⌛ Sympathetic Nervous System Research Paper
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Sympathetic Nervous System Anatomy - Part 1
In parallel, in GF animals, also memory dysfunction has been reported [ 35 ] probably to be ascribed to an altered expression of brain-derived neurotrophic factor BDNF , one of the most important factors involved in memory. This molecule is a neurotrophic factor, mainly located in the hippocampus and cerebral cortex, which regulates different aspects of brain activities and cognitive functions as well as muscle repair, regeneration, and differentiation [ 36 ].
Finally, the presence of the microbiota results also to modulation of the serotoninergic system, since an increase in serotonin turnover and altered levels of related metabolites have been reported in the limbic system of GF animals [ 24 ]. These studies also confirm that microbiota affects anxiety and HPA system by influencing brain neurochemistry [ 37 ]. In comparison to mice with controlled diet, GABA B1b increased in cortical cingulate and prelimbic regions while concomitantly decreased in the hippocampus, amygdala, and locus coeruleus.
The probiotics, in parallel, reduced stress-induced release of cortisol, anxiety- and depression-related behavior [ 38 ]. Similarly, transient alteration of microbiota composition, obtained by administration of oral antimicrobials neomycin, bacitracin, and pimaricin in specific-pathogen-free mice, increased exploratory behavior and hippocampal expression of BDNF [ 39 ]. Furthermore, change in microbiota composition with the probiotics association VSL 3 leads to an increase in BDNF expression, attenuation of age-related alterations in the hippocampus [ 40 ], and reversion of neonatal maternal separation-induced visceral hypersensitivity in a rat model of IBS [ 41 ]. In this latter model of stress, a change in the expression of subsets of genes involved in pain transmission and inflammation has also been described, that was reset by the early life administration of probiotics.
Evidence indicates that microbiota communication with the brain involves the vagus nerve, which transmits information from the luminal environment to CNS. In fact, neurochemical and behavioral effects were not present in vagotomized mice, identifying the vagus as the major modulatory constitutive communication pathway between microbiota and the brain [ 38 ]. In a model of chronic colitis associated to anxiety-like behavior, the anxiolytic effect obtained with a treatment with Bifidobacterium longum , was absent in mice that were vagotomized before the induction of colitis [ 42 ].
Microbiota may interact with GBA through different mechanisms Table 1 , the principal one likely being modulation of the intestinal barrier, whose perturbation can influence all the underlying compartments. Probiotic species-specific central effects are indeed associated with restoration of tight-junction integrity and the protection of intestinal barrier, as recently reported in an animal model of water avoidance stress [ 43 ]. Pre-treatment of animals with probiotic combined formulation of Lactobacillus helveticus R and Bifidobacterium longum R restored tight junction barrier integrity and attenuated HPA axis and autonomic nervous system activities, assessed through plasma cortisol and catecholamine measurements.
Probiotics also prevented changes in hippocampal neurogenesis and expression in hypothalamic genes involved in synaptic plasticity. Microbiota can interact with GBA also through the modulation of afferent sensory nerves as reported for Lactobacillus reuteri that, enhancing their excitability by inhibiting calcium-dependent potassium channels opening, modulates gut motility and pain perception [ 44 ]. Furthermore, microbiota can influence ENS activity by producing molecules that can act as local neurotransmitters, such as GABA, serotonin, melatonin, histamine and acetylcholine [ 45 ] and by generating a biologically active form of catecholamines in the lumen of the gut [ 46 ].
Lactobacilli also utilize nitrate and nitrite to generate nitric oxide [ 47 ] and to produce hydrogen sulfide that modulates gut motility by interacting with the vanilloid receptor on capsaicin-sensitive nerve fibers [ 48 ]. The ENS represents also the target of bacterial metabolites. One of the main product of bacterial metabolism are short-chain fatty acid SCFAs , such as butyric acid, propionic acid and acetic acid, that are able to stimulate sympathetic nervous system [ 49 ], mucosal serotonin release [ 50 ] and to influence memory and learning process [ 51 , 52 ]. In this context, it is interesting to report that diet manipulation of microbiota may influence behavior. Given the ability of gut microbiota to alter nutrient availability and the close relationship between nutrient sensing and peptide secretion by enteroendocrine cells, the interaction of microbiota and GBA might also occur through the release of biologically active peptides from enteroendocrine cells that can affect the GBA [ 54 ].
For example, galanin stimulates the activity of the central branch of the HPA axis i. Galanin also is able to stimulate directly cortisol secretion from adrenocortical cells, and norepinephrine release from adrenal medulla [ 55 ]. Last but not least, microbiota affects mucosal immune activation. The enhanced mucosal inflammation induced in mice after treatment with oral antimicrobials, increases substance P expression in ENS, an effect normalized by the administration of Lactobacillus paracasei which also attenuates antibiotic-induced visceral hypersensitivity [ 57 ].
The effects of microbiota on immune activation might be in part mediated by proteases. These enzymes are upregulated in intestinal-immune mediated disorders and become the end-stage effectors of mucosal and enteric nervous damage [ 58 - 59 ]. Increased concentration of proteases have been detected in fecal samples of IBS patients associated to specific intestinal bacterial species [ 60 , 61 ]. The current working hypothesis in IBS is that an abnormal microbiota activates mucosal innate immune responses, which increase epithelial permeability, activate nociceptive sensory pathways inducing visceral pain, and dysregulates the enteric nervous system [ 62 , 63 ].
Similar mechanisms may be involved in the effects induced by the gastric mucosa-colonizing microorganism, Helicobacter pylori H. The effects induced by this microorganism may arise through both activation of neurogenic inflammatory processes and microelements deficiency secondary to functional and morphological changes in the digestive tract [ 64 ]. Nevertheless, unequivocal data concerning the direct and immediate effects of H. Different types of psychological stressors modulate the composition and total biomass of the enteric microbiota, independently from duration. In fact, also the use of short stressors impact the microbiota, being the exposure to social stressor for only 2 h significantly able to change the community profile and to reduce the relative proportions of the main microbiota phyla [ 66 ].
These effects may be mediated, through the parallel neuroendocrine output efferent systems i. The direct influence is mediated by the secretion, under the regulation of brain, of signaling molecules by neurons, immune cells and enterocromaffin cells, which might affect microbiota. Communication between CNS effectors and bacteria relies on the presence of neurotransmitter receptors on bacteria.
Several studies have reported that binding sites for enteric neurotransmitters produced by the host are present on bacteria and can influence the function of components of the microbiota, contributing to increase predisposition to inflammatory and infection stimuli [ 67 ]. High affinity for GABA system has been reported in Pseudomonas fluorescens with binding properties similar to those of a brain receptor [ 68 ]. Besides, brain has a prominent role in the modulation of gut functions, such as motility, secretion of acid, bicarbonates and mucus, intestinal fluid handling and mucosal immune response, all important for the maintenance of the mucus layer and biofilm where individual groups of bacteria grow in a multiplicity of different microhabitats and metabolic niches associated with the mucosa [ 70 ].
A dysregulation of GBA can then affect gut microbiota through the perturbation of the normal mucosal habitat. Stress induces variation in size and quality of mucus secretion [ 71 ]. Acoustic stress affects gastric and intestinal postprandial motility in dogs, delaying the recovery of the migrating motor complex pattern and inducing a transient slowing of gastric emptying [ 72 ]. Mental stress too increases the frequency of cecocolonic spike-burst activity through the central release of CRF [ 73 ]. Regional and global changes in gastrointestinal transit can have profound effects on the delivery of important nutrients, mainly prebiotics and dietary fibers, to the enteric microbiota. Brain might also affect microbiota composition and function by alteration of intestinal permeability, allowing bacterial antigens to penetrate the epithelium and stimulate an immune response in the mucosa.
Acute stress increased colonic paracellular permeability involving overproduction of interferon-g and decrease in mRNA expression of ZO-2 and occluding [ 74 ]. Brain, through the ANS, may also modulate immune function. The sympathetic branch modulates number, degranulation and activity of mast cells with consequent imbalance in tryptase and histamine release in stress-related muscle dysfunction [ 75 ].
Other mast cell products, such as CRF, in turn, can increase epithelial permeability to bacteria, which facilitates their access to immune cells in the lamina propria [ 1 ]. Also corticotropin releasing hormone receptors are involved in colonic barrier dysfunction in response to mild stress in neonatal maternal separation in adult rats that [ 76 ] leads to depression and enhanced vulnerability to colitis [ 77 ]. Bilateral olfactory bulbectomy induced depression-like behavior associated to elevated central CRF expression and serotonin levels, associated to alterations in colonic motility and intestinal microbial profile in mice [ 78 ].
Another possible perturbation in the microbiota habitat induced by stress occurs through the enhancement in secretion of a-defensin, an antimicrobial peptide, from Paneth cells [ 79 ]. Finally, it is important to remark that gut alterations associated to stress facilitate the expression of virulent bacteria. Norepinephrine released during surgery induces the expression of Pseudomonas aeruginosa , which might result in gut sepsis [ 80 ].
Besides, norepinephrine can also stimulate proliferation of several strains of enteric pathogens and increase the virulent properties of Campylobacter jejuni [ 81 ] and might favor overgrowth of non-pathogenic isolates of Escherichia coli , as well as of pathogenic Escherichia coli H [ 82 , 83 ]. Strong evidence suggests that gut microbiota has an important role in bidirectional interactions between the gut and the nervous system. It interacts with CNS by regulating brain chemistry and influencing neuro-endocrine systems associated with stress response, anxiety and memory function. Many of these effects appear to be strain-specific, suggesting a potential role of certain probiotic strains as novel adjuvant strategy for neurologic disorders.
University Sapienza, Rome; S. Conflict of Interest: None. National Center for Biotechnology Information , U. Journal List Ann Gastroenterol v. Ann Gastroenterol. Author information Article notes Copyright and License information Disclaimer. Received Sep 5; Accepted Dec 7. This is an open-access article distributed under the terms of the Creative Commons Attribution-Noncommercial-Share Alike 3. This article has been corrected. See Ann Gastroenterol. This article has been cited by other articles in PMC. Abstract The gut-brain axis GBA consists of bidirectional communication between the central and the enteric nervous system, linking emotional and cognitive centers of the brain with peripheral intestinal functions.
Keywords: Gut-brain axis, enteric microbiota, central nervous system, enteric nervous system, irritable bowel syndrome. Introduction Insights into the gut-brain crosstalk have revealed a complex communication system that not only ensures the proper maintenance of gastrointestinal homeostasis, but is likely to have multiple effects on affect, motivation, and higher cognitive functions.
Open in a separate window. Figure 1. Microbiome gut-brain axis structure The central nervous system and in particular hypothalamic pituitary adrenal HPA axis in dashed line can be activated in response to environmental factors, such as emotion or stress. Role of microbiota in GBA Both clinical and experimental evidence suggest that enteric microbiota has an important impact on GBA, interacting not only locally with intestinal cells and ENS, but also directly with CNS through neuroendocrine and metabolic pathways. From gut microbiota to brain In the last years there has been a proliferation of experimental works, conducted mainly on animals, aimed to explore the contribution of the microbiota in modulating GBA.
Table 1 Main principal mechanisms of the bidirectional brain-gut-microbiota axis. From brain to gut microbiota Different types of psychological stressors modulate the composition and total biomass of the enteric microbiota, independently from duration. Concluding remarks Strong evidence suggests that gut microbiota has an important role in bidirectional interactions between the gut and the nervous system. Acknowledgment The authors kindly thank Dr Laura Carabotti for the artwork of the figures. Footnotes Conflict of Interest: None. References 1. Principles and clinical implications of the brain-gut-enteric microbiota axis. Nat Rev Gastroenterol Hepatol. Tsigos C, Chrousos GP. Hypothalamic-pituitary-adrenal axis, neuroendocrine factors and stress.
J Psychosom Res. Brain-gut microbiome interactions and functional bowel disorders. Diversity of the human intestinal microbial flora. Morgan MY. The treatment of chronic hepatic encephalopathy. Gut-brain axis: how the microbiome influences anxiety and depression. Trends Neurosci. Correlation between the human fecal microbiota and depression. Neurogastroenterol Motil. Altered brain-gut axis in autism: comorbidity or causative mechanisms? Real-time PCR quantitation of clostridia in feces of autistic children. Appl Environ Microbiol. Rome Foundation Committee. Intestinal microbiota in functional bowel disorders: a Rome foundation report. Mayer EA, Tillisch K.
The brain-gut axis in abdominal pain syndromes. Annu Rev Med. An observational study of cognitive function in patients with irritable bowel syndrome and inflammatory bowel disease. The brain-gut pathway in functional gastrointestinal disorders is bidirectional: a year prospective population-based study. Dupont HL. Review article: evidence for the role of gut microbiota in irritable bowel syndrome and its potential influence on therapeutic targets. Aliment Pharmacol Ther. Spiller R, Lam C. J Neurogastroenterol Motil. Quigley EM. Small intestinal bacterial overgrowth: what it 77 is and what it is not.
Curr Opin Gastroenterol. Rifaximin therapy for patients with irritable bowel syndrome without constipation. N Engl J Med. The hypersensitivity to colonic distension of IBS patients can be transferred to rats through their fecal microbiota. Irritable bowel syndrome: A microbiome-gut-brain axis disorder? World J Gastroenterol. Communication between gastrointestinal bacteria and the nervous system. Curr Opin Pharmacol. Interactions between commensal bacteria and gut sensorimotor function in health and disease. Am J Gastroenterol. Microbial genes, brain and behaviour - epigenetic regulation of the gut-brain axis. Genes Brain Behav. The microbiome-gut-brain axis during early life regulates the hippocampal serotonergic system in a sex-dependent manner.
When someone confronts an oncoming car or other danger, the eyes or ears or both send the information to the amygdala, an area of the brain that contributes to emotional processing. The amygdala interprets the images and sounds. When it perceives danger, it instantly sends a distress signal to the hypothalamus. When someone experiences a stressful event, the amygdala, an area of the brain that contributes to emotional processing, sends a distress signal to the hypothalamus. This area of the brain functions like a command center, communicating with the rest of the body through the nervous system so that the person has the energy to fight or flee.
The hypothalamus is a bit like a command center. This area of the brain communicates with the rest of the body through the autonomic nervous system, which controls such involuntary body functions as breathing, blood pressure, heartbeat, and the dilation or constriction of key blood vessels and small airways in the lungs called bronchioles. The autonomic nervous system has two components, the sympathetic nervous system and the parasympathetic nervous system. The sympathetic nervous system functions like a gas pedal in a car.
It triggers the fight-or-flight response, providing the body with a burst of energy so that it can respond to perceived dangers. The parasympathetic nervous system acts like a brake. It promotes the "rest and digest" response that calms the body down after the danger has passed. After the amygdala sends a distress signal, the hypothalamus activates the sympathetic nervous system by sending signals through the autonomic nerves to the adrenal glands. These glands respond by pumping the hormone epinephrine also known as adrenaline into the bloodstream. As epinephrine circulates through the body, it brings on a number of physiological changes.
The heart beats faster than normal, pushing blood to the muscles, heart, and other vital organs. Pulse rate and blood pressure go up. The person undergoing these changes also starts to breathe more rapidly. Small airways in the lungs open wide. This way, the lungs can take in as much oxygen as possible with each breath. Extra oxygen is sent to the brain, increasing alertness. Sight, hearing, and other senses become sharper. Meanwhile, epinephrine triggers the release of blood sugar glucose and fats from temporary storage sites in the body. These nutrients flood into the bloodstream, supplying energy to all parts of the body.
All of these changes happen so quickly that people aren't aware of them. In fact, the wiring is so efficient that the amygdala and hypothalamus start this cascade even before the brain's visual centers have had a chance to fully process what is happening. That's why people are able to jump out of the path of an oncoming car even before they think about what they are doing. As the initial surge of epinephrine subsides, the hypothalamus activates the second component of the stress response system — known as the HPA axis. This network consists of the hypothalamus, the pituitary gland, and the adrenal glands. The HPA axis relies on a series of hormonal signals to keep the sympathetic nervous system — the "gas pedal" — pressed down.
If the brain continues to perceive something as dangerous, the hypothalamus releases corticotropin-releasing hormone CRH , which travels to the pituitary gland, triggering the release of adrenocorticotropic hormone ACTH. This hormone travels to the adrenal glands, prompting them to release cortisol. The body thus stays revved up and on high alert. When the threat passes, cortisol levels fall. The parasympathetic nervous system — the "brake" — then dampens the stress response. Many people are unable to find a way to put the brakes on stress. Chronic low-level stress keeps the HPA axis activated, much like a motor that is idling too high for too long.
After a while, this has an effect on the body that contributes to the health problems associated with chronic stress. Persistent epinephrine surges can damage blood vessels and arteries, increasing blood pressure and raising risk of heart attacks or strokes. Elevated cortisol levels create physiological changes that help to replenish the body's energy stores that are depleted during the stress response. But they inadvertently contribute to the buildup of fat tissue and to weight gain. For example, cortisol increases appetite, so that people will want to eat more to obtain extra energy.
It also increases storage of unused nutrients as fat. Relaxation response. Herbert Benson, director emeritus of the Benson-Henry Institute for Mind Body Medicine at Massachusetts General Hospital, has devoted much of his career to learning how people can counter the stress response by using a combination of approaches that elicit the relaxation response. These include deep abdominal breathing, focus on a soothing word such as peace or calm , visualization of tranquil scenes, repetitive prayer, yoga, and tai chi.
Most of the research using objective measures to evaluate how effective the relaxation response is at countering chronic stress have been conducted in people with hypertension and other forms of heart disease. Those results suggest the technique may be worth trying — although for most people it is not a cure-all. For example, researchers at Massachusetts General Hospital conducted a double-blind, randomized controlled trial of patients with hypertension, ages 55 and older, in which half were assigned to relaxation response training and the other half to a control group that received information about blood pressure control.
After eight weeks, 34 of the people who practiced the relaxation response — a little more than half — had achieved a systolic blood pressure reduction of more than 5 mm Hg, and were therefore eligible for the next phase of the study, in which they could reduce levels of blood pressure medication they were taking. Physical activity.In the meantime, emerging data support the role of microbiota in influencing anxiety Sympathetic Nervous System Research Paper depressive-like behaviors [ 6Sympathetic Nervous System Research Paper ] and, Sympathetic Nervous System Research Paper recently, Sympathetic Nervous System Research Paper dysbiosis in autism. Not only Sympathetic Nervous System Research Paper certain foods like simple sugars boosts the Sympathetic Nervous System Research Paper Dionysus: The Classical Ancient Greek Theatre the sympathetic nervous system, but a Sympathetic Nervous System Research Paper diet Sympathetic Nervous System Research Paper an equally important role when combating the overactive sympathetic nervous system. In a study on Sympathetic Nervous System Research Paper hospitalized patients, administration of lavender odor showed a trend towards an improved quality of daytime wakefulness and Dental Care Scenarios sustained sleep Character Analysis: Rameck night [ 80 ]. Johnson V. Mcintosh (1974) genus Lavandula is native to the lands surrounding the Mediterranean Sea and southern Europe through northern and eastern Africa Sympathetic Nervous System Research Paper Middle Eastern countries to Sympathetic Nervous System Research Paper Asia and southeast India. Close banner Close. Its role is Sympathetic Nervous System Research Paper monitor and integrate gut functions as well as to link emotional and cognitive centers of the brain John Conway Research Paper peripheral intestinal Sympathetic Nervous System Research Paper and mechanisms such Sympathetic Nervous System Research Paper immune activation, intestinal permeability, enteric reflex, and entero-endocrine signaling.