Low levels of survival motor neuron (SMN) protein result in spinal muscular atrophy (SMA), a severe genetic disease characterized by motor impairment and premature lethality. Although SMN is a ubiquitous protein, motor neurons are much more vulnerable to low levels of SMN than other cells. To gain insight into the pathogenesis of SMA, we have compared synaptic function of motor terminals in wild-type and severe SMA mice at different ages and in two proximal muscles. Our results show that mutant muscle fibers fire normal action potentials and that multi-innervated terminals are functional. By studying the characteristics of the three main components of synaptic transmission in nerve terminals (spontaneous, evoked, and asynchronous release), we found that the kinetics of the postsynaptic potentials are slowed and evoked neurotransmitter release is decreased by ϳ55%. In addition, asynchronous release is increased ϳ300%, indicating an anomalous augmentation of intraterminal bulk Ca 2ϩ during repetitive stimulation. Together, these results show that the reduction of SMN affects synaptic maturation, evoked release, and regulation of intraterminal Ca 2ϩ levels.
Synchronous neurotransmitter release is a highly regulated process that takes place at specializations at the presynaptic membrane called active zones (AZs). The relationships between AZs, quantal release, and vesicle replenishment are not well understood in a mature synapse. We have measured the number, distribution, and other properties of AZs in mouse motor nerve terminals and combined these observations with electrophysiological estimates of the size of the readily releasable pool (RRP) of synaptic vesicles. On average, we counted 850 AZs per terminal. Assuming two primary docked vesicles per AZ, we predict a total of ϳ1700 vesicles optimally positioned for exocytosis. Electrophysiological estimates of the size of the RRP, using a simple kinetic model that assumes exponential depletion of the initial pool and refilling by recruitment, gave an average value of 1730 quanta during 100 Hz stimulation, in satisfying agreement with the morphology. At lower stimulus frequencies, however, the model revealed that the estimated RRP size is smaller, suggesting that not all AZs participate in release at low stimulation frequencies.
Low levels of the Survival Motor Neuron (SMN) protein produce Spinal Muscular Atrophy (SMA), a severe monogenetic disease in infants characterized by muscle weakness and impaired synaptic transmission. We report here severe structural and functional alterations in the organization of the organelles and the cytoskeleton of motor nerve terminals in a mouse model of SMA. The decrease in SMN levels resulted in the clustering of synaptic vesicles (SVs) and Active Zones (AZs), reduction in the size of the readily releasable pool (RRP), and the recycling pool (RP) of synaptic vesicles, a decrease in active mitochondria and limiting of neurofilament and microtubule maturation. We propose that SMN is essential for the normal postnatal maturation of motor nerve terminals and that SMN deficiency disrupts the presynaptic organization leading to neurodegeneration.
Non-alcoholic fatty liver disease (NAFLD) is considered the most common liver disorder, affecting around 25% of the population worldwide. It is a complex disease spectrum, closely linked with other conditions such as obesity, insulin resistance, type 2 diabetes mellitus, and metabolic syndrome, which may increase liver-related mortality. In light of this, numerous efforts have been carried out in recent years in order to clarify its pathogenesis and create new prevention strategies. Currently, the essential role of environmental pollutants in NAFLD development is recognized. Particularly, endocrine-disrupting chemicals (EDCs) have a notable influence. EDCs can be classified as natural (phytoestrogens, genistein, and coumestrol) or synthetic, and the latter ones can be further subdivided into industrial (dioxins, polychlorinated biphenyls, and alkylphenols), agricultural (pesticides, insecticides, herbicides, and fungicides), residential (phthalates, polybrominated biphenyls, and bisphenol A), and pharmaceutical (parabens). Several experimental models have proposed a mechanism involving this group of substances with the disruption of hepatic metabolism, which promotes NAFLD. These include an imbalance between lipid influx/efflux in the liver, mitochondrial dysfunction, liver inflammation, and epigenetic reprogramming. It can be concluded that exposure to EDCs might play a crucial role in NAFLD initiation and evolution. However, further investigations supporting these effects in humans are required.
The metabolic syndrome (MS) is a conglomerate of interrelated risk factors-including obesity, atherogenic dyslipidemia, arterial hypertension, and insulin resistance-which exponentially increase the risk of developing cardiovascular disease and type 2 diabetes mellitus. The purpose of this study was to determine the prevalence of MS according to the criteria published by the International Diabetes Federation, in individuals of both sexes over 18 years of age. This is a cross-sectional study based on MS prevalence in a representative sample from the Maracaibo district, Zulia State. The population of Maracaibo, according to the last census in 2001, was 1,219,927 habitants, with a 2007 population estimation of 1,428,043 habitants according to the National Institute of Statistics (NIS). Likewise, NIS projects that for the year 2009, 59.7% of the population of Venezuela will have individuals over 18 years of age. Using these data, the sample for Maracaibo District corresponds to 1986 individuals with or above 18 years of age. The data recollection was conducted by health professionals and medicine students, previously trained. The participants were subject to inquiry previous written consent and a medical examination, and qualitative variables such as smoking habit, socioeconomic status, physical activity, race, alcoholism, and nutritional habits, and quantitative ones like blood pressure, anthropometry, and blood works were determined. There is clear evidence that there is a lack of research and validated values to use as reference in our country and maybe in Latin America. Taking into account all that has been exposed here, this study will serve as a pilot for the numerous statistical determinations that will soon come afterward, providing first-hand accurate evidence on the behavior of the MS in the Latin American populace.
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