Skip to main content
NCBI home page
The Journal of Physiology logoLink to The Journal of Physiology
. 2014 Feb 17;592(Pt 6):1411–1421. doi: 10.1113/jphysiol.2013.270108

Acute pancreatitis decreases the sensitivity of pancreas-projecting dorsal motor nucleus of the vagus neurones to group II metabotropic glutamate receptor agonists in rats

Tanja Babic 1, R Alberto Travagli 1,✉
PMCID: PMC3961096  PMID: 24445314

Abstract

Recent studies have shown that pancreatic exocrine secretions (PES) are modulated by dorsal motor nucleus of the vagus (DMV) neurones, whose activity is finely tuned by GABAergic and glutamatergic synaptic inputs. Group II metabotropic glutamate receptors (mGluR) decrease synaptic transmission to pancreas-projecting DMV neurones and increase PES. In the present study, we used a combination of in vivo and in vitro approaches aimed at characterising the effects of caerulein-induced acute pancreatitis (AP) on the vagal neurocircuitry modulating pancreatic functions. In control rats, microinjection of bicuculline into the DMV increased PES, whereas microinjections of kynurenic acid had no effect. Conversely, in AP rats, microinjection of bicuculline had no effect, whereas kynurenic acid decreased PES. DMV microinjections of the group II mGluR agonist APDC and whole cell recordings of excitatory currents in identified pancreas-projecting DMV neurones showed a reduced functional response in AP rats compared to controls. Moreover, these changes persisted up to 3 weeks following the induction of AP. These data demonstrate that AP increases the excitatory input to pancreas-projecting DMV neurones by decreasing the response of excitatory synaptic terminals to group II mGluR agonist.

Introduction

Acute pancreatitis (AP) is a severe and sometimes fatal disorder of the exocrine pancreas, it has an annual incidence of 40 cases per 100,000 adults (Granger & Remick, 2005) and is the most common reason for hospital admissions due to gastrointestinal (GI) problems (Peery et al. 2012). AP is characterized by premature activation of zymogens leading to acinar cell injury, release of chemokines and cytokines and an inflammatory response. Pain is the major symptom of AP and usually resolves within 1 week; however, severe cases of AP can lead to tissue autodigestion, multiorgan failure and even death (Saluja et al. 2007).

Although early events involved in the development of AP are initiated in the pancreas itself, it has been suggested that the central nervous system (CNS) modulates the severity of symptoms in AP. Denervation of the pancreas by neonatal capsaicin treatment or coeliac gangliectomy attenuates the severity of experimental AP (Nathan et al. 2002; Noble et al. 2006), conversely, stimulation of duodenal afferents with ethanol and mustard oil increases the severity of AP by means of TRPA1 channel activation (Li et al. 2013).

While the majority of studies investigating the role of the CNS in AP have focused on spinal pain pathways, it has also been demonstrated that the vagus nerve plays a role in AP. In fact, AP has been shown to increase the excitability of primary vagal afferent fibres (Schwartz et al. 2011), whereas cervical vagotomy has been shown to increase the severity of AP (van Westerloo et al. 2006); however, mechanisms that lead to changes in vagal signalling in AP have not been investigated.

Pancreatic exocrine functions are modulated by vago-vagal reflexes (Travagli & Browning, 2011; Chandra & Liddle, 2013; Mussa & Verberne, 2013). Sensory information from the pancreas and other regions of the upper GI tract is relayed by the afferent vagus nerve, which has cell bodies in the nodose ganglion and terminates in the nucleus tractus solitarius (NTS). NTS neurones integrate this sensory information and relay it to the parasympathetic preganglionic neurones in the dorsal motor nucleus of the vagus (DMV) via GABAergic, glutamatergic and catecholaminergic inputs. DMV neurones have direct projections to post-ganglionic neurones within the pancreas (Browning et al. 2005a). Under basal conditions, GABAergic neurones provide tonic inhibition of pancreas-projecting DMV neurones, as microinjections of the GABAA receptor antagonist bicuculline (BIC) into the DMV increase pancreatic exocrine secretions (PES) (Mussa & Verberne, 2008a). In contrast, glutamate does not have a prominent tonic influence over DMV neurones in resting conditions (Travagli et al. 2006; Travagli & Browning, 2011).

Both glutamatergic and GABAergic synaptic inputs to DMV neurones display considerable plasticity and respond to numerous neurotransmitters and hormones. Data from our laboratory have demonstrated that both excitatory and inhibitory inputs to pancreas-projecting neurones are under modulatory control of several peptides released from the GI tract, including glucagon-like peptide 1, pancreatic polypeptide and cholecystokinin (CCK) (Browning et al. 2005b; Wan et al. 2007a,b2007b; Babic et al. 2013) and microinjections of these agents into the dorsal vagal complex (DVC) elicit changes in PES and insulin release (Jung et al. 1987; Viard et al. 2007; Babic et al. 2012, 2013). These data suggest that synaptic inputs on to pancreas-projecting neurones can be modified to fine-tune the activity of DMV neurones to adjust the function of vago-vagal reflexes to the changing hormonal and physiological conditions of the organism.

A recent study from our laboratory (Babic et al. 2012) has demonstrated that synaptic transmission to pancreas-projecting DMV neurones is modulated by group II and group III metabotropic glutamate receptors (mGluRs). Specifically, we demonstrated that (i) group II and III mGluRs decrease GABAergic and glutamatergic synaptic transmission to these neurones, and (ii) microinjections of the group II mGluR agonist APDC increased PES and decreased plasma insulin levels, whereas microinjections of the group III mGluRs decreased plasma insulin, but had no effect on PES. These data suggested that exocrine and endocrine pancreatic functions are regulated by distinct populations of DMV neurones and that PES is regulated exclusively by group II mGluR (Babic et al. 2012). These data also raised the possibility that pathological conditions affecting specific pancreatic functions may selectively target group II or group III mGluR neurotransmission.

The aims of this study were to determine whether AP alters synaptic inputs to pancreas-projecting DMV neurones and to investigate the effects of AP on modulation of synaptic transmission by group II mGluR.

Methods

All experiments were conducted on Sprague–Dawley rats of either sex (200–500 g), the protocols were conducted according to the guidelines set forth by the National Institute of Health and were approved by the Penn State University Institutional Animal Care and Use Committee.

Induction of acute pancreatitis

Animals received five injections of caerulein (50 μg kg−1, i.p.) 60 min apart. Femoral vein blood samples were taken 18–24 h after the last injection of caerulein; plasma was isolated by centrifugation and the levels of amylase were measured by QuantiChrom™ colorimetric analysis (Bioassay Systems, Hayward, CA, USA). The elevated levels of amylase and histological analysis of pancreatic tissue confirmed the presence of AP and the experiments were conducted either 18–24 h (AP) or 2–3 weeks (post-AP) following the last administration of caerulein.

Pancreatic duct cannulation

Rats were fasted overnight (water ad libitum) and anaesthetized with Inactin (135 mg kg−1, i.p.) before performing a midline laparotomy. The common bile–pancreatic duct was cannulated to collect PES at 10 min intervals, the total volume of PES was measured, protein content was assessed in 5 μl samples using a BCA protein assay kit (Pierce, Rockford, IL, USA) and expressed as μg of protein in 10 min. Baseline and drug-induced protein secretion were measured over a 30 min equilibration period before and 90 min after drug administration, respectively (Viard et al. 2007; Babic et al. 2012, 2013).

Microinjection in the dorsal vagal complex

Following cannulation of the pancreatic duct, rats were placed in a stereotaxic frame and the lower medulla was exposed by blunt dissection; rectal temperature was monitored and maintained at 37 ± 1°C. A glass micropipette (30–40 μm tip diameter) was directed into the DVC under microscopic guidance (from calamus scriptorius, in mm: +0.2–0.5 rostrocaudal, 0.1–0.3 mediolateral and −0.5 dorsoventral) for drug delivery; vehicle (saline), APDC (0.18–1.04 nmol; Babic et al. 2012), EGLU (15 nmol; Babic et al. 2012), kynurenic acid (KYN, 100 pmol; Sivarao et al. 1998) or BIC (50 pmol; Sivarao et al. 1998; Mussa & Verberne, 2008a,b2008b) were applied by pressure injection in 60 nl volumes, as assessed via a calibrated monocular microscope, over a 1 min period. Fluorescent microspheres (Fluoresbrite carboxy NYO; Polysciences, Warrington, PA, USA) were included in the injectate for post hoc verification of the injection site.

Verification of injection sites

At the end of the experiment, the rat was perfused transcardially with saline followed by fixative (4% paraformaldehyde in 0.1 m phosphate-buffered saline). The brainstem was removed and stored in fixative with 20% sucrose at 4°C for at least 48 h before cutting 50 μm thick coronal slices. A Nikon E400 (Melville, NY, USA) microscope equipped with TRITC (Melville, NY, USA) filters and Element software was used to visualize and record the injection site.

Duodenal Ensure infusions

Following laparotomy, a cannula (PE-190 tubing) was inserted through a small incision (2–3 mm) into the duodenum approximately 1 cm distal to the pylorus to allow infusion of Ensure at a rate of 4 ml h−1 for 75 min. The pancreatic duct was cannulated as described above, the abdominal laparotomy was closed with 6/0 suture and the rat placed on a heated pad to maintain body temperature at 37 ± 1°C. PES was collected in 10 min intervals for 30 min before Ensure infusion, throughout the entire infusion period, and for 60 min after cessation of infusion; control animals received infusions of 0.9% saline; all animals were then killed 90 min after Ensure infusions.

Retrograde tracing

For electrophysiology experiments, pancreas-projecting DMV neurones were labelled by application of the fluorescent neuronal tracer DiI to the pancreas as described previously (Browning et al. 2005a; Babic et al. 2012). Briefly, after isoflurane (2.5% with air, 600 ml min−1) anaesthesia, the abdominal area of juvenile rats of either sex was cleaned and the pancreas exposed following a laparotomy, the pancreas was isolated and DiI crystals were affixed to its surface using a fast-hardening epoxy resin. The abdomen was closed and rats were allowed to recover for 7–15 days before experimentation; histological sections of the pancreas (not shown) or plasma amylase values did not indicate inflammatory processes due to resin applications in control animals.

Electrophysiological recording

Rat brainstem slices were prepared as described previously (Browning et al. 1999). Briefly, rats were anaesthetized with isoflurane, the brainstem was removed, placed in chilled, oxygenated Krebs’ solution (in mm: 126 NaCl, 25 NaHCO3, 2.5 KCl, 1.2 MgCl2, 2.4 CaCl2, 1.2 NaH2PO4 and 11 glucose, maintained at pH 7.4 by bubbling with 95% O2–5% CO2), five to six coronal slices containing the DVC were cut at 300 μm and incubated in Krebs’ solution at 30°C for at least 90 min before recording. A single slice was transferred to a custom-made perfusion chamber, kept in place with a nylon mesh and maintained at 30°C by perfusion with warm Krebs’ solution at a rate of 2.5–3.0 ml min−1. Pancreas-projecting neurones were identified using a Nikon E600FN microscope equipped with epifluorescent filters; electrophysiological recordings were then made under bright-field illumination using Nomarski optics.

Whole cell recordings were made with patch pipettes of resistance 2–3 MΩ when filled with intracellular solution: potassium gluconate (in mm: 128 potassium gluconate, 10 KCl, 0.3CaCl2, 1 MgCl2, 10 Hepes, 1 EGTA, 2 ATP-Na and 0.25 GTP-Na, adjusted to pH 7.35 with KOH) was used to study excitatory postsynaptic currents (EPSCs), while KCl (in mm: 140 KCl, 1 CaCl2, 1 MgCl2, 10 Hepes, 10 EGTA, 2 ATP-Na and 0.25 GTP-Na, adjusted to pH7.35 with KOH) was used to study inhibitory postsynaptic currents (IPSCs).

Data were acquired using clampex 9 software and an Axopatch 1D amplifier (Molecular Devices, Sunnyvale, CA, USA) at a rate of 10 kHz, filtered at 2 kHz, digitized via a Digidata 1320 interface (Molecular Devices) before being analysed on a personal computer using MiniAnalysis software (Jaejin Software, Leonia, NJ, USA). Only recordings with a series resistance <15 MΩ were considered acceptable.

The experiments were done in the presence of tetrodotoxin (1 μm) and the GABAA receptor antagonist BIC (50 μm) to isolate miniature EPSCs (mEPSCs) or in the presence of tetrodotoxin and KYN (1 mm) to isolate miniature IPSCs (mIPSCs).

Drugs were applied via perfusion through a series of manually operated valves at concentrations demonstrated as previously effective (Browning & Travagli, 2007; Babic et al. 2012). Agonists were applied for periods sufficient for the response to reach a plateau and neurones were allowed to recover fully between drug additions. Antagonists were perfused for at least 5 min before assessment of their effects. Each neurone served as its own control, a minimum variation in frequency of 50% from baseline was considered as effective.

Statistical analysis

Data are expressed as means ± s.e.m. with significance defined as P < 0.05. An unpaired Student's t test was used to compare plasma amylase activity, baseline volume and protein output between control and AP; the effects of different treatments on PES volume were compared using Student's paired t test. A two-way ANOVA followed by Bonferroni post hoc test was used to compare effects of different treatments and concentrations of drugs; the EC50 values were calculated and compared between groups using GraphPad Prism software; a one-way ANOVA followed by Bonferroni post hoc test was used to compare the frequency of baseline miniature currents within groups. The number of neurons that responded to different pharmacological treatments was compared between groups using the χ2 test.

Drugs and chemicals

APDC and EGLU were purchased from Tocris (Ellisville, MO, USA); tetrodotoxin was purchased from Alomone Labs (Jerusalem, Israel). All other chemicals were purchased from Sigma (St Louis, MO, USA).

Results

Plasma amylase activity was 553 ± 31 U l−1 and 1297 ± 300 U l−1 in control (n = 7) and caerulein-injected animals (n = 13), respectively (P < 0.05). Histological analysis of pancreatic tissue confirmed the presence of oedema and leucocyte infiltration in caerulein-treated rats, indicating that caerulein treatment was effective in inducing AP; these animals will therefore be called ‘AP rats’ hereafter.

In control animals, the volume of PES over 10 min was 203 ± 55.4 μl (n = 41) and was not altered by pharmacological treatments. In control rats, baseline protein output was 260 ± 91.7 μg protein in 10 min; conversely, in AP rats, the baseline PES volume was 249 ± 66 μl/10 min and baseline protein output was 322 ± 125.9 μg protein/10 min (n = 22; P < 0.05 vs. control for both).

Effects of intraduodenal Ensure infusions on pancreatic exocrine secretions

To determine whether AP alters the ability of intraduodenal nutrients to activate vagal afferent fibres, we tested the effect of intraduodenal Ensure infusions on PES of control and AP rats. In five control animals, Ensure infusions increased PES from 191 ± 30 to 996 ± 323 μg protein/10 min (P < 0.05); the peak effect on PES was observed within 30–40 min after the start of Ensure infusion and returned to baseline approximately 40 min after the infusion was stopped. Conversely, in four AP rats, intraduodenal infusion with Ensure failed to increase PES (224 ± 35 before and 286 ± 24 μg protein/10 min during Ensure infusions; P > 0.05; Fig. 1), indicating that AP decreases the ability of duodenal nutrients to increase in PES.

Figure 1.

Figure 1

Open in a new tab

A, effect of intraduodenal Ensure infusions on PES in control (n = 5) and AP (n = 4) animals. Note that Ensure increased PES (expressed as normalized data) in control, but not in AP animals. B, time course of the effect of Ensure infusion into the duodenum on the total protein output, measured at 10 min intervals. Perfusion was started at time 0 and data are expressed as total protein output in 10 min. Note that Ensure increased PES in controls, but not AP animals. *P < 0.05 vs. baseline. AP, acute pancreatitis; PES, pancreatic exocrine secretions.

Acute pancreatitis alters the effects of bicuculline and kynurenic acid on pancreatic exocrine secretions

To determine whether altered responses of intraduodenal Ensure on PES in AP were accompanied by alterations in glutamate and GABA inputs to DMV neurones, we tested the effects of microinjections in the DVC of the GABAA receptor antagonist BIC and the ionotropic glutamate receptor antagonist KYN on PES. In control animals, microinjections of BIC (50 pmol) increased PES from 255 ± 77 to 342 ± 62 μg protein/10 min (147 ± 16% of baseline; n = 4; P < 0.05), PES returned to baseline approximately 20 min following the microinjections; conversely, in AP rats, microinjections of BIC into the DVC had no effect on PES (393 ± 100 μg/10 min before and 328 ± 77 μg/10 min after BIC injections; n = 4; P > 0.05; Fig. 2).

Figure 2.

Figure 2

Open in a new tab

A, effect of BIC microinjections into the DVC on PES in controls (n = 4), AP (n = 4) and post-AP (n = 4) animals. B, effect of KYN microinjections into the DVC on PES in control (n = 5), AP (n = 5) and post-AP (n = 4) animals. C, location of a representative injection site into the DVC. Note that in control animals, microinjections of BIC elicit an increase in PES whereas KYN has no effect. In AP, BIC microinjections have no effect, whereas KYN elicits a decrease in PES. Two to 3 weeks post-AP, BIC microinjections elicited an increase in PES in only one of four animals tested, whereas microinjections of KYN elicited a decrease in PES in two of four animals tested. AP, acute pancreatitis; ap, area postrema; BIC, bicuculline; cc, central canal; DMV, dorsal motor nucleus of the vagus; DVC, dorsal vagal complex; KYN, kynurenic acid; NTS, nucleus tractus solitarius; PES, pancreatic exocrine secretions.

Microinjections of KYN (100 pmol) into the DVC of control animals had no effect on PES (245 ± 47 and 212 ± 32 μg protein/10 min at baseline and after KYN injections, respectively; n = 5; P > 0.05). In AP rats, microinjections of KYN decreased PES from 318 ± 64 to 205 ± 55 μg protein/10 min (P < 0.05) in four of five animals tested and had no effect on PES in the remaining animal (Fig. 2).

These data suggest that AP decreases the tonic GABAergic and increases glutamatergic tone on to DMV neurones that regulate PES.

Effects of microinjection of APDC into the dorsal vagal complex on pancreatic exocrine secretions

We have shown previously that mGluRs modulate the activity of NTS-DMV synapses (Browning & Travagli, 2007; Babic et al. 2012). To determine whether the changes in responses to BIC and KYN were due to changes in the sensitivity of DVC to group II mGluR agonist APDC, we assessed the effects of APDC microinjections into the DVC on PES in control and AP rats. As reported previously, microinjection of APDC increased PES in a dose-dependent manner, for example, microinjection of 600 pmol APDC into the DVC increased PES from 249 ± 28 to 446 ± 58 μg protein/10 min (n = 4; P < 0.05; Fig. 3).

Figure 3.

Figure 3

Open in a new tab

A, effect of APDC on PES in control, AP and post-AP animals (n = 3–6 for each data point). B, schematic drawing of the DVC showing the location of APDC injection sites in control, AP and post-AP rats. Note that all microinjections were done in the left DVC; however, for clarity, they are shown in both sides of the DVC. C, effect of group II metabotropic glutamate receptor antagonist EGLU on PES of control and AP animals (n = 5 for both groups). Note that in control animals, APDC induced a dose-dependent increase in PES. In AP, microinjections of low doses of APDC failed to induce an increase in PES, whereas 1036 pmol of APDC decreased PES. Two to 3 weeks post-AP, only the highest dose of APDC elicited a significant increase in PES. AP, acute pancreatitis; DMV, dorsal motor nucleus of the vagus; DVC, dorsal vagal complex; NTS, nucleus tractus solitarius; PES, pancreatic exocrine secretions; sol, solitary tract.

In AP rats, DVC microinjection of 180 or 600 pmol of APDC into the DMV had no effect on PES (n = 3 and 6 for 180 and 600 pmol, respectively; Fig. 3), while microinjection of 1036 pmol of APDC decreased PES from 276 ± 27 to 170 ± 20 μg protein/10 min (n = 6; P < 0.05). In control animals, microinjections of 1036 pmol APDC caused respiratory distress and was not tested further (Babic et al. 2012).

Microinjections of group II mGluR antagonist EGLU (15 nmol) into the DVC had no effect on PES in control (265 ± 53 and 264 ± 72 μg protein/10 min before and after EGLU, respectively; P > 0.05; n = 5) or AP rats 294 ± 4 before and 288 ± 46 μg protein/10 min before and after EGLU, respectively; P > 0.05; n = 5; Fig. 3).

These data suggest that the lack of effect of APDC on PES in AP rats is likely due to a decrease in the efficacy of APDC rather than to tonic activation of group II mGluRs.

We then conducted a series of electrophysiological experiments to test the modulation of synaptic inputs on to identified pancreas-projecting DMV neurones.

Acute pancreatitis decreases the sensitivity of excitatory postsynaptic currents to pancreas-projecting dorsal motor nucleus of the vagus neurones to APDC

In control animals, baseline frequency of mEPSCs in pancreas-projecting DMV neurones was 1.6 ± 0.1 events s−1 and baseline mEPSC amplitude was 27 ± 1.8 pA (n = 44). Perfusion with APDC decreased mEPSC frequency in a concentration-dependent manner (n = 5–8 per concentration; Fig. 4); the estimated EC50 for the APDC-induced inhibition of mEPSC frequency was 2.3 ± 0.2 μm and the estimated Emax was 300 μm, at which concentration APDC decreased mEPSC frequency from 1.8 ± 0.4 to 0.4 ± 0.04 events s−1 (P < 0.05). Perfusion of the slices with APDC had no effect on mEPSC amplitude at any of the concentrations tested (27 ± 7.5 pA before and 26 ± 5.4 pA during perfusion with 300 μm APDC; P > 0.05). Perfusion of the slice with group II mGluR antagonist EGLU had no effect on mEPSC frequency (1.9 ± 0.6 events s−1 before and 1.5 ± 0.4 events s−1 during EGLU perfusion; P > 0.05) or amplitude (21 ± 1.5 pA before and 20 ± 1.4 pA during EGLU; P > 0.05). These data indicate that the effects of APDC are presynaptic and that there is no tonic activation of group II mGluR on the mEPSC impinging on pancreas-projecting DMV neurones.

Figure 4.

Figure 4

Open in a new tab

A, representative traces from pancreas-projecting DMV neurone showing the effect of APDC on mEPSCs in a control (left) and an AP animal (right). B, concentration–response curve of mEPSCs to APDC in control (n = 5–8 for each data point), AP (n = 4–7 for each data point) and post-AP (n = 3–7 for each data point) neurones. C, effect of 10 μm and 300 μm APDC on mEPSC frequency in DMV neurones from control (n = 7 and 5, respectively), AP (n = 4 for both concentrations) and post-AP (n = 6 and 4, respectively) rats. *P < 0.05 vs. control (P < 0.05 vs. control also at 3 and 100 μm, not shown). D, concentration–response of mIPSCs to APDC in neurones from control (n = 3–5 for each data point) and AP (n = 4–6 for each data point) animals. E, effect of 10 μm and 300 μm APDC on mIPSC frequency in neurones from control (n = 5 and 4, respectively) and AP (n = 5 and 4, respectively) animals. Note that AP shifts the concentration–response curve of mEPSCs to APDC to the right, whereas it has no effect on the response of mIPSCs to APDC. In addition, note that 2–3 weeks post-AP, the concentration–response curve to APDC remains shifted to the right compared to control animals. AP, acute pancreatitis; DMV, dorsal motor nucleus of the vagus; mEPSC miniature excitatory postsynaptic current; mIPSC, miniature inhibitory postsynaptic current.

In neurones from AP rats, baseline mEPSC frequency was significantly higher than that in control animals (2.0 ± 0.2 events s−1; n = 48; P < 0.05), whereas mEPSC amplitude did not differ between the two groups (25 ± 1.4 pA in AP rats). Perfusion of the slice with APDC decreased mEPSC frequency in a concentration-dependent manner that was significantly different from that in control rats (n = 6–10 per concentration; P < 0.05; Fig 4). Perfusion of the slice with 3–300 μm APDC resulted in a significantly lower reduction in mEPSC frequency in DMV neurones from AP compared to control animals (n = 7–10 per concentration; P < 0.05). The EC50 for the APDC-induced inhibition of mEPSC frequency was 34 ± 0.2 μm (P < 0.05 vs. control animals) and the Emax was ∼300 μm, at which APDC concentration decreased mEPSC frequency from 1.4 ± 0.4 to 0.4 ± 0.07 events s−1 (P < 0.05 vs. baseline).

As in control rats, in AP animals perfusion of pancreas-projecting DMV neurones with EGLU (200 μm) had no effect on mEPSC frequency (2.7 ± 0.8 before and 2.9 ± 0.7 events s−1 during EGLU; n = 5), suggesting that group II mGluR are not tonically active in this neuronal subpopulation.

These data indicate that AP reduces the sensitivity of excitatory synaptic terminals impinging on pancreas-projecting DMV neurones to the group II mGluR agonist.

Acute pancreatitis does not alter the response of inhibitory synaptic currents to APDC

In control animals, baseline mIPSC frequency was 1.2 ± 0.2 events s−1 (n = 28). Baseline mIPSC amplitude was 75 ± 4.8 pA and was not altered significantly by any treatments. Perfusion of the slice with APDC (0.1–300 μm) induced a concentration-dependent decrease in mIPSC frequency (n = 4–5 per concentration; Fig. 4). The maximal decrease in mIPSC frequency was observed with 100 μm APDC, which reduced the mIPSC frequency from 0.9 ± 0.2 to 0.4 ± 0.02 pA (to 54% of baseline; P < 0.05; n = 4). The estimated EC50 for APDC-induced decrease in mIPSC frequency was 71 ± 12 μm. APDC had no effect on mIPSC amplitude (56 ± 4.0 and 63 ± 6.2 pA before and during APDC; P > 0.05). Perfusion of the slice with the group II mGluR antagonist EGLU (200 μm) had no effect on mIPSC frequency in control animals (1.9 ± 0.6 events s−1 before and 1.5 ± 0.4 events s−1 during EGLU perfusion; P < 0.05; n = 5; Fig. 4).

These data indicate that the effects of APDC are presynaptic and that there is no tonic activation of group II mGluR on the mIPSC impinging on pancreas-projecting DMV neurones.

In AP rats, baseline mIPSC frequency was not different from control rats (1.2 ± 0.2 events s−1; n = 13; P > 0.05 vs. control), although the baseline mIPSC amplitude was reduced (43 ± 2.4 pA (P < 0.05 vs. controls) it was not altered by any treatments. Perfusion of the slice with APDC resulted in a concentration-dependent reduction in mIPSC frequency that was not significantly different from control animals (n = 4–6 per concentration; P > 0.05; Fig. 4). The estimated EC50 for APDC-induced decrease in mIPSC frequency was 66 ± 24 μm (P > 0.05 vs. control) and the maximal decrease in mIPSC frequency was observed with 100 μm APDC, at which concentration APDC reduced mIPSC frequency from 1.0 ± 0.1 to 0.5 ± 0.08 events s−1 (51% of baseline; P < 0.05).

As in control rats, perfusion of the slice with EGLU had no effect on mIPSC frequency in AP rats (1.3 ± 0.4 before and 1.1 ± 0.3 events s−1 during EGLU perfusion; P > 0.05; n = 5; Fig. 4).

These data indicate that AP does not alter the ability of group II mGluRs to reduce inhibitory synaptic transmission to pancreas-projecting neurones in the DMV.

Acute pancreatitis does not alter the response of pancreas-projecting dorsal motor nucleus of the vagus neurones to the group III metabotropic glutamate receptor agonist L-AP4

In control animals, perfusion of the slices with 100 μm L-AP4 resulted in a decrease in mEPSC frequency from 1.7 ± 0.2 to 0.9 ± 0.1 events s−1 in 17 of 26 neurones tested. In AP rats, L-AP4 decreased mEPSC frequency from 1.8 ± 0.2 to 0.9 ± 0.3 events s−1 in four of five neurones tested. Neither the magnitude of L-AP4 induced effect nor the number of neurones affected was different from those in control animals (P > 0.05; χ2 > 0.05, respectively).

These data suggest that AP does not affect the ability of group III mGluR agonist to decrease excitatory synaptic transmission to pancreas-projecting DMV neurons, confirming that group III mGluRs are not involved in the modulation of the exocrine pancreas (Babic et al. 2012).

Effects of acute pancreatitis on long-term changes in group II metabotropic glutamate receptor expression in the dorsal vagal complex

To determine whether changes in group II mGluRs persist after the resolution of AP, we tested the ability of APDC to alter PES and mEPSC frequency 2–3 weeks following administration of caerulein.

Two to 3 weeks post-AP, plasma amylase activity recovered to the values observed in control animals (553 ± 31 U l−1 in control and 604 ± 127 U l−1 post-AP; P > 0.05; n = 4); similarly, the baseline PES volume (230 ± 63 μl/10 min) and PES protein output (283 ± 144 μg protein/10 min) were lower than those observed in AP rats and recovered toward control values (P > 0.05 vs. control; n = 14).

BIC (50 pmol) microinjections in the DVC did not elicit a change in PES in three of four animals tested (404 ± 32 and 354 ± 41 μg protein/10 min before and after BIC injections, respectively; P > 0.05) and caused an increase in PES in the remaining animal (425.1 μg protein/10 min before and 597 μg protein/10 min after BIC). Microinjections of KYN (100 pmol) elicited a decrease in PES in two animals (191 ± 28 and 144 ± 22 μg protein/10 min before and after KYN microinjection, respectively) with no change in PES in the remaining two animals (162 ± 24 before and 170 ± 24 μg protein/10 min after KYN); overall, these data indicate a partial recovery of the responses to BIC or KYN microinjections.

As observed in AP rats 18–24 h after caerulein injection, 2–3 weeks post-AP microinjections of 600 pmol of APDC into the DVC had no effect upon PES (344 ± 64 and 340 ± 84 μg protein/10 min before and after APDC; P > 0.05; n = 4). In contrast to AP rats, however, microinjections of a higher dose of APDC (1036 pmol) increased PES from 249 ± 9 to 328 ± 34 μg protein/10 min; P < 0.05; n = 4; Fig. 3), indicating a partial recovery of the responses to APDC.

Two to 3 weeks following caerulein injection, baseline mEPSC frequency (1.83 ± 0.2 events s−1) and amplitude (20.7 ± 1.3 pA) in pancreas-projecting DMV neurones were not significantly different from control or AP animals (P > 0.05; n = 34). Perfusion of the slices with APDC (0.1–300 μm; n = 4–7 per concentration) elicited a concentration-dependent decrease in mEPSC frequency that was significantly different from the control group. Perfusion of the slices with 10, 30 or 100 μm elicited a significantly lower decrease in mEPSC frequency in post-AP than in control group (P < 0.05; Fig. 4). The mEPSC responses to APDC were not statistically different from those in AP animals at any concentrations studied (Fig. 4; P > 0.05). APDC did not elicit a change in mEPSC amplitude at any concentration tested.

These data suggest that AP-induced changes in group II mGluR on vagal circuits regulating PES persist, in part, for up to 3 weeks post-AP, although there was a trend toward recovery of control responses.

Discussion

In this study we have demonstrated that in AP rats: (1) intraduodenal nutrient infusions fail to increase PES; (2) baseline tonic glutamatergic synaptic inputs play a major role in the control of PES; (3) APDC-induced increase in PES is blocked; (4) the sensitivity of excitatory synaptic inputs to pancreas-projecting DMV neurones to group II mGluR agonist is decreased, whereas the sensitivity of inhibitory inputs to APDC is unaffected; and (5) changes in group II mGluR expression persist following the resolution of AP, although there is a trend toward recovery of baseline responses to pharmacological challenges. These data suggest that changes in PES observed in AP may be partly mediated by a decreased efficacy of group II mGluR agonist on glutamatergic synaptic terminals between NTS and pancreas-projecting DMV neurones, although the nature of the microinjection studies does not exclude the possibility of involvement of the glutamatergic synapse between the tractus solitarius and second-order neurones of the NTS.

Our study demonstrates that AP induces changes in vago-vagal circuits regulating PES, which is consistent with previous reports showing that AP increases the excitability of primary vagal afferent fibres and that vagotomy increases the severity of AP (van Westerloo et al. 2006; Schwartz et al. 2011). In the present study, intraduodenal infusions of Ensure failed to induce an increase in PES, and this lack of an effect of Ensure may be due to the increased activation of vagal afferent fibres induced by AP, which rendered further activation undetectable. This suggestion stems from previous studies, which have demonstrated that AP as well as other inflammatory conditions, such as gastric ulcers, increase the excitability of vagal afferent neurones (Dang et al. 2004; Schwartz et al. 2011). It has also been shown that several models of inflammation, including gastric irritation, infections and injections of inflammatory cytokines or lipopolysaccharide, increase the activity of GI afferent fibres (Ek et al. 1998; Aerssens et al. 2007; Liu et al. 2007; Krolczyk et al. 2008) and alter gene expression in nodose ganglion neurones (Aerssens et al. 2007; Schwartz et al. 2011). In addition, CCK is a potent activator of vagal afferent fibres, and CCK release is induced in response to ingestion of meals containing fat and carbohydrates. As caerulein is a stable analogue of CCK, which induces AP via activation of CCK1 receptors, our findings suggest that further activation of vagal afferent fibres by Ensure infusion may not be detectable.

One of the major findings of this study is that AP influences the inputs to DMV neurones that provide regulation of the exocrine pancreas. Under control conditions, tonic GABAergic inhibition provides the primary influence over the activity of DMV neurones that regulate upper GI functions, while glutamatergic inputs play only a minor role. This notion is supported by evidence that microinjections of the GABAA antagonist BIC into the DVC increase PES (Mussa & Verberne, 2008a), gastric pressure and motility (Sivarao et al. 1998), whereas microinjections of the glutamatergic antagonist KYN have no effect on PES (this study) or gastric motility (Sivarao et al. 1998).

In this study, we have demonstrated that AP shifts the balance of synaptic inputs to pancreas-projecting neurones in the DMV towards a predominantly excitatory influence. The evidence for this suggestion is provided by the observation that, following AP, microinjections of KYN decreased PES, whereas BIC had no effect. This shift in balance towards an excitatory input on to pancreas-projecting neurones may be due to either an increased glutamatergic or a decreased GABAergic tone to DMV neurones. Although the lack of an effect of BIC on PES could be indicative of decreased GABAergic transmission, AP did not alter the frequency of mIPSCs impinging on pancreas-projecting DMV neurones. Taken together, these observations indicate that in AP rats an increase in glutamatergic signalling may exert a stronger influence on PES compared to a decrease in GABAergic tone, therefore rendering BIC unable to elicit an overall effect on PES.

Further indication that AP selectively affects glutamatergic input to pancreas-projecting neurones is provided by evidence that the sensitivity to agonists of group II mGluRs is decreased on excitatory, but not inhibitory synaptic terminals impinging on to DMV neurones. Activation of group II mGluRs has been shown to decrease excitatory and inhibitory synaptic transmission to pancreas-and GI-projecting DMV neurones (Browning & Travagli, 2007; Babic et al. 2012) as well as in other regions of the CNS (Cartmell & Schoepp, 2000). A decreased efficacy of group II mGluR activation on excitatory terminals, therefore, would increase the amount of glutamate released on to DMV neurones, by consequence an increase in excitatory inputs to pancreas-projecting neurones could account, in part, for the increased PES observed in the initial stages of AP.

The mechanisms that mediate changes in mGluR expression on glutamatergic terminals in AP have not been investigated. Previous studies have demonstrated, however, that inflammatory mediators alter the expression of group II mGluRs in cultured glial cells and the spinal cord (Dolan et al. 2003; Berger et al. 2012). These findings raise the possibility that inflammatory cytokines released during AP may also alter the expression of mGluRs on pancreas-projecting neurones. Future investigations are warranted to determine the role of inflammatory mediators on synaptic transmission in vago-vagal circuits controlling PES and, should this hypothesis be confirmed, the mechanisms that made glutamatergic transmission the preferred target.

We have demonstrated previously that PES is regulated selectively by group II mGluRs, whereas pancreatic insulin release is regulated by both group II and group III mGluR (Babic et al. 2012). AP, which affects the exocrine pancreas, affected the function of group II mGluR specifically on excitatory terminals in the DMV, whereas it had no effect on group III mGluR. This observation further supports the notion that exocrine secretion and insulin release are under modulatory control by distinct neuronal populations, a conclusion we put forward recently (Wan et al. 2007a,b2007b,c2007c; Babic et al. 2012, 2013). Furthermore, the selective effect of AP on group II mGluR provides a potential pharmacological target for the treatment of symptoms of AP.

Although AP usually resolves within a week, patients with AP are often prone to recurrent episodes of the disease (Steinberg & Tenner, 1994); morphological changes in the pancreas, impaired exocrine and endocrine pancreatic functions have also been reported in patients up to 7 years following the initial AP episode (Fernandez-Cruz et al. 1997; Tsiotos et al. 1998; Pelli et al. 2000; Tzovaras et al. 2004). In this study, the observed changes in GABAergic and glutamatergic signalling, as well as efficacy of the group II mGluR agonist to modulate excitatory synaptic transmission, were not fully recovered toward the responses observed in control animals 2–3 weeks following induction of AP. Taken together with previous studies and observations from patients with AP, these results suggest that long-term changes in pancreatic functions may be due, at least in part, to alterations in mGluR activity in the DMV. A similar observation has been made in a study of an animal model of colitis, which demonstrated that hyperexcitability and changes in excitatory synaptic transmission in myenteric neurones persist 8 weeks following the induction of colitis (Krauter et al. 2007; Linden, 2012). A persistent increase in glutamate release may sensitize vagal circuits to future insults, making them more prone to changes in subsequent episodes of AP. Moreover, as exocrine pancreatic insufficiency is commonly observed in patients following an episode of AP, an increased glutamatergic tone to DMV neurones that regulate PES may function as an adaptive mechanism that serves to increase baseline PES.

In summary, the present study has demonstrated that AP decreases the efficacy of group II mGluR agonist on glutamatergic synaptic terminals, thus shifting the balance of synaptic inputs impinging on pancreas-projecting DMV neurones to a predominantly glutamatergic influence. Moreover, these changes in the organization of mGluRs persist up to 3 weeks following induction of AP. These data indicate that alterations in group II mGluR function and the resulting synaptic transmission in the DVC may underlie short-and long-term changes in exocrine pancreatic functions in AP.

Key points

  • Acute pancreatitis is one of the most severe disorders of the exocrine pancreas.

  • Pancreatic exocrine secretions (PES) are under regulatory control of dorsal motor nucleus of the vagus (DMV) neurones and their activity is regulated by inhibitory GABAergic and excitatory glutamatergic synaptic inputs.

  • Group II metabotropic glutamate receptors (mGluR) decrease synaptic transmission to pancreas-projecting DMV neurones and modulate PES.

  • In this study, we show that acute pancreatitis induces a long-lasting increase in excitatory synaptic transmission to pancreas-projecting neurones by decreasing the response of excitatory synaptic terminals to group II mGluR agonists.

  • These data suggest that changes in group II mGluR expression in the DMV may underlie short-and long-term changes in PES in acute pancreatitis.

Acknowledgments

We thank Dr Kirsteen N. Browning for comments on previous versions of this manuscript and Cesare M. and Zoraide Travagli for support and encouragement.

Glossary

AP

acute pancreatitis

BIC

bicuculline

CCK

cholecystokinin

CNS

central nervous system

DAB

diaminobenzidine

DMV

dorsal motor nucleus of the vagus

DVC

dorsal vagal complex

GI

gastrointestinal

KYN

kynurenic acid

mEPSC

miniature excitatory postsynaptic current

mGluR

metabotropic glutamate receptor

mIPSC

miniature inhibitory postsynaptic current

NHS

normal horse serum

NTS

nucleus tractus solitarius

PES

pancreatic exocrine secretion

Additional information

Competing interests

None.

Author contributions

T.B. and R.A.T. were involved in: the conception and design of the experiments; collection, analysis and interpretation of data; and drafting the article or revising it critically for important intellectual content. All authors read and approved the submission.

Funding

This work was supported by NSF grant 1049618 and NIH grant DK55530.

References

  1. Aerssens J, Hillsley K, Peeters PJ, de HR, Stanisz A, Lin JH, Van dW I, Gohlmann HW, Grundy D, Stead RH, Coulie B. Alterations in the brain-gut axis underlying visceral chemosensitivity in Nippostrongylus brasiliensis-infected mice. Gastroenterology. 2007;132:1375–1387. doi: 10.1053/j.gastro.2007.02.019. [DOI] [PubMed] [Google Scholar]
  2. Babic T, Browning KN, Kawaguchi Y, Tang X, Travagli RA. Pancreatic insulin and exocrine secretion are under the modulatory control of distinct subpopulations of vagal motoneurones in the rat. J Physiol. 2012;590:3611–3622. doi: 10.1113/jphysiol.2012.234955. [DOI] [PMC free article] [PubMed] [Google Scholar]
  3. Babic T, Bhagat R, Wan S, Browning KN, Snyder M, Fortna SR, Travagli RA. Role of the vagus in the reduced pancreatic exocrine function in copper-deficient rats. Am J Physiol Gastrointest Liver Physiol. 2013;304:G437–G448. doi: 10.1152/ajpgi.00402.2012. [DOI] [PMC free article] [PubMed] [Google Scholar]
  4. Berger JV, Dumont AO, Focant MC, Vergouts M, Sternotte A, Calas AG, Goursaud S, Hermans E. Opposite regulation of metabotropic glutamate receptor 3 and metabotropic glutamate receptor 5 by inflammatory stimuli in cultured microglia and astrocytes. Neuroscience. 2012;205:29–38. doi: 10.1016/j.neuroscience.2011.12.044. [DOI] [PubMed] [Google Scholar]
  5. Browning KN, Travagli RA. Functional organization of presynaptic metabotropic glutamate receptors in vagal brainstem circuits. J Neurosci. 2007;27:8979–8988. doi: 10.1523/JNEUROSCI.1105-07.2007. [DOI] [PMC free article] [PubMed] [Google Scholar]
  6. Browning KN, Renehan WE, Travagli RA. Electrophysiological and morphological heterogeneity of rat dorsal vagal neurones which project to specific areas of the gastrointestinal tract. J Physiol. 1999;517:521–532. doi: 10.1111/j.1469-7793.1999.0521t.x. [DOI] [PMC free article] [PubMed] [Google Scholar]
  7. Browning KN, Coleman FH, Travagli RA. Characterization of pancreas-projecting rat dorsal motor nucleus of the vagus neurons. Am J Physiol Gastrointest Liver Physiol. 2005a;288:G950–G955. doi: 10.1152/ajpgi.00549.2004. [DOI] [PubMed] [Google Scholar]
  8. Browning KN, Coleman FH, Travagli RA. Effects of pancreatic polypeptide on pancreas-projecting rat dorsal motor nucleus of the vagus neurons. Am J Physiol Gastrointest Liver Physiol. 2005b;289:G209–G219. doi: 10.1152/ajpgi.00560.2004. [DOI] [PubMed] [Google Scholar]
  9. Cartmell J, Schoepp DD. Regulation of neurotransmitter release by metabotropic glutamate receptors. J Neurochem. 2000;75:889–907. doi: 10.1046/j.1471-4159.2000.0750889.x. [DOI] [PubMed] [Google Scholar]
  10. Chandra R, Liddle RA. Modulation of pancreatic exocrine and endocrine secretion. Curr Opin Gastroenterol. 2013;29:517–522. doi: 10.1097/MOG.0b013e3283639326. [DOI] [PMC free article] [PubMed] [Google Scholar]
  11. Dang K, Bielefeldt K, Gebhart GF. Gastric ulcers reduce A-type potassium currents in rat gastric sensory ganglion neurons. Am J Physiol Gastrointest Liver Physiol. 2004;286:G573–G579. doi: 10.1152/ajpgi.00258.2003. [DOI] [PubMed] [Google Scholar]
  12. Dolan S, Kelly JG, Monteiro AM, Nolan AM. Up-regulation of metabotropic glutamate receptor subtypes 3 and 5 in spinal cord in a clinical model of persistent inflammation and hyperalgesia. Pain. 2003;106:501–512. doi: 10.1016/j.pain.2003.09.017. [DOI] [PubMed] [Google Scholar]
  13. Ek M, Kurosawa M, Lundeberg T, Ericsson A. Activation of vagal afferents after intravenous injection of interleukin-1beta: role of endogenous prostaglandins. J Neurosci. 1998;18:9471–9479. doi: 10.1523/JNEUROSCI.18-22-09471.1998. [DOI] [PMC free article] [PubMed] [Google Scholar]
  14. Fernandez-Cruz L, Navarro S, Castells A, Saenz A. Late outcome after acute pancreatitis: functional impairment and gastrointestinal tract complications. World J Surg. 1997;21:169–172. doi: 10.1007/s002689900210. [DOI] [PubMed] [Google Scholar]
  15. Granger J, Remick D. Acute pancreatitis: models, markers, and mediators. Shock. 2005;24(Suppl 1):45–51. doi: 10.1097/01.shk.0000191413.94461.b0. [DOI] [PubMed] [Google Scholar]
  16. Jung G, Louie DS, Owyang C. Pancreatic polypeptide inhibits pancreatic enzyme secretion via a cholinergic pathway. Am J Physiol Gastrointest Liver Physiol. 1987;253:G706–G710. doi: 10.1152/ajpgi.1987.253.5.G706. [DOI] [PubMed] [Google Scholar]
  17. Krauter EM, Strong DS, Brooks EM, Linden DR, Sharkey KA, Mawe GM. Changes in colonic motility and the electrophysiological properties of myenteric neurons persist following recovery from trinitrobenzene sulfonic acid colitis in the guinea pig. Neurogastroenterol Motil. 2007;19:990–1000. doi: 10.1111/j.1365-2982.2007.00986.x. [DOI] [PubMed] [Google Scholar]
  18. Krolczyk G, Gil K, Zurowski D, Jung A, Thor PJ. The vagal afferents discharge and myoelectrical activity in the gastric hyperalgesia model in rats. J Physiol Pharmacol. 2008;59:707–716. [PubMed] [Google Scholar]
  19. Li C, Zhu Y, Shenoy M, Pai R, Liu L, Pasricha PJ. Anatomical and functional characterization of a duodeno-pancreatic neural reflex that can induce acute pancreatitis. Am J Physiol Gastrointest Liver Physiol. 2013;304:G490–G500. doi: 10.1152/ajpgi.00012.2012. [DOI] [PMC free article] [PubMed] [Google Scholar]
  20. Linden DR. Colitis is associated with a loss of intestinofugal neurons. Am J Physiol Gastrointest Liver Physiol. 2012;303:G1096–G1104. doi: 10.1152/ajpgi.00176.2012. [DOI] [PMC free article] [PubMed] [Google Scholar]
  21. Liu CY, Mueller MH, Grundy D, Kreis ME. Vagal modulation of intestinal afferent sensitivity to systemic LPS in the rat. Am J Physiol Gastrointest Liver Physiol. 2007;292:G1213–G1220. doi: 10.1152/ajpgi.00267.2006. [DOI] [PubMed] [Google Scholar]
  22. Mussa BM, Verberne AJ. Activation of the dorsal vagal nucleus increases pancreatic exocrine secretion in the rat. Neurosci Lett. 2008a;433:71–76. doi: 10.1016/j.neulet.2007.12.048. [DOI] [PubMed] [Google Scholar]
  23. Mussa BM, Verberne AJ. Activation of the dorsal vagal nucleus increases pancreatic exocrine secretion in the rat. Neurosci Lett. 2008b;433:71–76. doi: 10.1016/j.neulet.2007.12.048. [DOI] [PubMed] [Google Scholar]
  24. Mussa BM, Verberne AJ. The dorsal motor nucleus of the vagus and regulation of pancreatic secretory function. Exp Physiol. 2013;98:25–37. doi: 10.1113/expphysiol.2012.066472. [DOI] [PubMed] [Google Scholar]
  25. Nathan JD, Peng RY, Wang Y, McVey DC, Vigna SR, Liddle RA. Primary sensory neurons: a common final pathway for inflammation in experimental pancreatitis in rats. Am J Physiol Gastrointest Liver Physiol. 2002;283:G938–G946. doi: 10.1152/ajpgi.00105.2002. [DOI] [PubMed] [Google Scholar]
  26. Noble MD, Romac J, Wang Y, Hsu J, Humphrey JE, Liddle RA. Local disruption of the celiac ganglion inhibits substance P release and ameliorates caerulein-induced pancreatitis in rats. Am J Physiol Gastrointest Liver Physiol. 2006;291:G128–G134. doi: 10.1152/ajpgi.00442.2005. [DOI] [PubMed] [Google Scholar]
  27. Peery AF, Dellon ES, Lund J, Crockett SD, McGowan CE, Bulsiewicz WJ, Gangarosa LM, Thiny MT, Stizenberg K, Morgan DR, Ringel Y, Kim HP, Dibonaventura MD, Carroll CF, Allen JK, Cook SF, Sandler RS, Kappelman MD, Shaheen NJ. Burden of gastrointestinal disease in the United States: 2012 update. Gastroenterology. 2012;143:1179–1187. doi: 10.1053/j.gastro.2012.08.002. [DOI] [PMC free article] [PubMed] [Google Scholar]
  28. Pelli H, Sand J, Laippala P, Nordback I. Long-term follow-up after the first episode of acute alcoholic pancreatitis: time course and risk factors for recurrence. Scand J Gastroenterol. 2000;35:552–555. doi: 10.1080/003655200750023840. [DOI] [PubMed] [Google Scholar]
  29. Saluja AK, Lerch MM, Phillips PA, Dudeja V. Why does pancreatic overstimulation cause pancreatitis. Annu Rev Physiol. 2007;69:249–269. doi: 10.1146/annurev.physiol.69.031905.161253. [DOI] [PubMed] [Google Scholar]
  30. Schwartz ES, Christianson JA, Chen X, La JH, Davis BM, Albers KM, Gebhart GF. Synergistic role of TRPV1 and TRPA1 in pancreatic pain and inflammation. Gastroenterology. 2011;140:1283–1291. doi: 10.1053/j.gastro.2010.12.033. [DOI] [PMC free article] [PubMed] [Google Scholar]
  31. Sivarao DV, Krowicki ZK, Hornby PJ. Role of GABAA receptors in rat hindbrain nuclei controlling gastric motor function. Neurogastroenterol Motil. 1998;10:305–313. doi: 10.1046/j.1365-2982.1998.00110.x. [DOI] [PubMed] [Google Scholar]
  32. Steinberg W, Tenner S. Acute pancreatitis. N Engl J Med. 1994;330:1198–1210. doi: 10.1056/NEJM199404283301706. [DOI] [PubMed] [Google Scholar]
  33. Travagli RA, Browning KN. Central autonomic control of the pancreas. In: Llewellyn-Smith I, Verberne AJ, editors. Central Regulation of Autonomic Functions. New York: Oxford University Press; 2011. pp. 274–291. [Google Scholar]
  34. Travagli RA, Hermann GE, Browning KN, Rogers RC. Brainstem circuits regulating gastric function. Annu Rev Physiol. 2006;68:279–305. doi: 10.1146/annurev.physiol.68.040504.094635. [DOI] [PMC free article] [PubMed] [Google Scholar]
  35. Tsiotos GG, Luque-de LE, Sarr MG. Long-term outcome of necrotizing pancreatitis treated by necrosectomy. Br J Surg. 1998;85:1650–1653. doi: 10.1046/j.1365-2168.1998.00950.x. [DOI] [PubMed] [Google Scholar]
  36. Tzovaras G, Parks RW, Diamond T, Rowlands BJ. Early and long-term results of surgery for severe necrotising pancreatitis. Dig Surg. 2004;21:41–46. doi: 10.1159/000075825. [DOI] [PubMed] [Google Scholar]
  37. van Westerloo DJ, Giebelen IA, Florquin S, Bruno MJ, Larosa GJ, Ulloa L, Tracey KJ, van der PT. The vagus nerve and nicotinic receptors modulate experimental pancreatitis severity in mice. Gastroenterology. 2006;130:1822–1830. doi: 10.1053/j.gastro.2006.02.022. [DOI] [PubMed] [Google Scholar]
  38. Viard E, Zheng Z, Wan S, Travagli RA. Vagally mediated, nonparacrine effects of cholecystokinin-8s on rat pancreatic exocrine secretion. Am J Physiol Gastrointest Liver Physiol. 2007;293:G494–G500. doi: 10.1152/ajpgi.00118.2007. [DOI] [PubMed] [Google Scholar]
  39. Wan S, Browning KN, Travagli RA. Glucagon-like peptide-1 modulates synaptic transmission to identified pancreas-projecting vagal motoneurons. Peptides. 2007a;28:2184–2191. doi: 10.1016/j.peptides.2007.08.016. [DOI] [PubMed] [Google Scholar]
  40. Wan S, Coleman FH, Travagli RA. Cholecystokinin-8s excites identified rat pancreatic-projecting vagal motoneurons. Am J Physiol Gastrointest Liver Physiol. 2007b;293:G484–G492. doi: 10.1152/ajpgi.00116.2007. [DOI] [PubMed] [Google Scholar]
  41. Wan S, Coleman FH, Travagli RA. Glucagon-like peptide-1 (GLP-1) excites pancreas-projecting preganglionic vagal motoneurons. Am J Physiol Gastrointest Liver Physiol. 2007c;292:G1474–G1482. doi: 10.1152/ajpgi.00562.2006. [DOI] [PubMed] [Google Scholar]

Articles from The Journal of Physiology are provided here courtesy of The Physiological Society

RESOURCES