A mechanochemical model of striae distensae

Striae distensae, otherwise known as stretch marks, are common skin lesions found in a variety of clinical settings. They occur frequently during adolescence or pregnancy where there is rapid tissue expansion and in clinical situations associated with corticosteroid excess. Heralding their onset is the appearance of parallel inflammatory streaks aligned perpendicular to the direction of skin tension. Despite a considerable amount of investigative research, the pathogenesis of striae remains obscure. The interpretation of histologic samples – the major investigative tool – demonstrates an association between dermal lymphocytic inflammation, elastolysis, and a scarring response. Yet the primary causal factor in their aetiology is mechanical; either skin stretching due to underlying tissue expansion or, less frequently, a compromised dermis affected by normal loads. In this paper, we investigate the pathogenesis of striae by addressing the coupling between mechanical forces and dermal pathology. We develop a mathematical model that incorporates the mechanical properties of cutaneous fibroblasts and dermal extracellular matrix. By using linear stability analysis and numerical simulations of our governing nonlinear equations, we show that this quantitative approach may provide a realistic framework that may account for the initiating events

Electrophysiological and morphological heterogeneity of neurons in slices of rat suprachiasmatic nucleus

Whole cell patch clamp recordings of neurons in slices of the suprachiasmatic nucleus (SCN) were made in order to assess their electrophysiological and morphological heterogeneity. This assessment was accomplished by (i) quantification of intrinsic membrane properties recorded in current clamp mode, (ii) studying frequency distributions of these properties, (iii) grouping of cells based on visual inspection of data records, and (iv) use of cluster analysis methods.Marked heterogeneity was found in the resting membrane potential, input resistance, time constant, rate of frequency adaptation, size of rebound depolarization (low-threshold Ca2+ potential) and regularity of firing. The frequency distribution of these membrane properties deviated significantly from a normal distribution. Other parameters, including spike amplitude and width, amplitude and rising slope of the spike after-hyperpolarization (AHP) and amplitude of the spike train AHP, showed considerable variability as well but generally obeyed a normal distribution.Visual inspection of the data led to partitioning of cells into three clusters, viz. cluster I characterized by monophasic spike AHPs and irregular firing in the frequency range from 1.5 to 5.0 Hz; cluster II with biphasic spike AHPs and regular firing in the same range; and cluster III with large rebound depolarizations and biphasic spike AHPs. In a post hoc analysis, these clusters also appeared to differ in other membrane properties. This grouping was confirmed by hierarchical tree clustering and multidimensional scaling.The light microscopic properties of recorded neurons were studied by biocytin labelling. Neurons had monopolar, bipolar or multipolar branching patterns and were often varicose. Axons sometimes originated from distal dendritic segments and usually branched into multiple collaterals. Many cells with extra-SCN projections also possessed intranuclear axon collaterals. We found no morphological differences between clusters except that cluster III neurons possessed more axon collaterals than cluster I or II cells.These results suggest that SCN neurons are heterogeneous in some basic as well as active membrane properties and can be partitioned into at least three clusters. Cluster I and II cells fire spontaneously in a regular and irregular mode, respectively, and sustain prolonged spike trains. In contrast, cluster III cells have low firing rates but may adopt a burst-like firing mode when receiving appropriate input. While all clusters transmit output to target cells within and outside SCN, cluster III cells in particular are suggested to affect excitability of large numbers of SCN neurons by their extensive local network of axon collaterals

An investigation of striae distensae using reflectance confocal microscopy

  Striae distensae, otherwise known as stretch marks, are white or red scar-like streaks on the skin. Although they are not associated with adverse health outcomes, striae are associated with significant cosmetic morbidity. While they have been well characterised histopathologically, a non-invasive method of microscopic lesion assessment of striae would be welcome.  To gain insight into the small-scale morphological features associated with striae we undertook an in vivo investigation of nine patients with striae alba and one with striae rubra utilising reflectance confocal microscopy (RCM).  Here we demonstrate that features known to be present using light microscopy, such as parallel collagen bundles in the dermis, and some features that are not well recognised by light microscopy, including distortion of dermal papillae, are demonstrable using RCM.  Characterising the features of early and established striae distensae with confocal microscopy is an important foundation for future work. The potential ability to reliably identify the earliest pathological changes in skin in early lesions or before clinically manifest striae develop--a task facilitated by our findings--will increase the understanding of their pathogenesis and will have significant practical utility in monitoring the impact of future preventative interventions