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Werner CM, Willing LB, Goudsward HJ, McBride AR, Stella SL, Holmes GM. Plasticity of colonic enteric nervous system following spinal cord injury in male and female rats. Neurogastroenterol Motil 2023; 35:e14646. [PMID: 37480186 PMCID: PMC11298951 DOI: 10.1111/nmo.14646] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/10/2023] [Revised: 05/30/2023] [Accepted: 06/27/2023] [Indexed: 07/23/2023]
Abstract
BACKGROUND Neurogenic bowel is a dysmotility disorder following spinal cord injury (SCI) that negatively impacts quality of life, social integration, and physical health. Colonic transit is directly modulated by the enteric nervous system. Interstitial Cells of Cajal (ICC) distributed throughout the small intestine and colon serve as specialized pacemaker cells, generating rhythmic electrical slow waves within intestinal smooth muscle, or serve as an interface between smooth muscle cells and enteric motor neurons of the myenteric plexus. Interstitial Cells of Cajal loss has been reported for other preclinical models of dysmotility, and our previous experimental SCI study provided evidence of reduced excitatory and inhibitory enteric neuronal count and smooth muscle neural control. METHODS Immunohistochemistry for the ICC-specific marker c-Kit was utilized to examine neuromuscular remodeling of the distal colon in male and female rats with experimental SCI. KEY RESULTS Myenteric plexus ICC (ICC-MP) exhibited increased cell counts 3 days following SCI in male rats, but did not significantly increase in females until 3 weeks after SCI. On average, ICC-MP total primary arborization length increased significantly in male rats at 3-day, 3-week, and 6-week time points, whereas in females, this increase occurred most frequently at 6 weeks post-SCI. Conversely, circular muscle ICC (ICC-CM) did not demonstrate post-SCI changes. CONCLUSIONS AND INFERENCES These data demonstrate resiliency of the ICC-MP in neurogenic bowel following SCI, unlike seen in other related disease states. This plasticity underscores the need to further understand neuromuscular changes driving colonic dysmotility after SCI in order to advance therapeutic targets for neurogenic bowel treatment.
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Affiliation(s)
- Claire M Werner
- Department of Neural and Behavioral Sciences, Penn State University College of Medicine, Hershey, Pennsylvania, USA
| | - Lisa B Willing
- Department of Neural and Behavioral Sciences, Penn State University College of Medicine, Hershey, Pennsylvania, USA
| | - Hannah J Goudsward
- Department of Neural and Behavioral Sciences, Penn State University College of Medicine, Hershey, Pennsylvania, USA
| | - Amanda R McBride
- Department of Neural and Behavioral Sciences, Penn State University College of Medicine, Hershey, Pennsylvania, USA
| | - Salvatore L Stella
- Department of Neural and Behavioral Sciences, Penn State University College of Medicine, Hershey, Pennsylvania, USA
| | - Gregory M Holmes
- Department of Neural and Behavioral Sciences, Penn State University College of Medicine, Hershey, Pennsylvania, USA
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Holmes GM, Willing LB, Horvath N, Hajnal A. Feasibility Study of Bariatric Surgery in a Rat Model of Spinal Cord Injury to Achieve Beneficial Body Weight Outcome. Neurotrauma Rep 2022; 3:292-298. [PMID: 36060457 PMCID: PMC9438445 DOI: 10.1089/neur.2022.0027] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/29/2022] Open
Affiliation(s)
- Gregory M. Holmes
- Department of Neural and Behavioral Sciences, Penn State University College of Medicine, Hershey, Pennsylvania, USA
| | - Lisa B. Willing
- Department of Neural and Behavioral Sciences, Penn State University College of Medicine, Hershey, Pennsylvania, USA
| | - Nelli Horvath
- Department of Neural and Behavioral Sciences, Penn State University College of Medicine, Hershey, Pennsylvania, USA
| | - Andras Hajnal
- Department of Neural and Behavioral Sciences, Penn State University College of Medicine, Hershey, Pennsylvania, USA
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Musleh-Vega S, Ojeda J, Vidal PM. Gut Microbiota–Brain Axis as a Potential Modulator of Psychological Stress after Spinal Cord Injury. Biomedicines 2022; 10:biomedicines10040847. [PMID: 35453597 PMCID: PMC9024710 DOI: 10.3390/biomedicines10040847] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2022] [Revised: 04/01/2022] [Accepted: 04/02/2022] [Indexed: 12/12/2022] Open
Abstract
A growing body of evidence from preclinical and clinical studies has associated alterations of the gut microbiota–brain axis with the progression and development of a number of pathological conditions that also affect cognitive functions. Spinal cord injuries (SCIs) can be produced from traumatic and non-traumatic causes. It has been reported that SCIs are commonly associated with anxiety and depression-like symptoms, showing an incidence range between 11 and 30% after the injury. These psychological stress-related symptoms are associated with worse prognoses in SCIs and have been attributed to psychosocial stressors and losses of independence. Nevertheless, emotional and mental modifications after SCI could be related to changes in the volume of specific brain areas associated with information processing and emotions. Additionally, physiological modifications have been recognized as a predisposing factor for mental health depletion, including the development of gut dysbiosis. This condition of imbalance in microbiota composition has been shown to be associated with depression in clinical and pre-clinical models. Therefore, the understanding of the mechanisms underlying the relationship between SCIs, gut dysbiosis and psychological stress could contribute to the development of novel therapeutic strategies to improve SCI patients’ quality of life.
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Spinal cord injury-mediated changes in electrophysiological properties of rat gastric nodose ganglion neurons. Exp Neurol 2022; 348:113927. [PMID: 34798136 PMCID: PMC8727501 DOI: 10.1016/j.expneurol.2021.113927] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2021] [Revised: 10/30/2021] [Accepted: 11/11/2021] [Indexed: 02/03/2023]
Abstract
In preclinical rodent models, spinal cord injury (SCI) manifests as gastric vagal afferent dysfunction both acutely and chronically. However, the mechanism that underlies this dysfunction remains unknown. In the current study, we examined the effect of SCI on gastric nodose ganglia (NG) neuron excitability and on voltage-gated Na+ (NaV) channels expression and function in rats after an acute (i.e. 3-days) and chronic (i.e. 3-weeks) period. Rats randomly received either T3-SCI or sham control surgery 3-days or 3-weeks prior to experimentation as well as injections of 3% DiI solution into the stomach to identify gastric NG neurons. Single cell qRT-PCR was performed on acutely dissociated DiI-labeled NG neurons to measure NaV1.7, NaV1.8 and NaV1.9 expression levels. The results indicate that all 3 channel subtypes decreased. Current- and voltage-clamp whole-cell patch-clamp recordings were performed on acutely dissociated DiI-labeled NG neurons to measure active and passive properties of C- and A-fibers as well as the biophysical characteristics of NaV1.8 channels in gastric NG neurons. Acute and chronic SCI did not demonstrate deleterious effects on either passive properties of dissociated gastric NG neurons or biophysical properties of NaV1.8. These findings suggest that although NaV gene expression levels change following SCI, NaV1.8 function is not altered. The disruption throughout the entirety of the vagal afferent neuron has yet to be investigated.
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Blanke EN, Holmes GM, Besecker EM. Altered physiology of gastrointestinal vagal afferents following neurotrauma. Neural Regen Res 2021; 16:254-263. [PMID: 32859772 PMCID: PMC7896240 DOI: 10.4103/1673-5374.290883] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
The adaptability of the central nervous system has been revealed in several model systems. Of particular interest to central nervous system-injured individuals is the ability for neural components to be modified for regain of function. In both types of neurotrauma, traumatic brain injury and spinal cord injury, the primary parasympathetic control to the gastrointestinal tract, the vagus nerve, remains anatomically intact. However, individuals with traumatic brain injury or spinal cord injury are highly susceptible to gastrointestinal dysfunctions. Such gastrointestinal dysfunctions attribute to higher morbidity and mortality following traumatic brain injury and spinal cord injury. While the vagal efferent output remains capable of eliciting motor responses following injury, evidence suggests impairment of the vagal afferents. Since sensory input drives motor output, this review will discuss the normal and altered anatomy and physiology of the gastrointestinal vagal afferents to better understand the contributions of vagal afferent plasticity following neurotrauma.
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Affiliation(s)
- Emily N Blanke
- Department of Neural and Behavioral Sciences, Penn State University College of Medicine, Hershey, PA, USA
| | - Gregory M Holmes
- Department of Neural and Behavioral Sciences, Penn State University College of Medicine, Hershey, PA, USA
| | - Emily M Besecker
- Department of Health Sciences, Gettysburg College, Gettysburg, PA, USA
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Herrera J, Bockhorst K, Bhattarai D, Uray K. Gastrointestinal vascular permeability changes following spinal cord injury. Neurogastroenterol Motil 2020; 32:e13834. [PMID: 32163655 DOI: 10.1111/nmo.13834] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/09/2019] [Revised: 02/06/2020] [Accepted: 02/18/2020] [Indexed: 12/11/2022]
Abstract
BACKGROUND Gastrointestinal (GI) dysfunction is observed clinically after spinal cord injury (SCI) and contributes to the diminished long-term quality of life. Our study examined the acute and chronic GI vascular changes that occur following SCI. We demonstrated that the GI vascular tract in SCI mice becomes compromised during the acute phase of injury and persists into the chronic phase of injury. METHODS Gastrointestinal vasculature permeability was measured using dynamic contrast-enhanced magnetic resonance imaging (DCE MRI) at 48 hours, and 2 and 4 weeks following contusion spinal cord injury. Angiopoietin-1, a vascular stabilizing protein, was administered intravenously following injury. Intestinal contractile activity assessments were performed following the last imaging session. KEY RESULTS Our results indicated that a single administration of Ang-1 reduced vascular permeability at 48 hours but the effect was only transient. However, when the treatment paradigm was changed from a single administration to multiple administrations of Ang-1 following contusion injury, our DCE MRI data indicated a significant decrease in GI vascular permeability 4 weeks after injury compared with vehicle control treated animals. This improved GI vascular permeability was associated with improved sustained intestinal contractile activity. We also demonstrated that Ang-1 reduced the expression of sICAM-1 in the ileum compared with the saline-treated group. CONCLUSIONS AND INFERENCES We show that the GI vasculature is compromised in the acute and chronic phase of injury following spinal contusion. Our results also indicate that multiple administrations of Ang-1 can attenuate GI vascular permeability, possibly reduce inflammation, and improve sustained agonist-induced contraction compared with saline treatment.
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Affiliation(s)
- Juan Herrera
- Diagnostic and Interventional Imaging, University of Texas Health Science Center at Houston, Houston, Texas, USA
| | - Kurt Bockhorst
- Diagnostic and Interventional Imaging, University of Texas Health Science Center at Houston, Houston, Texas, USA
| | - Deepa Bhattarai
- Pediatric Surgery University of Texas Medical School at Houston, Houston, Texas, USA
| | - Karen Uray
- Pediatric Surgery University of Texas Medical School at Houston, Houston, Texas, USA.,Medicinal Chemistry, University of Debrecen, Debrecen, Hungary
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White AR, Werner CM, Holmes GM. Diminished enteric neuromuscular transmission in the distal colon following experimental spinal cord injury. Exp Neurol 2020; 331:113377. [PMID: 32526238 DOI: 10.1016/j.expneurol.2020.113377] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2020] [Revised: 05/14/2020] [Accepted: 06/03/2020] [Indexed: 12/30/2022]
Abstract
Neurogenic bowel following spinal cord injury (SCI) leads to decreased colonic motility, remodeling of the neuromuscular compartment and results in chronic evacuation difficulties. The distal colon of the rat serves a dual role for fluid absorption and storage that is homologous to the descending colon of humans. Dysmotility of the descending colon is one component of neurogenic bowel. We investigated the integrity of the enteric neuromuscular transmission responsible for the generation of excitatory and inhibitory junction potentials (EJPs and IJPs, respectively) in the distal colon of rats. We previously demonstrated a chronic reduction in colonic enteric neurons from rats with acute and chronic high-thoracic (T3) SCI and hypothesized that neurogenic bowel following T3-SCI results from diminished enteric neuromuscular transmission. Immunohistochemical labeling for myenteric neuronal nitric oxide synthase (nNOS) and choline acetyltransferase (ChAT) neurons demonstrated a significant loss of presumptive nitric oxide (NO) and acetylcholine (ACh) immunoreactive neurons in both 3-day and 3-week injured animals. Colonic neuromuscular transmission in response to transmural electrical stimulation of the colon was significantly reduced 3-days and 3-weeks following SCI in male rats. Specifically, cholinergic-mediated excitatory junction potentials (EJPs) and nitrergic-mediated slow inhibitory junction potentials (IJPs) were significantly reduced while ATP-mediated fast IJPs remained unaffected. We conclude that a reduction in excitatory and inhibitory enteric neuromuscular transmission contributes to neurogenic bowel observed following SCI, and that these loss-of-function changes involve enteric-mediated cholinergic and nitrergic pathways.
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Affiliation(s)
- Amanda R White
- Department of Neural and Behavioral Sciences, Penn State University College of Medicine, Hershey, PA 17033, United States of America
| | - Claire M Werner
- Department of Neural and Behavioral Sciences, Penn State University College of Medicine, Hershey, PA 17033, United States of America
| | - Gregory M Holmes
- Department of Neural and Behavioral Sciences, Penn State University College of Medicine, Hershey, PA 17033, United States of America.
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Bhattacharyya S, Sahu S, Kaur S, Jain S. Effect of Low Intensity Magnetic Field Stimulation on Calcium-Mediated Cytotoxicity After Mild Spinal Cord Contusion Injury in Rats. Ann Neurosci 2020; 27:49-56. [PMID: 33335356 PMCID: PMC7724432 DOI: 10.1177/0972753120950072] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023] Open
Abstract
BACKGROUND Magnetic field (MF) stimulation has the potential to reduce secondary damage and promote functional recovery after neural tissue injury. The study aimed to observe the effect of very low intensity (17.96µT) MF on general body condition, secondary damage, pain status, and locomotion. METHODS We exposed rats to MF (2 h/day × 3 weeks) after 6.25 mm contusion spinal injury. Locomotor behavior was evaluated by BBB score, pain assessment was done by recording threshold for tail flick, expression of voltage-gated calcium channels and extent of secondary damage in the spinal cord was assessed by immunofluorescence and Cresyl violet staining, respectively. RESULTS A significant (p ≤ .001) improvement in bladder function as well as BBB score was observed after MF exposure in comparison with sham and SCI over the observation period of 3 weeks. SCI group showed an increase in the threshold for vocalization after discharge, which decreased following MF exposure. Cresyl violet staining showed significantly higher tissue sparing (73%) at the epicenter after MF exposure when compared to SCI group. This was accompanied with a significant decrease in calcium channel expression in MF group as compared to SCI. CONCLUSION The results suggest facilitation of sensory-motor recovery after MF exposure, which could be due to attenuation of secondary damage and calcium-mediated excitotoxicity in a mild contusion rat model of SCI.
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Affiliation(s)
| | - Shivani Sahu
- Institute of Microbial Technology,
Chandigarh, India
| | - Sajeev Kaur
- Department of Physiology, All India
Institute of Medical Sciences, New Delhi, India
| | - Suman Jain
- Department of Physiology, All India
Institute of Medical Sciences, New Delhi, India
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Besecker EM, Blanke EN, Deiter GM, Holmes GM. Gastric vagal afferent neuropathy following experimental spinal cord injury. Exp Neurol 2019; 323:113092. [PMID: 31697943 DOI: 10.1016/j.expneurol.2019.113092] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2019] [Revised: 09/11/2019] [Accepted: 10/23/2019] [Indexed: 01/01/2023]
Abstract
Dramatic impairment of gastrointestinal (GI) function accompanies high-thoracic spinal cord injury (T3-SCI). The vagus nerve contains mechano- and chemosensory fibers as well as the motor fibers necessary for the central nervous system (CNS) control of GI reflexes. Cell bodies for the vagal afferent fibers are located within the nodose gangla (NG) and the majority of vagal afferent axons are unmyelinated C fibers that are sensitive to capsaicin through activation of transient receptor potential vanilloid-1 (TRPV1) channels. Vagal afferent fibers also express receptors for GI hormones, including cholecystokinin (CCK). Previously, T3-SCI provokes a transient GI inflammatory response as well as a reduction of both gastric emptying and centrally-mediated vagal responses to GI peptides, including CCK. TRPV1 channels and CCK-A receptors (CCKar) expressed in vagal afferents are upregulated in models of visceral inflammation. The present study investigated whether T3-SCI attenuates peripheral vagal afferent sensitivity through plasticity of TRPV1 and CCK receptors. Vagal afferent response to graded mechanical stimulation of the stomach was significantly attenuated by T3-SCI at 3-day and 3-week recovery. Immunocytochemical labeling for CCKar and TRPV1 demonstrated expression on dissociated gastric-projecting NG neurons. Quantitative assessment of mRNA expression by qRT-PCR revealed significant elevation of CCKar and TRPV1 in the whole NG following T3-SCI in 3-day recovery, but levels returned to normal after 3-weeks. Three days after injury, systemic administration of CCK-8 s showed a significantly diminished gastric vagal afferent response in T3-SCI rats compared to control rats while systemic capsaicin infusion revealed a significant elevation of vagal response in T3-SCI vs control rats. These findings demonstrate that T3-SCI provokes peripheral remodeling and prolonged alterations in the response of vagal afferent fibers to the physiological signals associated with digestion.
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Affiliation(s)
- Emily M Besecker
- Department of Neural and Behavioral Sciences, Penn State University College of Medicine, Hershey, PA 17033, United States of America; Department of Health Sciences, Gettysburg College, Gettysburg, PA 17325, United States of America
| | - Emily N Blanke
- Department of Neural and Behavioral Sciences, Penn State University College of Medicine, Hershey, PA 17033, United States of America
| | - Gina M Deiter
- Department of Neural and Behavioral Sciences, Penn State University College of Medicine, Hershey, PA 17033, United States of America
| | - Gregory M Holmes
- Department of Neural and Behavioral Sciences, Penn State University College of Medicine, Hershey, PA 17033, United States of America.
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Holmes GM, Blanke EN. Gastrointestinal dysfunction after spinal cord injury. Exp Neurol 2019; 320:113009. [PMID: 31299180 PMCID: PMC6716787 DOI: 10.1016/j.expneurol.2019.113009] [Citation(s) in RCA: 40] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2019] [Revised: 06/13/2019] [Accepted: 07/07/2019] [Indexed: 12/12/2022]
Abstract
The gastrointestinal tract of vertebrates is a heterogeneous organ system innervated to varying degrees by a local enteric neural network as well as extrinsic parasympathetic and sympathetic neural circuits located along the brainstem and spinal axis. This diverse organ system serves to regulate the secretory and propulsive reflexes integral to the digestion and absorption of nutrients. The quasi-segmental distribution of the neural circuits innervating the gastrointestinal (GI) tract produces varying degrees of dysfunction depending upon the level of spinal cord injury (SCI). At all levels of SCI, GI dysfunction frequently presents life-long challenges to individuals coping with injury. Growing attention to the profound changes that occur across the entire physiology of individuals with SCI reveals profound knowledge gaps in our understanding of the temporal dimensions and magnitude of organ-specific co-morbidities following SCI. It is essential to understand and identify these broad pathophysiological changes in order to develop appropriate evidence-based strategies for management by clinicians, caregivers and individuals living with SCI. This review summarizes the neurophysiology of the GI tract in the uninjured state and the pathophysiology associated with the systemic effects of SCI.
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Affiliation(s)
- Gregory M Holmes
- Department of Neural and Behavioral Sciences, Penn State University College of Medicine, Hershey, PA 17033, United states of America.
| | - Emily N Blanke
- Department of Neural and Behavioral Sciences, Penn State University College of Medicine, Hershey, PA 17033, United states of America
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Besecker EM, White AR, Holmes GM. Diminished gastric prokinetic response to ghrelin in a rat model of spinal cord injury. Neurogastroenterol Motil 2018; 30:e13258. [PMID: 29205695 PMCID: PMC5878704 DOI: 10.1111/nmo.13258] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/21/2017] [Accepted: 11/01/2017] [Indexed: 12/15/2022]
Abstract
BACKGROUND Patients with cervical or high-thoracic spinal cord injury (SCI) often present reduced gastric emptying and early satiety. Ghrelin provokes motility via gastric vagal neurocircuitry and ghrelin receptor agonists offer a therapeutic option for gastroparesis. We have previously shown that experimental high-thoracic injury (T3-SCI) diminishes sensitivity to another gastrointestinal peptide, cholecystokinin. This study tests the hypothesis that T3-SCI impairs the vagally mediated response to ghrelin. METHODS We investigated ghrelin sensitivity in control and T3-SCI rats at 3-days or 3-weeks after injury utilizing: (i) acute (3-day post-injury) fasting and post-prandial serum levels of ghrelin; (ii) in vivo gastric reflex recording following intravenous or central brainstem ghrelin; and (iii) in vitro whole cell recording of neurons within the dorsal motor nucleus of the vagus (DMV). KEY RESULTS The 2-day food intake of T3-SCI rats was reduced while fasting serum ghrelin levels were higher than in controls. Intravenous and fourth ventricle ghrelin increased in vivo gastric motility in fasted 3-day control rats but not fasted T3-SCI rats. In vitro recording of DMV neurons from 3-day T3-SCI rats were insensitive to exogenous ghrelin. For each measure, vagal responses returned after 3-weeks. CONCLUSIONS AND INFERENCES Hypophagia accompanying T3-SCI produces a significant and physiologically appropriate elevation in serum ghrelin levels. However, higher ghrelin levels did not translate into increased gastric motility in the acute stage of T3-SCI. We propose that this may reflect diminished sensitivity of peripheral vagal afferents to ghrelin or a reduction in the responsiveness of medullary gastric vagal neurocircuitry following T3-SCI.
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Affiliation(s)
- Emily M. Besecker
- Department of Neural and Behavioral Sciences, Penn State University
College of Medicine, Hershey, PA 17033,Department of Health Sciences, Gettysburg College, Gettysburg, PA
17325
| | - Amanda R. White
- Department of Neural and Behavioral Sciences, Penn State University
College of Medicine, Hershey, PA 17033
| | - Gregory M. Holmes
- Department of Neural and Behavioral Sciences, Penn State University
College of Medicine, Hershey, PA 17033,Corresponding Author: Dr. Gregory M. Holmes, Penn State
University College of Medicine, 500 University Dr., H181, Hershey, PA 17033,
Tel: +1 717 531-6413, fax; +1 717 531-5184,
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White AR, Holmes GM. Anatomical and Functional Changes to the Colonic Neuromuscular Compartment after Experimental Spinal Cord Injury. J Neurotrauma 2018; 35:1079-1090. [PMID: 29205096 DOI: 10.1089/neu.2017.5369] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
A profound reduction in colorectal transit time accompanies spinal cord injury (SCI), yet the colonic alterations after SCI have yet to be understood fully. The loss of descending supraspinal input to lumbosacral neural circuits innervating the colon is recognized as one causal mechanism. Remodeling of the colonic enteric nervous system/smooth muscle junction in response to inflammation, however, is recognized as one factor leading to colonic dysmotility in other pathophysiological models. We investigated the alterations to the neuromuscular junction in rats with experimental high-thoracic (T3) SCI. One day to three weeks post-injury, both injured and age-matched controls underwent in vivo experimentation followed by tissue harvest for histological evaluation. Spontaneous colonic contractions were reduced significantly in the proximal and distal colon of T3-SCI rats. Histological evaluation of proximal and distal colon demonstrated significant reductions of colonic mucosal crypt depth and width. Markers of intestinal inflammation were assayed by qRT-PCR. Specifically, Icam1, Ccl2 (MCP-1), and Ccl3 (MIP-1α) mRNA was acutely elevated after T3-SCI. Smooth muscle thickness and collagen content of the colon were increased significantly in T3-SCI rats. Colonic cross sections immunohistochemically processed for the pan-neuronal marker HuC/D displayed a significant decrease in colonic enteric neuron density that became more pronounced at three weeks after injury. Our data suggest that post-SCI inflammation and remodeling of the enteric neuromuscular compartment accompanies SCI. These morphological changes may provoke the diminished colonic motility that occurs during this same period, possibly through the disruption of intrinsic neuromuscular control of the colon.
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Affiliation(s)
- Amanda R White
- Department of Neural and Behavioral Sciences, Penn State University College of Medicine , Hershey, Pennsylvania
| | - Gregory M Holmes
- Department of Neural and Behavioral Sciences, Penn State University College of Medicine , Hershey, Pennsylvania
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13
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Besecker EM, Deiter GM, Pironi N, Cooper TK, Holmes GM. Mesenteric vascular dysregulation and intestinal inflammation accompanies experimental spinal cord injury. Am J Physiol Regul Integr Comp Physiol 2017; 312:R146-R156. [PMID: 27834292 PMCID: PMC5283935 DOI: 10.1152/ajpregu.00347.2016] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2016] [Revised: 10/26/2016] [Accepted: 11/04/2016] [Indexed: 01/23/2023]
Abstract
Cervical and high thoracic spinal cord injury (SCI) drastically impairs autonomic nervous system function. Individuals with SCI at thoracic spinal level 5 (T5) or higher often present cardiovascular disorders that include resting systemic arterial hypotension. Gastrointestinal (GI) tissues are critically dependent upon adequate blood flow and even brief periods of visceral hypoxia triggers GI dysmotility. The aim of this study was to test the hypothesis that T3-SCI induces visceral hypoperfusion, diminished postprandial vascular reflexes, and concomitant visceral inflammation. We measured in vivo systemic arterial blood pressure and superior mesenteric artery (SMA) and duodenal blood flow in anesthetized T3-SCI rats at 3 days and 3 wk postinjury either fasted or following enteral feeding of a liquid mixed-nutrient meal (Ensure). In separate cohorts of fasted T3-SCI rats, markers of intestinal inflammation were assayed by qRT-PCR. Our results show that T3-SCI rats displayed significantly reduced SMA blood flow under all experimental conditions (P < 0.05). Specifically, the anticipated elevation of SMA blood flow in response to duodenal nutrient infusion (postprandial hyperemia) was either delayed or absent after T3-SCI. The dysregulated SMA blood flow in acutely injured T3-SCI rats coincides with abnormal intestinal morphology and elevation of inflammatory markers, all of which resolve after 3 wk. Specifically, Icam1, Ccl2 (MCP-1), and Ccl3 (MIP-1α) were acutely elevated following T3-SCI. Our data suggest that arterial hypotension diminishes mesenteric blood flow necessary to meet mucosal demands at rest and during digestion. The resulting GI ischemia and low-grade inflammation may be an underlying pathology leading to GI dysfunction seen following acute T3-SCI.
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Affiliation(s)
- Emily M Besecker
- Department of Neural & Behavioral Sciences, Penn State University College of Medicine, Hershey, Pennsylvania
- Department of Health Sciences, Gettysburg College, Gettysburg, Pennsylvania
| | - Gina M Deiter
- Department of Cellular and Molecular Physiology, Penn State University College of Medicine, Hershey, Pennsylvania
| | - Nicole Pironi
- Department of Biology, Muhlenberg College, Allentown, Pennsylvania
| | - Timothy K Cooper
- Department of Comparative Medicine, Penn State University College of Medicine, Hershey, Pennsylvania Hershey, Pennsylvania; and
| | - Gregory M Holmes
- Department of Neural & Behavioral Sciences, Penn State University College of Medicine, Hershey, Pennsylvania;
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Gifre L, Vidal J, Carrasco JL, Muxi A, Portell E, Monegal A, Guañabens N, Peris P. Risk factors for the development of osteoporosis after spinal cord injury. A 12-month follow-up study. Osteoporos Int 2015; 26:2273-80. [PMID: 25939310 DOI: 10.1007/s00198-015-3150-x] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/23/2015] [Accepted: 04/22/2015] [Indexed: 12/14/2022]
Abstract
UNLABELLED Spinal cord injury (SCI) has been associated with a marked bone loss after injury and a consequent increased risk of osteoporosis. The evaluation of bone mineral density shortly after SCI is a simple and effective method for predicting the development of osteoporosis during the first year after SCI. INTRODUCTION Spinal cord injury (SCI) has been associated with a marked bone loss after injury and a consequent increased risk of osteoporosis and fractures. The aim of this study was to analyze the factors associated with osteoporosis development short-term after SCI. METHODS We included patients with complete recent SCI (<6 months) evaluating bone turnover markers (P1NP, bone ALP, and sCTx), 25-OH-vitamin D (25OHD) levels, and lumbar and femoral BMD (Lunar, Prodigy) at baseline, 6 and 12 months after SCI. The risk factors for osteoporosis analyzed included the following: age, gender, BMI, toxic habits, bone turnover markers, 25OHD levels, lumbar and femoral BMD, level, severity and type of SCI, and days-since-injury. Osteoporosis was defined according to WHO criteria. RESULTS Thirty-five patients aged 35 ± 16 years were included, and 52 % developed osteoporosis during the 12-month follow-up. These latter patients had lower BMD values at femur and lumbar spine and higher bone turnover markers at baseline. On multivariate analysis, the principal factors related to osteoporosis development were as follows: total femur BMD <1 g/cm(2) (RR, 3.61; 95 % CI 1.30-10.06, p = 0.002) and lumbar BMD <1.2 g/cm(2) at baseline (0.97 probability of osteoporosis with both parameters under these values). Increased risk for osteoporosis was also associated with increased baseline values of bone ALP (>14 ng/mL) (RR 2.40; 95 % CI 1.10-5.23, p = 0.041) and P1NP (>140 ng/mL) (RR 3.08; 95 % CI 1.10-8.57, p = 0.017). CONCLUSIONS The evaluation of BMD at the lumbar spine and femur short-term after SCI is a simple, effective method for predicting the development of osteoporosis during the first year after SCI. Our results also indicate the need to evaluate and treat these patients shortly after injury.
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Affiliation(s)
- L Gifre
- Metabolic Bone Diseases Unit, Service of Rheumatology, Hospital Clinic of Barcelona, Villarroel 170, 08036, Barcelona, Spain,
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Browning KN, Travagli RA. Central nervous system control of gastrointestinal motility and secretion and modulation of gastrointestinal functions. Compr Physiol 2015; 4:1339-68. [PMID: 25428846 DOI: 10.1002/cphy.c130055] [Citation(s) in RCA: 322] [Impact Index Per Article: 35.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Although the gastrointestinal (GI) tract possesses intrinsic neural plexuses that allow a significant degree of autonomy over GI functions, the central nervous system (CNS) provides extrinsic neural inputs that regulate, modulate, and control these functions. While the intestines are capable of functioning in the absence of extrinsic inputs, the stomach and esophagus are much more dependent upon extrinsic neural inputs, particularly from parasympathetic and sympathetic pathways. The sympathetic nervous system exerts a predominantly inhibitory effect upon GI muscle and provides a tonic inhibitory influence over mucosal secretion while, at the same time, regulates GI blood flow via neurally mediated vasoconstriction. The parasympathetic nervous system, in contrast, exerts both excitatory and inhibitory control over gastric and intestinal tone and motility. Although GI functions are controlled by the autonomic nervous system and occur, by and large, independently of conscious perception, it is clear that the higher CNS centers influence homeostatic control as well as cognitive and behavioral functions. This review will describe the basic neural circuitry of extrinsic inputs to the GI tract as well as the major CNS nuclei that innervate and modulate the activity of these pathways. The role of CNS-centered reflexes in the regulation of GI functions will be discussed as will modulation of these reflexes under both physiological and pathophysiological conditions. Finally, future directions within the field will be discussed in terms of important questions that remain to be resolved and advances in technology that may help provide these answers.
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Affiliation(s)
- Kirsteen N Browning
- Department of Neural and Behavioral Sciences, Penn State College of Medicine, Hershey, Pennsylvania
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16
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Bhagat R, Fortna SR, Browning KN. Exposure to a high fat diet during the perinatal period alters vagal motoneurone excitability, even in the absence of obesity. J Physiol 2014; 593:285-303. [PMID: 25556801 DOI: 10.1113/jphysiol.2014.282806] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2014] [Accepted: 10/24/2014] [Indexed: 01/02/2023] Open
Abstract
KEY POINTS Obesity is recognized as being multifactorial in origin, involving both genetic and environmental factors. The perinatal period is known to be critically important in the development of neural circuits responsible for energy homeostasis and the integration of autonomic reflexes. Diet-induced obesity alters the biophysical, pharmacological and morphological properties of vagal neurocircuits regulating upper gastrointestinal tract functions, including satiety. Less information is available, however, regarding the effects of a high fat diet (HFD) itself on the properties of vagal neurocircuits. The present study was designed to test the hypothesis that exposure to a HFD during the perinatal period alters the electrophysiological, pharmacological and morphological properties of vagal efferent motoneurones innervating the stomach. Our data indicate that perinatal HFD decreases the excitability of gastric-projecting dorsal motor nucleus neurones and dysregulates neurotransmitter release from synaptic inputs and that these alterations occur prior to the development of obesity. These findings represent the first direct evidence that exposure to a HFD modulates the processing of central vagal neurocircuits even in the absence of obesity. The perinatal period is critically important to the development of autonomic neural circuits responsible for energy homeostasis. Vagal neurocircuits are vital to the regulation of upper gastrointestinal functions, including satiety. Diet-induced obesity modulates the excitability and responsiveness of both peripheral vagal afferents and central vagal efferents but less information is available regarding the effects of diet per se on vagal neurocircuit functions. The aims of this study were to investigate whether perinatal exposure to a high fat diet (HFD) dysregulated dorsal motor nucleus of the vagus (DMV) neurones, prior to the development of obesity. Whole cell patch clamp recordings were made from gastric-projecting DMV neurones in thin brainstem slices from rats that were exposed to either a control diet or HFD from pregnancy day 13. Our data demonstrate that following perinatal HFD: (i) DMV neurones had decreased excitability and input resistance with a reduced ability to fire action potentials; (ii) the proportion of DMV neurones excited by cholecystokinin (CCK) was unaltered but the proportion of neurones in which CCK increased excitatory glutamatergic synaptic inputs was reduced; (iii) the tonic activation of presynaptic group II metabotropic glutamate receptors on inhibitory nerve terminals was attenuated, allowing modulation of GABAergic synaptic transmission; and (iv) the size and dendritic arborization of gastric-projecting DMV neurones was increased. These results suggest that perinatal HFD exposure compromises the excitability and responsiveness of gastric-projecting DMV neurones, even in the absence of obesity, suggesting that attenuation of vago-vagal reflex signalling may precede the development of obesity.
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Affiliation(s)
- Ruchi Bhagat
- Department of Neural and Behavioral Sciences, Penn State College of Medicine, Hershey, PA 17033, USA
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Swartz EM, Holmes GM. Gastric vagal motoneuron function is maintained following experimental spinal cord injury. Neurogastroenterol Motil 2014; 26:1717-29. [PMID: 25316513 PMCID: PMC4245370 DOI: 10.1111/nmo.12452] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/30/2014] [Accepted: 09/13/2014] [Indexed: 12/22/2022]
Abstract
BACKGROUND Clinical reports indicate that spinal cord injury (SCI) initiates profound gastric dysfunction. Gastric reflexes involve stimulation of sensory vagal fibers, which engage brainstem circuits that modulate efferent output back to the stomach, thereby completing the vago-vagal reflex. Our recent studies in a rodent model of experimental high thoracic (T3-) SCI suggest that reduced vagal afferent sensitivity to gastrointestinal (GI) stimuli may be responsible for diminished gastric function. Nevertheless, derangements in efferent signals from the dorsal motor nucleus of the vagus (DMV) to the stomach may also account for reduced motility. METHODS We assessed the anatomical, neurophysiological, and functional integrity of gastric-projecting DMV neurons in T3-SCI rats using: (i) retrograde labeling of gastric-projecting DMV neurons; (ii) whole cell recordings from gastric-projecting neurons of the DMV; and, (iii) in vivo measurements of gastric contractions following unilateral microinjection of thyrotropin-releasing hormone (TRH) into the DMV. KEY RESULTS Immunohistochemical analysis of gastric-projecting DMV neurons demonstrated no difference between control and T3-SCI rats. Whole cell in vitro recordings showed no alteration in DMV membrane properties and the neuronal morphology of these same, neurobiotin-labeled, DMV neurons were unchanged after T3-SCI with regard to cell size and dendritic arborization. Central microinjection of TRH induced a significant facilitation of gastric contractions in both control and T3-SCI rats and there were no significant dose-dependent differences between groups. CONCLUSIONS & INFERENCES Our data suggest that the acute, 3 day to 1 week post-SCI, dysfunction of vagally mediated gastric reflexes do not include derangements in the efferent DMV motoneurons.
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Affiliation(s)
| | - Gregory M. Holmes
- Corresponding author: Dr. Gregory M. Holmes, Department of Neural and Behavioral Sciences, Penn State College of Medicine, 500 University Drive, MC H109, Hershey, PA 17033,
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Lee KZ, Chang YS. Recovery of the pulmonary chemoreflex and functional role of bronchopulmonary C-fibers following chronic cervical spinal cord injury. J Appl Physiol (1985) 2014; 117:1188-98. [PMID: 25257870 DOI: 10.1152/japplphysiol.00723.2014] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Persistent impairment of pulmonary defense reflexes is a critical factor contributing to pulmonary complications in patients with spinal cord injuries. The pulmonary chemoreflex evoked by activation of bronchopulmonary C-fibers has been reported to be abolished in animals with acute cervical hemisection (C2Hx). The present study examined whether the pulmonary chemoreflex can recover during the chronic injury phase and investigated the role of bronchopulmonary C-fibers on the altered breathing pattern after C2Hx. In the first protocol, bronchopulmonary C-fibers were excited by intrajugular capsaicin administration in uninjured and complete C2Hx animals 8 wk postsurgery. Capsaicin evoked pulmonary chemoreflexes in both groups, but the reflex intensity was significantly weaker in C2Hx animals. To examine whether spared spinal white matter tissue contributes to pulmonary chemoreflex recovery, the reflex was evaluated in animals with different extents of lateral injury. Linear regression analyses revealed that tidal volume significantly correlated with the extent of spared tissue; however, capsaicin-induced apnea was not related to injury severity when the ipsilateral-to-contralateral white matter ratio was <50%. In the second protocol, the influence of background bronchopulmonary C-fiber activity on respiration was investigated by blocking C-fiber conduction via perivagal capsaicin treatment. The rapid shallow breathing of C2Hx animals persisted after perivagal capsaicin treatment despite attenuation of pulmonary chemoreflexes. These results indicate that the pulmonary chemoreflex can recover to some extent following spinal injury, but remains attenuated even when there is moderate spinal tissue sparing, and that altered breathing pattern of C2Hx animals cannot be attributed to endogenous activation of bronchopulmonary C-fibers.
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Affiliation(s)
- Kun-Ze Lee
- Department of Biological Sciences, National Sun Yat-sen University, Kaohsiung, Taiwan; Institute of Medical Science and Technology, National Sun Yat-sen University, Kaohsiung, Taiwan; Center for Neuroscience, National Sun Yat-sen University, Kaohsiung, Taiwan; and Department of Biomedical Science and Environmental Biology, Kaohsiung Medical University, Kaohsiung, Taiwan
| | - Yu-Shuo Chang
- Department of Biological Sciences, National Sun Yat-sen University, Kaohsiung, Taiwan
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Holmes GM, Swartz EM, McLean MS. Fabrication and implantation of miniature dual-element strain gages for measuring in vivo gastrointestinal contractions in rodents. J Vis Exp 2014:51739. [PMID: 25285858 DOI: 10.3791/51739] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023] Open
Abstract
Gastrointestinal dysfunction remains a major cause of morbidity and mortality. Indeed, gastrointestinal (GI) motility in health and disease remains an area of productive research with over 1,400 published animal studies in just the last 5 years. Numerous techniques have been developed for quantifying smooth muscle activity of the stomach, small intestine, and colon. In vitro and ex vivo techniques offer powerful tools for mechanistic studies of GI function, but outside the context of the integrated systems inherent to an intact organism. Typically, measuring in vivo smooth muscle contractions of the stomach has involved an anesthetized preparation coupled with the introduction of a surgically placed pressure sensor, a static pressure load such as a mildly inflated balloon or by distending the stomach with fluid under barostatically-controlled feedback. Yet many of these approaches present unique disadvantages regarding both the interpretation of results as well as applicability for in vivo use in conscious experimental animal models. The use of dual element strain gages that have been affixed to the serosal surface of the GI tract has offered numerous experimental advantages, which may continue to outweigh the disadvantages. Since these gages are not commercially available, this video presentation provides a detailed, step-by-step guide to the fabrication of the current design of these gages. The strain gage described in this protocol is a design for recording gastric motility in rats. This design has been modified for recording smooth muscle activity along the entire GI tract and requires only subtle variation in the overall fabrication. Representative data from the entire GI tract are included as well as discussion of analysis methods, data interpretation and presentation.
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Affiliation(s)
- Gregory M Holmes
- Department of Neural and Behavioral Sciences, Penn State University College of Medicine;
| | - Emily M Swartz
- Department of Neural and Behavioral Sciences, Penn State University College of Medicine
| | - Margaret S McLean
- Department of Neural and Behavioral Sciences, Penn State University College of Medicine
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Swartz EM, Browning KN, Travagli RA, Holmes GM. Ghrelin increases vagally mediated gastric activity by central sites of action. Neurogastroenterol Motil 2014; 26:272-82. [PMID: 24261332 PMCID: PMC3907172 DOI: 10.1111/nmo.12261] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/04/2013] [Accepted: 10/19/2013] [Indexed: 12/31/2022]
Abstract
BACKGROUND Vagally dependent gastric reflexes are mediated through vagal afferent fibers synapsing upon neurons of the nucleus tractus solitarius (NTS) which, in turn modulate the preganglionic parasympathetic dorsal motor nucleus of the vagus (DMV) neurons within the medullary dorsal vagal complex (DVC). The expression and transport of ghrelin receptors has been documented for the afferent vagus nerve, and functional studies have confirmed that vagal pathways are integral to ghrelin-induced stimulation of gastric motility. However, the central actions of ghrelin within the DVC have not been explored fully. METHODS We assessed the responses to ghrelin in fasted rats using: (i) in vivo measurements of gastric tone and motility following IVth ventricle application or unilateral microinjection of ghrelin into the DVC and (ii) whole cell recordings from gastric-projecting neurons of the DMV. KEY RESULTS (i) IVth ventricle application or unilateral microinjection of ghrelin into the DVC-elicited contractions of the gastric corpus via excitation of a vagal cholinergic efferent pathway and (ii) ghrelin facilitates excitatory, but not inhibitory, presynaptic transmission to DMV neurons. CONCLUSIONS & INFERENCES Our data indicate that ghrelin acts centrally by activating excitatory synaptic inputs onto DMV neurons, resulting in increased cholinergic drive by way of vagal motor innervation to the stomach.
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Affiliation(s)
| | | | | | - Gregory M. Holmes
- Corresponding Author: Dr. Gregory M. Holmes, Penn State University College of Medicine, 500 University Dr., H181, Hershey, PA 17033, Tel: +1 717 531-6413, fax; +1 717 531-5184,
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Holmes GM. Upper gastrointestinal dysmotility after spinal cord injury: is diminished vagal sensory processing one culprit? Front Physiol 2012; 3:277. [PMID: 22934031 PMCID: PMC3429051 DOI: 10.3389/fphys.2012.00277] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2012] [Accepted: 06/27/2012] [Indexed: 12/12/2022] Open
Abstract
Despite the widely recognized prevalence of gastric, colonic, and anorectal dysfunction after spinal cord injury (SCI), significant knowledge gaps persist regarding the mechanisms leading to post-SCI gastrointestinal (GI) impairments. Briefly, the regulation of GI function is governed by a mix of parasympathetic, sympathetic, and enteric neurocircuitry. Unlike the intestines, the stomach is dominated by parasympathetic (vagal) control whereby gastric sensory information is transmitted via the afferent vagus nerve to neurons of the nucleus tractus solitarius (NTS). The NTS integrates this sensory information with signals from throughout the central nervous system. Glutamatergic and GABAergic NTS neurons project to other nuclei, including the preganglionic parasympathetic neurons of the dorsal motor nucleus of the vagus (DMV). Finally, axons from the DMV project to gastric myenteric neurons, again, through the efferent vagus nerve. SCI interrupts descending input to the lumbosacral spinal cord neurons that modulate colonic motility and evacuation reflexes. In contrast, vagal neurocircuitry remains anatomically intact after injury. This review presents evidence that unlike the post-SCI loss of supraspinal control which leads to colonic and anorectal dysfunction, gastric dysmotility occurs as an indirect or secondary pathology following SCI. Specifically, emerging data points toward diminished sensitivity of vagal afferents to GI neuroactive peptides, neurotransmitters and, possibly, macronutrients. The neurophysiological properties of rat vagal afferent neurons are highly plastic and can be altered by injury or energy balance. A reduction of vagal afferent signaling to NTS neurons may ultimately bias NTS output toward unregulated GABAergic transmission onto gastric-projecting DMV neurons. The resulting gastroinhibitory signal may be one mechanism leading to upper GI dysmotility following SCI.
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Affiliation(s)
- Gregory M. Holmes
- Neural and Behavioral Sciences, Penn State University College of MedicineHershey, PA, USA
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