Modulation of murine gastric vagal afferent mechanosensitivity by neuropeptide W

AIM

Neuropeptide W (NPW) is an endogenous ligand for the receptors GPR7 and GPR8 and is involved in central regulation of energy homeostasis. NPW in the periphery is found in gastric gastrin (G) cells. In the stomach, energy intake is influenced by vagal afferent signals, so we aimed to determine the effect of NPW on mechanosensitive gastric vagal afferents under different feeding conditions.

METHODS

Female C57BL/6 mice (N > 10 per group) were fed a standard laboratory diet (SLD), high-fat diet (HFD) or were food restricted. The relationship between NPW immunopositive cells and gastric vagal afferent endings was determined by anterograde tracing and NPW immunohistochemistry. An in vitro gastro-oesophageal preparation was used to determine the functional effects of NPW on gastric vagal afferents. Expression of NPW in the gastric mucosa and GPR7 in whole nodose ganglia was determined by quantitative RT-PCR (QRT-PCR). The expression of GPR7 in gastric vagal afferent neurones was determined by retrograde tracing and QRT-PCR.

RESULTS

Neuropeptide W immunoreactive cells were found in close proximity to traced vagal afferents. NPW selectively inhibited responses of gastric vagal tension receptors to stretch in SLD but not HFD or fasted mice. In the nodose ganglia, GPR7 mRNA was specifically expressed in gastric vagal afferent neurones. In fasted mice gastric mucosal NPW and nodose GPR7, mRNA was reduced compared with SLD. A HFD had no effect on gastric NPW mRNA, but down-regulated nodose GPR7 expression.

CONCLUSION

Neuropeptide W modulates gastric vagal afferent activity, but the effect is dynamic and related to feeding status.

Altered gastric vagal mechanosensitivity in diet-induced obesity persists on return to normal chow and is accompanied by increased food intake

BACKGROUND AND AIMS

Gastric vagal afferents convey satiety signals in response to mechanical stimuli. The sensitivity of these afferents is decreased in diet-induced obesity. Leptin, secreted from gastric epithelial cells, potentiates the response of vagal afferents to mechanical stimuli in lean mice, but has an inhibitory effect in high-fat diet (HFD)-induced obese mice. We sought to determine whether changes in vagal afferent function and response to leptin in obesity were reversible by returning obese mice consuming a HFD to standard laboratory chow diet (SLD).

METHODS

Eight-week-old female C57BL/6 mice were either fed a SLD (N=20) or HFD (N=20) for 24 weeks. A third group was fed a HFD for 12 weeks and then a SLD for a further 12 weeks (RFD, N=18). An in vitro gastro-oesophageal vagal afferent preparation was used to determine the mechanosensitivity of gastric vagal afferents and the modulatory effect of leptin (0.1-10 nM) was examined. Retrograde tracing and quantitative RT-PCR were used to determine the expression of leptin receptor (LepR) messenger RNA (mRNA) in whole nodose and specific cell bodies traced from the stomach.

RESULTS

After 24 weeks, both the HFD and RFD mice had increased body weight, gonadal fat mass, plasma leptin, plasma insulin and daily energy consumption compared with the SLD mice. The HFD and RFD mice had reduced tension receptor mechanosensitivity and leptin further inhibited responses to tension in HFD, RFD but not SLD mice. Mucosal receptors from both the SLD and RFD mice were potentiated by leptin, an effect not seen in HFD mice. LepR expression was unchanged in the whole nodose, but was reduced in the mucosal afferents of the HFD and RFD mice.

CONCLUSION

Disruption of gastric vagal afferent function by HFD-induced obesity is only partially reversible by dietary change, which provides a potential mechanism preventing maintenance of weight loss.

Inhibition of mechanosensitivity in visceral primary afferents by GABAB receptors involves calcium and potassium channels

GABA(B) receptors inhibit mechanosensitivity of visceral afferents. This is associated with reduced triggering of events that lead to gastro-esophageal reflux, with important therapeutic consequences. In other neuronal systems, GABA(B) receptor activation may be linked via G-proteins to reduced N-type Ca(2+) channel opening, increased inward rectifier K(+) channel opening, plus effects on a number of intracellular messengers. Here we aimed to determine the role of Ca(2+) and K(+) channels in the inhibition of vagal afferent mechanoreceptor function by the GABA(B) receptor agonist baclofen. The responses of three types of ferret gastro-esophageal vagal afferents (mucosal, tension and tension mucosal receptors) to graded mechanical stimuli were investigated in vitro. The effects of baclofen (200 microM) alone on these responses were quantified, and the effects of baclofen in the presence of the G-protein-coupled inward rectifier potassium channel blocker Rb(+) (4.7 mM) and/or the N-type calcium channel blocker omega-conotoxin GVIA (0.1 microM). Baclofen inhibition of mucosal receptor mechanosensitivity was abolished by both blockers. Its inhibitory effect on tension mucosal receptors was partly reduced by both. The inhibitory effect of baclofen on tension receptors was unaffected. The data indicate that the inhibitory action of GABA(B) receptors is mediated via different pathways in mucosal, tension and tension mucosal receptors via mechanisms involving both N-type Ca(2+) channels and inwardly rectifying K(+) channels and others.

GABA(B) receptor-mediated effects on vagal pathways to the lower oesophageal sphincter and heart

GABA(B) receptors influencing vagal pathways to the lower oesophageal sphincter and heart were investigated. In urethane-anaesthetized ferrets, the GABA(B) agonist baclofen (7 micromol kg(-1) i.v.) increased basal lower oesophageal sphincter (LOS) pressure. This was reversed by antagonism with CGP35348 (100 micromol kg(-1) i.v.). Baclofen's effect was abolished by vagotomy, suggesting a central action, yet it was ineffective when given centrally (3 - 6 nmol i.c.v.). Peripheral vagal stimulation (10 Hz, 5 s duration) caused LOS inhibition, followed by excitation, then prolonged inhibition. Bradycardia was also evoked during stimulation. Bradycardia and LOS responses were abolished after chronic supranodose vagotomy, indicating that they were due to stimulation of vagal pre-ganglionic neurones, not antidromic stimulation of afferents. Baclofen (1 - 10 micromol kg(-1)) reduced bradycardia and enhanced LOS excitation, which was also seen in animals pretreated with atropine (400 microgram kg(-1) i.v.) and guanethidine (5 mg kg(-1) i.v.), but not in those pretreated with L-NAME (100 mg kg(-1) i.v.). Effects of baclofen (7 micromol kg(-1) i.v.) on vagal stimulation-induced LOS and cardiac responses were unchanged by the GABA(B) antagonists CGP35348 or CGP36742 (up to 112 micromol kg(-1) i.v.), but were reversed by CGP62349 (ED(50) 37 nmol kg(-1) i.v.) or CGP54626 (ED(50) 100 nmol kg(-1) i.v.). Responses of isolated LOS strips to electrical stimulation, capsaicin, NK-1, NK-2 and nicotinic receptor agonists were all unaffected by baclofen (</=200 microM). We conclude that baclofen reduces vagal output at two peripheral sites: one presynaptically on pre-ganglionic neurones (CGP35348-insensitive), and another (CGP35348-sensitive) that could not be identified. This demonstrates heterogeneity of GABA(B) receptors through differential sensitivity to antagonists.

P2X purinoceptor-induced sensitization of ferret vagal mechanoreceptors in oesophageal inflammation

1. Using an in vitro single unit recording technique we studied the changes in mechanical and chemical sensitivity of vagal afferent fibres in acute oesophagitis, with particular attention to inflammatory products such as purines. 2. Histologically verified oesophagitis was induced by oesophageal perfusion of 1 mg ml-1 pepsin in 150 mM HCl in anaesthetized ferrets for 30 min on two consecutive days. Controls were infused with 154 mM NaCl. 3. The number of action potentials evoked in oesophageal mucosal afferents by mucosal stroking with calibrated von Frey hairs (10-1000 mg) was stimulus dependent. In oesophagitis responsiveness was reduced across the range of stimuli compared with controls. 4. Topical application of the P2X purinoceptor agonist alphabeta-methylene ATP had no direct excitatory effect on afferents. In oesophagitis, but not in controls, there was a significant increase in responses to stroking with von Frey hairs during superfusion with alphabeta-methylene ATP (1 microM). 5. Mucosal afferents responded directly to one or more chemical stimuli: 26 % (5/19 afferents) responded in controls, and 47 % (7/15 afferents) in oesophagitis. There were no differences in responsiveness to bradykinin (1 microM), prostaglandin E2 (100 microM), 5-hydroxytryptamine (100 microM), capsaicin (1 mM) or hydrochloric acid (150 mM) between control and oesophagitis groups. 6. We conclude that a sensitizing effect of a P2X purinoceptor agonist on mechanosensory function is induced in oesophagitis. This effect is offset by a decrease in basal mechanosensitivity.

Reactivity of transition metal fluorides. VIII. Reactions of rhenium heptafluoride and hexafluoride

Oxidation-reduction and halogen-exchange reactions of the higher fluorides of rhenium with a series of selected reagents have been investigated. The results correlate with studies of reactivities of higher fluorides of other transition metals previously reported. The reactions reported provide markedly improved preparative routes to the hexachloride, pentabromide, and pentafluoride of rhenium.

Reactivity of transition metal fluorides. VII. Reactions of the tetrafluoride, pentafluoride, and intermediate fluorides of uranium

Following similar, previously reported studies of reactions of uranium hexafluoride, selected oxidation-reduction and halogen-exchange reactions of the tetra- fluoride, pentafluoride, and intermediate fluorides of uranium have been investigated.

Reactivity of transition metal fluorides. Vi. Halogen-exchange reactions of vanadium pentafluoride

In an earlier paper in this series, it was indicated that halogen-exchange reactions between vanadium pentafluoride and covalent chlorides are very complex. The present work shows that the results may be rationalized on the basis of an initial halogen-exchange reaction, producing vanadium tetrachloride, chlorine, and the appropriate fluoride. As soon as some vanadium tetrachloride is formed, competitive reactions commence, thus making the exact elucidation of the reaction schemes very difficult. In order to clarify the situation, some reactions of vanadium tetrachloride itself were studied.

Reactivity of transition metal fluorides. V. Reactions of hexafluorides of Molybdenum, Tungsten, and Uranium with ionic chlorides

An earlier investigation of the reactions of higher fluorides of transition elements with a range of covalent chlorides has now been extended to cover the reactions of the hexafluorides of molybdenum, tungsten, and uranium with binary ionic chlorides. The observed results correlate well with published thermodynamic data.

The vapour pressure of solid cadmium

An apparatus has been designed for measurement by the Knudsen effusion method of the vapour pressure of solid cadmium in the temperature range 200-260 �C. Reliability of the apparatus was checked by measurement of the vapour pressure of zinc, for which a recent, reliable determination has been reported. The vapour pressure of cadmium in the temperature range studied is given by the equation log10 Pmm = 9.413 ? 6078/T .

Measurement of the vapour pressure of Bismuth by a radioactive tracer technique

A radioactive tracer technique has been used to increase the sensitivity of the Knudsen method of vapour pressure determination. The vapour pressure of liquid bismuth in the temperature range 400 to 500 �C has been measured and is given by the equation ������������������� Log10 Pmm = 9.390 ? 10500/T .