Vagally mediated effects of brain stem dopamine on gastric tone and phasic contractions of the rat.

Dopamine (DA)-containing fibers and neurons are embedded within the brain stem dorsal vagal complex (DVC); we have shown previously that DA modulates the membrane properties of neurons of the dorsal motor nucleus of the vagus (DMV) via DA1 and DA2 receptors. The vagally dependent modulation of gastric tone and phasic contractions, i.e., motility, by DA, however, has not been characterized. With the use of microinjections of DA in the DVC while recording gastric tone and motility, the aims of the present study were 1) assess the gastric effects of brain stem DA application, 2) identify the DA receptor subtype, and, 3) identify the postganglionic pathway(s) activated. Dopamine microinjection in the DVC decreased gastric tone and motility in both corpus and antrum in 29 of 34 rats, and the effects were abolished by ipsilateral vagotomy and fourth ventricular treatment with the selective DA2 receptor antagonist L741,626 but not by application of the selective DA1 receptor antagonist SCH 23390. Systemic administration of the cholinergic antagonist atropine attenuated the inhibition of corpus and antrum tone in response to DA microinjection in the DVC. Conversely, systemic administration of the nitric oxide synthase inhibitor nitro-l-arginine methyl ester did not alter the DA-induced decrease in gastric tone and motility. Our data provide evidence of a dopaminergic modulation of a brain stem vagal neurocircuit that controls gastric tone and motility.NEW & NOTEWORTHY Dopamine administration in the brain stem decreases gastric tone and phasic contractions. The gastric effects of dopamine are mediated via dopamine 2 receptors on neurons of the dorsal motor nucleus of the vagus. The inhibitory effects of dopamine are mediated via inhibition of the postganglionic cholinergic pathway.

A critical re-evaluation of the specificity of action of perivagal capsaicin.

Perivagal application of capsaicin (1% solution) is considered to cause a selective degeneration of vagal afferent C fibres and has been used extensively to examine the site of action of many gastrointestinal (GI) neuropeptides. The actions of both capsaicin and GI neuropeptides may not be restricted to vagal afferent fibres, however, as other non-sensory neurones have displayed sensitivity to capsaicin and brainstem microinjections of these neuropeptides induce GI effects similar to those obtained upon systemic application. The aim of the present study was to test the hypothesis that perivagal capsaicin induces degeneration of vagal efferents controlling GI functions. Experiments were conducted 7-14 days after 30 min unilateral perivagal application of 0.1-1% capsaicin. Immunohistochemical analyses demonstrated that, as following vagotomy, capsaicin induced dendritic degeneration, decreased choline acetyltransferase but increased nitric oxide synthase immunoreactivity in rat dorsal motor nucleus of the vagus (DMV) neurones. Electrophysiological recordings showed a decreased DMV input resistance and excitability due, in part, to the expression of a large conductance calcium-dependent potassium current and the opening of a transient outward potassium window current at resting potential. Furthermore, the number of DMV neurones excited by thyrotrophin-releasing hormone and the gastric motility response to DMV microinjections of TRH were decreased significantly. Our data indicate that perivagal application of capsaicin induced DMV neuronal degeneration and decreased vagal motor responses. Treatment with perivagal capsaicin cannot therefore be considered selective for vagal afferent C fibres and, consequently, care is needed when using perivagal capsaicin to assess the mechanism of action of GI neuropeptides.

Characterization of the Basic Membrane Properties of Neurons of the Rat Dorsal Motor Nucleus of the Vagus in Paraquat-Induced Models of Parkinsonism.

Most of Parkinson's disease (PD) patients experience gastrointestinal dysfunctions, including gastric hypomotility. The dorsal motor nucleus of the vagus (DMV) modulates the motility of the upper gastrointestinal (GI) tract. Paraquat (P) administration induces Parkinsonism in experimental models, and we have developed recently an environmental model of Parkinsonism in which rats are treated with subthreshold doses of P and lectins (P + L), in both models rats develop reduced gastric motility prodromal to the full extent of motor deficits. The aim of the present study was to examine whether the membrane properties of DMV neurons in these two experimental models of Parkinsonism were altered. Whole cell recordings in slices containing DMV neurons were conducted in male Sprague Dawley rats which received either injections of paraquat (10 mg/kg i.p.; 10P), or oral administration of paraquat (1 mg/kg) and lectin (0.05% w/v; P + L). Morphological reconstructions of DMV neurons were conducted at the end of the recordings. The repolarization kinetics of the afterhyperpolarization phase of the action potential was accelerated in 10P neurons vs control, while the phase plot revealed a slower depolarizing slope. At baseline, the amplitude of miniature excitatory postsynaptic currents was increased in P + L neurons. No differences in the morphology of DMV neurons were observed. These data indicate that the membrane and synaptic properties of DMV neurons are altered in rodent models of Parkinsonism, in which neurons of 10P and P + L rats demonstrate an increased excitatory transmission, perhaps in an attempt to counteract the paraquat-induced gastric hypomotility.

Perinatal high fat diet increases inhibition of dorsal motor nucleus of the vagus neurons regulating gastric functions.

BACKGROUND: Previous studies suggest an increased inhibition of dorsal motor nucleus of the vagus (DMV) neurons following exposure to a perinatal high fat diet (PNHFD); the underlying neural mechanisms, however, remain unknown. This study assessed the effects of PNHFD on inhibitory synaptic inputs to DMV neurons and the vagally dependent control of gastric tone and motility. METHODS: Whole-cell patch clamp recordings were made from DMV neurons in thin brainstem slices from Sprague-Dawley rats fed either a control diet or HFD (14 or 60% kcal from fat, respectively) from embryonic day 13 onwards; gastric tone and motility were recorded in in vivo anesthetized rats. KEY RESULTS: The non-selective GABAA antagonist, BIC (10 µmol L-1 ), induced comparable inward currents in PNHFD and control DMV neurons, but a larger current in PNHFD neurons at higher concentrations (50 µmol L-1 ). Differences were not apparent in neuronal responses to the phasic GABAA antagonist, gabazine (GBZ), the extrasynaptic GABAA agonist, THIP, the GABA transport blocker, nipecotic acid, or the gliotoxin, fluoroacetate, suggesting that PNHFD altered inhibitory transmission but not GABAA receptor density or function, GABA uptake or glial modulation of synaptic strength. Similarly, the increase in gastric motility and tone following brainstem microinjection of low doses of BIC (1-10 pmoles) and GBZ (0.01-0.1 pmoles) were unchanged in PNHFD rats while higher doses of BIC (25 pmoles) induced a significantly larger increase in gastric tone compared to control. CONCLUSIONS AND INFERENCES: These studies suggest that exposure to PNHFD increases the tonic inhibition of DMV neurons, possibly contributing to dysregulated vagal control of gastric functions.

Ingestion of subthreshold doses of environmental toxins induces ascending Parkinsonism in the rat.

Increasing evidence suggests that environmental neurotoxicants or misfolded α-synuclein generated by such neurotoxicants are transported from the gastrointestinal tract to the central nervous system via the vagus nerve, triggering degeneration of dopaminergic neurons in the substantia nigra pars compacta (SNpc) and causing Parkinson's disease (PD). We tested the hypothesis that gastric co-administration of subthreshold doses of lectins and paraquat can recreate the pathology and behavioral manifestations of PD in rats. A solution containing paraquat + lectin was administered daily for 7 days via gastric gavage, followed by testing for Parkinsonian behavior and gastric dysmotility. At the end of the experiment, brainstem and midbrain tissues were analyzed for the presence of misfolded α-synuclein and neuronal loss in the SNpc and in the dorsal motor nucleus of the vagus (DMV). Misfolded α-synuclein was found in DMV and SNpc neurons. A significant decrease in tyrosine hydroxylase positive dopaminergic neurons was noted in the SNpc, conversely there was no apparent loss of cholinergic neurons of the DMV. Nigrovagally-evoked gastric motility was impaired in treated rats prior to the onset of parkinsonism, the motor deficits of which were improved by l-dopa treatment. Vagotomy prevented the development of parkinsonian symptoms and constrained the appearance of misfolded α-synuclein to myenteric neurons. These data demonstrate that co-administration of subthreshold doses of paraquat and lectin induces progressive, l-dopa-responsive parkinsonism that is preceded by gastric dysmotility. This novel preclinical model of environmentally triggered PD provides functional support for Braak's staging hypothesis of idiopathic PD.

Downregulation of neuronal vasoactive intestinal polypeptide in Parkinson's disease and chronic constipation.

BACKGROUND: Chronic constipation (CC) is a common and severe gastrointestinal complaint in Parkinson's disease (PD), but its pathogenesis remains poorly understood. This study evaluated functionally distinct submucosal neurons in relation to colonic motility and anorectal function in PD patients with constipation (PD/CC) vs both CC and controls. METHODS: Twenty-nine PD/CC and 10 Rome III-defined CC patients were enrolled. Twenty asymptomatic age-sex matched subjects served as controls. Colonic transit time measurement and conventional anorectal manometry were evaluated in PD/CC and CC patients. Colonoscopy was performed in all three groups. Colonic submucosal whole mounts from PD/CC, CC, and controls were processed for immunohistochemistry with antibodies for vasoactive intestinal polypeptide (VIP) and peripheral choline acetyltransferase, markers for functionally distinct submucosal neurons. The mRNA expression of VIP and its receptors were also assessed. KEY RESULTS: Four subgroups of PD/CC patients were identified: delayed colonic transit plus altered anorectal manometry (65%); delayed colonic transit (13%); altered manometric pattern (13%); and no transit and manometric impairment (9%). There were no differences in the number of neurons/ganglion between PD/CC vs CC or vs controls. A reduced number of submucosal neurons containing VIP immunoreactivity was found in PD/CC vs controls (P<.05). VIP, VIPR1, and VIPR2 mRNA expression was significantly reduced in PD/CC vs CC and controls (P<.05). CONCLUSIONS AND INFERENCES: Colonic motor and rectal sensory functions are impaired in most PD/CC patients. These abnormalities are associated with a decreased VIP expression in submucosal neurons. Both sensory-motor abnormalities and neurally mediated motor and secretory mechanisms are likely to contribute to PD/CC pathophysiology.

Melanin concentrating hormone innervation of caudal brainstem areas involved in gastrointestinal functions and energy balance.

Neural signaling by melanin-concentrating hormone and its receptor (SLC-1) has been implicated in the control of energy balance, but due to the wide distribution of melanin-concentrating hormone-containing fibers throughout the neuraxis, its critical sites of action for a particular effect have not been identified. The present study aimed to anatomically and functionally characterize melanin-concentrating hormone innervation of the rat caudal brainstem, as this brain area plays an important role in the neural control of ingestive behavior and autonomic outflow. Using retrograde tracing we demonstrate that a significant proportion (5-15%) of primarily perifornical and far-lateral hypothalamic melanin-concentrating hormone neurons projects to the dorsal vagal complex. In the caudal brainstem, melanin-concentrating hormone-ir axon profiles are distributed densely in most areas including the nucleus of the solitary tract, dorsal motor nucleus of the vagus, and sympathetic premotor areas in the ventral medulla. Close anatomical appositions can be demonstrated between melanin-concentrating hormone-ir axon profiles and tyrosine hydroxylase, GABA, GLP-1, NOS-expressing, and nucleus of the solitary tract neurons activated by gastric nutrient infusion. In medulla slice preparations, bath application of melanin-concentrating hormone inhibited in a concentration-dependent manner the amplitude of excitatory postsynaptic currents evoked by solitary tract stimulation via a pre-synaptic mechanism. Fourth ventricular administration of melanin-concentrating hormone (10 microg) in freely moving rats decreased core body temperature but did not change locomotor activity and food and water intake. We conclude that the rich hypothalamo-medullary melanin-concentrating hormone projections in the rat are mainly inhibitory to nucleus of the solitary tract neurons, but are not involved in the control of food intake. Projections to ventral medullary sites may play a role in the inhibitory effect of melanin-concentrating hormone on energy expenditure.

Characterization of neurons of the nucleus tractus solitarius pars centralis.

Esophageal sensory afferent inputs terminate principally in the central subnucleus of the tractus solitarius (cNTS). Neurons of the cNTS comprise two major neurochemical subpopulations. One contains neurons that are nitric oxide synthase (NOS) immunoreactive (-IR) while the other comprises neurons that are tyrosine hydroxylase (TH)-IR. We have shown recently that TH-IR neurons are involved in esophageal-distention induced gastric relaxation. We used whole cell patch clamp techniques in rat brainstem slices combined with immunohistochemical and morphological reconstructions to characterize cNTS neurons. Postrecording reconstruction of cNTS neurons revealed two morphological neuronal subtypes; one group of cells (41 out of 131 neurons, i.e., 31%) had a multipolar soma, while the other group (87 out of 131 neurons, i.e., 66%) had a bipolar soma. Of the 43 cells in which we conducted a neurochemical examination, 15 displayed TH-IR (9 with bipolar morphology, 6 with multipolar morphology) while the remaining 28 neurons did not display TH-IR (18 with bipolar morphology, 10 with multipolar morphology). Even though the range of electrophysiological properties varied significantly, morphological or neurochemical distinctions did not reveal characteristics peculiar to the subgroups. Spontaneous excitatory postsynaptic currents (sEPSC) recorded in cNTS neurons had a frequency of 1.5 +/- 0.15 events s(-1) and an amplitude of 27 +/- 1.2 pA (Vh = -50 mV) and were abolished by pretreatment with 30 muM AP-5 and 10 muM CNQX, indicating the involvement of both NMDA and non-NMDA receptors. Some cNTS neurons also received a GABAergic input that was abolished by perfusion with 30-50 muM bicuculline. In conclusion, our data show that despite the heterogeneity of morphological and neurochemical membrane properties, the electrophysiological characteristics of cNTS neurons are not a distinguishing feature.

Baclofen inhibits with high affinity an L-type-like voltage-dependent calcium channel in cerebellar granule cell cultures.

In primary cultures of cerebellar granule cells, D,L baclofen (p-chlorophenyl-GABA) inhibited approximately 50% of the calcium-45 influx induced with cell depolarization. The half maximal effective concentration for baclofen was 4 nM. Basal calcium influx was not influenced by baclofen thus suggesting that its inhibitory action could be exerted via a voltage dependent calcium channel (VDCC). Whole-cell recordings by patch-clamp technique showed a calcium current that appeared to be similar to the reported L-type VDCC. Nanomolar concentrations of baclofen also inhibited this calcium current by about 60%. However, in order for baclofen to be active, it needed to be placed into the incubation buffer at least five minutes before patching a cell raising the possibility that baclofen may be acting to inhibit the VDCC via a second messenger system.

Selective gastric projections of nitric oxide synthase-containing vagal brainstem neurons.

Nitric oxide has been proposed to act as an intercellular messenger in central brainstem circuits controlling gastrointestinal motility. In particular, a subpopulation of preganglionic vagal neurons of the dorsal motor nucleus of the vagus have been shown to be reduced nicotinamide adenine dinucleotide phosphate(NADPH)-diaphorase positive; NADPH-diaphorase positive preganglionic fibers are also known to make contact with enteric neurons in the stomach. No studies, however, have correlated the neurochemical phenotype of preganglionic vagal neurons to their stomach target. The purpose of this study was to identify the subpopulation of nitric oxide synthase positive vagal neurons projecting to the stomach. Fluorescent retrograde tracers were injected in the fundus, corpus or antrum (Rhodamine beads) or painted on the anterior gastric branch of the vagus (DiI); five to 15 days later the brainstem was processed for nitric oxide synthase immunoreactivity. Of the 532 DiI-labeled neurons from the vagal anterior gastric branch, 25 (4.7%, n=5 rats) were co-localized with nitric oxide synthase immunoreactivity. Of the neurons labeled following injection of rhodamine beads in the antrum (N=231 neurons, n=5 rats) or corpus (N=166 neurons, n=4 rats) only three neurons showed nitric oxide synthase immunoreactivity (two in antrum and one in corpus, respectively). Conversely, 26 of 222 neurons (12%, n=7 rats) labeled following injection of rhodamine in the fundus showed nitric oxide synthase immunoreactivity. These results provide evidence for a discrete phenotypic subpopulation of vagal motoneurons that project to the gastric fundus, and suggest that these neurons may be the ones involved in the receptive relaxation reflex.

Characterization of the in vitro effects of 5-hydroxytryptamine (5-HT) on identified neurones of the rat dorsal motor nucleus of the vagus (DMV).

1 Whole cell patch clamp techniques were used on thin brainstem slices to investigate the effects of 5-hydroxytryptamine (5-HT) on gastrointestinal-projecting dorsal motor nucleus of the vagus (DMV) neurones. Neurones were identified as projecting to the stomach (n=122) or intestine (n=84) if they contained the fluorescent tracer Dil after it had been applied to the gastric fundus, corpus or antrum/pylorus or to the duodenum or caecum. 2 A higher proportion of intestinal neurones (69%) than gastric neurones (47%) responded to 5-HT with a concentration-dependent inward current which was antagonized fully by the 5-HT2A receptor antagonist ketanserin (1 microM). 3 Stimulation of the nucleus tractus solitarius (NTS) induced inhibitory synaptic currents that were reduced in amplitude by application of the 5-HT1A receptor agonist 8-OHDPAT (1 microM) or the 5-HT1A/1B receptor agonist TFMPP (1 microM) in 61% and 52% of gastric- and intestinal-projecting neurones, respectively. 5-HT also significantly reduced the frequency but not the amplitude of spontaneous inhibitory currents. 4 These data show that 5-HT excites directly a larger proportion of intestinal projecting neurones than gastric-projecting neurones, as well as inhibiting synaptic transmission from the NTS to the DMV. These data imply that the response to DMV neurones to 5-HT may be determined and classified by their specific projections.

Patterns of innervation of sympathetic vascular neurons by peptide-containing primary sensory fibers.

The purpose of this study was to determine whether there is a specific organization of the primary sensory innervation on to identified vascular neurons in the inferior mesenteric ganglion (IMG) in guinea-pig. Retrograde tracers were placed intraluminally in inferior mesenteric artery (IMA) or inferior mesenteric vein (IMV) in vitro to identify ganglionic neurons as arterial, venous or unlabeled neurons. The distribution of primary sensory nerve fibers containing calcitonin gene-related peptide (CGRP), neuronal nitric oxide synthase (NOS) and substance P immunoreactivity (SP-IR) was compared before and after treatment with capsaicin. In control animals the density of immunoreactivity varied both with the transmitter and the type of neuron innervated. The density of immunoreactivity for all the three substances was reduced by capsaicin treatment. The degree of reduction of immunoreactivity in the fibers varied with the transmitter and the type of neuron. The density of CGRP and SP immunoreactive fibers was greatest around unlabeled neurons; 78% of the CGRP fibers were of primary sensory origin and all of the SP fibers were primary sensory. Around arterial neurons 44% of the CGRP fibers were of primary sensory origin and around venous 68% were primary sensory. NOS positive innervation around venous neurons was denser than around arterial neurons and all of it was completely (97%) eliminated by capsaicin, indicating that it was solely of primary sensory origin. We conclude that the primary sensory fibers innervating the IMG are differentially distributed to arterial and venous neurons and that the pattern of distribution is characteristic for each sensory neurotransmitter.

S-adenosyl-L-methionine modulates firing rate of dorsal motor nucleus of the vagus neurones in vitro.

We used the patch clamp technique applied to an in vitro brain slice preparation to examine the changes in firing activity of single dorsal vagal motoneurones exposed to S-adenosyl-methionine. In approximately 70% of the neurones tested, S-adenosyl-L-methionine (1-100 microM) decreased the spontaneously occurring firing in a dose dependent manner; the plateau decrease was 40 +/- 6%. The peak effect was observed approximately 5 min after the superfusion with S-adenosyl-L-methionine was started, and was usually reversible upon wash out of S-adenosyl-L-methionine from the superfusing chamber. No effect of the control salt of S-adenosyl-L-methionine, 1,4-butane-disulfonate.NA (100 microM), was observed. The frequency of discharge observed upon depolarization steps from hyperpolarized potentials was reduced to 34 +/- 17% (n = 11) of control upon S-adenosyl-L-methionine (100 microM) superfusion; no effect of S-adenosyl-L-methionine was observed on the action potential threshold. Preincubation with adenosine receptor antagonists, 8-cyclopentyl-1,3-dipropylxanthine (DPCPX, 10 nM) and 3,7-dimethyl-1-propargylxanthine (DMPX, 50 microM), reversed the S-adenosyl-L-methionine-induced inhibition of firing rate, and in fact, in the presence of these adenosine antagonists, S-adenosyl-L-methionine increased the firing rate of vagal motoneurones. This excitation of vagal motoneurones was blocked by pretreatment with S-adenosyl-homocysteine (100 microM), an inhibitor of methylation reactions. It is concluded that the inhibitory activity of S-adenosyl-L-methionine on the firing rate of vagal motoneurones is due to its metabolic transformation into adenosine which then acts on adenosine receptors. The excitatory effect on firing rate appears to be due to other actions, possibly including methylation reactions of key components of signal transduction mechanisms.

Quantitative evaluation of alpha- and beta-adrenoceptor modulation of [3H]choline release in guinea pig superior cervical ganglia.

[3H] Overflow evoked by 5 min supramaximal preganglionic stimulation at 1 pps has been studied in isolated guinea pig superior cervical ganglion preparations preincubated with [3H]choline. At 15 microM norepinephrine (NE) reduced both the [3H]choline overflow and endogenous acetylcholine release by 59.4 and 54.1% respectively; the dose-response curve for NE inhibitory action is described. Evidence is given that endogenous catecholamines effectively reduce ACh release from the ganglia. After blocking the inhibitory action of endogenous NE, a significant beta-adrenoceptor-mediated facilitatory effect on ACh release could be observed. Preincubation of the ganglia with different combinations of alpha 1 and alpha 2 agonists (phenylephrine, 10 microM and clonidine, 1 microM respectively) and antagonists (prazosin, 10 microM and yohimbine, 3 microM) showed that the adrenoceptors involved in alpha-mediated NE inhibition of ACh output are exclusively of the alpha 2-type.

Molecular aspects of cloricromene (AD6) distribution in human platelets and its pharmacological effects.

Cloricromene (AD6) is an investigational drug which inhibits platelet aggregation and release reaction. We studied the relationship between its action and its distribution and metabolism in platelets. Incubation of anticoagulated whole blood or platelet-rich plasma (PRP) without exogenous aggregating agents resulted in a progressive decrease of platelet count with a concomitant increase of beta-thromboglobulin (BTG) release. AD6 (20-50 mumols/l), but not acetylsalicylic acid (ASA), incubated with whole blood or PRP, prevented the fall in platelet count and the release of BTG for at least 150 min. Moreover, incubation of PRP with AD6 (50 mumols/l) and subsequent stimulation by ADP at threshold concentrations resulted in a significant reduction (about 30%) in aggregation for at least 90 min. AD6 (20 mumols/l) added to PRP was rapidly metabolized by hydrolysis of an ester bond to AD6 acid, a stable catabolite pharmacologically inactive in platelets. Significant amounts of AD6 acid (up to 13.26 +/- 2.80 pmol/10(6) platelets) were associated with the platelets after incubation either at 37 degrees C or 4 degrees C. The amount of AD6 acid in the platelet pellet was proportional to AD6 concentration (2 to 100 mumols/l). PRP incubation with AD6 acid (20 mumols/l) resulted in very low levels (less than 1 pmol/10(6) platelets) of the same compound in the platelet pellet after 1, 5 or 30 min. These data suggest that AD6 is taken up as an ester and converted to its acid catabolite with a consequent long-lasting inhibition of platelet function.

In vitro inhibition of human polymorphonuclear cell function by cloricromene.

Cloricromene, a coumarin derivative with antiaggregating and vasodilating properties, was tested in vitro on polymorphonuclear cell (PMN) adhesion to the endothelium, superoxide anion generation and chemotaxis. PMN adhesion was measured using cultured human umbilical vein endothelial cells (EC) either untreated or previously activated with interleukin-1 (IL-1). Cloricromene (5-50 microM) induced dose-related inhibition of PMN adhesion to untreated and IL-1 treated EC. Cloricromene also inhibited PMN superoxide generation induced by the tumor promoter 12-O-tetradecanoyl-phorbol-13-acetate (TPA) or by N-formyl-methionyl-leucyl-phenylalanine (FMLP). PMN and monocyte chemotaxis was evaluated by a modification of the Boyden chamber technique. Cloricromene inhibited both types of cell motility induced by FMLP in a concentration-dependent fashion. The major cloricromene metabolite (cloricromene acid) had no effect on any of the biological parameters studied up to a concentration of 500 microM. HPLC measurement showed that cloricromene accumulated in PMN within a few minutes and levels of the drug were still high after 60 min. In contrast its acid metabolite was not taken up in a significant amount during incubation periods up to 60 min. We conclude that cloricromene inhibits a series of PMN activities in vitro. This effect might be of pharmacological interest in view of the role of PMN activation in different pathophysiological conditions.

Alterations of the vegetative nervous system, experimental diabetes and pharmacological use of gangliosides.

We studied in diabetic animals several variables related to the vegetative innervation of the heart and the urinary bladder. Cardiac content of norepinephrine was lower in the heart of the diabetic mice (db/db) as compared to the heart of their heterozygote littermates (db/m). Bladder responses were clearly altered in alloxan treated rats as compared to normal rats, as shown by an increased vesical weight, an increased threshold for micturition reflex and a reduced rate of rhythmic contraction. Ganglioside administration was able to prevent partly or completely these alterations observed in the diabetic animals.

Ghrelin increases vagally mediated gastric activity by central sites of action.

BACKGROUND: Vagally dependent gastric reflexes are mediated through vagal afferent fibers synapsing upon neurons of the nucleus tractus solitarius (NTS) which, in turn modulate the preganglionic parasympathetic dorsal motor nucleus of the vagus (DMV) neurons within the medullary dorsal vagal complex (DVC). The expression and transport of ghrelin receptors has been documented for the afferent vagus nerve, and functional studies have confirmed that vagal pathways are integral to ghrelin-induced stimulation of gastric motility. However, the central actions of ghrelin within the DVC have not been explored fully. METHODS: We assessed the responses to ghrelin in fasted rats using: (i) in vivo measurements of gastric tone and motility following IVth ventricle application or unilateral microinjection of ghrelin into the DVC and (ii) whole cell recordings from gastric-projecting neurons of the DMV. KEY RESULTS: (i) IVth ventricle application or unilateral microinjection of ghrelin into the DVC-elicited contractions of the gastric corpus via excitation of a vagal cholinergic efferent pathway and (ii) ghrelin facilitates excitatory, but not inhibitory, presynaptic transmission to DMV neurons. CONCLUSIONS & INFERENCES: Our data indicate that ghrelin acts centrally by activating excitatory synaptic inputs onto DMV neurons, resulting in increased cholinergic drive by way of vagal motor innervation to the stomach.

Diminished vagal tone is a predictive biomarker of necrotizing enterocolitis-risk in preterm infants.

BACKGROUND: Necrotizing enterocolitis (NEC) is an acute neonatal inflammatory disease which may lead to intestinal necrosis, multisystem failure, and death. Currently, NEC is diagnosed by a combination of laboratory and radiographic tests conducted a posteriori i.e., when NEC is already clinically significant. Given the acute onset and rapid progression of NEC, a non-invasive biomarker that allows early detection of patients at risk is required as a matter of urgency. We evaluated whether the high frequency (HF) component of heart rate variability (HRV), a measure of vagal efferent tonic cholinergic activity may be used as a predictive biomarker for NEC-risk before the onset of clinical disease. METHODS: In this prospective study, stable preterm (gestational age 28-35 weeks) infants had HRV power spectra analyzed from surface electrocardiogram waveforms taken at rest on day 5-8 of life. We used regression modeling to determine the utility of HF-HRV in predicting NEC. KEY RESULTS: HF-HRV power was 21.5 ± 2.7 and 3.9 ± 0.81 ms(2) in infants that remained healthy and those that later developed stage 2+ NEC, respectively (p < 0.001). Nine of 70 enrolled infants developed NEC. The ROC discriminated a HF-HRV value of 4.68 ms(2) predictive for developing NEC with a sensitivity and specificity of 89% and 87%, and positive and negative predictive value of 50% and 98%, respectively. With predictive regression modeling, the risk (odds ratio) of developing NEC was 10 per every one SD decrease in HF-HRV. CONCLUSIONS & INFERENCES: Our preliminary data indicate that HF-HRV may serve as a potential, non-invasive predictive biomarker of NEC-risk in NICU infants.

Experimental spinal cord injury in rats diminishes vagally-mediated gastric responses to cholecystokinin-8s.

BACKGROUND: We have shown recently that our model of experimental high-thoracic spinal cord injury (T3-SCI) mirrors the gastrointestinal clinical presentation of neurotrauma patients, whereby T3-SCI animals show diminished gastric emptying and dysmotility. In this study we used cholecystokinin as a model peptide to test the hypothesis that the T3-SCI induced gastroparesis is due, in part, to an impaired vagally-mediated response to gastrointestinal peptides. METHODS: We measured the responses to sulfated cholecystokinin (CCK-8s) in control and T3-SCI (3 or 21 days after injury) rats utilizing: (i) c-fos expression in the nucleus tractus solitarius (NTS) following peripherally administered CCK-8s; (ii) in vivo gastric tone and motility following unilateral microinjection of CCK-8s into the dorsal vagal complex (DVC); and (iii) whole cell recordings of glutamatergic synaptic inputs to NTS neurons. KEY RESULTS: Our results show that: (i) medullary c-fos expression in response to peripheral CCK-8s was significantly lower in T3-SCI rats 3 days after the injury, but recovered to control values at 3 weeks post-SCI, (ii) Unilateral microinjection of CCK-8s in the DVC induced a profound gastric relaxation in control animals, but did not induce any response in T3-SCI rats at both 3 and 21 days after SCI, (iii) Perfusion with CCK-8s increased glutamatergic currents in 55% of NTS neurons from control rats, but failed to induce any response in NTS neurons from T3-SCI rats. CONCLUSIONS & INFERENCES: Our data indicate alterations of vagal responses to CCK-8s in T3-SCI rats that may reflect a generalized impairment of gastric vagal neurocircuitry, leading to a reduction of gastric functions after SCI.