It controls our muscle movements, the secretions of our glands, and even our breathing and internal temperature.The brain is a organ. Our brain gives us awareness of ourselves and of our environment, processing a constant stream of sensory data. The brain is one of the most complex and magnificent organs in the human body.
The brain is an important organ that controls thought, memory, emotion, touch. 1Department of Chemistry, Materials and Chemical Engineering “Giulio Natta”, Politecnico di Milano, Milan, ItalyThe central nervous system (CNS) consists of the brain and spinal cord. There are three major divisions of. The brain and spinal cord are the two main structures of the central nervous system. This amazing organ acts as a control center by receiving, interpreting, and directing sensory information throughout the body. The anatomy of the brain is complex due its intricate structure and function.
Thanks to three-dimensional (3D) cultures and microfluidics, engineered in vitro models could improve the scientific knowledge in this field, also from a therapeutic perspective. The most noticeable hypothesis for a pathological action of gut microbiota on the brain is based on microbial release of soluble neurotransmitters, hormones, immune molecules and neuroactive metabolites, but this complex scenario requires reliable and controllable tools for its causal demonstration. 3Department of Neuroscience, Istituto di Ricerche Farmacologiche Mario Negri IRCCS, Milan, ItalyWe are accumulating evidence that intestinal microflora, collectively named gut microbiota, can alter brain pathophysiology, but researchers have just begun to discover the mechanisms of this bidirectional connection (often referred to as microbiota-gut-brain axis, MGBA).
During behavioral tests, they have observed alterations in germ-free (GF) and specific pathogen-free (SPF) mice treated with antibiotics ( Al-Asmakh and Zadjali, 2015 Möhle et al., 2016). Have studied the influence of gut dysbiosis on hippocampal neurogenesis. For instance, alterations in resident gut microbiota ( dysbiosis) activate the immune system (including T-cells) and increase the levels of inflammatory mediators, the permeability of the gut barrier ( Groschwitz and Hogan, 2009 Rea et al., 2016) and mucus production, which in turn promote neuroinflammation, neural injury and neurodegeneration ( Kowalski and Mulak, 2019).Möhle et al. Its composition may change during life ( Thursby and Juge, 2017) and its maintenance during development and maturation is important to prevent inflammation and disorders. It also influences microglial activation and development ( Erny et al., 2015 Fung et al., 2017), astrocyte functions ( Fung et al., 2017), the integrity of the blood-brain barrier (BBB) ( Braniste et al., 2014 Michel and Prat, 2016), the production of neurotransmitters ( Luczynski et al., 2016), and neuroimmune activation ( Sampson et al., 2016 Dinan and Cryan, 2017).The determination and formation of the gut microbiota involves several factors, like stress, diet, smoking, surgery and environment ( Biedermann et al., 2013 Tyakht et al., 2013 Jiang et al., 2015 Rodríguez et al., 2015).
In fact, the bidirectional microbiota-gut-brain communication (the so-called microbiota-gut-brain axis, MGBA) is not limited to digestive functions and satiety, but the gut microbiota also influences behavior and cognitive abilities ( Di Meo et al., 2018 Cryan et al., 2019).AD leads to a progressive and irreversible decline in memory and a deterioration of cognitive abilities. With respect to controls with gut microbiota, other groups have found alterations in BBB functions and cortical myelination ( Hoban et al., 2013 Braniste et al., 2014), defects in gut motility, progressive deficits in fine and gross motor skills, reduced microglial activation, the presence of α-syn inclusions and motor deficits ( Sampson et al., 2016).There is increasing evidence that dysbiosis is involved in several pathological states, including epilepsy ( Iannone et al., 2019), inflammatory bowel disease ( Tung et al., 2011 Moser et al., 2018), anxiety and depression ( Jia et al., 2008 Wang and Kasper, 2014 Foster et al., 2017), autism spectrum disorders ( Mayer et al., 2014 Li and Zhou, 2016 Yarandi et al., 2016), schizophrenia ( Nemani et al., 2015), and neurodegenerative disorders ( Sarkar and Banerjee, 2019), such as Alzheimer's disease (AD) ( Vogt et al., 2017 Van Giau et al., 2018), Parkinson's disease (PD) ( Foster and McVey Neufeld, 2013 Nemani et al., 2015 Sampson et al., 2016 Harach et al., 2017) and multiple sclerosis (MS) ( Cekanaviciute et al., 2017 Mowry and Glenn, 2018). Oppositely, SPF mice are free of a defined list of mouse pathogens, depending on the husbandry methods ( Hirayama et al., 1990).
They are double-transgenic mice expressing the KM670/671NL Swedish mutation of human amyloid precursor protein and the L166P mutation of human presenilin 1 under the control of thymocyte differentiation antigen 1 (Thy-1) promoter and they show an age-dependent accumulation of parenchymal Aβ plaques, with minimal vascular Aβ. For instance, APP/PS1 mice are a mouse model of early-onset AD. Kowalski and Mulak reviewed the results in both animal models and clinical trials, supporting the evidence of a correlation between dysbiosis and AD ( Kowalski and Mulak, 2019). Its hallmarks are intracellular neurofibrillary tangles ( Arriagada et al., 1992 Reitz et al., 2011) and extracellular senile plaques mainly composed of β-amyloid (Aβ) ( Scheuner et al., 1996 Shankar et al., 2008).
Recent studies have highlighted the possibility that some bacterial taxa are significantly associated with MS. Some studies have hypothesized that α-syn is involved in GI dysfunctions and damage to enteric neurons by showing its accumulation in the enteric nervous system ( Braak et al., 2006 Forsyth et al., 2011 Gold et al., 2013 Gelpi et al., 2014), whose neurons are specifically associated with the GI tract to control several activities, such as mucosal transport, secretion and modulation of immune and endocrine functions ( Gold et al., 2013 Sánchez-Ferro et al., 2015).MS is an inflammatory, autoimmune disease characterized by damage to the myelin sheaths, axonal degeneration, atrophy of nerve fibers and progressive neuronal loss. This accumulation also leads to an increase in intestinal permeability and to the possible translocation of bacterial or microbial inflammatory compounds into the bloodstream ( Forsyth et al., 2011 Perez-Pardo et al., 2017). Its pathological hallmark is the deposition of α-synuclein (α-syn) in susceptible neurons in the form of Lewy bodies and Lewy neurites ( Dauer and Przedborski, 2003).
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