Splanchnic Nerve Research Articles

Extrinsic innervation of the pelvic organs in the lesser pelvis of human embryos.

Realistic models to understand the developmental appearance of the pelvic nervous system in mammals are scarce. We visualized the development of the inferior hypogastric plexus and its preganglionic connections in human embryos at 4–8 weeks post‐fertilization, using Amira 3D reconstruction and Cinema 4D‐remodelling software. We defined the embryonic lesser pelvis as the pelvic area caudal to both umbilical arteries and containing the hindgut. Neural crest cells (NCCs) appeared dorsolateral to the median sacral artery near vertebra S1 at ~5 weeks and had extended to vertebra S5 1 day later. Once para‐arterial, NCCs either formed sympathetic ganglia or continued to migrate ventrally to the pre‐arterial region, where they formed large bilateral inferior hypogastric ganglionic cell clusters (IHGCs). Unlike more cranial pre‐aortic plexuses, both IHGCs did not merge because the 'pelvic pouch', a temporary caudal extension of the peritoneal cavity, interposed. Although NCCs in the sacral area started to migrate later, they reached their pre‐arterial position simultaneously with the NCCs in the thoracolumbar regions. Accordingly, the superior hypogastric nerve, a caudal extension of the lumbar splanchnic nerves along the superior rectal artery, contacted the IHGCs only 1 day later than the lumbar splanchnic nerves contacted the inferior mesenteric ganglion. The superior hypogastric nerve subsequently splits to become the superior hypogastric plexus. The IHGCs had two additional sources of preganglionic innervation, of which the pelvic splanchnic nerves arrived at ~6.5 weeks and the sacral splanchnic nerves only at ~8 weeks. After all preganglionic connections had formed, separate parts of the inferior hypogastric plexus formed at the bladder neck and distal hindgut.

Increased sympathetic responses induced by chronic obstructive sleep apnea are caused by sleep fragmentation.

Obstructive sleep apnea (OSA) is often associated with sympathetic overactivity and hypertension. These associations are mainly attributed to hypoxia acting on arterial chemoreceptors. However, the contribution of arousal from sleep is unclear. We measured the effect of OSA and sleep fragmentation on cardiovascular and sympathetic function and gene expression in the brain in rats. Male Wistar rats were fitted with a tracheal balloon and EEG and electromyogram electrodes and assigned to control (n = 6), OSA (n = 9), or arousal (n = 8) treatments. The OSA group was subjected to obstructive apnea, each time the rat entered sleep, for 8 h/day for 15 days. The arousal group was similarly exposed to vibration, which was produced with a miniature vibration motor mounted on the rat's head. Vibration intensity slowly increased until the rat awoke. One day after the last apnea or arousal, rats were anesthetized and arterial blood pressure and splanchnic sympathetic nerve activity (SSNA) were recorded. Baseline mean and diastolic pressure were increased after OSA. Resting SSNA was similar in the three groups, but both OSA and sleep fragmentation increased sympathetic activation in response to airway obstruction and chemoreflex activation by cyanide. OSA increased superoxide dismutases 1 and 2 in the brainstem, whereas sleep fragmentation did not. Our results suggest that sympathetic overactivity to chemoreceptor stimulation was a consequence of arousal from sleep. Our study suggests that sleep disruption may have an important role in the development of apnea-related sympathetic activation.NEW & NOTEWORTHY Obstructive sleep apnea causes a hyperactive chemoreflex, with increased sympathetic activation. However, it is not clear whether this pathophysiologic mechanism is due to repeated hypoxia or to sleep disruption. The present study suggests that sleep fragmentation contributes importantly to increased sympathetic activation after chemoreceptor stimulation. This suggests that sleep fragmentation has an important role in the sympathetic activation seen in sleep apnea patients.

Pelvic Neuroanatomy: An Overview of Commonly Encountered Pelvic Nerves in Gynecologic Surgery

This video tutorial identifies key anatomic landmarks useful in identifying the path of the most commonly encountered pelvic nerves in benign gynecologic surgery. This is a narrated overview of commonly encountered pelvic nerves during benign gynecology, their origin, sensory, and motor function, as well as sequelae related to injury. The unintended injury of pelvic neural connections can be a complication of any pelvic surgery, however, surgery for malignancy or endometriosis may increase the likelihood of encountering these nerves. The majority of focus surrounding surgical nerve injury, however, relates to patient positioning [1]. Injury to the pelvic nerves can lead to lifelong sexual, bladder, and defecatory dysfunction [2]. We review the Genitofemoral, Lateral Femoral Cutaneous, Ilioinguinal, Obturator, Superior and Inferior Hypogastric nerves, Pelvic Splanchnic nerves, and the Sacral nerves. Surgical illustrations are used (Fig. 1) alongside real-time narrated video to help viewers recognize the normal course of commonly encountered pelvic nerves at the time of gynecologic surgery (Figs2-3). The surgical management of complex pelvic disease can unfortunately carry significant patient morbidity [3]. The neural pathways traveling through the pelvis via the hypogastric nerves are responsible for proprioception, vaginal lubrication, and proper functioning or the urethral and anal sphincters [4]. Sparing these nerves during pelvic surgery, and especially when anatomic planes are distorted by pelvic disease, requires surgical expertise and an immense understanding of pelvic neuroanatomy [4,5]. Preservation of the pelvic neural pathways is necessary to deliver the best patient outcomes while minimizing unwanted surgical complications. This video tutorial also highlights the origin of these nerves, their anatomic location, procedures in which these nerves may be encountered, and what sequelae occur from their unintended injury.

A Comprehensive Review of the Celiac Plexus Block for the Management of Chronic Abdominal Pain.

Chronic abdominal pain (CAP) is a significant health problem that can dramatically affect quality of life and survival. Pancreatic cancer is recognized as one of the most painful malignancies with 70-80% suffering from substantial pain, often unresponsive to typical medical management. Celiac plexus neurolysis and celiac plexus block (CPB) can be performed to mitigate pain through direct destruction or blockade of visceral afferent nerves. The objective of this manuscript is to provide a comprehensive review of the CPB as it pertains to CAP with a focus on the associated anatomy, indications, techniques, neurolysis/blocking agents, and complications observed in patients who undergo CPB for the treatment of CAP. The CAP is difficult to manage due to lack of precision in diagnosis and limited evidence from available treatments. CAP can arise from both benign and malignant causes. Treatment options include pharmacologic, interventional, and biopsychosocial treatments. Opioid therapy is typically utilized for the treatment of CAP; however, opioid therapy is associated with multiple complications. CPB has successfully been used to treat a variety of conditions resulting in CAP. The majority of the literature specifically related to CPB is surrounding chronic pain associated with pancreatic cancer. The literature shows emerging evidence in managing CAP with CPB, specifically in pancreatic cancer. This review provides multiple aspects of CAP and CPB, including anatomy, medical necessity, indications, technical considerations, available evidence, and finally complications related to the management.

Splanchnic Nerve Block for Chronic Heart Failure

ObjectivesWe hypothesized that splanchnic nerve blockade (SNB) would attenuate increased exercise-induced cardiac filling pressures in patients with chronic HF. BackgroundChronic heart failure (HF) is characterized by limited exercise capacity driven in part by an excessive elevation of cardiac filling pressures. MethodsThis is a prospective, open-label, single-arm interventional study in chronic HF patients. Eligible patients had a wedge pressure ≥15 mm Hg at rest or ≥25 mm Hg with exercise on baseline right heart catheterization. Patients underwent cardiopulmonary exercise testing with invasive hemodynamic assessment, followed by percutaneous SNB with ropivacaine. ResultsNineteen patients were enrolled, 15 of whom underwent SNB. The average age was 58 ± 13 years, 7 (47%) patients were women and 6 (40%) were black. Left ventricular ejection fraction was ≤35% in 14 (93%) patients. No procedural complications were encountered. SNB reduced mean pulmonary arterial pressure at peak exercise from 54.1 ± 14.4 (pre-SNB) to 45.8 ± 17.7 mm Hg (p < 0.001) (post-SNB). Similarly, SNB reduced exercise-induced wedge pressure from 34.8 ± 10.0 (pre-SNB) to 25.1 ± 10.7 mm Hg (p < 0.001) (post-SNB). The cardiac index changed with peak exercise from 3.4 ± 1.2 (pre-SNB) to 3.8 ± 1.1 l/min/m2 (p = 0.011) (post-SNB). After SNB, patients exercised for approximately the same duration at a greater workload (33 ± 24 W vs. 50 ± 30 W; p = 0.019) and peak oxygen consumption VO2 (9.1 ± 2.5 vs. 9.8 ± 2.7 ml/kg/min; p = 0.053). ConclusionsSNB reduced resting and exercise-induced pulmonary arterial and wedge pressure with favorable effects on cardiac output and exercise capacity. Continued efforts to investigate short- and long-term effects of SNB in chronic HF are warranted. Clinical Trials Registration (Abdominal Nerve Blockade in Chronic Heart Failure; NCT03453151)

Multi-target Treatment for Irritable Bowel Syndrome with STW 5: Pharmacological Modes of Action.

Irritable bowel syndrome (IBS) is a heterogeneous and complex functional gastrointestinal disorder with a global prevalence of approximately 11% and high geographic variation. IBS encompasses various symptom clusters considered to reflect complex patho-etiological mechanisms, and effective treatment options are limited, with most medications targeting individual mechanisms and symptoms. Therefore, multi-targeted treatment is required. IBS is currently viewed as a disorder of disturbed gut-brain interactions with abnormalities at different sites along the gut-brain axis, including altered gastrointestinal motility, visceral hypersensitivity, increased intestinal permeability, and altered gut microbiota. All of these abnormalities represent individual targets for STW 5, a herbal preparation with nine different extracts indicated for the treatment of functional dyspepsia and IBS. As a multi-targeted medicinal drug, STW 5 possesses multiple pharmacodynamic effects. Several in vitro and in vivo studies have demonstrated STW 5 efficacy on numerous IBS patho-mechanisms targeting gastrointestinal smooth muscles, visceral afferent nerves, inflammation, gut permeability, and the gut microbiome.

Useful Pelvic Retroperitoneal Neuroanatomy for Benign Gynecologic Surgery: A Cadaveric Dissection

Knowledge of the retroperitoneal anatomy is particularly important to facilitate surgical procedure and reduce the number of complications. The objective of this video is to demonstrate pelvic neuroanatomic structures and their relationships in the pelvic sidewall and the presacral space in a laparoscopic cadaveric dissection. Case report (anatomic study). Medical training center (AdventHealth Nicholson Center, Orlando, FL). The dissection started with the mobilization of the iliac vessels from the pelvic sidewall to identify the obturator nerve. The peritoneum of the ovarian fossa was opened, and the ureter was dissected up to the level of the uterine artery. The hypogastric nerve was identified. The close relationship between the ovarian fossa and the obturator nerve could be demonstrated. The deep dissection of the obturator fossa allowed for the identification of the lumbosacral trunk, S1, the sciatic nerve, S2, S3, S4, and the splanchnic nerves. Then, the ischial spine and the sacrospinous ligament were identified. The pudendal nerve and vessels could be observed passing below the sacrospinous ligament, entering the pudendal canal (Alcock's canal). The presacral space was dissected, and the hypogastric fascia was opened. S1 to S4 were identified coming from the sacral foramens. The laparoscopic dissection, using the cadaveric model, allowed for the development of the entire retroperitoneal anatomy, focusing on the dissection of the pelvic innervation. Anatomic relationships among the ureter, the hypogastric nerve, the uterosacral ligament, the splanchnic nerves, the inferior hypogastric plexus, and the organs (bowel, vagina, uterus, and bladder) could be demonstrated. A laparoscopic cadaveric dissection can be used as a resource to demonstrate and educate surgeons about the neurologic retroperitoneal structures and their relationships.

Anatomy of the female pelvic nerves: a macroscopic study of the hypogastric plexus and their relations and variations.

The autonomic nerves of the lesser pelvis are particularly prone to iatrogenic lesions due to their exposed position during manifold surgical interventions. Nevertheless, the cause of rectal and urinary incontinence or sexual dysfunctions, for example after rectal cancer resection or hysterectomy, remains largely understudied, particularly with regard to the female pelvic autonomic plexuses. This study focused on the macroscopic description of the superior hypogastric plexus, hypogastric nerves, inferior hypogastric plexus, the parasympathetic pelvic splanchnic nerves and the sympathetic fibres. Their arrangement is described in relation to commonly used surgical landmarks such as the sacral promontory, ureters, uterosacral ligaments, uterine and rectal blood vessels. Thirty-one embalmed female pelvises from 20 formalin-fixed and 11 Thiel-fixed cadavers were prepared. In all cases explored, the superior hypogastric plexus was situated anterior to the bifurcation of the abdominal aorta. In 60% of specimens, it reached the sacral promontory, whereas in 40% of specimens, it continued across the pelvic brim until S1. In about 25% of the subjects, we detected an accessory hypogastric nerve, which has not been systematically described so far. It originated medially from the inferior margin of the superior hypogastric plexus and continued medially into the presacral space. The existence of an accessory hypogastric nerve was confirmed during laparoscopy and by histological examination. The inferior hypogastric plexuses formed fan-shaped plexiform structures at the end of both hypogastric nerves, exactly at the junction of the ureter and the posterior wall of the uterine artery at the uterosacral ligament. In addition to the pelvic splanchnic nerves from S2-S4, which joined the inferior hypogastric plexus, 18% of the specimens in the present study revealed an additional pelvic splanchnic nerve originating from the S1 sacral root. In general, form, breadth and alignment of the autonomic nerves displayed large individual variations, which could also have a clinical impact on the postoperative function of the pelvic organs. The study serves as a basis for future investigations on the autonomic innervation of the female pelvic organs.

Interaction between angiotensin II and GABA in the spinal cord regulates sympathetic vasomotor activity in Goldblatt hypertension

Previous studies have been described changes in brain regions contributing to the sympathetic vasomotor overactivity in Goldblatt hypertension (2K1C). Furthermore, changes in the spinal cord are also involved in the cardiovascular and autonomic dysfunction in renovascular hypertension, as intrathecal (i.t.) administration of Losartan (Los) causes a robust hypotensive/sympathoinhibitory response in 2K1C but not in control rats. The present study evaluated the role of spinal γ-aminobutyric acid (GABA)-ergic inputs in the control of sympathetic vasomotor activity in the 2K1C rats. Hypertension was induced by clipping the renal artery. After six weeks, a catheter (PE-10) was inserted into the subarachnoid space and advanced to the T10-11 vertebral level in urethane-anaesthetized rats. The effects of i.t. injection of bicuculline (Bic) on blood pressure (BP), renal and splanchnic sympathetic nerve activity (rSNA and sSNA, respectively) were evaluated over 40 consecutive minutes in the presence or absence of spinal AT1 antagonism. I.t. Bic triggered a more intense pressor and sympathoexcitatory response in 2K1C rats, however, these responses were attenuated by previous i.t. Los. No differences in the gene expression of GAD 65 and GABA-A receptors subunits in the spinal cord segments were found. Thus, the sympathoexcitation induced by spinal GABA-A blockade is dependent of local AT1 receptor in 2K1C but not in control rats. Excitatory angiotensinergic inputs to sympathetic preganglionic neurons are tonic controlled by spinal GABAergic actions in Goldblatt hypertension.

Rapports anatomiques des nerfs végétatifs constituant la fosse para rectale, application à la chirurgie de l’endométriose rectale

ObjectivesThe objective of the study was to describe the inferior hypogastric plexus and nerves constituting the para-rectal fossa in order to study the importance of anatomical knowledge in rectal endometriosis surgery. MethodsIn order to discover the complete anatomy of the study area, we carried out a review of the literature and relied on dissection of a female cadaver and operative dissections in patients treated for rectal endometriosis. ResultsThe inferior hypogastric plexus, the hypogastric nerve and the pelvic splanchnic nerves are the nervous elements component the para-rectal fossa. These nerves were important urinary, digestive and sexual functions. The dissection of the Okabayashi and the Latzko spaces within the para-rectal fossa and sparing nerve within this zone is more important for the prevention of traumatic nervous sequelae during rectal endometriosis surgery. The pelvic anatomy can be by attraction and sheathing nerve structures by endometriosis lesions which can complicate preservation techniques. ConclusionLesions of pelvic vegetative nerves running through the para-rectal fossa can be responsible for urinary, digestive and sexual disorders that can affect patients quality of life. There is currently only one standardized “nerve sparing” technique in pelvic endometriosis surgery. Knowledge of the anatomy of the nerves making up the para-rectal fossa helps to orient the operative dissection and prevent postoperative nerve complications after surgery for rectal endometriosis.

Prior Ablation of the Splanchnic Sympathetic Nerves Increases Plasma Inflammatory Cytokine Levels and Suppresses Bacteremia in Response to Systemically Administered E. coli in Sheep

The splanchnic sympathetic nerves exert a powerful anti‐inflammatory action in response to systemic administration of lipopolysaccharide in rats (Martelli et al. J. Physiol. 592: 1677–1686, 2014). However, it is not known how this endogenous anti‐inflammatory influence of the splanchnic nerve affects the body’s ability to fight infection. The aim of this study was to determine if and how the endogenous reflex activation of the splanchnic anti‐inflammatory pathway affects blood cytokine levels and the disease course of bacteremia after intravenous infusion of live E. coli into a conscious large animal (sheep). One month prior to infection, the greater splanchnic nerve was cut bilaterally (SplancX, n = 8) or sham surgery (Sham, n = 7) performed in anesthetized sheep (isoflurane/O2). After 1 month, these conscious sheep were infused with live E. coli (2.8 × 109 CFU in 30 min) into a jugular vein. Blood samples were obtained at 1.5, 3, 6, 24 and 48 h after bacterial injection. As expected, i.v. infusion of E. coli caused systemic bacteremia with high blood counts of E. coli [3.02 ± 0.64 Log10(CFU/ml + 1), mean ± sem] in 5 of 7 sham sheep. By contrast, no significant bacteremia was observed in any of the 8 SplancX sheep (0.18 ± 0.18 Log10[CFU/ml + 1], p &lt; 0.01, c.f. Sham sheep). Plasma levels of tumour necrosis factor‐α peaked after 1.5 h, and were significantly greater in SplancX vs Sham sheep (2.4 ± 0.6 vs 1.5 ± 0.2 ng/ml, p &lt; 0.05) at this time. Plasma levels of another pro‐inflammatory cytokine, interleukin‐6, peaked at 6h and were higher in SplancX vs Sham sheep (7.4 ± 0.6 vs 2.4 ± 0.6 ng/ml, p &lt; 0.01). Although plasma levels of the anti‐inflammatory cytokine interleukin‐10 increased in both groups, they were lower in SplancX vs Sham sheep from 1.5 h to 24 h (2.9 ± 0.4 vs 6.7 ± 1.1 ng/ml at 24 h, p &lt; 0.01). All plasma cytokine levels measured had returned to baseline by 48 h. Plasma cortisol levels were higher (p&lt;0.01) in SplancX sheep only at 6 h (298 ± 29 vs 138 ± 37 ng/ml), while the fever was less (p &lt; 0.05) in SplancX at 6 h (40.3 ± 0.3 vs 40.8 ± 0.3°C). The greater pro‐inflammatory response in splanchnic denervated animals most likely contributes to their enhanced ability to clear bacteremia. The present findings demonstrate the powerful consequences of neural control of inflammation in the context of an acute systemic infection.Support or Funding InformationSupported by the National Heart Foundation of Australia

Activation of Bradykinin‐Sensitive Pericardial Afferents Increases Splanchnic Nerve Activity

Sympathetic drive plays a key role in control of cardiovascular function. The heart performs an important sensory function via a variety of cardiac receptors that modulate sympathetic drive. Bradykinin‐sensitive sympathetic afferent nerves from the heart can trigger marked increases in efferent sympathetic nerve activity to some cardiovascular targets such as the kidney. We reported previously that pericardial injection of bradykinin increased venous tone and cardiac output. The splanchnic vascular compartment plays an important role in control of venous return and cardiac output. This work tested the hypothesis that activation of bradykinin‐sensitive pericardial afferents increases postganglionic splanchnic sympathetic nerve activity.Sprague Dawley rats were anesthetized with a cocktail of alpha chloralose (80 mg/kg) and urethane (800 mg/kg). Catheters were placed in the femoral artery and vein to record arterial pressure (MAP) and heart rate (HR). A PE10 catheter was placed in the pericardial space for the injection of bradykinin (BK), an agent known to stimulate cardiac sympathetic afferents. The chest was closed and the rat allowed to breathe spontaneously. The splanchnic sympathetic nerve was isolated via a dorsal approach and placed on recording electrodes. After stabilization, the blood pressure, heart rate, and integrated splanchnic nerve activity (SPLNA) responses to pericardial injection of BK or vehicle were recorded. Responses were also recorded for intravenous injection of dimethylphenylpiperazinium (DMPP 150 ug/kg), a ganglionic stimulant, and a ganglion blocker (hexamethonium 20 mg/kg).Pericardial injection of saline vehicle had little effect (MAP: 0.1±0.4 mm Hg; HR: 1.2±1.4 bpm; SPLNA 1±2%). In contrast, intravenous injection of a ganglionic stimulant, DMPP, increased MAP (23±1 mm Hg) and SPLNA (95±46%). Pericardial injection of BK (10 ug/kg) increased MAP (21±3 mm Hg), HR (28±7 bpm) and SPLNA (93±37%). Ganglionic blockade with hexamethonium reduced SPLNA (−75±6%) and abolished the responses to pericardial injection of BK (MAP: −1±3 mm Hg; HR: −2±1 bpm; SPLNA: 7±30 %).We interpret these data to indicate that activation of bradykinin‐sensitive pericardial afferents increases postganglionic splanchnic sympathetic nerve activity. This finding is consistent with the view that activation of the cardiac sympathetic afferent reflex elicits a venoconstrictor response to increase venous return from the splanchnic vascular compartment.Support or Funding InformationSupported by NIH R01 HL136741‐03 (DM), R01 DK114663‐1 (HZ), and the Basic Biomedical Sciences program of the Sanford School of Medicine, University of South Dakota.

Selective afferent renal denervation mitigates renal and splanchnic sympathetic nerve overactivity and renal function in chronic kidney disease-induced hypertension.

Clinical and experimental evidence have shown that renal denervation, by removing both the sympathetic and afferent nerves, improves arterial hypertension and renal function in chronic kidney disease (CKD). Given the key role of renal sympathetic innervation in maintaining sodium and water homeostasis, studies have indicated that the total removal of renal nerves leads to impaired compensatory mechanisms during hemodynamic challenges. In the present study, we hypothesized that afferent (or sensory) fibers from the diseased kidney contribute to sympathetic overactivation to the kidney and other target organ, such as the splanchnic region, contributing to hypertension in CKD. We used a method to remove selectively the afferent renal fibers (periaxonal application of 33 mmol/l capsaicin) in a rat model of CKD, the 5/6 nephrectomy. Three weeks after afferent renal denervation (ARD), we found a decrease in mean arterial pressure (∼15%) and normalization in renal and splanchnic sympathetic nerve hyperactivity in the CKD group. Interestingly, intrarenal renin--angiotensin system, as well as renal fibrosis and function and proteinuria were improved after ARD in CKD rats. The findings demonstrate that afferent fibers contribute to the maintenance of arterial hypertension and reduced renal function that are likely to be mediated by increased sympathetic nerve activity to the renal territory as well as to other target organs in CKD.

Spinal Oxygen Sensors (SOS): A Novel Oxygen Sensing Mechanism Involved in Cardiovascular Responses to Hypoxia

BACKGROUNDIn healthy individuals, when blood oxygenation decreases, cardiorespiratory reflexes are triggered in an attempt to restore oxygen supply to vital organs. The carotid bodies are the primary respiratory oxygen chemoreceptors but cardiovascular responses to hypoxia such as increase in heart rate and blood pressure persist in their absence, suggesting an additional high‐fidelity oxygen sensor. Previously we discovered that spinal sympathetic preganglionic neurons (SPN), are exquisitely sensitive to oxygen; here we investigate the oxygen sensing mechanisms and test the role of these spinal oxygen sensors (SOS) in cardiorespiratory responses to asphyxia‐like stimuli.OBJECTIVETo study the cellular oxygen sensing mechanism and contribution of the SOS in responses to cardiorespiratory crisis.METHODSWe investigated the cellular mechanism of oxygen sensing in artificially‐perfused (in situ) and slice (in vitro) thoracic spinal cord preparations, recording sympathetic nerve root and single cell responses to hypoxia during pharmacological interrogation. To determine if the SOS are involved in cardiorespiratory responses to asphyxia, we also used an in situ rat spinal cord – carotid body ‐ brainstem preparation in which each oxygen sensitive compartment is separately perfused while recording phrenic (respiratory) and splanchnic (sympathetic) nerve activity.RESULTSOur data suggest the SOS use a novel oxygen sensing mechanism. This mechanism involves two interacting NADPH and oxygen‐dependent enzymes: Neuronal Nitric Oxide Synthase (NOS1) and NADPH oxidase (NOX2). NOS1 is expressed in surprising abundance in the SOS and is oxygen sensitive across the entire physiological range. Hence, in the presence of oxygen, NOS1 is likely to utilize most of the available NADPH in the cell. When oxygenation falls during hypoxia, NOS1 activity is reduced, increasing NADPH availability for NOX2. NOX2 produces Reactive Oxygen Species (ROS) which in turn, activate ROS‐dependent internal Ca2+ stores and/or Ca2+ channels leading to increased intracellular Ca2+, neuronal firing and, consequently, SOS responses to hypoxia. Functionally, during hypoxia, the SOS enhance sympathetic and breathing activity, while shortening apnea and gasping towards recovery, and are capable of triggering brief periods of sympathetic and respiratory‐like activity in the brainstem’s absence.CONCLUSIONSThe results provide critical new knowledge required to unlock the cellular mechanisms involved in how the body mounts emergency responses to conditions that involve chronic and acute hypoxia.Support or Funding InformationUniversity of Calgary Eyes High; Hotchkiss Brain Institute; Alberta Children’s Hospital Research Institute; Alberta Innovates Health Solutions; MITACS Globalink; Canadian Institutes of Health Research.

PVN‐projecting NTS Neurons is Involved in Sympathetic Long‐Term Facilitation After Acute Intermittent Optogenetic Stimulation

Caudal Nucleus Tractus Solitarius (NTS) neurons receive inputs from cardiorespiratory visceral afferents and send projections to the paraventricular nucleus of the hypothalamus (PVN). Acute intermittent optogenetic (AIO) stimulation of caudal NTS induces sympathetic long‐term facilitation (LTF), a progressive increase of sympathetic nerve activity. The contribution of PVN‐projecting NTS neurons to sympathetic LTF is unknown. This study used an intersectional viral approach to test the effects of acute intermittent optogenetic (AIO) stimulation of PVN‐projecting NTS neurons in sympathetic LTF. Adult male Sprague‐Dawley rats were anesthetized with isoflurane and injected rAAV2/Ef1a‐DIO‐hchR2(H134R)‐mCherry in the NTS and a retrograde AAV9.hSyn.HI.eGFP‐cre.WPRE.SV40 in the PVN four week prior to LTF experiments. This method was used to induce the CRE dependent expression of channel rhodopsin in PVN‐projecting NTS neurons. To measure LTF, we recorded splanchnic sympathetic nerve activity (SSNA), arterial pressure, and heart rate (HR) in anesthetized (urethane (800mg/kg) and α‐chloralose (80 mg/kg) cocktail delivered by intraperitoneal injection), paralyzed with gallamine triethiodide (20 mg/ml, 0.25 ml/h, iv) and mechanically ventilated adult rats. The caudal NTS was stimulated to induce AIO with a train of 10 stimuli each consisting of pulse of light of 10‐ms duration delivered at 20 Hz for 1 min every 6 min. Twenty minutes after AIO, SSNA amplitude increased by 25.36 ± 24.16% (n=3), and mean arterial pressure (MAP) increased by 7.43 ± 12.88 mmHg (n=3). During AIO induction, the acute SSNA and MAP varied with some rats demonstrating increases (n=2) or decreases (n=1) of SSNA, MAP, and HR. In other animals (n=3) where AIO decreases SSNA (‐58.96 ± 36.18%) and MAP (‐14.37 ± 8.57 mmHg), we tested the possible contribution of the baroreceptors in these decreases by bilateral muscimol (1–10 pmol/100nL) injections in the Caudal Ventrolateral Medulla (CVLM). AIO stimulation after inhibition of CVLM caused an increase in SSNA (1.293 ± 17.65%) and smaller decrease in MAP (−2.46± 6.2 mmHg). These results suggest that the splanchnic sympathetic LTF induced by acute intermittent stimulation of NTS neurons might be mediated by the PVN‐projecting neurons, although the acute responses may be excitatory or inhibitory. Further study is needed to clarify the mechanisms responsible for the differences in the cardiovascular and SSNA responses to acute, single optogenetic stimulation of PVN‐projecting NTS neurons. Despite the observed differences in the acute responses, the results indicate that sympathetic LTF can be induced by the optogenetic activation of NTS neurons that project to PVN.Support or Funding InformationNIH Grant P01 HL088052

Hypertension and Exaggerated Sympatho‐excitatory Reflexes are Reduced by Low Salt Diet in Male Obese Zucker Rats with no Effect in Lean Zucker Rats

Adult male obese Zucker rats (OZRs) develop sympathetically‐driven hypertension and exaggerated sympatho‐excitatory reflexes compared to age‐matched male lean Zucker rats (LZRs). Compared to LZRs, male OZRs on a standard rodent diet (0.5–1% NaCl) display attributes seen in salt sensitive rats consuming a high salt diet, such as suppressed plasma renin activity and exaggerated sympatho‐excitatory reflexes. The present study examined whether these attributes would be reduced in male OZRs on a low salt diet (0.1% NaCl). Rats were placed on diets with 0.5–0.85% NaCl (control diet; 10 OZRs and 8 LZRs) or a diet with 0.1% NaCl (low salt diet; 12 OZRs and 10 LZRs) for 14–28 days. After consumption of a low salt diet, baseline mean arterial pressure (MAP) was reduced in urethane‐anesthetized OZRs (125.7±4.4 vs 111.8±4.1 mmHg, P &lt;0.05) but not in LZRs (116.3±4.6 vs. 113.1±5.6 mmHg). Stimulation of sciatic nerve (1 msec pulses for 5 sec at 20 Hz, 100–800 μA) evoked intensity‐dependent increases in MAP and splanchnic sympathetic nerve activity (SNA) in OZRs and LZRs on both diets. Consumption of a low salt diet reduced the sciatic stimulation‐induced rises in SNA in OZRs (800 μA increased SNA 96±7.6% with control diet and 75.3±4.7% with low salt diet, P &lt;0.05) with no effect of diet in LZRs (800 μA increased SNA 87.4±4.4% with control diet and 83.0±8.8% in with low salt diet, n.s.). In contrast, low salt diet reduced the sciatic stimulation‐induced rises in MAP in OZRs and LZRs. These data suggest that consuming a diet containing 0.5–1.0% NaCl contributes to elevated baseline MAP in OZRs and exaggerated sympatho‐excitatory reflexes compared to male LZRs. However, both OZRs and LZRs show reduced sympathetically‐mediated rises in MAP on low salt diet. This study suggests that in male OZRs consumption of a standard rodent diet with 0.5–1.0% NaCl promotes some physiological effects observed in salt‐sensitive strains of rats on a high salt diet.Support or Funding InformationMechanisms for Impaired Short‐Term Control of Blood Pressure with Obesity (R01HL132568, Dr. Ann M. Schreihofer)

SPARC: Modelling a Bidirectional Bioelectric Pelvic Nerve Interface

BackgroundMicturition (urination) and continence are controlled by the autonomic nervous system; disruptions to urinary control due to disease or injury significantly impair patients’ quality‐of‐life. The pelvic nerves (in human, the pelvic splanchnic nerves) provide the primary source of autonomic sensory and motor innervation to the bladder and are prime targets for electrical stimulation to treat over‐ or under‐active bladder. The pelvic nerves in both human and rat are fasciculated, but differ from other well‐studied nerves such as the vagus or sciatic nerves in largely lacking a resistive epineurium. The pelvic nerves also comprise a much higher proportion of smaller‐caliber axons than are currently implemented in existing myelinated axon models.ObjectiveTo determine the significance of the macro‐ and micro‐anatomical properties of the pelvic nerve on the stimulation and recording performance of bioelectric neural interfaces.MethodsThe functional composition of the different fascicles of the pelvic nerve were determined using a combination of immunolabeling and tract tracing from the specific regions of the lower urinary tract or large intestine in male rats. Using this data, a model of the pelvic nerves and electrode array was implemented in SIM4LIFE (zmt.swiss) and EIDORS (eidors.org) to simulate electrical stimulation and recording, respectively. Established models for myelinated and unmyelinated axons were adapted to the small‐diameter axons found in the pelvic nerve and implemented in NEURON (neuron.yale.edu), and parameter sensitivity was established using Sobel’ sensitivity analysis for different fascicle arrangements and orientations.ResultsThe pelvic nerve consists of mixed sensory and motor fascicles, with sensory projections to lower urinary or intestinal tracts projecting in distinct fascicles. Sensitivity profiles to extracellular stimulation depend on the size and orientation of the fascicles, as well as their axon type and diameter. Within‐fascicle selectivity is enhanced in the largest fascicles of the pelvic nerve, and overall thresholds are reduced in the smallest fascicles. The stimulus thresholds and conduction velocities of the small myelinated axons depend on the ultrastructural geometry of the nodal and internodal regions, with less dependence on the juxtanode, in an axon‐type‐dependent manner. Extracellular recording sensitivity profiles for clinically realistic electrodes were computed in EIDORS and validated in SIM4LIFE for predicting spontaneous and electrically evoked activity recordings. Extracellular recording sensitivity and stimulus thresholds were both most closely correlated with axon‐electrode distance.ConclusionThe macroscopic and microscopic structure of the pelvic nerve alters its sensitivity to electrical stimulation, as well as the selectivity of extracellular electrical recording. EIDORS can be used to accurately simulate extracellular recording in complex, heterogenous neural geometries.Support or Funding InformationNIH SPARC 3OT2OD023872‐01S4

Conceptual Considerations for Device-Based Therapy in Acute Decompensated Heart Failure: DRI2P2S.

Acute decompensated heart failure remains the most common cause of hospitalization in older adults, and studies of pharmacological therapies have yielded limited progress in improving outcomes for these patients. This has prompted the development of novel device-based interventions, classified mechanistically based on the way in which they intend to improve central hemodynamics, increase renal perfusion, remove salt and water from the body, and result in clinically meaningful degrees of decongestion. In this review, we provide an overview of the pathophysiology of acute decompensated heart failure, current management strategies, and failed pharmacological therapies. We provide an in depth description of seven investigational device classes designed to target one or more of the pathophysiologic derangements in acute decompensated heart failure, denoted by the acronym DRI2P2S. Dilators decrease central pressures by increasing venous capacitance through splanchnic nerve modulation. Removers remove excess fluid through peritoneal dialysis, aquaphoresis, or hemodialysis. Inotropes directly modulate the cardiac nerve plexus to enhance ventricular contractility. Interstitial devices enhance volume removal through lymphatic duct decompression. Pushers are novel descending aorta rotary pumps that directly increase renal artery pressure. Pullers reduce central venous pressures or renal venous pressures to increase renal perfusion. Selective intrarenal artery catheters facilitate direct delivery of short acting vasodilator therapy. We also discuss challenges posed in clinical trial design for these novel device-based strategies including optimal patient selection and appropriate end points to establish efficacy.

Sympathetic Preganglionic Neurons (SPNs): a Promising Target to Regain Cardiorespiratory Control in Spinal Cord Injured (SCI) Patients

BackgroundThe consequences of spinal cord injuries (SCI) are massive and become more severe with higher levels of injury. Lesions located on cervical portions, specifically between C1‐C3 cause an interruption of the descending bulbospinal pathways. These pathways include a key component of the neural control of respiration, linking the brainstem breathing rhythm generator with phrenic motor neurons that activate the diaphragm. Disruption to these pathways result in respiratory muscle paresis and/or paralysis, requiring mechanical ventilation. Respiratory complications, such as pneumonia and atelectasis complicate the process of weaning patients from ventilators, contributing to patient mortality. Previous data collected in the Wilson lab demonstrated that sympathetic preganglionic neurons (SPNs) located at the thoracic spinal cord have remarkable oxygen and pressure‐sensitive capabilities. Here, we hypothesized that SPNs can stimulate phrenic motor neurons independent of the brainstem.AimTo study the novel direct influence of SPNs on the phrenic motor nucleus.MethodsAn in situ artificially‐perfused cervico‐thoracic rat spinal cord preparation was used to record phrenic and splanchnic nerve activity while having the cervical and thoracic spinal cord separately perfused. This approach allowed us to selectively expose the thoracic segment to acute hypoxia (30 Torr; 10 min) in order to observe if cardiorespiratory responses elicited by the SPN’s could stimulate phrenic motor neurons located at the cervical spinal cord. Additionally, we recorded the electromyography activity from the diaphragm during hypoxia and ischemia (0 mmHg; 10 min).ResultsThe results demonstrated that stimulation of the SPNs with hypoxia evoked phrenic nerve and diaphragm activity. This indicates that even without inputs from the brainstem, SPNs are responsive to hypoxia and ischemia and might have capability to stimulate phrenic motor neurons.ConclusionThe implications of these findings point to the thoracic SPNs as a unique and promising target to regain cardiorespiratory control in SCI patients. Further pharmacological investigations may reveal effective treatment strategies to improve life quality and reduce mortality of SCI patients.Support or Funding InformationAlberta Innovates Health Solutions (LL), Eyes High (NB), NSERC (HY), Canadian Institute of Health Research (RW).

SPARC: Noise Analysis and Signal Drift Correction in Long‐Period Multi‐Unit Recordings of Action Potentials in Autonomic Nerves

Recordings of spike activity in small peripheral autonomic nerves close to organs can provide real‐time information about the functional states of those organs (afferent traffic) and the neural systems that control them (efferent traffic). However, maintaining long‐term multifiber recordings from autonomic nerves in vivo poses significant and unique technical challenges. Many visceral nerves consist almost entirely of C fiber axons in which action potentials produce very small currents with little spatial segregation, making individual units difficult to distinguish based on spike shape in multifiber filaments recorded conventionally under mineral oil, especially when signal‐to‐noise ratios are low. Ongoing activity can be due to hundreds of active axons, each firing at relatively low frequency. Slow changes in recording conditions can have large effects on the amplitudes of spikes and the signal‐to‐noise ratio over time, potentially causing spurious/artefactual changes in recorded spiking frequency when activity is quantified via thresholding. Previous approaches to drift compensation in recordings from neuronal somata or myelinated axons have utilized spatial information from multi‐electrode arrays or tracked changes in the amplitudes of single units differentiated by spike shape. Such approaches are not useful when recording the activity of C fibers due to their lack of spatial segregation and similar spike shapes. We have developed a method to track drift in signal and noise separately and to compensate for drift without the need for spike sorting. The method is robust to changes in the signal‐to‐noise ratio and can be applied online during data acquisition. It employs a recursive piecewise linear model that predicts resistance as a function of recording time. The implicit assumption is that the current source is constant and, conversely, the extracellular path resistance of the system is dynamic, being impacted by events such as mechanical disruption, or subtle movement of aqueous conducting fluid. We evaluated our method using recordings of gastrointestinal afferent axons during responses to inflammation. We also developed a simulation suite to generate artificial data that mimics the conditions in our recordings and a conventional spike sorting algorithm optimized to distinguish activity in single units and spike families in low noise C fiber recordings lasting hours. We have used these tools to validate the performance of our drift compensation algorithm and found it could compensate for drift effectively without spike sorting and could also improve the efficiency of spike sorting routines in long recordings where drift was present. The simulation suite, the analysis algorithms, and a graphical user interface are freely available via online repositories. We anticipate that, in future, as recording technologies improve, our algorithm will allow online assessment of activity in multi‐unit recordings in vivo that may provide a basis for closed‐loop therapy systems.Support or Funding InformationFunded by the Defense Advanced Research Projects Agency (DARPA) BTO, Contract No. N66001‐15‐2‐4060.