Locations and innervation of cell bodies of sympathetic neurons projecting to the gastrointestinal tract in the rat

Protocol for the isolation of the mouse sympathetic splanchnic-celiac-superior mesenteric ganglion complex

Neurons that originate from pre-vertebral sympathetic ganglia, the splanchnic-celiac-superior mesenteric ganglion complex (SCSMG) in mouse, have important roles in control of organs of the upper abdomen. Here, we present a protocol for the isolation of the mouse sympathetic SCSMG. We describe steps for surgical incision, ganglia isolation, ganglia fine dissection, and whole-mount SCSMG after clearing-enhanced 3D (Ce3D) clearing method and immunohistochemistry. Given the importance of mice in studies of that control, this protocol aims to assist biomedical researchers in the dissection of the mouse SCSMG.

The Sympathetic-Immune Milieu in Metabolic Health and Diseases: Insights from Pancreas, Liver, Intestine, and Adipose Tissues

Sympathetic innervation plays a crucial role in maintaining energy balance and contributes to metabolic pathophysiology. Recent evidence has begun to uncover the innervation landscape of sympathetic projections and sheds light on their important functions in metabolic activities. Additionally, the immune system has long been studied for its essential roles in metabolic health and diseases. In this review, the aim is to provide an overview of the current research progress on the sympathetic regulation of key metabolic organs, including the pancreas, liver, intestine, and adipose tissues. In particular, efforts are made to highlight the critical roles of the peripheral nervous system and its potential interplay with immune components. Overall, it is hoped to underscore the importance of studying metabolic organs from a comprehensive and interconnected perspective, which will provide valuable insights into the complex mechanisms underlying metabolic regulation and may lead to novel therapeutic strategies for metabolic diseases.

Sympathetic innervation of the development, maturity, and aging of the gastrointestinal tract

The sympathetic nervous system inhibits gut motility, secretion, and blood flow in the gut microvasculature and can modulate gastrointestinal inflammation. Sympathetic neurons signal via catecholamines, neuropeptides, and gas mediators. In the current review, we summarize the current understanding of the mature sympathetic innervation of the gastrointestinal tract with a focus mainly on the prevertebral sympathetic ganglia as the main output to the gut. We also highlight recent work regarding the developmental processes of sympathetic innervation. The anatomy, neurochemistry, and connections of the sympathetic prevertebral ganglia with different parts of the gut are considered in adult organisms during prenatal and postnatal development and aging. The processes and mechanisms that control the development of sympathetic neurons, including their migratory pathways, neuronal differentiation, and aging, are reviewed.

Optogenetic stimulation of the brainstem dorsal motor nucleus ameliorates acute pancreatitis

Introduction

Inflammation is an inherently self-amplifying process, resulting in progressive tissue damage when unresolved. A brake on this positive feedback system is provided by the nervous system which has evolved to detect inflammatory signals and respond by activating anti-inflammatory processes, including the cholinergic anti-inflammatory pathway mediated by the vagus nerve. Acute pancreatitis, a common and serious condition without effective therapy, develops when acinar cell injury activates intrapancreatic inflammation. Prior study has shown that electrical stimulation of the carotid sheath, which contains the vagus nerve, boosts the endogenous anti-inflammatory response and ameliorates acute pancreatitis, but it remains unknown whether these anti-inflammatory signals originate in the brain.

Methods

Here, we used optogenetics to selectively activate efferent vagus nerve fibers originating in the brainstem dorsal motor nucleus of the vagus (DMN) and evaluated the effects on caerulein-induced pancreatitis.

Results

Stimulation of the cholinergic neurons in the DMN significantly attenuates the severity of pancreatitis as indicated by reduced serum amylase, pancreatic cytokines, tissue damage, and edema. Either vagotomy or silencing cholinergic nicotinic receptor signaling by pre-administration of the antagonist mecamylamine abolishes the beneficial effects.

Discussion

These results provide the first evidence that efferent vagus cholinergic neurons residing in the brainstem DMN can inhibit pancreatic inflammation and implicate the cholinergic anti-inflammatory pathway as a potential therapeutic target for acute pancreatitis.

The sympathetic nervous system in the 21st century: Neuroimmune interactions in metabolic homeostasis and obesity

The sympathetic nervous system maintains metabolic homeostasis by orchestrating the activity of organs such as the pancreas, liver, and white and brown adipose tissues. From the first renderings by Thomas Willis to contemporary techniques for visualization, tracing, and functional probing of axonal arborizations within organs, our understanding of the sympathetic nervous system has started to grow beyond classical models. In the present review, we outline the evolution of these findings and provide updated neuroanatomical maps of sympathetic innervation. We offer an autonomic framework for the neuroendocrine loop of leptin action, and we discuss the role of immune cells in regulating sympathetic terminals and metabolism. We highlight potential anti-obesity therapeutic approaches that emerge from the modern appreciation of SNS as a neural network vis a vis the historical fear of sympathomimetic pharmacology, while shifting focus from post- to pre-synaptic targeting. Finally, we critically appraise the field and where it needs to go.

Mapping and targeted viral activation of pancreatic nerves in mice reveal their roles in the regulation of glucose metabolism

A lack of comprehensive mapping of ganglionic inputs into the pancreas and of technology for the modulation of the activity of specific pancreatic nerves has hindered the study of how they regulate metabolic processes. Here we show that the pancreas-innervating neurons in sympathetic, parasympathetic and sensory ganglia can be mapped in detail by using tissue clearing and retrograde tracing (the tracing of neural connections from the synapse to the cell body), and that genetic payloads can be delivered via intrapancreatic injection to target sites in efferent pancreatic nerves in live mice through optimized adeno-associated viruses and neural-tissue-specific promoters. We also show that, in male mice, the targeted activation of parasympathetic cholinergic intrapancreatic ganglia and neurons doubled plasma-insulin levels and improved glucose tolerance, and that tolerance was impaired by stimulating pancreas-projecting sympathetic neurons. The ability to map the peripheral ganglia innervating the pancreas and to deliver transgenes to specific pancreas-projecting neurons will facilitate the examination of ganglionic inputs and the study of the roles of pancreatic efferent innervation in glucose metabolism.

Unravelling innervation of pancreatic islets

The central and peripheral nervous systems play critical roles in regulating pancreatic islet function and glucose metabolism. Over the last century, in vitro and in vivo studies along with examination of human pancreas samples have revealed the structure of islet innervation, investigated the contribution of sympathetic, parasympathetic and sensory neural pathways to glucose control, and begun to determine how the structure and function of pancreatic nerves are disrupted in metabolic disease. Now, state-of-the art techniques such as 3D imaging of pancreatic innervation and targeted in vivo neuromodulation provide further insights into the anatomy and physiological roles of islet innervation. Here, we provide a summary of the published work on the anatomy of pancreatic islet innervation, its roles, and evidence for disordered islet innervation in metabolic disease. Finally, we discuss the possibilities offered by new technologies to increase our knowledge of islet innervation and its contributions to metabolic regulation.

Hypoglycemic Effect of Electroacupuncture at ST25 Through Neural Regulation of the Pancreatic Intrinsic Nervous System

Electroacupuncture (EA) is considered to have potential antidiabetic effects; however, the role of the pancreatic intrinsic nervous system (PINS) in EA-induced amelioration of type 2 diabetes (T2DM) remains unclear. Therefore, we investigated whether EA at ST25 exerts any beneficial effects on insulin resistance (IR), inflammation severity, and pancreatic β cell function via the PINS in a rat model of a high-fat diet-streptozotocin (HFD/STZ)-induced diabetes. To this end, Sprague Dawley rats were fed with HFD to induce IR, followed by STZ (35 mg/kg, i.p.) injection to establish the T2DM model. After hyperglycemia was confirmed as fasting glucose level > 16.7 mmol/L, the rats were treated with EA (2 mA, 2/15 Hz) for the next 28 days. Model rats showed increased serum glucose, insulin, IR, and TNF-α levels with a concomitant decrease in β cell function. Microscopy examination of the pancreas revealed pathological changes in islets, which reverted to near-normal levels after EA at ST25. EA improved islet cell morphology by increasing islet area and reducing vacuolation. EA at ST25 decreased transient receptor potential vanilloid 1 (TRPV1) and increased substance P (SP) and calcitonin gene-related peptide (CGRP) expression. Subsequently, insulin secretion decreased and impaired pancreatic endocrine function was restored through the TRPV1 channel (SP/CGRP)-insulin circuit. EA increased choline acetyltransferase and neuropeptide Y expression and controlled inflammation. It also enhanced the cocaine and amphetamine-regulated transcript prepropeptide expression and promoted glucagon-like peptide-1 secretion. Additionally, the electrophysiological activity of PINS during acupuncture (2.71 ± 1.72 Hz) was significantly increased compared to the pre-acupuncture frequency (0.32 ± 0.37 Hz, P < 0.05). Thus, our study demonstrated the beneficial effect of EA on β cell dysfunction via the PINS in rat models of HFD-STZ-induced T2DM.

Effects of highly selective sympathectomy on neurogenic bowel dysfunction in spinal cord injury rats

Neurogenic bowel dysfunction, including hyperreflexic and areflexic bowel, is a common complication in patients with spinal cord injury (SCI). We hypothesized that removing part of the colonic sympathetic innervation can alleviate the hyperreflexic bowel, and investigated the effect of sympathectomy on the hyperreflexic bowel of SCI rats. The peri-arterial sympathectomy of the inferior mesenteric artery (PSIMA) was performed in T8 SCI rats. The defecation habits of rats, the water content of fresh faeces, the intestinal transmission function, the defecation pressure of the distal colon, and the down-regulation of Alpha-2 adrenergic receptors in colon secondary to PSIMA were evaluated. The incidence of typical hyperreflexic bowel was 95% in SCI rats. Compared to SCI control rats, PSIMA increased the faecal water content of SCI rats by 5–13% (P < 0.05), the emptying rate of the faeces in colon within 24 h by 14–40% (P < 0.05), and the defecation pressure of colon by 10–11 mmHg (P < 0.05). These effects lasted for at least 12 weeks after PSIMA. Immunofluorescence label showed the secondary down-regulation of Alpha-2 adrenergic receptors after PSIMA occurred mainly in rats’ distal colon. PSIMA mainly removes the sympathetic innervation of the distal colon, and can relieve the hyperreflexic bowel in rats with SCI. The possible mechanism is to reduce the inhibitory effect of sympathetic activity, and enhance the regulatory effect of parasympathetic activity on the colon. This procedure could potentially be used for hyperreflexic bowel in patients with SCI.

Pancreas-Brain Crosstalk

The neural regulation of glucose homeostasis in normal and challenged conditions involves the modulation of pancreatic islet-cell function. Compromising the pancreas innervation causes islet autoimmunity in type 1 diabetes and islet cell dysfunction in type 2 diabetes. However, despite the richly innervated nature of the pancreas, islet innervation remains ill-defined. Here, we review the neuroanatomical and humoral basis of the cross-talk between the endocrine pancreas and autonomic and sensory neurons. Identifying the neurocircuitry and neurochemistry of the neuro-insular network would provide clues to neuromodulation-based approaches for the prevention and treatment of diabetes and obesity.

Analgesic effects of cuminic alcohol (4-isopropylbenzyl alcohol), a monocyclic terpenoid, in animal models of nociceptive and neuropathic pain: Role of opioid receptors, L-arginine/NO/cGMP pathway, and inflammatory cytokines

Cuminic alcohol (4-isopropylbenzyl alcohol; 4-IPBA) is a monocyclic terpenoid found in the analgesic medicinal plants Cuminum cyminum and Bunium persicum. The current study assessed the analgesic effects of 4-IPBA in different animal models of pain. Hot plate, formalin, and acetic acid tests were used to evaluate nociceptive pain in mice. The involvement of opioid receptors and the L-arginine/NO/cGMP/K⁺ channel pathway in 4-IPBA effects were investigated. Allodynia and hyperalgesia were assessed following peripheral neuropathy induced by chronic constriction of the sciatic nerve in rats. The spinal levels of inflammatory cytokines were measured using the ELISA method. The drugs and compounds were administered intraperitoneally. The results showed that 4-IPBA (200 and 400 mg/kg) significantly prolonged the hot plate latency. This effect was antagonized by naloxone (2 mg/kg). 4-IPBA (25-100 mg/kg) also significantly attenuated formalin- and acetic acid-induced nociceptive pain. L-arginine (200 mg/kg), sodium nitroprusside (0.25 mg/kg), and sildenafil (0.5 mg/kg) reversed while L-NAME (30 mg/kg) and methylene blue (20 mg/kg) potentiated the antinociceptive effects of 4-IPBA in the writhing test. Glibenclamide (10 mg/kg) and tetraethylammonium chloride (4 mg/kg) did not have any influence on the 4-IPBA effect. Furthermore, 4-IPBA (6.25-25 mg/kg) significantly relieved mechanical allodynia, cold allodynia, and hyperalgesia in rats. The concentrations of TNF-α and IL-1β in the spinal cord of rats were decreased by 4-IPBA. No evidence of 4-IPBA-induced toxicity was found in behavioral or histopathological examinations. These results demonstrate that 4-IPBA attenuates nociceptive and neuropathic pain through the involvement of opioid receptors, the L-arginine/NO/cGMP pathway, and anti-inflammatory functions.

Optical Imaging of Pancreatic Innervation

At the time of Ivan Pavlov, pancreatic innervation was studied by looking at pancreas secretions in response to electrical stimulation of nerves. Nowadays we have ways to visualize neuronal activity in real time thanks to advances in fluorescent reporters and imaging techniques. We also have very precise optogenetic and pharmacogenetic approaches that allow neuronal manipulations in a very specific manner. These technological advances have been extensively employed for studying the central nervous system and are just beginning to be incorporated for studying visceral innervation. Pancreatic innervation is complex, and the role it plays in physiology and pathophysiology of the organ is still not fully understood. In this review we highlight anatomical aspects of pancreatic innervation, techniques for pancreatic neuronal labeling, and approaches for imaging pancreatic innervation in vitro and in vivo.

P2Y12 shRNA normalizes inflammatory dysfunctional hepatic glucokinase activity in type 2 diabetic rats

The celiac ganglion projects its postganglionic (including purinergic) fibers to the liver. P2Y12 receptor is one of the P2Y family members. We found that the expression levels of P2Y12 receptor in both celiac ganglia and liver were increased in type 2 diabetes mellitus (T2DM) rats which also displayed an enhanced activity of celiac sympathetic nerve discharge (SND). In addition, a marked decrease of hepatic glucokinase (GK) expression was accompanied by reduced hepatic glycogen synthesis in T2DM rats, whereas meanwhile the levels of NLRP3, active caspase-1, NF-κB, and interleukin-1β were elevated. All these abnormal alterations could be largely reversed after treatment of short hairpin RNA (shRNA) targeting P2Y12. Our results indicate that the silence of P2Y12 by shRNA may effectively correct the anomalous activity of celiac SND and improve the dysfunctional hepatic glucokinase by counteracting hepatocyte inflammation and likely pyroptosis due to activated NLRP3 inflammasome and caspase-1 signaling, thereby attenuating hyperglycemia in T2DM rats.

CD40L reverse signaling suppresses prevertebral sympathetic axon growth and tissue innervation

CD40‐activated CD40L reverse signaling is a major physiological regulator of the growth of neural processes in the developing nervous system. Previous work on superior cervical ganglion (SCG) neurons of the paravertebral sympathetic chain has shown that CD40L reverse signaling enhances NGF‐promoted axon growth and tissue innervation. Here we show that CD40L reverse signaling has the opposite function in prevertebral ganglion (PVG) sympathetic neurons. During a circumscribed perinatal window of development, PVG neurons cultured from Cd40^–/– mice had substantially larger, more exuberant axon arbors in the presence of NGF than PVG neurons cultured from wild‐type mice. Tissues that receive their sympathetic innervation from PVG neurons were markedly hyperinnervated in Cd40^–/– mice compared with wild‐type mice. The exuberant axonal growth phenotype of cultured CD40‐deficient perinatal PVG neurons was pared back to wild‐type levels by activating CD40L reverse signaling with a CD40‐Fc chimeric protein, but not by activating CD40 forward signaling with CD40L. The co‐expression of CD40 and CD40L in PVG neurons suggests that these proteins engage in an autocrine signaling loop in these neurons. Our work shows that CD40L reverse signaling is a physiological regulator of NGF‐promoted sympathetic axon growth and tissue innervation with opposite effects in paravertebral and prevertebral neurons.

Anatomical and clinical implications of vagal modulation of the spleen

The vagus nerve coordinates most physiologic functions including the cardiovascular and immune systems. This mechanism has significant clinical implications because electrical stimulation of the vagus nerve can control inflammation and organ injury in infectious and inflammatory disorders. The complex mechanisms that mediate vagal modulation of systemic inflammation are mainly regulated via the spleen. More specifically, vagal stimulation prevents organ injury and systemic inflammation by inhibiting the production of cytokines in the spleen. However, the neuronal regulation of the spleen is controversial suggesting that it can be mediated by either monosynaptic innervation of the splenic parenchyma or secondary neurons from the celiac ganglion depending on the experimental conditions. Recent physiologic and anatomic studies suggest that inflammation is regulated by neuro-immune multi-synaptic interactions between the vagus and the splanchnic nerves to modulate the spleen. Here, we review the current knowledge on these interactions, and discuss their experimental and clinical implications in infectious and inflammatory disorders.

The Vagus Nerve and the Celiaco-mesenteric Ganglia Participate in the Feeding Responses Evoked by Non-sulfated Cholecystokinin-8 in Male Sprague Dawley Rats

We have shown that non-sulfated cholecystokinin-8 (NS CCK-8) reduces food intake in adult male Sprague Dawley rats by activating cholecystokinin-B receptor (CCK-BR). Here, we tested the hypothesis that the vagus nerve and the celiaco-mesenteric ganglia may play a role in this reduction. The hypothesis stems from the following facts. The vagus and the celiaco-mesenteric ganglia contain NS CCK-8, they express and have binding sites for CCK-BR, NS CCK-8 activates CCK-BR on afferent vagal and sympathetic fibers and the two structures link the gastrointestinal tract to central feeding nuclei in the brain, which also contain the peptide and CCK-BR. To test this hypothesis, three groups of free-feeding rats, vagotomy (VGX), celiaco-mesenteric ganglionectomy (CMGX) and sham-operated, received NS CCK-8 (0, 0.5 and 1 nmol/kg) intraperitoneally prior to the onset of the dark cycle and various feeding behaviors were recorded. We found that in sham-operated rats both doses of NS CCK-8 reduced meal size (MS), prolonged the intermeal interval (IMI, time between first and second meal), increased satiety ratio (SR = IMI/MS), reduced 24-h food intake and reduced the number of meals relative to saline control. In the VGX and the CMGX groups, all of the previous responses were attenuated. Consistent with our hypothesis, the findings of the current work suggest a role for the vagus nerve and the celiaco-mesenteric ganglia in the feeding responses evoked by NS CCK-8.

Regional Differences in the Contributions of TNF Reverse and Forward Signaling to the Establishment of Sympathetic Innervation

Members of the TNF and TNF receptor superfamilies acting by both forward and reverse signaling are increasingly recognized as major physiological regulators of axon growth and tissue innervation in development. Studies of the experimentally tractable superior cervical ganglion (SCG) neurons and their targets have shown that only TNF reverse signaling, not forward signaling, is a physiological regulator of sympathetic innervation. Here, we compared SCG neurons and their targets with prevertebral ganglion (PVG) neurons and their targets. Whereas all SCG targets were markedly hypoinnervated in both TNF-deficient and TNFR1-deficient mice, PVG targets were not hypoinnervated in these mice and one PVG target, the spleen, was significantly hyperinnervated. These in vivo regional differences in innervation density were related to in vitro differences in the responses of SCG and PVG neurons to TNF reverse and forward signaling. Though TNF reverse signaling enhanced SCG axon growth, it did not affect PVG axon growth. Whereas activation of TNF forward signaling in PVG axons inhibited growth, TNF forward signaling could not be activated in SCG axons. These latter differences in the response of SCG and PVG axons to TNF forward signaling were related to TNFR1 expression, whereas PVG axons expressed TNFR1, SCG axons did not. These results show that both TNF reverse and forward signaling are physiological regulators of sympathetic innervation in different tissues.

Non-sulfated cholecystokinin-8 reduces meal size and prolongs the intermeal interval in male Sprague Dawley rats

The current study measured seven feeding responses by non-sulfated cholecystokinin-8 (NS CCK-8) in freely fed adult male Sprague Dawley rats. The peptide (0, 0.5, 1, 3, 5 and 10 nmol/kg) was given intraperitoneally (ip) prior to the onset of the dark cycle, and first meal size (MS), second meal size, intermeal interval (IMI) length, satiety ratio (SR = IMI/MS), latency to first meal, duration of first meal, number of meals and 24-hour food intake were measured. We found that NS CCK-8 (0.5 and 1.0 nmol/kg) reduced MS, prolonged IMI length and increased SR during the dark cycle. Furthermore, the specific CCK-B receptor antagonist L365, 260 (1 mg/kg, ip) attenuated these responses. These results support a possible role for NS CCK-8 in regulating food intake.

Effects of dipyrone on the digestive tract

Dipyrone (metamizole), acting through its main metabolites 4-methyl-amino-antipyrine and 4-amino-antipyrine, has established analgesic, antipyretic, and spasmolytic pharmacological effects, which are mediated by poorly known mechanisms. In rats, intravenously administered dipyrone delays gastric emptying (GE) of liquids with the participation of capsaicin-sensitive afferent fibers. This effect seems to be mediated by norepinephrine originating from the sympathetic nervous system but not from the superior celiac-mesenteric ganglion complex, which activates β2-adrenoceptors. In rats, in contrast to nonselective non-hormonal anti-inflammatory drugs, dipyrone protects the gastric mucosa attenuating the development of gastric ulcers induced by a number of agents. Clinically, it has been demonstrated that dipyrone is effective in the control of colic-like abdominal pain originating from the biliary and intestinal tracts. Since studies in humans and animals have demonstrated the presence of β2-adrenoceptors in biliary tract smooth muscle and β2-adrenoceptor activation has been shown to occur in dipyrone-induced delayed GE, it is likely that this kind of receptors may participate in the reduction of smooth muscle spasm of the sphincter of Oddi induced by dipyrone. There is no evidence that dipyrone may interfere with small bowel and colon motility, and the clinical results of its therapeutic use in intestinal colic appear to be due to its analgesic effect.

Sympathetic Innervation of Stomach in Postnatal Development

Sympathetic innervation of the stomach was studied in rats by the method of retrograde axon transport of Fast Blue in postnatal ontogenesis. The number of labeled neurons increased in the first 10 days of life and then did not change until the senescence. All labeled neurons innervating the stomach contain the catecholamine synthesis enzyme, tyrosine hydroxylase. The proportion of labeled neuropeptide Y-immunopositive neurons did not change in the development, the percentage of labeled calbindin-immunoreactive neurons decreased in the first month of life.

Cocaine- and amphetamine-regulated transcript (CART) peptide in the enteric nervous system of the porcine esophagus

Cocaine- and amphetamine-regulated transcript peptide (CART) is widely distributed within the central and peripheral nervous system. In the brain, CART is considered as the main anorectic peptide involved in the regulation of food intake. Contrary to the central nervous system, a lot of aspects connected with the distribution and functions of CART within the enteric nervous system (ENS) still remain unknown. The aim of the present study was to investigate, for the first time, the population of CART-like immunoreactive (CART-LI) neurons within the porcine esophagus and the denotation of their neurochemical coding. During this experiment, the distribution of CART-LI neurons and the colocalization of CART with other neuronal active substances were examined using standard double- and triple-immunofluorescence techniques in enteric plexuses of cervical, thoracic, and abdominal esophagus fragments. The obtained results showed that CART is present in a relatively high percentage of esophageal neurons (values fluctuated from 45.2±0.9% in the submucous plexus of the thoracic esophagus to 58.1±5.0% in the myenteric plexus of the same fragment of the esophagus). Moreover, CART colocalized with a wide range of other active neuronal substances, mainly with the vesicular acetylcholine transporter (VAChT, a marker of cholinergic neurons), neuronal isoform of nitric oxide synthase (nNOS, a marker of nitrergic neurons), vasoactive intestinal polypeptide (VIP) and galanin (GAL). The number of CART-positive neuronal cells and their neurochemical coding clearly depended on the fragment of esophagus studied and the type of enteric plexus. The obtained results suggest that CART may play important and multidirectional roles in the neuronal regulation of esophageal functions.

Early sympathetic islet neuropathy in autoimmune diabetes: lessons learned and opportunities for investigation

This review outlines the current state of knowledge regarding a unique neural defect of the pancreatic islet in autoimmune diabetes, one that we have termed early sympathetic islet neuropathy (eSIN). We begin with the findings that a majority of islet sympathetic nerves are lost near the onset of type 1, but not type 2, diabetes and that this nerve loss is restricted to the islet. We discuss later work demonstrating that while the loss of islet sympathetic nerves and the loss of islet beta cells in type 1 diabetes both require infiltration of the islet by lymphocytes, their respective mechanisms of tissue destruction differ. Uniquely, eSIN requires the activation of a specific neurotrophin receptor and we propose two possible pathways for activation of this receptor during the immune attack on the islet. We also outline what is known about the functional consequences of eSIN, focusing on impairment of sympathetically mediated glucagon secretion and its application to the clinical problem of insulin-induced hypoglycaemia. Finally, we offer our view on the important remaining questions regarding this unique neural defect.

Individual sympathetic postganglionic neurons coinnervate myenteric ganglia and smooth muscle layers in the gastrointestinal tract of the rat

A full description of the terminal architecture of sympathetic axons innervating the gastrointestinal (GI) tract has not been available. To label sympathetic fibers projecting to the gut muscle wall, dextran biotin was injected into the celiac and superior mesenteric ganglia (CSMG) of rats. Nine days postinjection, animals were euthanized and stomachs and small intestines were processed as whole mounts (submucosa and mucosa removed) to examine CSMG efferent terminals. Myenteric neurons were counterstained with Cuprolinic Blue; catecholaminergic axons were stained immunohistochemically for tyrosine hydroxylase. Essentially all dextran-labeled axons (135 of 136 sampled) were tyrosine hydroxylase-positive. Complete postganglionic arbors (n = 154) in the muscle wall were digitized and analyzed morphometrically. Individual sympathetic axons formed complex arbors of varicose neurites within myenteric ganglia/primary plexus and, concomitantly, long rectilinear arrays of neurites within circular muscle/secondary plexus or longitudinal muscle/tertiary plexus. Very few CSMG neurons projected exclusively (i.e., ∼100% of an arbor's varicose branches) to myenteric plexus (∼2%) or smooth muscle (∼14%). With less stringent inclusion criteria (i.e., ≥85% of an axon's varicose branches), larger minorities of neurons projected predominantly to either myenteric plexus (∼13%) or smooth muscle (∼27%). The majority (i.e., ∼60%) of all individual CSMG postganglionics formed mixed, heterotypic arbors that coinnervated extensively (>15% of their varicose branches per target) both myenteric ganglia and smooth muscle. The fact that ∼87% of all sympathetics projected either extensively or even predominantly to smooth muscle, while simultaneously contacting myenteric plexus, is consistent with the view that these neurons control GI muscle directly, if not exclusively. J. Comp. Neurol. 524:2577-2603, 2016. © 2016 Wiley Periodicals, Inc.

Effect of selective β-adrenoceptor blockade and surgical resection of the celiac-superior mesenteric ganglion complex on delayed liquid gastric emptying induced by dipyrone, 4-aminoantipyrine, and antipyrine in rats

There is evidence for participation of peripheral β-adrenoceptors in delayed liquid gastric emptying (GE) induced in rats by dipyrone (Dp), 4-aminoantipyrine (AA), and antipyrine (At). The present study aimed to determine whether β-adrenoceptors are involved in delayed GE induced by phenylpyrazole derivatives and the role of the prevertebral sympathetic nervous system in this condition. Male Wistar rats weighing 220-280 g were used in the study. In the first experiment rats were intravenously pretreated with vehicle (V), atenolol 30 mg/kg (ATE, β₁-adrenergic antagonist), or butoxamine 25 mg/kg (BUT, β₂-adrenergic antagonist). In the second experiment, rats were pretreated with V or SR59230A 2 mg/kg (SRA, β₃-adrenergic antagonist). In the third experiment, rats were subjected to surgical resection of the celiac-superior mesenteric ganglion complex or to sham surgery. The groups were intravenously treated with saline (S), 240 µmol/kg Dp, AA, or At, 15 min after pretreatment with the antagonists or V and nine days after surgery. GE was determined 10 min later by measuring the percentage of gastric retention (%GR) of saline labeled with phenol red 10 min after gavage. The %GR (means±SE, n=6) values indicated that BUT abolished the effect of Dp (BUT+Dp vs V+Dp: 35.0%±5.1% vs 56.4%±2.7%) and At (BUT+At vs V+At: 33.5%±4.7% vs 52.9%±2.6%) on GE, and significantly reduced (P<0.05) the effect of AA (BUT+AA vs V+AA: 48.0%±5.0% vs 65.2%±3.8%). ATE, SRA, and sympathectomy did not modify the effects of treatments. These results suggest that β₂-adrenoceptor activation occurred in delayed liquid gastric emptying induced by the phenylpyrazole derivatives dipyrone, 4-aminoantipyrine, and antipyrine. Additionally, the released neurotransmitter did not originate in the celiac-superior mesenteric ganglion complex.

Neurochemical Plasticity of the Coeliac-Superior Mesenteric Ganglion Complex Neurons Projecting to the Prepyloric Area of the Porcine Stomach following Hyperacidity

This study was designed to determine neurochemical properties of the coeliac-superior mesenteric ganglion (CSMG) neurons supplying the prepyloric area of the porcine stomach in physiological state and following experimentally induced hyperacidity. To localize sympathetic neurons innervating the studied area of stomach, the neuronal retrograde tracer Fast Blue (FB) was applied to control animals and hydrochloric acid infusion (HCl) groups. After 23 days, animals of the HCl group were reintroduced into a state of general anesthesia and intragastrically given 5 mL/kg of body weight of 0.25 M aqueous solution of hydrochloric acid. On the 28th day, all animals were sacrificed. The CSMG complexes were then collected and processed for double-labeling immunofluorescence. In the control animals, FB-positive perikarya displayed immunoreactivity to tyrosine hydroxylase (TH), dopamine β-hydroxylase (DβH), neuropeptide Y (NPY), and galanin (GAL). Experimentally induced gastric hyperacidity changed the neurochemical phenotype of the studied neurons. An upregulated expression of GAL and NPY and the de novo synthesis of neuronal nitric oxide synthase (nNOS) and leu5-enkephalin (LENK) as well as downregulated expression of TH and DβH in the stomach-projecting neurons were observed. These findings enrich existing knowledge about the participation of these active substances in adaptive mechanism(s) of the sympathetic neurons during pathological processes within the gastrointestinal tract.

Gene Therapy of the Peripheral Nervous System: Celiac Ganglia

Gene therapy has played an integral role in advancing our understanding of the central nervous system. However, gene therapy techniques have yet to be widely utilized in the peripheral nervous system. Critical targets for gene therapy within the PNS are the neurons in sympathetic ganglia, which are the final pathway to end organs. Thus they are the most specific targets for organ-specific neuron modification. This presents challenges because neurons are not viscerotopically organized within the ganglia and therefore cannot be targeted by their location. However, organ-specific neurons have been identified in sympathetic ganglia of some species and this offers an opportunity for targeting and transducing neurons by way of their target. In fact, alterations in sympathetic neurons have had pathological effects, and transducing organ-specific sympathetic neurons offer an exciting opportunity to selectively modify sympathetic pathology. In this chapter, we describe a method to virally transduce the celiac ganglion (CG), a prevertebral sympathetic ganglion that innervates abdominal organs, with AAV serotypes 1 and 6; thereby, providing a potential avenue to modulate specific subsets of neurons within the celiac ganglion.

The Influence of Prolonged Acetylsalicylic Acid Supplementation-Induced Gastritis on the Neurochemistry of the Sympathetic Neurons Supplying Prepyloric Region of the Porcine Stomach

This experiment was designed to establish the localization and neurochemical phenotyping of sympathetic neurons supplying prepyloric area of the porcine stomach in a physiological state and during acetylsalicylic acid (ASA) induced gastritis. In order to localize the sympathetic perikarya the stomachs of both control and acetylsalicylic acid treated (ASA group) animals were injected with neuronal retrograde tracer Fast Blue (FB). Seven days post FB injection, animals were divided into a control and ASA supplementation group. The ASA group was given 100 mg/kg of b.w. ASA orally for 21 days. On the 28^th day all pigs were euthanized with gradual overdose of anesthetic. Then fourteen-micrometer-thick cryostat sections were processed for routine double-labeling immunofluorescence, using primary antisera directed towards tyrosine hydroxylase (TH), dopamine β-hydroxylase (DβH), neuropeptide Y (NPY), galanin (GAL), neuronal nitric oxide synthase (nNOS), leu 5-enkephalin (LENK), cocaine- and amphetamine- regulated transcript peptide (CART), calcitonin gene-related peptide (CGRP), substance P (SP) and vasoactive intestinal peptide (VIP). The data obtained in this study indicate that postganglionic sympathetic nerve fibers supplying prepyloric area of the porcine stomach originate from the coeliac-cranial mesenteric ganglion complex (CCMG). In control animals, the FB-labelled neurons expressed TH (94.85 ± 1.01%), DβH (97.10 ± 0.97%), NPY (46.88 ± 2.53%) and GAL (8.40 ± 0.53%). In ASA group, TH- and DβH- positive nerve cells were reduced (85.78 ± 2.65% and 88.82 ± 1.63% respectively). Moreover, ASA- induced gastritis resulted in increased expression of NPY (76.59 ± 3.02%) and GAL (26.45 ± 2.75%) as well as the novo-synthesis of nNOS (6.13 ± 1.11%) and LENK (4.77 ± 0.42%) in traced CCMG neurons. Additionally, a network of CART-, CGRP-, SP-, VIP-, LENK-, nNOS- immunoreactive (IR) nerve fibers encircling the FB-positive perikarya were observed in both intact and ASA-treated animals. The results of this study indicate involvement of these neuropeptides in the development or presumably counteraction of gastric inflammation.

Short-term diabetic hyperglycemia suppresses celiac ganglia neurotransmission, thereby impairing sympathetically mediated glucagon responses

Short-term hyperglycemia suppresses superior cervical ganglia neurotransmission. If this ganglionic dysfunction also occurs in the islet sympathetic pathway, sympathetically mediated glucagon responses could be impaired. Our objectives were 1) to test for a suppressive effect of 7 days of streptozotocin (STZ) diabetes on celiac ganglia (CG) activation and on neurotransmitter and glucagon responses to preganglionic nerve stimulation, 2) to isolate the defect in the islet sympathetic pathway to the CG itself, and 3) to test for a protective effect of the WLD(S) mutation. We injected saline or nicotine in nondiabetic and STZ-diabetic rats and measured fos mRNA levels in whole CG. We electrically stimulated the preganglionic or postganglionic nerve trunk of the CG in nondiabetic and STZ-diabetic rats and measured portal venous norepinephrine and glucagon responses. We repeated the nicotine and preganglionic nerve stimulation studies in nondiabetic and STZ-diabetic WLD(S) rats. In STZ-diabetic rats, the CG fos response to nicotine was suppressed, and the norepinephrine and glucagon responses to preganglionic nerve stimulation were impaired. In contrast, the norepinephrine and glucagon responses to postganglionic nerve stimulation were normal. The CG fos response to nicotine, and the norepinephrine and glucagon responses to preganglionic nerve stimulation, were normal in STZ-diabetic WLD(S) rats. In conclusion, short-term hyperglycemia's suppressive effect on nicotinic acetylcholine receptors of the CG impairs sympathetically mediated glucagon responses. WLD(S) rats are protected from this dysfunction. The implication is that this CG dysfunction may contribute to the impaired glucagon response to insulin-induced hypoglycemia seen early in type 1 diabetes.

Peripheral α2-β1 adrenergic interactions mediate the ghrelin response to brain urocortin 1 in rats

The autonomic nervous system (ANS) conveys neuronal input from the brain to the stomach. We investigated mechanisms through which urocortin 1 (UCN1) injected intracerebroventricularly (ICV, 300 pmol/rat) inhibits circulating ghrelin in rats. This was achieved by assessing (1) the induction of c-fos gene expression as a marker of neuronal activation in specific hypothalamic and caudal brainstem regulating ANS; (2) the influence of vagotomy and pharmacological blockade of central and peripheral α- and β-adrenergic receptor (AR) on ICV UCN1-induced reduction of plasma ghrelin levels (determined by ELISA); and (3) the relevance of this pathway in the feeding response to a fast in rats. UCN1 increased c-fos mRNA expression in key brain sites influencing sympathetic activity namely the hypothalamic paraventricular and ventromedial nuclei, locus coeruleus, nucleus of the solitary tract, and rostral ventrolateral medulla, by 16-, 29-, 6-, 37-, and 13-fold, respectively. In contrast, the dorsal motor nucleus of the vagus had little c-fos mRNA expression and ICV UCN1 induced a similar reduction in acylated ghrelin in the sham-operated (31%) and vagotomized (41%) rats. An intraperitoneal (IP) injection of either a non-selective α- or selective α2-AR antagonist reduced, while a selective α2-AR agonist enhanced ICV UCN1-induced suppression of plasma acylated ghrelin levels. In addition, IP injection of a non-selective β- or selective β1-AR agonist blocked, and selective β1-AR antagonist augmented, the ghrelin response to ICV UCN1. The IP injections of a selective α1- or non-selective β or β2-AR antagonists, or any of the pretreatments given ICV had no effect. ICV UCN1 reduced the 2-h food intake in response to a fast by 80%, and this effect was partially prevented by a selective α2-AR antagonist. These data suggest that ICV UCN1 reduces plasma ghrelin mainly through the brain sympathetic component of the ANS and peripheral AR specifically α2-AR activation and inactivation of β1-AR. The α2-AR pathway contributes to the associated reduction in food intake.

Spinally projecting preproglucagon axons preferentially innervate sympathetic preganglionic neurons

•

Spinal GLP-1 axons target primarily sympathetic preganglionic neurons.

•

Spinal GLP-1 axons innervate interneurons that may regulate sympathetic outflow.

•

Many GLP-1 neurons in the medulla are spinally-projecting.

•

The lumbar cord contains YFP-expressing neurons that do not innervate the brain.

Glucagon-like peptide-1 (GLP-1) affects central autonomic neurons, including those controlling the cardiovascular system, thermogenesis, and energy balance. Preproglucagon (PPG) neurons, located mainly in the nucleus tractus solitarius (NTS) and medullary reticular formation, produce GLP-1. In transgenic mice expressing glucagon promoter-driven yellow fluorescent protein (YFP), these brainstem PPG neurons project to many central autonomic regions where GLP-1 receptors are expressed. The spinal cord also contains GLP-1 receptor mRNA but the distribution of spinal PPG axons is unknown.

Here, we used two-color immunoperoxidase labeling to examine PPG innervation of spinal segments T1–S4 in YFP-PPG mice. Immunoreactivity for YFP identified spinal PPG axons and perikarya. We classified spinal neurons receiving PPG input by immunoreactivity for choline acetyltransferase (ChAT), nitric oxide synthase (NOS) and/or Fluorogold (FG) retrogradely transported from the peritoneal cavity. FG microinjected at T9 defined cell bodies that supplied spinal PPG innervation.

The deep dorsal horn of lower lumbar cord contained YFP-immunoreactive neurons. Non-varicose, YFP-immunoreactive axons were prominent in the lateral funiculus, ventral white commissure and around the ventral median fissure. In T1–L2, varicose, YFP-containing axons closely apposed many ChAT-immunoreactive sympathetic preganglionic neurons (SPN) in the intermediolateral cell column (IML) and dorsal lamina X. In the sacral parasympathetic nucleus, about 10% of ChAT-immunoreactive preganglionic neurons received YFP appositions, as did occasional ChAT-positive motor neurons throughout the rostrocaudal extent of the ventral horn. YFP appositions also occurred on NOS-immunoreactive spinal interneurons and on spinal YFP-immunoreactive neurons. Injecting FG at T9 retrogradely labeled many YFP-PPG cell bodies in the medulla but none of the spinal YFP-immunoreactive neurons.

These results show that brainstem PPG neurons innervate spinal autonomic and somatic motor neurons. The distributions of spinal PPG axons and spinal GLP-1 receptors correlate well. SPN receive the densest PPG innervation. Brainstem PPG neurons could directly modulate sympathetic outflow through their spinal inputs to SPN or interneurons.

Neural control of the endocrine pancreas

The autonomic nervous system affects glucose metabolism partly through its connection to the pancreatic islet. Since its discovery by Paul Langerhans, the precise innervation patterns of the islet has remained elusive, mainly because of technical limitations. Using 3-dimensional reconstructions of axonal terminal fields, recent studies have determined the innervation patterns of mouse and human islets. In contrast to the mouse islet, endocrine cells within the human islet are sparsely contacted by autonomic axons. Instead, the invading sympathetic axons preferentially innervate smooth muscle cells of blood vessels. This innervation pattern suggests that, rather than acting directly on endocrine cells, sympathetic nerves may control hormone secretion by modulating blood flow in human islets. In addition to autonomic efferent axons, islets also receive sensory innervation. These axons transmit sensory information to the brain but also have the ability to locally release neuroactive substances that have been suggested to promote diabetes pathogenesis. We discuss recent findings on islet innervation, the connections of the islet with the brain, and the role islet innervation plays during the progression of diabetes.

The p75 neurotrophin receptor is required for the major loss of sympathetic nerves from islets under autoimmune attack

Our goal was to determine the role of the p75 neurotrophin receptor (p75NTR) in the loss of islet sympathetic nerves that occurs during the autoimmune attack of the islet. The islets of transgenic (Tg) mice in which β-cells express a viral glycoprotein (GP) under the control of the insulin promotor (Ins2) were stained for neuropeptide Y before, during, and after virally induced autoimmune attack of the islet. Ins2-GP(Tg) mice injected with lymphocytic choriomeningitis virus (LCMV) lost islet sympathetic nerves before diabetes development but coincident with the lymphocytic infiltration of the islet. The nerve loss was marked and islet-selective. Similar nerve loss, chemically induced, was sufficient to impair sympathetically mediated glucagon secretion. In contrast, LCMV-injected Ins2-GP(Tg) mice lacking the p75NTR retained most of their islet sympathetic nerves, despite both lymphocytic infiltration and development of diabetes indistinguishable from that of p75NTR wild-type mice. We conclude that an inducible autoimmune attack of the islet causes a marked and islet-selective loss of sympathetic nerves that precedes islet collapse and hyperglycemia. The p75NTR mediates this nerve loss but plays no role in mediating the loss of islet β-cells or the subsequent diabetes. p75NTR-mediated nerve loss may contribute to the impaired glucose counterregulation seen in type 1 diabetes.

Physical (in)activity-dependent structural plasticity in bulbospinal catecholaminergic neurons of rat rostral ventrolateral medulla

Increased activity of the sympathetic nervous system is thought to play a role in the development and progression of cardiovascular disease. Recent work has shown that physical inactivity versus activity alters neuronal structure in brain regions associated with cardiovascular regulation. Our physiological studies suggest that neurons in the rostral ventrolateral medulla (RVLM) are more responsive to excitation in sedentary versus physically active animals. We hypothesized that enhanced functional responses in the RVLM may be due, in part, to changes in the structure of RVLM neurons that control sympathetic activity. We used retrograde tracing and immunohistochemistry for tyrosine hydroxylase (TH) to identify bulbospinal catecholaminergic (C1) neurons in sedentary and active rats after chronic voluntary wheel-running exercise. We then digitally reconstructed their cell bodies and dendrites at different rostrocaudal levels. The dendritic arbors of spinally projecting TH neurons from sedentary rats were more branched than those of physically active rats (P < 0.05). In sedentary rats, dendritic branching was greater in more rostral versus more caudal bulbospinal C1 neurons, whereas, in physically active rats, dendritic branching was consistent throughout the RVLM. In contrast, cell body size and the number of primary dendrites did not differ between active and inactive animals. We suggest that these structural changes provide an anatomical underpinning for the functional differences observed in our in vivo studies. These inactivity-related structural and functional changes may enhance the overall sensitivity of RVLM neurons to excitatory stimuli and contribute to an increased risk of cardiovascular disease in sedentary individuals.

Expression of β2 adrenoceptors within enteric neurons of the horse ileum

The activity of the gastrointestinal tract is regulated through the activation of adrenergic receptors (ARs). Since data concerning the distribution of ARs in the horse intestine is virtually absent, we investigated the distribution of β2-AR in the horse ileum using double-immunofluorescence. The β2-AR-immunoreactivity (IR) was observed in most (95%) neurons located in submucosal plexus (SMP) and in few (8%) neurons of the myenteric plexus (MP). Tyrosine hydroxylase (TH)-IR fibers were observed close to neurons expressing β2-AR-IR. Since β2-AR is virtually expressed in most neurons located in the horse SMP and in a lower percentage of neurons in the MP, it is reasonable to retain that this adrenergic receptor could regulate the activity of both secretomotor neurons and motor neurons innervating muscle layers and blood vessels. The high density of TH-IR fibers near β2-AR-IR enteric neurons indicates that the excitability of these cells could be directly modulated by the sympathetic system.

Immunoreactivity for the NMDA NR1 subunit in bulbospinal catecholamine and serotonin neurons of rat ventral medulla

Bulbospinal neurons in the ventral medulla play important roles in the regulation of sympathetic outflow. Physiological evidence suggests that these neurons are activated by N-methyl-D-aspartate (NMDA) and non-NMDA subtypes of glutamate receptors. In this study, we examined bulbospinal neurons in the ventral medulla for the presence of immunoreactivity for the NMDA NR1 subunit, which is essential for NMDA receptor function. Rats received bilateral injections of cholera toxin B into the tenth thoracic spinal segment to label bulbospinal neurons. Triple immunofluorescent labeling was used to detect cholera toxin B with a blue fluorophore, NR1 with a red fluorophore, and either tyrosine hydroxylase or tryptophan hydroxylase with a green fluorophore. In the rostral ventrolateral medulla, NR1 occurred in all bulbospinal tyrosine hydroxylase-positive neurons and 96% of bulbospinal tyrosine hydroxylase-negative neurons, which were more common in sections containing the facial nucleus. In the raphe pallidus, the parapyramidal region, and the marginal layer, 98% of bulbospinal tryptophan hydroxylase-positive neurons contained NR1 immunoreactivity. NR1 was also present in all of the bulbospinal tryptophan hydroxylase-negative neurons, which comprised 20% of bulbospinal neurons in raphe pallidus and the parapyramidal region. These results show that virtually all bulbospinal tyrosine hydroxylase and non-tyrosine hydroxylase neurons in the rostral ventrolateral medulla and virtually all bulbospinal serotonin and non-serotonin neurons in raphe pallidus and the parapyramidal region express NR1, the obligatory subunit of the NMDA receptor. NMDA receptors on bulbospinal neurons in the rostral ventral medulla likely influence sympathoexcitation in normal and pathological conditions.

Early alterations in plasma ghrelin levels in offspring of calorie-restricted rats during gestation may be linked to lower sympathetic drive to the stomach

Serum ghrelin concentration is generally reduced in obesity. We aimed to assess whether this alteration is present in rats predisposed to obesity because of moderate undernutrition during gestation, and to explore whether this could be related with alterations in stomach sympathetic innervation, which is involved in gastric ghrelin secretion. Offspring of control and 20% gestational calorie-restricted dams (CR) exposed to normal-fat-diet from weaning onward were studied. Circulating ghrelin levels were measured at 25 days and 4 months of age. Morphometry, number of ghrelin-positive (ghrelin(+)) cells, ghrelin mRNA and protein levels, and tyrosine hydroxylase (TH) protein levels in stomach were determined at 25 days. Adult CR male animals, but not females, exhibited greater body-weight (BW) than their controls, but both males and females showed lower circulating ghrelin levels. This alteration in ghrelin levels was already present at 25 days, prior to any difference in BW. At this juvenile age, no differences in gastric morphometry, number of ghrelin(+) cells or ghrelin mRNA/protein levels were found between control and CR animals, however, CR animals showed lower TH stomach content. These results suggest that circulating ghrelin concentration is early altered in rats prenatally programmed to develop obesity. This does not seem to be associated with lower ghrelin production capacity but with specific alterations in sympathetic drive to the stomach.

Involvement of the oestrogenic receptors in superior mesenteric ganglion on the ovarian steroidogenesis in rat

Oestradiol (E(2)) is a key hormone in the regulation of reproductive processes. The aims of this work were a) to examine the distributions of oestrogen receptor α (ERα) and ERβ in the neurons of the superior mesenteric ganglion (SMG) in the oestrus stage by immunohistochemistry, b) to demonstrate whether E(2) in the SMG modifies progesterone (P(4)), androstenedione (A(2)) and nitrite release in the ovarian compartment on oestrus day and c) to demonstrate whether E(2) in the ganglion modifies the activity and gene expression in the ovary of the steroidogenic enzymes 3β-hydroxysteroid dehydrogenase (3β-HSD) and 20α-hydroxysteroid dehydrogenase (20α-HSD). The ex vivo SMG-ovarian nervous plexus-ovary system was used. E(2), tamoxifen (Txf) and E(2) plus Txf were added in the ganglion to measure ovarian P(4) release, while E(2) alone was added to measure ovarian A(2) and nitrites release. Immunohistochemistry revealed cytoplasmic ERα immunoreactivity only in the neural somas in the SMG. E(2) increased ovarian P(4) and A(2) release at 15, 30 and 60 min but decreased nitrites. The activity and gene expression of 3β-HSD increased, while the activity and gene expression of 20α-HSD did not show changes with respect to the control. Txf in the ganglion diminished P(4) release only at 60 min. E(2) plus Txf in the ganglion reverted the effect of E(2) alone and the inhibitory effect of Txf. The results of this study demonstrate that ERα activation in the SMG has an impact on ovarian steroidogenesis in rats, thus providing evidence for the critical role of peripheral system neurons in the control of ovarian functions under normal and pathological conditions.

Gastrin releasing peptides increase Fos-like immunoreactivity in the enteric nervous system and the dorsal vagal complex

We and others have shown that gastrin-releasing peptide (GRP) reduces food intake. In this study, we determined the activation of the gastrointestinal and dorsal vagal complex (DVC) neurons by various forms of GRP to determine the pathway involved in this reduction. We found the following: (1) GRP-10, -27 and -29 (2.1 nmol/kg, i.p.) increased the Fos-like immunoreactivity (Fos-LI, a marker for neuronal activation) in the myenteric neurons of the stomach and the area postrema (AP) of the DVC; (2) GRP-27 and GRP-29 increased the Fos-LI in the myenteric plexus of the duodenum; and (3) only GRP-29 increased the Fos-LI in the submucosal plexus of the duodenum. In conclusion, GRP may reduce food intake by activating the area postrema. The enteric neurons may have a potential role in this reduction through the direct activation of the AP or exerting local gut actions, such as the stimulation of gut motility or secretions.

The influence of autonomic interventions on the sleep-wake-related changes in gastric myoelectrical activity in rats

BACKGROUND

Significant changes in autonomic activity occur at sleep-wake transitions and constitute an ideal setting for investigating the modulatory role of the autonomic nervous system on gastric myoelectrical activity (GMA).

METHODS

Using continuous power spectral analysis of electroencephalogram, electromyogram, and electrogastromyogram (EGMG) data from freely moving rats that had undergone chemical sympathetomy and/or truncal vagotomy, sleep-wake-related fluctuations in GMA were compared among the intervention groups.

KEY RESULTS

The pattern and extent of fluctuations in EGMG power across the sleep-wake states was blunted most significantly in rats undergoing both chemical sympathectomy and truncal vagotomy. The effect of these interventions also varied with respect to the transition between different sleep-wake states. The most prominent influences were observed between active waking and quiet sleep and between paradoxical sleep and quiet sleep.

CONCLUSIONS & INFERENCES

The sleep-wake-related fluctuations in EGMG power are a result of joint contributions from both sympathetic and vagal innervation. Vagotomy mainly resulted in a reduction in EGMG power, while the role of sympathetic innervation was unveiled by vagotomy and this was reflected most obviously in the extent of the fluctuations in EGMG power.

Sympathetic innervation of the ileocecal junction in horses

The distribution and chemical phenotypes of sympathetic and dorsal root ganglion (DRG) neurons innervating the equine ileocecal junction (ICJ) were studied by combining retrograde tracing and immunohistochemistry. Immunoreactivity (IR) for tyrosine hydroxylase (TH), dopamine beta-hydroxylase (DBH), neuronal nitric oxide synthase (nNOS), calcitonin gene-related peptide (CGRP), substance P (SP), and neuropeptide Y (NPY) was investigated. Sympathetic neurons projecting to the ICJ were distributed within the celiac (CG), cranial mesenteric (CranMG), and caudal mesenteric (CaudMG) ganglia, as well as in the last ganglia of the thoracic sympathetic chain and in the splanchnic ganglia. In the CG and CranMG 91 +/- 8% and 93 +/- 12% of the neurons innervating the ICJ expressed TH- and DBH-IR, respectively. In the CaudMG 90 +/- 15% and 94 +/- 5% of ICJ innervating neurons were TH- and DBH-IR, respectively. Sympathetic (TH-IR) fibers innervated the myenteric and submucosal ganglia, ileal blood vessels, and the muscle layers. They were more concentrated at the ICJ level and were also seen encircling myenteric plexus (MP) and submucosal plexus (SMP) descending neurons that were retrogradely labeled from the ICJ. Among the few retrogradely labeled DRG neurons, nNOS-, CGRP-, and SP-IR nerve cells were observed. Dense networks of CGRP-, nNOS-, and SP-IR varicosities were seen around retrogradely labeled prevertebral ganglia neurons. The CGRP-IR fibers are probably the endings of neurons projecting from the intestine to the prevertebral ganglia. These findings indicate that this crucial region of the intestinal tract is strongly influenced by the sympathetic system and that sensory information of visceral origin influences the sympathetic control of the ICJ.

Distribution pattern and chemical coding of neurons of the sympathetic chain ganglia supplying the descending colon in the pig

Sympathetic chain ganglia (SChG) neurons projecting to the descending colon of the pig were studied by means of retrograde tracing (Fast Blue, FB) and double-labelling immunofluorescence methods. FB was injected into the gut wall and after three weeks survival time the animals were transcardially perfused with paraformaldehyde and the bilateral sympathetic trunks were collected. The FB-positive neurons were localised only in the lumbar (L(1)-L(5)) ganglia of the sympathetic trunk and appeared either as small (30-50 microm in diameter) round-shaped perikarya forming clusters localised in caudal-ventral area or, rarely, as bigger (50-80 microm) and dispersed solitary irregular perikarya. Immunohistochemical staining revealed the catecholaminergic (tyrosine hydroxylase-/dopamine beta-hydroxylase-immunoreactive) character of the great majority of FB-positive neurons which preferentially co-expressed neuropeptide Y. In addition, none of the FB-positive perikarya was immunopositive to galanin, somatostatin, choline acetyltransferase, vasoactive intestinal peptide, pituitary adenylate cyclase-activating peptide, leu(5)-enkephalin, nitric oxide synthase, substance P and calcitonin-generelated peptide.

Impaired activation of celiac ganglion neurons in vivo after damage to their sympathetic nerve terminals

Because damage to sympathetic nerve terminals occurs in a variety of diseases, we tested the hypothesis that nerve terminal damage per se is sufficient to impair ganglionic neurotransmission in vivo. First, we measured the effect of nerve terminal damage produced by the sympathetic nerve terminal toxin 6-hydroxydopamine (6-OHDA) on ganglionic levels of several neurotrophins thought to promote neurotransmission. 6-OHDA-induced nerve terminal damage did not decrease the expression of neurotrophin-4 or brain-derived neurotrophic factor mRNA in the celiac ganglia but did decrease the ganglionic content of both nerve growth factor protein (nadir = -63%) and the mRNA of the alpha-3 subunit of the nicotinic cholinergic receptor (nadir = -49%), a subunit required for neurotransmission. Next, we tested whether this degree of receptor deficiency was sufficient to impair activation of celiac ganglia neurons. Impaired fos mRNA responses to nicotine administration in the celiac ganglia of 6-OHDA-pretreated rats correlated temporally with suppressed expression of functional nicotinic receptors. We verified by Fos protein immunohistochemistry that this ganglionic impairment was specific to principal ganglionic neurons. Last, we tested whether centrally initiated ganglionic neurotransmission is also impaired following nerve terminal damage. The principal neurons in rat celiac ganglia were reflexively activated by 2-deoxy-glucose-induced glucopenia, and the Fos response in the celiac ganglia was markedly inhibited by pretreatment with 6-OHDA. We conclude that sympathetic nerve terminal damage per se is sufficient to impair ganglionic neurotransmission in vivo and that decreased nicotinic receptor production is a likely mediator.

Splanchnic Circulation Is a Critical Neural Target in Angiotensin II Salt Hypertension in Rats

Chronic angiotensin II (Ang II) infusion, in rats fed high salt, engages the sympathetic nervous system to increase venomotor tone. The splanchnic sympathetic nervous system is the most important regulator of venous tone, indicating that splanchnic sympathetic nervous system activity may be increased in Ang II salt hypertension. We hypothesized that celiac ganglionectomy (CGx), to selectively disrupt sympathetic innervation to the splanchnic circulation, would attenuate arterial pressure (AP), and venous tone increases in Ang II salt hypertension. Rats fed 2% or 0.4% NaCl were instrumented to allow AP measurement by radiotelemetry at the same time as surgical CGx or sham operation. Ang II was delivered by minipump (150 ng/kg per minute) for 14 days. CGx reduced AP independent of salt diet during control. CGx markedly attenuated Ang II hypertension in rats on 2% NaCl but had little effect in rats fed 0.4% NaCl. To test the possibility that CGx exerted its effects via renal denervation, rats were subjected to the same protocol but received selective bilateral renal denervation. Renal denervation decreased AP during control but had no protective effect on Ang II hypertension and actually tended to exacerbate the pressor response. Finally, separate groups of rats underwent CGx or sham operation and were instrumented to allow repeated measures of mean circulatory filling pressure, an index of venous tone. In addition to attenuating Ang II salt hypertension, CGx completely prevented Ang II salt-induced increases in mean circulatory filling pressure and substantially attenuated depressor responses to acute ganglion blockade. We conclude that, in the presence of high salt, Ang II activates the splanchnic sympathetic nervous system to increase venomotor tone and AP.