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Posterior Zone (posterior + zone)
Selected AbstractsMorphology and ultrastructure of the swimming larvae of Crambe crambe (Demospongiae, Poecilosclerida)INVERTEBRATE BIOLOGY, Issue 4 2001Marķa J. Uriz Abstract. We describe the morphology and ultrastructure of the free-swimming larvae of the sponge Crambe crambe, one of the most abundant encrusting sponges on shallow rocky bottoms of the western Mediterranean. Larvae of C. crambe are released in July and August. The larva is uniformly flagellated except at the posterior zone. Flagellated cells are extraordinarily slender, elongate, and sinuous and form a pseudo-stratified layer. Their distal zone contains abundant mitochondria, some small vesicles, a Golgi complex, and the basal apparatus of the flagellum. Abundant lipid droplets are present throughout the cell. The nucleus is most often in a basal position. The flagellum projects from the bottom of an asymmetrical socket formed by cytoplasmic expansions. The basal body extends in a conical tuft and a laminar rootlet in close association with the Golgi system. The cells at the posterior pole are flat and polygonal on the surface, with long overlapping pseudopodia in the typical shape of a pinacoderm. Sparse collagen is present throughout the whole larva including the flagellated layer. Archeocytes and sclerocytes are abundant in the posterior region. Typical collencytes and spherulous cells seem to be absent. Intracellular and extracellular rod-like bacteria with conspicuous fimbria occur exclusively in the posterior region of the larva. The asymmetrical cytoplasmic prolongations, which surround the flagellum, and the basal apparatus of the flagellum are suggested as the sites of stimulus reception and triggering of locomotor responses, respectively. This ultrastructural study of the larva of C. crambe has shown features directly linked to its behavior and ecology. [source] Acrosomal exocytosis of mouse sperm progresses in a consistent direction in response to zona pellucidaJOURNAL OF CELLULAR PHYSIOLOGY, Issue 3 2009Mariano G. Buffone Sperm acrosomal exocytosis is essential for successful fertilization, and the zona pellucida (ZP) has been classically considered as the primary initiator in vivo. At present, following what is referred to as primary binding of the sperm to the ZP, the acrosome reaction paradigm posits that the outer acrosomal membrane and plasma membrane fuse at random points, releasing the contents of the acrosome. It is then assumed that the inner acrosomal membrane mediates secondary binding of the sperm to the ZP. In the present work we used a live fluorescence imaging system and mouse sperm containing enhanced green fluorescent protein (EGFP) in their acrosomes. We compared the processes of acrosomal exocytosis stimulated by the calcium ionophore ionomycin or by solubilized ZP. As monitored by the loss of EGFP from the sperm, acrosomal exocytosis driven by these two agents occurred differently. When ionomycin was used, exocytosis started randomly (no preference for the anterior, middle or posterior acrosomal regions). In contrast, following treatment with solubilized ZP, the loss of acrosomal components always started at the posterior zone of the acrosome and progressed in an anterograde direction. The exocytosis was slower when stimulated with ZP and on the order of 10 sec, which is in accordance with other reports. These results demonstrate that ZP stimulates acrosomal exocytosis in an orderly manner and suggest that a receptor-mediated event controls this process of membrane fusion and release of acrosomal components. These findings are incorporated into a model. J. Cell. Physiol. 220: 611,620, 2009. © 2009 Wiley-Liss, Inc. [source] Neurogranin expression identifies a novel array of Purkinje cell parasagittal stripes during mouse cerebellar developmentTHE JOURNAL OF COMPARATIVE NEUROLOGY, Issue 2 2006Matt Larouche Abstract Markers that reveal the parasagittal organization of cerebellar Purkinje cells may be grouped into two classes based on the time during development when they are expressed. In mice, early-onset markers are defined by their heterogeneous expression in clusters of Purkinje cells during late embryogenesis, which disappears shortly following birth. Late-onset markers are generally not expressed until about 1 week after birth and do not reach a stable striped expression pattern until about 3 weeks postnatally. Currently, no endogenous markers are known that are heterogeneously expressed in the temporal gap between these two classes. Here we present immunocytochemical evidence that parasagittal stripes of Purkinje cells express a member of the calpacitin protein family, neurogranin, possibly from as early as embryonic day (E) 13 and definitively from E15, in a pattern that persists up to postnatal day (P) 20. Neurogranin is thus the first endogenous marker of a Purkinje cell subset capable of bridging the temporal gap between the early- and late-onset patterns. In the early neonate, up to five pairs of neurogranin-immunopositive Purkinje cell stripes run parasagittally through the cerebellum, with the exact number dependent on the rostrocaudal position. Expression is lost during postnatal development in a transverse zone-dependent fashion. Purkinje cells in the central and nodular zones lose neurogranin expression between approximately P4 and P6, whereas expression in the posterior zone persists until approximately P20. Neurogranin immunoreactivity will be a valuable tool in helping to clarify the relationships between early- and late-onset patterns. J. Comp. Neurol. 494:215,227, 2006. © 2005 Wiley-Liss, Inc. [source] Drug effect on EEG connectivity assessed by linear and nonlinear couplingsHUMAN BRAIN MAPPING, Issue 3 2010Joan F. Alonso Abstract Quantitative analysis of human electroencephalogram (EEG) is a valuable method for evaluating psychopharmacological agents. Although the effects of different drug classes on EEG spectra are already known, interactions between brain locations remain unclear. In this work, cross mutual information function and appropriate surrogate data were applied to assess linear and nonlinear couplings between EEG signals. The main goal was to evaluate the pharmacological effects of alprazolam on brain connectivity during wakefulness in healthy volunteers using a cross-over, placebo-controlled design. Eighty-five pairs of EEG leads were selected for the analysis, and connectivity was evaluated inside anterior, central, and posterior zones of the scalp. Connectivity between these zones and interhemispheric connectivity were also measured. Results showed that alprazolam induced significant changes in EEG connectivity in terms of information transfer in comparison with placebo. Trends were opposite depending on the statistical characteristics: decreases in linear connectivity and increases in nonlinear couplings. These effects were generally spread over the entire scalp. Linear changes were negatively correlated, and nonlinear changes were positively correlated with drug plasma concentrations; the latter showed higher correlation coefficients. The use of both linear and nonlinear approaches revealed the importance of assessing changes in EEG connectivity as this can provide interesting information about psychopharmacological effects. Hum Brain Mapp, 2010. © 2009 Wiley-Liss, Inc. 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