Perivascular Nerves Research Articles

Investigation of the vascular effects of short chain fatty acids in rat mesenteric resistance arteries

Fiber rich diets have been shown to prevent the onset and reduce severity of hypertension1, a condition affecting 20-30% of adults in North America. High fiber diets facilitate the production of short chain fatty acids (SCFAs) by gut bacteria of which, in humans, acetate is the most abundant, followed by propionate and butyrate. It has been proposed that these three SCFAs may have direct effects on blood vessels and so may contribute to regulation of blood pressure2. Further research is needed to determine the mechanisms underlying the vascular actions of SCFAs. We tested the hypothesis that SCFAs can induce vasodilation and limit nerve-evoked vasoconstriction in rat mesenteric vasculature. Direct effects on vascular tone were assessed by constructing cumulative concentration-response curves to SCFAs in isolated third order rat mesenteric arteries mounted in a wire myograph and pre-stimulated with phenylephrine (PE) to increase tone. The effects of SCFAs on nerve-evoked vasoconstriction were assessed by constructing frequency-responses curves to perivascular nerve stimulation in a perfused rat mesenteric bed in the presence and absence of SCFAs added to the perfusate. In both experimental approaches, pharmacological tools were used to investigate the mechanism of action of SCFAs. Propionate (3 μM - 1 mM) and acetate (0.3 μM - 1 mM) caused reductions in PE-evoked tone with maximum relaxation of 32.7 ± 7% and 31.6 ± 8.2%, respectively, and attenuated nerve-evoked vasoconstriction in mesenteric arteries at 10 mM - 60 mM propionate and 30 mM - 50 mM acetate. These effects were inhibited by blockers of nitric oxide (NO) synthase (L-NG-nitroarginine methyl ester, L-NAME, 100 μM) and endothelial Ca2+-activated K+ (KCa) channels (apamin, 50 nM; TRAM-34, 1 μM). L-NAME alone significantly inhibited relaxations elicited by acetate indicating a predominant role for NO, whereas the actions of propionate were significantly inhibited by apamin and TRAM-34, indicating a predominant role for endothelial KCa channels in this response. These data indicate that SCFAs may cause vasodilation in mesenteric resistance arteries via activation of endothelial pathways and that there may be a differential contribution of NO and KCa channels to responses of individual SCFAs. 1. Appel LJ, Moore TJ, Obarzanek E, et al. A clinical trial of the effects of dietary patterns on blood pressure. DASH Collaborative Research Group. N Engl J Med. 1997;336(16):1117-1124. doi:10.1056/NEJM199704173361601 2. Pluznick J. A novel SCFA receptor, the microbiota, and blood pressure regulation. Gut Microbes. 2014;5(2):202-207. doi:10.4161/gmic.27492

Role of Transient Receptor Potential Vanilloid 4 in Vascular Function.

Transient receptor potential vanilloid 4 (TRPV4) channels are widely expressed in systemic tissues and can be activated by many stimuli. TRPV4, a Ca2+-permeable cation channel, plays an important role in the vasculature and is implicated in the regulation of cardiovascular homeostasis processes such as blood pressure, vascular remodeling, and pulmonary hypertension and edema. Within the vasculature, TRPV4 channels are expressed in smooth muscle cells, endothelial cells, and perivascular nerves. The activation of endothelial TRPV4 contributes to vasodilation involving nitric oxide, prostacyclin, and endothelial-derived hyperpolarizing factor pathways. TRPV4 activation also can directly cause vascular smooth muscle cell hyperpolarization and vasodilation. In addition, TRPV4 activation can evoke constriction in some specific vascular beds or under some pathological conditions. TRPV4 participates in the control of vascular permeability and vascular damage, particularly in the lung capillary endothelial barrier and lung injury. It also participates in vascular remodeling regulation mainly by controlling vasculogenesis and arteriogenesis. This review examines the role of TRPV4 in vascular function, particularly in vascular dilation and constriction, vascular permeability, vascular remodeling, and vascular damage, along with possible mechanisms, and discusses the possibility of targeting TRPV4 for therapy.

RETURN OF NERVE FUNCTION FOLLOWING RENAL DENERVATION IN THE PRESENCE OF ANGIOTENSIN-CONVERTING ENZYME INHIBITION IN SPONTANEOUSLY HYPERTENSIVE RATS

Objective: Regrowth of renal nerves and functional restoration occurs following renal denervation (RDN). There is little information regarding the impact of concomitant anti-hypertensive therapies on the extent of reinnervation following RDN. Angiotensin-II has previously been shown to promote renal vessel innervation. We hypothesised that angiotensin-converting enzyme inhibition (ACEi) prolongs the antihypertensive effects of RDN by delaying renal nerve regrowth. The aim of this study was to examine the effect of ACEi treatment on the return of nerve function at 12-weeks post-RDN in spontaneously hypertensive rats (SHR). Design and method: Male SHRs (∼12 weeks of age, n > 7/group) were implanted with a radiotelemetry probe to record mean arterial pressure (MAP). Rats were infused with enalapril (1 mg/kg/day s.c.) or vehicle for two weeks. Rats then underwent sham or surgical RDN procedures and ACEi/vehicle infusion continued for an additional 12 weeks following RDN. Vascular contraction to perivascular nerve stimulation in renal lobar arteries was assessed using wire myography to determine the extent of renal nerve function return. Results: ACEi and RDN independently caused an immediate and sustained reduction in MAP (ACEi: -12 ± 3 mmHg, RDN: -19 ± 4 mmHg, both P < 0.05) across the 12-week period compared to untreated counterparts. However, the blood pressure-lowering effect of RDN was not enhanced by concomitant ACEi. Heart mass was ∼16% less in ACEi-RDN rats compared to untreated counterparts. Return of neurovascular function was observed in RDN-treated rats, but levels were only partially restored to that of untreated rats (P < 0.001). ACEi alone attenuated the response to perivascular nerve stimulation (P < 0.05) but the effects of ACEi in combination with RDN were not additive. Conclusions: Here we show partial functional reinnervation is evident 12 weeks following RDN in the SHR. This may account for the sustained reduction in MAP following RDN. ACEi infusion alone attenuated neurovascular function, but ACEi combined with RDN did not affect the return of renal neurovascular function. These findings suggest that RDN and ACEi effectively lower blood pressure in the long term and may confer cardioprotective benefits despite the return of nerve function. However, ACE inhibition does not provide additive benefits to delaying renal reinnervation.

The Role of Neurogenic Bioamines in Nerve Fibers of Uterus during the Postpartum Involution in Experimental Animal Models.

Biogenic amines (BAs) secreted by the sympathetic neural apparatus of rat uterus are reported to be conducive to the uterine functional activity during postpartum involution; the imbalance in BAs ratio could confer postpartum reproductive disorders including improper postpartum involution. The objective of this study is to identify the changes in the density of uterine sympathetic nerves implicated in the pathology of endometriosis, adenomyosis, and delayed uterine involution. The present study aims to ascertain 'serotonin' and 'catecholamine' concentrations in mesenteric mast cells (MCs), and structural elements of nerve fibers across the perivascular plexuses (PPs) and single sympathetic nerve terminals (SST). Furthermore, the density of their spatial distribution (SDP and SDT) in the uterine body, cervix, and mesometrium was determined during postpartum involution. Tissue specimens of postpartum uterus were obtained from 55 nulliparous female Wistar outbred strain rats, which were grouped according to the days after parturition at the time of sacrifice. The nerve fibers of PP and SST exhibited emerald green fluorescence, which was detected by glyoxylic acid fluorescence technique; the fluorescence invoked by BAs was identified by microspectrofluorimetry. Concentrations of BAs were extensive in the varicosities of PP and SST on the 10th day. However, the highest BA concentrations were found in structural elements of PP in the uterine mesometrium in the initial days of postpartum. In mesenteric MC, serotonin and catecholamines were at the highest concentration on the 10th day of postpartum. Histamines peaked on the 6th day. SDP and SDT were increased significantly in all structural elements of uterine nerve fibers in the uterine body and cervix compared to SDP in mesentery. Considering that catecholamines and serotonin are antagonists in many aspects of their biological action, the ratio of BAs should be well-balanced to maintain anabolic- catabolic equilibrium in the rat uterus.

Role of perivascular nerve and sensory neurotransmitter dysfunction in inflammatory bowel disease.

Inflammatory bowel disease (IBD) is associated with both impaired intestinal blood flow and increased risk of cardiovascular disease, but the functional role of perivascular nerves that control vasomotor function of mesenteric arteries (MAs) perfusing the intestine during IBD is unknown. Because perivascular sensory nerves and their transmitters calcitonin gene-related peptide (CGRP) and substance P (SP) are important mediators of both vasodilation and inflammatory responses, our objective was to identify IBD-related deficits in perivascular sensory nerve function and vascular neurotransmitter signaling. In MAs from an interleukin-10 knockout (IL-10-/-) mouse model, IBD significantly impairs electrical field stimulation (EFS)-mediated sensory vasodilation and inhibition of sympathetic vasoconstriction, despite decreased sympathetic nerve density and vasoconstriction. The MA content and EFS-mediated release of both CGRP and SP are decreased with IBD, but IBD has unique effects on each transmitter. CGRP nerve density, receptor expression, hyperpolarization, and vasodilation are preserved with IBD. In contrast, SP nerve density and receptor expression are increased, and SP hyperpolarization and vasodilation are impaired with IBD. A key finding is that blockade of SP receptors restores EFS-mediated sensory vasodilation and enhanced CGRP-mediated vasodilation in MAs from IBD but not Control mice. Together, these data suggest that an aberrant role for the perivascular sensory neurotransmitter SP and its downstream signaling in MAs underlies vascular dysfunction with IBD. We propose that with IBD, SP signaling impedes CGRP-mediated sensory vasodilation, contributing to impaired blood flow. Thus, substance P and NK1 receptors may represent an important target for treating vascular dysfunction in IBD.NEW & NOTEWORTHY Our study is the first to show that IBD causes profound impairment of sensory vasodilation and inhibition of sympathetic vasoconstriction in mesenteric arteries. This occurs alongside decreased SP-containing nerve density and increased expression of NK1 receptors for SP. In contrast, CGRP dilation, nerve density, and receptor expression are unchanged. Blocking NK1 receptors restores sensory vasodilation in MAs and increases CGRP-mediated vasodilation, indicating that SP interference with CGRP signaling may underlie impaired sensory vasodilation with IBD.

Intra-arterial Instillation of a Nociceptive Agent Modulates Cardiorespiratory Parameters Involving 5-HT3 and TRPV1 Receptors in Anesthetized Rats.

Since long back, it has been a matter of discussion regarding the role of peripheral blood vessels in the regulation of cardiorespiratory (CVR) system. The role of 5-HT3 and TRPV1 receptors present on perivascular nerves in elicitation of CVR reflexes was examined after intra-arterial instillation of bradykinin in urethane anesthetized rats. Femoral artery was cannulated retrogradely and was utilized for the instillation of saline/agonist/antagonist and recording of blood pressure (BP), using a double ported 24G cannula. BP, respiration and ECG were recorded for 30 min after bradykinin (1 μM) in the absence or presence of antagonists. Instillation of bradykinin produced immediate hypotensive (40%), bradycardiac (17%), tachypnoeic (45%) and hyperventilatory (96%) responses of shorter latencies (5-8 s) favoring the neural mechanisms in producing the responses. In lignocaine (2%) pretreated animals, bradykinin- induced hypotensive (10%), bradycardiac (1.7%), tachypnoeic (13%) and hyperventilatory (13%) responses attenuated significantly. Pretreatment with ondansetron (100 μg/kg), 5-HT3-antagonist attenuated the hypotensive (10%), bradycardiac (1.7%), tachypnoeic (11%) and hyperventilatory (11%) responses significantly. Pretreatment with capsazepine (1 mg/kg), transient receptor potential vanilloid 1- antagonist blocked the hypotensive (5%), bradycardiac (1.2%), tachypnoeic (6%) and hyperventilatory (6%) responses significantly. In conclusion, presence of a nociceptive agent in the local segment of an artery evokes vasosensory reflex responses modulating CVR parameters involving TRPV1 and 5-HT3 receptors present on the perivascular sensory nerve terminals in anesthetized rats.

Methyl palmitate modulates the nicotine-induced increase in basilar arterial blood flow.

Methyl palmitate (MP) is a fatty acid methyl ester. Our recent study indicated that adrenergic nerve-dependent functional sympathetic-sensory nerve interactions were abolished by MP in mesenteric arteries. However, the effect of MP on perivascular nerves and cerebral blood flow remains unclear. In this study, the increase in basilar arterial blood flow (BABF) after the topical application of nicotinic acetylcholine receptor agonists was measured using laser Doppler flowmetry in anesthetized rats. The choline (a selective α7-nicotinic acetylcholine receptor agonist)-induced increase in BABF was abolished by tetrodotoxin (a neurotoxin), NG -nitro-L-arginine (a nonselective NO synthase inhibitor), α-bungarotoxin (a selective α7-nicotinic acetylcholine receptor inhibitor), and chronic sympathetic denervation. In addition, the nicotine (a nicotinic acetylcholine receptor agonist)-induced increase in BABF was inhibited by MP in a concentration-dependent manner. The acetylcholine-induced increase in BABF was not affected by MP. The myography results revealed that nicotine-induced vasorelaxation was significantly inhibited by MP, but was reversed by chelerythrine (a protein kinase C inhibitor). MP-induced vasodilation was significantly greater in BA rings without endothelium compared to those with endothelium. Meanwhile, MP did not affect baseline BABF. Our results indicate that MP acts as a neuromodulator in the cerebral circulation where it activates the PKC pathway and causes a diminished nicotine-induced increase in blood flow in the brainstem, and that the vasorelaxation effect of MP may play a minor role.

Vascular Dysfunction in Diabetes and Obesity: Focus on TRP Channels.

Transient receptor potential (TRP) superfamily consists of a diverse group of non-selective cation channels that has a wide tissue distribution and is involved in many physiological processes including sensory perception, secretion of hormones, vasoconstriction/vasorelaxation, and cell cycle modulation. In the blood vessels, TRP channels are present in endothelial cells, vascular smooth muscle cells, perivascular adipose tissue (PVAT) and perivascular sensory nerves, and these channels have been implicated in the regulation of vascular tone, vascular cell proliferation, vascular wall permeability and angiogenesis. Additionally, dysfunction of TRP channels is associated with cardiometabolic diseases, such as diabetes and obesity. Unfortunately, the prevalence of diabetes and obesity is rising worldwide, becoming an important public health problems. These conditions have been associated, highlighting that obesity is a risk factor for type 2 diabetes. As well, both cardiometabolic diseases have been linked to a common disorder, vascular dysfunction. In this review, we briefly consider general aspects of TRP channels, and we focus the attention on TRPC (canonical or classical), TRPV (vanilloid), TRPM (melastatin), and TRPML (mucolipin), which were shown to be involved in vascular alterations of diabetes and obesity or are potentially linked to vascular dysfunction. Therefore, elucidation of the functional and molecular mechanisms underlying the role of TRP channels in vascular dysfunction in diabetes and obesity is important for the prevention of vascular complications and end-organ damage, providing a further therapeutic target in the treatment of these metabolic diseases.

Innervation of the Human Intervertebral Disc: A Scoping Review.

Back pain is an elusive symptom complicated by a variety of possible causes, precipitating and maintaining factors, and consequences. Notably, the underlying pathology remains unknown in a significant number of cases. Changes to the intervertebral disc (IVD) have been associated with back pain, leading many to postulate that the IVD may be a direct source of pain, typically referred to as discogenic back pain. Yet despite decades of research into the neuroanatomy of the IVD, there is a lack of consensus in the literature as to the distribution and function of neural elements within the tissue. The current scoping review provides a comprehensive systematic overview of studies that document the topography, morphology, and immunoreactivity of neural elements within the IVD in humans. Articles were retrieved from six separate databases in a three-step systematic search and were independently evaluated by two reviewers. Three categories of neural elements were described within the IVD: perivascular nerves, sensory nerves independent of blood vessels, and mechanoreceptors. Nerves were consistently localized within the outer layers of the annulus fibrosus. Neural ingrowth into the inner annulus fibrosus and nucleus pulposus was found to occur only in degenerative and disease states. While the pattern of innervation within the IVD is clear, the specific topographic arrangement and function of neural elements in the context of back pain remains unclear.

Nitric oxide‐mediated signal transmission in bladder vasculature underlies the therapeutic actions of PDE5 inhibitors in the rat

Background and PurposeWhile the bladder vasculature is considered as a target of PDE5 inhibitors to improve bladder storage dysfunctions, its characteristics are largely unknown. Thus, the functional and morphological properties of arteries/arterioles of the bladder focusing on the NO‐mediated signal transmission were explored.Experimental ApproachDiameter changes in rat bladder arteries/arterioles were measured using a video‐tracking system. Intercellular Ca2+ dynamics in pericytes or smooth muscle cells (SMCs) of suburothelial arterioles were visualised using transgenic mice expressing GCaMP6 under control of the NG2‐ or parvalbumin‐promoter. The perivascular innervation was investigated using fluorescence immunohistochemistry.Key ResultsIn rat suburothelial arterioles and vesical arteries, tadalafil (100 nM) attenuated nerve‐evoked sympathetic vasoconstrictions. In both vascular segments, tadalafil‐induced inhibition of sympathetic vasoconstriction was prevented by N ω‐propyl‐l‐arginine hydrochloride (l‐NPA, 1 μM), an nNOS inhibitor or N ω‐nitro‐l‐arginine (l‐NA, 100 μM). Both vascular segments were densely innervated with nNOS‐positive nitrergic nerves in close apposition to tyrosine hydroxylase‐immunoreactive sympathetic nerves. In pericyte‐covered pre‐capillary arterioles of the mouse bladder where sympathetic nerves were absent, nerve stimulation evoked transient reductions in pericyte Ca2+ levels that were shortened by l‐NPA and abolished by l‐NA. In SMC‐containing arterioles, tadalafil (10 nM) caused a l‐NPA‐sensitive suppression of sympathetic Ca2+ transients. In mice, nitrergic perivascular nerves were distributed in the arterioles and the pre‐capillary arterioles.Conclusion and ImplicationsBoth nitrergic nerve and nerve‐evoked endothelial NO release appear to be involved in vasodilatory signal transmission in bladder vasculature. The NO‐mediated signal transmission is a potential target for PDE5 inhibitor therapy in bladder dysfunctions.

Comparison of Adrenergic and Purinergic Receptor Contributions to Vasomotor Responses in Mesenteric Arteries of C57BL/6J Mice and Wistar Rats

Introduction: The sympathetic nervous system can modulate arteriolar tone through release of adenosine triphosphate and norepinephrine, which bind to purinergic and adrenergic receptors (ARs), respectively. The expression pattern of these receptors, as well as the composition of neurotransmitters released from perivascular nerves (PVNs), can vary both in organ systems within and across species, such as mice and rats. Objective: This study explores the function of α_1A subtypes in mouse and rat third-order mesenteric arteries and investigates PVN-mediated vasoconstriction to identify which neurotransmitters are released from sympathetic PVNs. Methods: Third-order mesenteric arteries from male C57BL/6J mice and Wistar rats were isolated and mounted on a wire myograph for functional assessment. Arteries were exposed to phenylephrine (PE) and then incubated with either α_1A antagonist RS100329 (RS) or α_1D antagonist BMY7378, before reexposure to PE. Electrical field stimulation was performed by passing current through platinum electrodes positioned adjacent to arteries in the absence and presence of a nonspecific alpha AR blocker phentolamine and/or P2X₁-specific purinergic receptor blocker NF449. Results: Inhibition of α₁ ARs by RS revealed that PE-induced vasoconstriction is primarily mediated through α_1A and that the contribution of the α_1A AR is greater in rats than in mice. In the mouse model, sympathetic nerve-mediated vasoconstriction is mediated by both ARs and purinergic receptors, whereas in rats, vasoconstriction appeared to only be mediated by ARs and a nonpurinergic neurotransmitter. Further, neither model demonstrated that α_1D ARs play a significant role in PE-mediated vasoconstriction. Conclusions: The mesenteric arteries of male C57BL/6J mice and Wistar rats have subtle differences in the signaling mechanisms used to mediate vasoconstriction. As signaling pathways in humans under physiological and pathophysiological conditions become better defined, the current study may inform animal model selection for preclinical studies.

Abstract 15228: Role of Sympathetic Innervation in the Pathogenesis of Abdominal Aortic Aneurysm

Introduction: The objective of this study is to understand the role of neurological factors, specifically those from the perivascular sympathetic nervous system (SNS), on the initiation and development of Abdominal Aortic Aneurysm (AAA). Hypothesis: We hypothesize that the formation of AAA is associated with the loss of perivascular SNS-induced vasoconstriction specific to the aneurysm region. Methods: We developed a rat Abdominal Aortic Denervation (AAD) model, where the infrarenal aorta of Spauge Dawley rats was denervated with surgical removal of nerve fibers and chemical denervation with 10% phenol ( Figure. A ). A sham control group was included where the infrarenal aorta was treated with PBS. The arteries were harvested at 1 month after the surgeries for histological assessment. Results: The denervated aortas exhibited significant thinning of the aortic wall including the media and the adventitia, compared to the sham controls ( Figure. B ). Moreover, degradation of elastin, demonstrated by the fragmentation of elastic fibers and the decreased number of lamellar units, was also observed in the dennervated aortas in comparison to the sham controls. While the control aortas were well innervated with perivascular nerve bundles adjacent to the adventitia, no nerves were found surrounding the denervated aortas, suggesting successful denervation. Conclusions: We generated an AAD model that could be used for mechanistic understanding and therapeutic development of AAA. The preliminary data suggest a direct link between the lack of aortic sympathetic innervation and AAA formation. Long-term studies are currently underway to further characterize changes in the aortic walls after sympathetic denervation. Figure. (A) Illustration of the denervated region on the rat infrarenal aorta. ( B ) Histological staining of control and denervated rat abdominal aortas at 1 month after surgery. Yellow stars: para-aortic nerve bundles. Scale bar = 200 μm.

Monoclonal therapy against calcitonin gene-related peptide lowers hyperglycemia and adiposity in type 2 diabetes mouse models

ObjectiveCalcitonin Gene-Related Peptide α (CGRPα) is a multifunctional neuropeptide found in the central and peripheral nervous system with cardiovascular, nociceptive, and gastrointestinal activities. CGRPα has been linked to obesity and insulin secretion but the role of this circulating peptide in energy metabolism remains unclear. Here, we thought to utilize a monoclonal antibody against circulating CGRPα to assess its ability to improve glucose homeostasis in mouse models of hyperglycemia and diabetes. MethodsWe examined the outcome of anti-CGRPα treatment in mouse models of diabetes and diet-induced obesity, using db/db mice, Streptozotocin (STZ) treatment to eliminate pancreatic islets, and high fat diet-fed mice. We also correlated these data with application of recombinant CGRPα peptide on cultured mature adipocytes to measure its impact on mitochondrial bioenergetics and fatty acid oxidation. Furthermore, we applied recombinant CGRPα to primary islets to measure glucose-stimulated insulin secretion (GSIS) and gene expression. ResultsBL6-db diabetic mice receiving anti-CGRPα treatment manifested weight loss, reduced adiposity, improved glucose tolerance, insulin sensitivity, GSIS and reduced pathology in adipose tissue and liver. Anti-CGRPα failed to modulate weight or glucose homeostasis in STZ-treated animals. High fat diet-fed mice showed reduced adiposity but no benefit on glucose homeostasis. Considering these findings, we postulated that CGRPα may have dual effects on adipocytes to promote lipid utilization while acting on pancreatic β-cells to modulate insulin secretion. Analysis of CGRPα in the pancreas showed that the peptide localized to insulin-positive cells and perivascular nerves surrounding islets. Ex-vivo analysis of pancreatic islets determined that CGRPα blocked GSIS and reduced insulin-2 gene expression. Mechanistical analysis revealed that recombinant CGRPα was able to reduce glycolytic capacity as well as fatty acid oxidation in primary white adipocytes. ConclusionsThese results establish a multifaceted role in energy metabolism for circulating CGRPα, with the ability to modulate thermogenic pathways in adipose tissue, as well as pancreatic β-cell dependent insulin secretion. Reducing circulating CGRPα levels with monoclonal therapy presents therapeutic potential for type 2 diabetes as shown in BL6-db/db mice but has reduced potential for models of hyperglycemia resulting from loss of β-cells (STZ treatment).

Effect of perivascular low dose ethanol on rat femoral vessels: Preliminary study

Vasospasm is one of the important causes of morbidity in free flap and replantation surgery. In secondary Raynaud’s phenomenon, nearly half of the patients experience digital ulceration, pain and loss of function at least once in their lifetime. The aim of this study is to investigate the vasodilation effect of ethanol-mediated chemical denervation on peripheral vessels by topical administration. In this study, 27 Wistar albino male rats weighing 250-300 grams were used. The rats were randomly divided into three groups: saline (group S, n = 8), lidocaine (group L, n = 9) and 96% ethanol (group E, n = 9). According to group, 0.1 mL saline, 0.1 mL lidocaine and 0.1 mL ethanol were applied around the rat femoral neurovascular bundle. After the application, on the 0th day and 3th weeks, femoral artery and vein diameters were measured. After 3. weeks, histopathological samples from femoral artery, vein and nerve were evaluated. On the 0th day, the mean diameter of the femoral artery and vein was similar in group E and L and higher than group S. After three weeks, the vasodilatation effect of ethanol was increased in group E. In Group L and S, the vasodilatation effect was lost. Histopathological examination showed that ethanol significantly caused perivascular inflammation and nerve degeneration compared to other agents and did not cause endothelial damage. Vasodilatation obtained by ethanol is a rapid onset and long-lasting effect. It is also inexpensive and effective for peripheral vasodilatation.

Hydrogen Protons Modulate Perivascular Axo-axonal Interactions in the Middle Cerebral Artery of Rats.

Previous studies have demonstrated that nicotine can induce relaxation of the middle cerebral artery (MCA). However, whether this relaxation is associated with the activity of sensory calcitonin gene-related peptide (CGRP) nerves and whether this is modulated by hydrogen protons (H), facilitating the release of CGRP from sensory CGRPergic nerve terminals in the MCA, remains unclear. In this study, we examined the role of H in the modulation of neurogenic vasomotor responses in the rat-isolated endothelium-denuded MCA. Wire myography was used to measure vasoreactivity and indicated that nicotine-induced relaxation was sensitive to tetrodotoxin and lidocaine and drastically reduced levels of guanethidine (an adrenergic neuronal blocker), N-nitro-L-arginine (L-NNA), CGRP8-37, vasoactive intestinal polypeptide (VIP)6-28, capsaicin, capsazepine (a transient receptor potential vanilloid-1 inhibitor), and tetraethylammonium. However, this nicotine-induced relaxation was not sensitive to propranolol. Lowering the pH of the buffer solution with HCl caused pH-dependent vasorelaxation and deceased intracellular pH in the MCA rings, which was sensitive to L-NNA, CGRP8-37, VIP6-28, capsazepine, 4-aminopyridine (a voltage-gated potassium channel antagonist), and paxilline (a large conductance Ca-activated K channel antagonist). However, HCl-induced relaxation was not inhibited by glibenclamide (an ATP-sensitive K channel blocker). These results suggested that electrical and chemical activation of cerebral perivascular adrenergic nerves led to the release of H, which then facilitated the release of NO, VIP, and CGRP, resulting in vasorelaxation. Lowering the pH of the buffer solution caused potassium channels of vascular smooth muscle cells and perivascular nerves to open. In conclusion, our results demonstrated that H may act as a modulator on MCA perivascular nerves and/or smooth muscles.

Laparoscopic-based perivascular renal sympathetic nerve denervation: a feasibility study in a porcine model

BackgroundThis study aims to evaluate the effects and safety of laparoscopic-based perivascular renal sympathetic nerve denervation (RDN) in a porcine model fed a high-fat diet.MethodThirty-six high-fat diet-fed Bama minipigs were randomly divided into an RDN group (n = 18), in which minipigs received laparoscopic-based perivascular RDN, and a sham group (n = 18). All pigs were fed the high-fat diet after the operation to establish a model of obesity-induced hypertension. Bama pigs in the RDN and sham groups were killed at 3 time points [2 days after RDN (n = 6), day 90 (n = 6) and day 180 (n = 6)].ResultThe systolic blood pressure (SBP) and noradrenaline (NE) concentration in the kidney tissue were significantly lower in the RDN group than in the sham group at 2 days (113.83 ± 3.26 mmHg vs 129.67 ± 3.32 mmHg, P = 0.011, and 112.02 ± 17.34 ng/g vs 268.48 ± 20.61 ng/g, P < 0.001, respectively), 90 days (116.83 ± 3.88 mmHg vs 145.00 ± 4.22 mmHg, P = 0.001, respectively) and 180 days (129.33 ± 2.87 mmHg vs 168.57 ± 2.86 mmHg, P < 0.001, and 152.15 ± 16.61 ng/g vs 318.97 ± 24.84 ng/g, P < 0.001, respectively) after the operation. The diastolic blood pressure (DBP) was significantly lower in the RDN group than in sham group at 90 and 180 days after the operation (72.17 ± 2.7 mmHg vs 81.50 ± 2.22 mmHg, P = 0.037, and 76.83 ± 2.75 mmHg vs 86.33 ± 2.22 mmHg P = 0.021, respectively). Based on the pathological evaluation, the renal sympathetic nerve fascicles were successfully disrupted by radiofrequency energy after laparoscopic-based perivascular RDN, but the intima was intact. Tyrosine hydroxylase (TH) expression was decreased, while the expression of the S100 protein was increased in treated renal arteries after RDN.ConclusionsLaparoscopic-based perivascular RDN prevented the occurrence and development of hypertension, and thus it may be an efficient and safe method for controlling blood pressure in an experimental model.

Relationship Between Nerve Fiber Layer Hemorrhages and Outcomes in Central Retinal Vein Occlusion.

PurposeTo evaluate the depth and pattern of retinal hemorrhage in acute central retinal vein occlusion (CRVO) and to correlate these with visual and anatomic outcomes.MethodsRetinal hemorrhages were evaluated with color fundus photography and fluorescein angiography at baseline and follow-up. Snellen visual acuity (VA), central foveal thickness (CFT), extent of retinal ischemia, and development of neovascularization were analyzed.Results108 eyes from 108 patients were evaluated. Mean age was 63.6 ± 16.1 years with a predilection for the right eye (73.1%). Average follow-up was 17.2 ± 19.2 months. Mean VA at baseline was 20/126 and 20/80 at final follow-up. Baseline (P = 0.005) and final VA (P = 0.02) in eyes with perivascular nerve fiber layer (NFL) hemorrhages were significantly worse than in eyes with deep hemorrhages alone. Baseline CFT was greater in the group with perivascular hemorrhages (826 ± 394 µm) compared to the group with deep hemorrhages alone (455 ± 273 µm, P < 0.001). The 10 disc areas of retinal ischemia was more common in patients with perivascular (80.0%) and peripapillary (31.3%) versus deep hemorrhages alone (16.1%, P < 0.001). Neovascularization of the iris was more common, although this differrence was not significant, in the groups with peripapillary (14.3%) and perivascular (2.0%) NFL versus deep hemorrhages alone (0.0%).ConclusionsNFL retinal hemorrhages at baseline correlate with more severe forms of CRVO, with greater macular edema, poorer visual outcomes, and greater risk of ischemia and neovascularization. This may be related to the organization of the retinal capillary plexus. The depth and pattern of distribution of retinal hemorrhages in CRVO may provide an easily identifiable early biomarker of CRVO prognosis.

Nitrergic perivascular innervation in health and diseases: Focus on vascular tone regulation.

For a long time, the vascular tone was considered to be regulated exclusively by tonic innervation of vasoconstrictor adrenergic nerves. However, accumulating experimental evidence has revealed the existence of nerves mediating vasodilatation, including perivascular nitrergic nerves (PNN), in a wide variety of mammalian species. Functioning of nitrergic vasodilator nerves is evidenced in several territories, including cerebral, mesenteric, pulmonary, renal, penile, uterine and cutaneous arteries. Nitric oxide (NO) is the main neurogenic vasodilator in cerebral arteries and acts as a counter-regulatory mechanism for adrenergic vasoconstriction in other vascular territories. In the penis, NO relaxes the vascular and cavernous smooth muscles leading to penile erection. Furthermore, when interacting with other perivascular nerves, NO can act as a neuromodulator. PNN dysfunction is involved in the genesis and maintenance of vascular disorders associated with arterial and portal hypertension, diabetes, ageing, obesity, cirrhosis and hormonal changes. For example defective nitrergic function contributes to enhanced sympathetic neurotransmission, vasoconstriction and blood pressure in some animal models of hypertension. In diabetic animals and humans, dysfunctional nitrergic neurotransmission in the corpus cavernosum is associated with erectile dysfunction. However, in some vascular beds of hypertensive and diabetic animals, an increased PNN function has been described as a compensatory mechanism to the increased vascular resistance. The present review summarizes current understanding on the role of PNN in control of vascular tone, its alterations under different conditions and the associated mechanisms. The knowledge of these changes can serve to better understand the mechanisms involved in these disorders and help in planning new treatments.

Comparison of Neurotransmitter Release from Perivascular Nerves in C57BL/6J Mice and Wistar Rats

It is thought that sympathetic nerve activation stimulates arterial constriction predominately through the release of three neurotransmitters: norepinephrine (NE), adenosine triphosphate (ATP) and neuropeptide Y (NPY). The aim of the current study was to examine the composition of neurotransmitter released in response to sympathetic nerve stimulation in mesenteric arteries of two commonly used wild‐type animal models. Isolated mesenteric arteries from male C57BL/6J mice and Wistar rats were mounted in a Danish Myotechnology 2‐Channel Wire Myograph System and isometric force measurements were recorded. Electrical field stimulation (EFS) was used to stimulate sympathetic perivascular nerves (PVNs) to release neurotransmitters in the presence and absence of the adrenergic receptor blocker phentolamine and/or purinergic receptor blocker NF449. Phentolamine alone blocked a significant proportion of the contractile response evoked by EFS in both mice and rats, suggesting that NE is the main sympathetic neurotransmitter in both species. Treatment with NF449 alone blocked a small proportion of the contractile response evoked by EFS in mice but did not have a significant effect in rat, suggesting that ATP may play a more important role in mice. The application of both phentolamine and NF449 nearly completely blocked the contractile response to EFS in mouse mesenteric arteries; however, in rat, a proportion of the contractile response, roughly equivalent to the response obtained in the presence of phentolamine alone, was still observed. These data suggest that the neurotransmitter composition is different between mice and rats, in particular mouse mesenteric sympathetic PVNs release NE and ATP while rat mesenteric sympathetic PVNs release NE and another non‐purinergic neurotransmitter(s).

Neural regulation of the contractility of nutrient artery in the guinea pig tibia.

Nutrient arteries provide the endosteal blood supply to maintain bone remodelling and energy metabolism. Here, we investigated the distribution and function of perivascular nerves in regulating the contractility of the tibial nutrient artery. Changes in artery diameter were measured using a video tracking system, while the perivascular innervation was investigated using fluorescence immunohistochemistry. Nerve-evoked phasic constrictions of nutrient arteries were suppressed by phentolamine (1μM), an α-adrenoceptor antagonist, guanethidine (10μM), a blocker of sympathetic transmission, or fluoxetine (10μM), a serotonin (5-hydroxytryptamine, 5-HT) reuptake inhibitor. In arteries pretreated with guanethidine, residual nerve-evoked constrictions were abolished by a high concentration of propranolol (10μM) that is known to inhibit 5-HT receptors, or ketanserin (100nM), a 5-HT2 receptor antagonist, but not SB207216 (1μM), an antagonist of 5-HT3 and 5-HT4 receptors. Bath-applied 5-HT (100nM) induced arterial constriction that was suppressed by propranolol (10μM) or ketanserin (100nM). Nerve-evoked arterial constrictions were enhanced by spantide (1μM), a substance P (SP) receptor antagonist, or L-nitro arginine (L-NA; 100μM), an inhibitor of nitric oxide synthase (NOS). Immunohistochemistry revealed 5-HT-positive nerves running along the arteries that are distinct from perivascular sympathetic or substance P-positive primary afferent nerves. For the first time, functional serotonergic nerves are identified in the tibial nutrient artery of the guinea pig. Thus, it appears that tibial nutrient arterial calibre is regulated by the balance between sympathetic and serotonergic vasoconstrictor nerves and vasodilator afferent nerves that release substance P-stimulating endothelial nitric oxide (NO) release.