The gut, or gastrointestinal tract, is an organ system responsible for the digestion of food. Several human diseases and conditions, including gastroparesis, obesity, and reflux disease, are associated with impaired regulation of gut function. Along with pharmaceutical, surgical, and dietary interventions, which are not always successful in treating these disorders, researchers have begun to explore electrical stimulation of the vagus nerve to precisely control gastrointestinal function. For this treatment strategy to work, scientists must understand the function of vagal nerve signals carried between the central nervous system and the gut.
A-funded research team at Purdue University is studying the effect of vagus nerve stimulation on emptying the stomach as food moves into the small intestine (gastric emptying) in rats. They observe the process of gastric emptying using a technique called Magnetic Resonance Imaging (MRI). They found that selective electrical stimulation of the vagus nerve significantly increased gastric emptying through relaxation of the pyloric sphincter, a valve-like band of muscle that separates the stomach from the small intestine, which allows movement of food out of the stomach. These findings suggest that electrical stimulation of the vagus nerve could be used to improve gut function to treat gastric emptying disorders like gastroparesis. In addition, their MRI protocol describes a new non-invasive method to assess the effectiveness of many different types of therapies on gastrointestinal function.
. Lu KH, Cao J, Oleson S, Ward MP, Phillips RJ, Powley TL, and Liu Z. October 2018. Wiley Publishers: Neurogastroenterology & Motility. e13380.
In the News:
MRI tool watches how electrical stimulation could cure digestive disorders, Purdue University News
Understanding the causes of inflammatory bowel disease is difficult because the associated abdominal pain can occur without any obvious changes to the structure of the colon or signs of inflammation. Because pain sensations can be carried by sensory neurons, one factor in the generation of abdominal pain could be abnormal sensory neuron activity, which can be influenced by secretions from cells called “epithelial cells” that line the interior of the colon. Understanding interactions between colon epithelial cells and sensory neurons could help us understand and treat abdominal pain. To study the interactions between the types of cells, a SPARC-funded team led by investigators Dr. Brian Davis and Dr. Kathryn Albers used genetically modified mice that contain blue light-activated colon epithelial cells to examine signaling between colon epithelial cells and neurons. These mouse colon epithelial cells could be specifically stimulated by blue light without any physical or chemical stimulation, allowing the study of their effects apart from other factors. Stimulating the epithelial cells caused activity in the pain-sensing neurons and behavioral responses similar to those that result from pain-inducing physical stimulation of the colon. Further study found that firing of neurons was likely triggered by release of a molecule called ATP from the colon epithelial cells. The results indicate that the activity of the colon epithelial cells alone, without any physical or chemical stimulation, could lead to abdominal pain through activation of the pain-sensing neurons. This study advances the understanding of how colon sensory neuron activity is regulated and could aid in development of new treatment strategies for inflammatory bowel disease.
Reference:. Makadia, PA, Naijar, SA, Saloman, JL, Adelman, P, Feng, B, Margiotta, J, Albers, KM, Davis, BM. June 2018. J Neurosci. 38(25): 5788-5798.
The Fat in Our Bones
You probably think of your bones as providing structure and support to your body and protecting your organs, but they have many other functions as well. The soft spongy area inside most bones, called the bone marrow, produces blood cells and stores energy in the form of fat and therefore plays an important role in bone health. The fat cells found in the bone marrow (bone marrow adipocytes) are very different from fat cells found in other parts of the body. Bone marrow adipocytes are also more difficult to study because they are found in small compartments inside of bones.program awardee Dr. Erica Scheller and her research team published a study in the journal Bone with some of the most detailed images ever acquired of bone marrow adipocytes. The images show that the bone marrow adipocytes interact with other components of their environment such as blood- and bone-forming cells and blood vessels. Of special interest to the SPARC program, a subset of the adipocytes were found to contact nerve cells. The results indicate that bone marrow adipocytes could send signaling molecules to nearby blood- and bone-forming cells and that nerves may coordinate the interactions between bone marrow adipocytes and these cells. This indicates that it could someday be possible to control or modulate bone formation and other bone processes by electrical stimulation of specific nerves. This could potentially lead to new treatments for conditions such as bone fragility, which occur more frequently in groups like the elderly and those with diabetes.
Reference:. Robles, H, Park, S, Joens, MS, Fitzpatrick, JAJ, Craft, CS, and Scheller, E. Jan 2018. Bone. Doi: 10.1016/j.bone.2018.01.020.
Click on the image to view a video of bone marrow innervation in Bone:
Getting the Gut Moving
The enteric nervous system (ENS) regulates stretching and contraction of muscles in the gastrointestinal tract (gut motility), which is critical for digestion. Gastrointestinal disorders resulting from irregular gut motility affect more than a quarter of the world’s population. One method of treating irregular organ function is neurostimulation, in which targeted electrical current is used to stimulate the ENS. However, this method has seen limited success for gastrointestinal disorders, because we don’t understand how electrical stimulation affects the ENS and gut motility. Current computational models that simulate the effects of electrical stimulation of the ENS are incomplete, which makes predicting the effects of different ENS stimulation patterns difficult in living organisms.
In a study funded by the NIH Common Fund SPARC Program, investigators Warren Grill and Xiling Shen developed a computational model of the ENS and used this model to assess neurostimulation strategies for regulating gut motility. The neuromechanical model included a network of parts involved in gut motility - enteric neurons, smooth muscle fibers, and interstitial cells of Cajal (ICCs, cells that act as electrical pacemakers and promote smooth muscle contraction during digestion). The team simulated intestinal tract motility by passing a virtual pellet that stimulates sensory neurons and responds to smooth muscle contractions through the ENS computer model. They found that simulated current pulses at a frequency of 0.5 Hz were more effective at regulating the pacemaker frequency of ICCs, and accelerating gut motility, than higher pulse frequencies that are more commonly used. They validated this model in experiments with rats, in which bead propulsion through the gut was measured during electrical stimulation of the colon and found to behave as predicted from the simulation. The results of this study have implications for the neurostimulation treatment of gastrointestinal disorders resulting from reduced gut motility.
Reference: Electrical stimulation of gut motility guided by an in silico model. Barth, BB, Henriquez, CS, Grill, WM, and Shen, X. Dec 2017. J. Neural Eng. 14(6): 066010.
Viruses Engineered for Good
One method of treating genetic diseases is to transfer new genes to cells affected by the disease. One tool scientists use to transfer genes is viruses, which interact with cells through an external covering, and then inject their DNA into the cells. Scientists take advantage of this ability by replacing virus DNA with DNA that encodes the genes they wish to deliver. In addition to treating diseases, this technique can be used to label cells with fluorescent colors in order to visualize them and identify their connections in the body. Using viruses to transfer genes to cells of the nervous system is difficult because neurons (nerve cells) are widely spread throughout the body, and reaching some neurons requires passage of the virus through the blood brain barrier, a selective layer that blocks the passage of many substances from reaching the brain and spinal cord tissue.
In a study led by NIH Common Fund SPARC program-funded investigator Viviana Gradinaru, a research team engineered viruses to efficiently deliver genes to neurons throughout the body of a mouse after injection into the bloodstream. They modified the external covering of existing viruses for more efficient gene delivery to neurons. They engineered one virus to pass the blood brain barrier and transfer genes to neurons in the brain and spinal cord (the central nervous system), and another virus to reach and transfer genes to neurons spread throughout the body (in the peripheral nervous system). The engineered viruses are highly efficient at gene delivery at low doses, can be designed for their delivered genes to be turned on only in certain cell types, and are able to precisely label cells with fluorescent colors for visualization. The viruses can be further customized and potentially used for future non-invasive treatments of neurological disorders, as well as for multi-color labeling of neurons for generation of neuron circuit maps. Neuron maps showing connections between neurons and organs could aid in development of treatments for a variety of human diseases by altering the activity of specific neurons through a process called neuromodulation.
Engineered AAVs for efficient noninvasive gene delivery to the central and peripheral nervous systems. Chan, KY, Jang, MJ, Yoo, BB, Greenbaum, A, Ravi, N, Wu, WL, Sanchez-Guardado, L, Lois, C, Manmanian, SK, Deverman, BE, and Gradinaru, V. June 2017. Nat Neurosci. 20(8): 1172-1179.
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Gene Therapy Vectors Come to Grips with Nervous System, Root and Branch, Genetic Engineering and Biotechnology News
This page last reviewed on October 29, 2018