presenting notes on its molt and breeding. The Long-tailed Reed Finch shows no sexual dichromatism, but males average longer-winged than females. The species shows three distinct age-related plumages, which are redescribed here. It also shows marked individual variation in plumage and size, also showing marked plumage variation due to feather wear. Geographic variation is also marked, with birds from dry grasslands in northern highlands typically being larger, paler, and less streaked than birds from wet grasslands in southern lowlands, but there at some exceptions to this geographic pattern. I conclude that there is no solid basis for splitting the species into two or more taxa, and suggest considering the Long-tailed Reed Finch as a single, highly polymorphic species.

The Eisenmenger malformation: a morphologic study

We studied 11 autopsied cases of the Eisenmenger malformation, comparing the findings with 11 hearts with intact ventricular septal structures, and nine hearts having perimembranous ventricular septal defects in the absence of aortic overriding. We found variable lengths for the subpulmonary infundibulum in the hearts with Eisenmenger defects. It was well developed in three hearts, of intermediate length in seven, and very short in one of the specimens. The muscular outlet septum was also of variable length compared with the free-standing subpulmonary infundibular sleeve. Except for one, all hearts had fibrous continuity between the aortic and tricuspid valvar leaflets, such that the ventricular septal defect was then perimembranous. In the remaining case, there was a completely subaortic muscular infundibulum, with the ventricular septal defect showing only muscular borders. The medial papillary muscle was absent in the majority of cases, but was well formed in three hearts, all with relatively short muscular outlet septums. We identified mild, intermediate, and severe degrees of rightward rotation of the aortic valve, and these findings correlated with the extent of aortic valvar overriding. In nine of the 11 hearts, the ventriculo-arterial connections were concordant, but there was double-outlet from the right ventricle in the other two specimens. Based on our anatomic and morphometric observations, we conclude that the hearts we have defined as having Eisenmenger defects show marked individual variation in their specific phenotypic anatomy.

Individual variation in competitive performance of juvenile cod and its consequences for growth

This communication reports on experiments, which studied the variation in competitive performance of juvenile cod (Gadus morhua L.) and their growth rates. The fish were held in groups of five in either summer or winter conditions and tested for their individual response to prey offered sequentially. There was marked individual variability. Fish that took the highest share of prey tended also to be those that took prey earlier than others. In winter conditions these fish were the largest, but in summer conditions size had no effect. There was a positive influence of the indices of competitive performance on individual growth rate but the relationship was not significant