Human visceral afferent recordings: preliminary report.

BACKGROUND: Conditions characterised by chronic visceral pain represent a significant healthcare burden with limited treatment options. While animal models have provided insights into potential mechanisms of visceral nociception and identified candidate drug targets, these have not translated into successful treatments in humans. OBJECTIVE: To develop an in vitro afferent nerve preparation using surgically excised freshly isolated human colon and vermiform appendix-mesentery tissues. METHODS: Non-inflamed appendix (n=18) and colon (n=9) were collected from patients undergoing right and left hemicolectomy. Electrophysiological recordings were made from mesenteric nerves and the tissue stimulated chemically and mechanically. RESULTS: Ongoing neuronal activity was sparse and where units occurred peak firing rates were: colon (2.0±0.4 spikes/s, n=4) and appendix (2.4±0.6 spikes/s, n=9). Afferent nerves innervating the appendix responded with a significant increase in activity following stimulation with inflammatory mediators (73±10.6 vs 3.0±0.3 spikes/s, n=6, p<0.001, inflammatory mediator vs baseline) and capsaicin (63±15.8 vs 2±0.3 spikes/s, n=3, p<0.001, capsaicin vs buffer). Afferent nerves innervating the colon responded with increased activity to blunt probing of the serosal surface. CONCLUSIONS: This first-in-human study demonstrates afferent nerve recordings from human gut tissue ex vivo and shows that tissue may be stimulated both chemically and mechanically to study neuronal responses. Collectively, the results provide preliminary evidence to validate this in vitro human tissue model as one that may aid future disease mechanistic studies and candidate drug testing.

Intestinal serotonin release, sensory neuron activation, and abdominal pain in irritable bowel syndrome.

OBJECTIVES: Serotonin (5-hydroxytryptamine, 5-HT) metabolism may be altered in gut disorders, including in the irritable bowel syndrome (IBS). We assessed in patients with IBS vs. healthy controls (HCs) the number of colonic 5-HT-positive cells; the amount of mucosal 5-HT release; their correlation with mast cell counts and mediator release, as well as IBS symptoms; and the effects of mucosal 5-HT on electrophysiological responses in vitro. METHODS: We enrolled 25 Rome II IBS patients and 12 HCs. IBS symptom severity and frequency were graded 0-4. 5-HT-positive enterochromaffin cells and tryptase-positive mast cells were assessed with quantitative immunohistochemistry on colonic biopsies. Mucosal 5-HT and mast cell mediators were assessed by high-performance liquid chromatography or immunoenzymatic assay, respectively. The impact of mucosal 5-HT on electrophysiological activity of rat mesenteric afferent nerves was evaluated in vitro. RESULTS: Compared with HCs, patients with IBS showed a significant increase in 5-HT-positive cell counts (0.37 ± 0.16% vs. 0.56 ± 0.26%; P=0.039), which was significantly greater in patients with diarrhea-predominant IBS vs. constipation-predominant IBS (P=0.035). Compared with HCs, 5-HT release in patients with IBS was 10-fold significantly increased (P < 0.001), irrespective of bowel habit, and was correlated with mast cell counts. A significant correlation was found between the mucosal 5-HT release and the severity of abdominal pain (r(s)=0.582, P=0.047). The area under the curve, but not peak sensory afferent discharge evoked by IBS samples in rat jejunum, was significantly inhibited by the 5-HT3 receptor antagonist granisetron (P<0.005). CONCLUSIONS: In patients with IBS, 5-HT spontaneous release was significantly increased irrespective of bowel habit and correlated with mast cell counts and the severity of abdominal pain. Our results suggest that increased 5-HT release contributes to development of abdominal pain in IBS, probably through mucosal immune activation.

CB1 receptors mediate the analgesic effects of cannabinoids on colorectal distension-induced visceral pain in rodents.

Activation of cannabinoid receptors (CB(1), CB(2) and GPR(55)) produces analgesic effects in several experimental pain models, including visceral pain arising from the gastrointestinal tract. We assessed the role of CB(1), CB(2), and GPR(55) receptors and the endogenous cannabinoid system on basal pain responses and acute mechanical hyperalgesia during colorectal distension (CRD) in rodents. The effects of cannabinoid receptor agonists and antagonists on pain-related responses to CRD were assessed in rats and in wild-type and CB(1) receptor knock-out mice. The dual CB(1/2) agonist, WIN55,212-2, and the peripherally acting CB(1)-selective agonist, SAB-378, inhibited pain-related responses to repetitive noxious CRD (80 mmHg) in a dose-related manner in rats. The analgesic effects of WIN55,212-2 and SAB-378 were blocked by the selective CB(1) antagonist SR141716, but were not affected by the selective CB(2) antagonist SR144528. SR141716, per se, increased the responses to repetitive noxious CRD, indicative of hyperalgesia, and induced pain-related responses during non-noxious CRD (20 mmHg), indicative of allodynia. The cannabinoid receptor agonists anandamide, virodhamine and O-1602 had no effect. At analgesic doses, WIN55,212-2 did not affect colonic compliance. In accordance to the rat data, WIN55,212-2 produced analgesia, whereas SR141716 induced hyperalgesia, during noxious CRD (55 mmHg) in wild-type but not in CB(1)-knock-out mice. These data indicate that peripheral CB(1) receptors mediate the analgesic effects of cannabinoids on visceral pain from the gastrointestinal tract. The allodynic and hyperalgesic responses induced by SR141716 suggest the existence of an endogenous cannabinoid tone and the activation of CB(1) receptors during noxious CRD.

Transient receptor potential ankyrin-1 has a major role in mediating visceral pain in mice.

The excitatory ion channel transient receptor potential ankyrin-1 (TRPA1) is prominently expressed by primary afferent neurons and is a mediator of inflammatory pain. Inflammatory agents can directly activate [e.g., hydroxynonenal (HNE), prostaglandin metabolites] or indirectly sensitize [e.g., agonists of protease-activated receptor (PAR(2))] TRPA1 to induce somatic pain and hyperalgesia. However, the contribution of TRPA1 to visceral pain is unknown. We investigated the role of TRPA1 in visceral hyperalgesia by measuring abdominal visceromotor responses (VMR) to colorectal distention (CRD) after intracolonic administration of TRPA1 agonists [mustard oil (MO), HNE], sensitizing agents [PAR(2) activating peptide (PAR(2)-AP)], and the inflammatory agent trinitrobenzene sulfonic acid (TNBS) in trpa1(+/+) and trpa1(-/-) mice. Sensory neurons innervating the colon, identified by retrograde tracing, coexpressed immunoreactive TRPA1, calcitonin gene-related peptide, and substance P, expressed TRPA1 mRNA and responded to MO with depolarizing currents. Intracolonic MO and HNE increased VMR to CRD and induced immunoreactive c-fos in spinal neurons in trpa1+/+ but not in trpa1(-/-) mice. Intracolonic PAR(2)-AP induced mechanical hyperalgesia in trpa1+/+ but not in trpa1(-/-) mice. TNBS-induced colitis increased in VMR to CRD and induced c-fos in spinal neurons in trpa1(+/+) but not in trpa1(-/-) mice. Thus TRPA1 is expressed by colonic primary afferent neurons. Direct activation of TRPA1 causes visceral hyperalgesia, and TRPA1 mediates PAR(2)-induced hyperalgesia. TRPA1 deletion markedly reduces colitis-induced mechanical hyperalgesia in the colon. Our results suggest that TRPA1 has a major role in visceral nociception and may be a therapeutic target for colonic inflammatory pain.

Targeted ablation of mesenteric projecting sympathetic neurons reduces the hemodynamic response to pain in conscious, spinal cord-transected rats.

Individuals with spinal cord injuries above thoracic level 6 (T(6)) experience episodic bouts of life-threatening hypertension as part of a condition termed autonomic dysreflexia. The paroxysmal hypertension can be caused by a painful stimulus below the level of the injury. Targeted ablation of mesenteric projecting sympathetic neurons may reduce the severity of autonomic dysreflexia by reducing sympathetic activity. Therefore, cholera toxin B subunit (CTB) conjugated to saporin (SAP; a ribosomal inactivating protein that binds to and inactivates ribosomes) was injected into the celiac ganglion to test the hypothesis that targeted ablation of mesenteric projecting sympathetic neurons reduces the pressor response to pain in conscious, spinal cord-transected rats. Nine Sprague-Dawley male rats underwent a spinal cord transection between thoracic vertebrae 4 and 5. Following recovery (5 wk), all rats were instrumented with a radio telemetry device for recording arterial pressure and bilateral catheters in the gluteus maximus muscles for the infusion of hypertonic saline (hNa(+)Cl(-)). Subsequently, the hemodynamic responses to intramuscular injection of hNa(+)Cl(-) (100 microl and 250 microl, in random order) were determined. Following the experiments in the no celiac ganglia injected condition (NGI), rats received injections of CTB-SAP (n = 5) or CTB (n = 3) into the celiac ganglia. CTB-SAP rats, compared with NGI and CTB rats, had reduced pressor responses to hNa(+)Cl(-). Furthermore, the number of stained neurons in the celiac ganglia and spinal cord (segments T(6)-T(12)), was reduced in CTB-SAP rats. Thus, CTB-SAP retrogradely transported from the celiac ganglia is effective at ablating mesenteric projecting sympathetic neurons and reducing the pressor response to pain in spinal cord-transected rats.

Oxytocin enhances cranial visceral afferent synaptic transmission to the solitary tract nucleus.

Cranial visceral afferents travel via the solitary tract (ST) to contact neurons within the ST nucleus (NTS) and activate homeostatic reflexes. Hypothalamic projections from the paraventricular nucleus (PVN) release oxytocin (OT) to modulate visceral afferent communication with NTS neurons. However, the cellular mechanisms through which OT acts are poorly understood. Here, we electrophysiologically identified second-order NTS neurons in horizontal brainstem slices by their low-jitter, ST-evoked glutamatergic EPSCs. OT increased the frequency of miniature EPSCs in half of the NTS second-order neurons (13/24) but did not alter event kinetics or amplitudes. These actions were blocked by a selective OT receptor antagonist. OT increased the amplitude of ST-evoked EPSCs with no effect on event kinetics. Variance-mean analysis of ST-evoked EPSCs indicated OT selectively increased the release probability of glutamate from the ST afferent terminals. In OT-sensitive neurons, OT evoked an inward holding current and increased input resistance. The OT-sensitive current reversed at the K(+) equilibrium potential. In in vivo studies, NTS neurons excited by vagal cardiopulmonary afferents were juxtacellularly labeled with Neurobiotin and sections were stained to show filled neurons and OT-immunoreactive axons. Half of these physiologically characterized neurons (5/10) showed close appositions by OT fibers consistent with synaptic contacts. Electron microscopy of medial NTS found immunoreactive OT within synaptic boutons. Together, these findings suggest that OT released from PVN axons acts on a subset of second-order neurons within medial NTS to enhance visceral afferent transmission via presynaptic and postsynaptic mechanisms.

Conditioned flavor preference learning by intragastric administration of L-glutamate in rats.

The preference for foods or fluids in rats is partly dependent on its postingestive consequences. Many studies have investigated postingestive effect of high caloric substances, such as carbohydrate or fat. In this study, we examined postingestive effect of L-glutamate at the preferable concentration using conditioned flavor preference paradigm. Adult male rats with chronic intragastric (IG) cannula were trained to drink a flavored solution (conditioned stimulus; CS+) paired with IG infusion of nutrient solution and another flavored solution (CS-) with IG distilled water infusion on alternate days. The nutrient solution was 60mM monosodium L-glutamate, sodium chloride or glucose. Before and after conditioning, rats received 30min two-bottle choice tests for CS+ and CS- solution. All groups exhibited no significant preference for CS+ in pre-test period. By the last half of conditioning period, intake of CS+ solution was significantly higher than that of CS- in MSG group, but not in NaCl and glucose groups. After conditioned, the MSG group showed significantly higher intake and preference for CS+ solution (69.9%), while the NaCl and glucose group did not show any significant intake and preference for CS+ solution (50.9%, 43.5%, respectively). These results indicate that the amino acid L-glutamate at a preferable concentration has a positive postingestive effect as demonstrated by its ability to condition a flavor preference. The mechanism(s) for this positive effect could be through a direct effect on gut Glu receptors rather than the provision of calories or glucose from metabolized Glu; Further studies are needed to test these hypotheses.

Nociceptive vascular reflexes evoked by scorpion venom modulate cardiorespiratory parameters involving vanilloid receptor 1 in anaesthetised rats.

Involvement of vanilloid and 5-HT(3) receptors in the cardiorespiratory reflexes evoked by intra-arterial (i.a.) injection of Mesobuthus tamulus (BT) venom was examined. In anaesthetised rats, blood pressure, respiratory excursions and ECG were recorded for 60min after the injection of venom in the absence or presence of antagonists. Injection of BT venom (1mg/kg, i.a.) produced alterations in respiratory frequency (RF), blood pressure (BP) and heart rate (HR). The changes in RF were manifested as immediate increase (40%) followed by a decrease (40%) and subsequent sustained increase (60%). In case of BP, the increase began around 40s, peaked at 5min (50%) and remained above the initial level subsequently. The bradycardiac response began around 5min which peaked (50% of the initial) around 25min and remained at that level. Thus, exhibiting immediate-tachypnoeic, intermediate-hypertensive and delayed-bradycardiac responses. Pretreatment with lignocaine, blocked the respiratory responses and attenuated the pressor responses evoked by venom. Pretreatment with capsazepine, vanilloid receptor 1 (VR1) antagonist, antagonized all the three parameters of cardiorespiratory responses evoked by venom. Whereas, ondansetron (5-HT(3) antagonist) attenuated the pressor and bradycardiac responses significantly but not the respiratory responses. These observations indicate that the cardiorespiratory changes induced by intra-arterial injection of venom are carried by afferents in addition to somatic nerves, involving mainly VR1 receptors and partially by 5-HT(3) receptors.

GM1 ganglioside contributes to retain the neuronal conduction and neuronal excitability in visceral and baroreceptor afferents.

GM1 ganglioside has a great impact on the function of nodes of Ranvier on myelinated fiber, suggesting its potential role to maintain the electrical and neuronal excitability of neurons. Here we first demonstrate that visceral afferent conduction velocity of myelinated and unmyelinated fibers are reduced significantly by tetrodotoxin (TTX) or cholera toxin-B subunits (CTX-B), and only the effects mediated by CTX-B are prevented by GM1 pre-treatment. At soma of myelinated A and unmyelinated C-type nodose ganglion neurons (NGNs), the action potential spike frequency reduced by CTX-B is also prevented by GM1. Additionally, the current density of both TTX-sensitive (TTX-S) and TTX-resistant (TTX-R) Na(+) channels were significantly decreased by CTX-B without changing the voltage-dependent property. These data confirm that endogenous GM1 may play a dominant role in maintaining the electrical and neuronal excitability via modulation of sodium (Na(+)) channel around nodes and soma as well, especially TTX-S Na(+) channel, which is also confirmed by the reduction of spike amplitude and depolarization. Similar data are also extended to fluorescently identified and electrophysiologically characterized aortic baroreceptor neurons. These findings suggest that GM1 plays an important role in the neural modulation of electric and neuronal excitability in visceral afferent system.

Modulation of taste sensitivity by GLP-1 signaling.

In many sensory systems, stimulus sensitivity is dynamically modulated through mechanisms of peripheral adaptation, efferent input, or hormonal action. In this way, responses to sensory stimuli can be optimized in the context of both the environment and the physiological state of the animal. Although the gustatory system critically influences food preference, food intake and metabolic homeostasis, the mechanisms for modulating taste sensitivity are poorly understood. In this study, we report that glucagon-like peptide-1 (GLP-1) signaling in taste buds modulates taste sensitivity in behaving mice. We find that GLP-1 is produced in two distinct subsets of mammalian taste cells, while the GLP-1 receptor is expressed on adjacent intragemmal afferent nerve fibers. GLP-1 receptor knockout mice show dramatically reduced taste responses to sweeteners in behavioral assays, indicating that GLP-1 signaling normally acts to maintain or enhance sweet taste sensitivity. A modest increase in citric acid taste sensitivity in these knockout mice suggests GLP-1 signaling may modulate sour taste, as well. Together, these findings suggest a novel paracrine mechanism for the regulation of taste function.

Functional changes in baroreceptor afferent, central and efferent components of the baroreflex circuitry in type 1 diabetic mice (OVE26).

Baroreflex control of heart rate (HR) is impaired in diabetes mellitus. We hypothesized that diabetes mellitus induced functional changes of neural components at multiple sites within the baroreflex arc. Type 1 diabetic mice (OVE26) and FVB control mice were anesthetized. Baroreflex-mediated HR responses to sodium nitroprusside- (SNP) and phenylephrine- (PE) induced mean arterial blood pressure (MAP) changes were measured. Baroreceptor function was characterized by measuring the percent (%) change of baseline integrated aortic depressor nerve activity (Int ADNA) in response to SNP- and PE-induced MAP changes. The HR responses to electrical stimulation of the left aortic depressor nerve (ADN) and the right vagus nerve were assessed. Compared with FVB control mice, we found in OVE26 mice that (1) baroreflex-mediated bradycardia and tachycardia were significantly reduced. (2) The baroreceptor afferent function in response to MAP increase did not differ, as assessed by the parameters of the logistic function curve. But, the inhibition of Int ADNA in response to MAP decrease was significantly attenuated. (3) The maximum amplitude of bradycardic responses to right vagal efferent stimulation was augmented. (4) In contrast, the maximum amplitude of bradycardic responses to left ADN stimulation was decreased. Since Int ADNA was preserved in response to MAP increase and HR responses to vagal efferent stimulation were augmented, we conclude that a deficit of the central mediation of baroreflex HR contributes to the overall attenuation of baroreflex sensitivity in OVE26 mice. The successful conduction of physiological experiments on the ADN in OVE26 mice may provide a foundation for the understanding of cellular and molecular mechanisms of diabetes-induced cardiac neuropathy.

Inhibition of spontaneous neurotransmission in the nucleus of solitary tract of the rat by the cannabinoid agonist WIN 55212-2 is not via CB1 or CB2 receptors.

Cannabinoids have been shown to modulate central autonomic regulation and baroreflex control of blood pressure. Both CB1 and CB2 cannabinoid receptors have been described in the nucleus tractus solitarius (NTS), which receives direct afferent projections of cardiovascular reflexes. In the present study we evaluated the effects of WIN 55212-2 (WIN), a cannabinoid agonist, on fast neurotransmission in the NTS. We recorded spontaneous post-synaptic currents using the whole-cell configuration in NTS cells in brainstem slices from young rats (25-30 days old). Application of 5 microM WIN inhibited the frequency of both glutamatergic and GABAergic sPSCs, without affecting their amplitudes. Effects of WIN were not blocked by application of the CB1 antagonist AM251, the CB2 antagonist AM630 or the vanniloid receptor TRPV1 antagonist AMG9810, suggesting that the effect of WIN is via a non-CB1 non-CB2 receptor. Neither the CB1/CB2 agonist HU210 nor the CB1 agonist ACPA affected the frequency of sPSCs. We conclude WIN inhibits the neurotransmission in the NTS of young rats via a receptor distinct from CB1 or CB2.

NMDA receptors in the basolateral amygdala and gustatory neophobia.

The attenuation of gustatory neophobia occurs during repeated exposures to an initially novel taste solution that is increasingly perceived as safe and familiar. The present study examined whether NMDA receptors in the basolateral region of the amygdala (BLA) are involved in this important behavioral phenomenon. The results, which show that the attenuation, but not initial occurrence, of gustatory neophobia is dependent upon NMDA receptors in the BLA, are discussed with reference to a similar finding involving NMDA receptors in the insular cortex.

Serotonergic receptor blockade in the lateral parabrachial nucleus: different effects on hypertonic and isotonic NaCl intake.

Hypertonic NaCl intake is produced by serotonin receptor antagonism in the lateral parabrachial nucleus (LPBN) of dehydrated rats or in rats pretreated with a mineralocorticoid, for example deoxycorticosterone (DOCA), that receive an intracerebroventricular injection (icv) of angiotensin II (ang II). The objective of the present work was to find out whether these two mechanisms are also involved with isotonic NaCl intake. Serotonin receptor blockade by methysergide in the LPBN (4 microg/0.2 microl bilaterally) had no effect on 0.15 M NaCl (methysergide: 19.3+/-5.2 ml/60 min; vehicle: 19.3+/-4.2 ml/60 min; n=7) or water (methysergide: 3.4+/-1.4 ml/60 min; vehicle 2.2+/-0.6 ml/60 min) intake induced by systemic diuretic furosemide combined with low dose of captopril (Furo/Cap). Methysergide treatment 4 days later in the same animals produced the expected enhancement in the 0.3 M NaCl intake induced by Furo/Cap (methysergide: 16.6+/-3.5 ml/60 min; vehicle: 6.6+/-1.5 ml/60 min). Similar result was obtained when another group was tested first with 0.3 M NaCl and later with 0.15 M NaCl. Isotonic NaCl intake induced by icv ang II was however enhanced by prior DOCA treatment. A de novo hypertonic NaCl intake was produced in another group by the same combined treatment. The results suggest that a facilitatory mechanism like the mineralocorticoid/ang II synergy may enhance NaCl solution intake at different levels of tonicity, while the action of an inhibitory mechanism, like the LPBN serotonergic system, is restricted to the ingestion at hypertonic levels.

Sustained hypertension increases the density of AMPA receptor subunit, GluR1, in baroreceptive regions of the nucleus tractus solitarii of the rat.

AMPA-type glutamate receptors in the nucleus tractus solitarii (NTS) are necessary for the baroreceptor reflex, a primary mechanism for homeostatic regulation of blood pressure. Within NTS, the GluR1 subunit of the AMPA receptor is found primarily in dendritic spines. We previously showed that both GluR1 and dendritic spine density are increased in NTS of spontaneously hypertensive rats (SHRs). We hypothesize that both receptor and synaptic plasticity are induced by a sustained elevation in arterial pressure. To test the general nature of this hypothesis, we examined whether similar changes in GluR1 density are found in a renovascular model of hypertension, the DOCA-salt rat, and if these changes are preventable by normalizing blood pressure with hydralazine, a peripherally acting vasodilator. Using immunoperoxidase detection, GluR1 appears as small puncta at the light microscopic level, and is found in dendritic spines at the ultrastructural level. Following the development of hypertension, GluR1 spine and puncta counts were significantly greater in DOCA-salt rats than controls. Hydralazine treatment (4-5 weeks) prevented the development of hypertension in DOCA-salt rats and reduced blood pressure of SHRs to normotensive levels. The density of GluR1 puncta in the NTS was significantly reduced by hydralazine treatment in the SHR model. These results show that hypertension alters dendritic spines containing AMPA-type glutamate receptors within NTS, suggesting that adjustments in GluR1 expression within NTS are part of the synaptic adaptations to the hypertensive state.

Transient receptor potential ankyrin-1 participates in visceral hyperalgesia following experimental colitis.

Transient receptor potential ankyrin-1 (TRPA1) is an important receptor that contributes to inflammatory pain. However, previous studies were mainly concerned with its function in somatic hyperalgesia while few referred to visceral, especially colonic inflammatory hyperalgesia. The present study was aimed to investigate the role of TRPA1 in visceral hyperalgesia after trinitrobenzene sulfonic acid (TNBS)-induced colitis. Results indicate that TNBS induced a significant increase in visceral sensitivity to colonic distension and chemical irritation accompanied by up-regulation of TRPA1 in colonic afferent dorsal root ganglia (DRG). Intrathecal administration of TRPA1 antisense (AS) oligodeoxynucleotide (ODN) reduced the TRPA1 expression in DRG as well as suppressed the colitis-induced hyperalgesia to nociceptive colonic distension and intracolonic allyl isothiocyanate (AITC). Meanwhile the TRPA1 antisense ODN had no effect on transient receptor potential vanilloid-1 (TRPV1) expression, which was proposed to highly co-express with TRPA1, and no effect on the response to TRPV1 agonist, capsaicin. These data suggest an apparent role of TRPA1 in visceral hyperalgesia following colitis that might provide a novel therapeutic target for the relief of pain.

The vagal afferent pathway does not play a major role in the induction of satiety by intestinal fatty acid in rats.

Intestinal infusion of long-chain fatty acids (LCFAs) strongly suppresses food intake and gut motility. Vagal afferents and cholecystokinin (CCK) signaling pathway are considered to play important roles in intestinal LCFA-induced satiety. Here, we first investigated the influence of vagus nerve on satiety following intestinal LCFA infusion in rats. Jejunal infusion of linoleic acid (LA) at 200 microL/h for 7 h suppressed food intake and the effect lasted for 24 h. The satiety induced by jejunal LA infusion occurred in a dose dependent manner. In contrast, the anorectic effect induced by octanoic acid, a medium-chain fatty acid, was weaker than that induced by LA. The reduction in food intake induced by jejunal LA infusion was not attenuated in rats treated with vagotomy, the ablation of bilateral subdiaphragmatic vagal trunks. Jejunal LA-induced satiety could also be observed in rats with bilateral midbrain transections, which ablates fibers between the hindbrain and hypothalamus. These findings suggest that the vagus nerve and fibers ascending from the hindbrain to the hypothalamus do not play a major role in intestinal LCFA-induced satiety. Jejunal LA infusion also reduced food intake in CCK-A receptor-deficient OLETF rats, suggesting that CCK signaling pathway is not critical for intestinal LCFA-induced anorexia. In conclusion, this study indicates that the vagus nerve and the CCK signaling pathway do not play major roles in conveying satiety signals induced by intestinal LCFA to the brain in rats.

Acute myocardial ischemia up-regulates nociceptin/orphanin FQ in dorsal root ganglion and spinal cord of rats.

Nociceptin/orphanin FQ (N/OFQ) possesses modulatory effects on somatic noxious signals in spinal cord, while the potential role in visceral nociception remains elusive. We designed this study to investigate the hypothesis that cardiac nociceptive signals from acute ischemic myocardium to the spinal cord are transmitted or modulated by mechanisms including N/OFQ. We examined the changes of N/OFQ and its mRNA in the dorsal root ganglia and spinal cord of upper thoracic segments innervating the heart of rats. Thoracic epidural anesthesia was performed to confirm neural mechanism underlying the changes. We observed that selective coronary artery occlusion significantly up-regulated N/OFQ and ppN/OFQ mRNA in the dorsal root ganglia and spinal cord. Thoracic epidural anesthesia abolished the changes in the expression of N/OFQ and its mRNA. The observations indicate that cardiac noxious neural afferent drive is responsible for the up-regulation of N/OFQ in the primary afferent neurons and intrinsic spinal neurons.

Immobilizing doses of halothane, isoflurane or propofol, do not preferentially depress noxious heat-evoked responses of rat lumbar dorsal horn neurons with ascending projections.

BACKGROUND: The spinal cord is an important site where volatile anesthetics decrease sensation and produce immobility. Beyond this knowledge, our understanding of a site of anesthetic action is limited. Previous evidence suggests that dorsal horn neurons with ascending projections may be more susceptible to depression by general anesthetics than local spinal interneurons. In this study we evaluated the effects of volatile and injectable general anesthetics on lumbar dorsal horn neurons with and without ascending projections. METHODS: Thirty-seven adult male rats underwent laminectomies at C1, for placement of a stimulating electrode, and T13/L1, for extracellular recording from the spinal cord dorsal horn. Neuronal responses to heat were evaluated under two doses of halothane, isoflurane, or propofol anesthesia. RESULTS: Under both halothane and isoflurane anesthesia, increasing the dose from 0.8 to 1.2 minimum alveolar concentration (MAC) had no significant effect on heat-evoked responses in neurons that had ascending projections identified via antidromic stimulation (AD) or those without ascending projections (nAD). Heat responses in AD neurons 1 min after i.v. administration of 3 and 5 mg/kg of propofol were reduced to 60% +/- 18% (mean +/- SE) and 39% +/- 14% of control respectively. Similarly, in nAD neurons responses were reduced to 56% +/- 14% and 50% +/- 10% of control by 3 and 5 mg/kg propofol respectively. CONCLUSIONS: Our findings suggest, at peri-MAC concentrations, these general anesthetics do not preferentially depress lumbar dorsal horn neurons with ascending projections compared to those with no identifiable ascending projections.

Altered urinary bladder function in mice lacking the vanilloid receptor TRPV1.

In the urinary bladder, the capsaicin-gated ion channel TRPV1 is expressed both within afferent nerve terminals and within the epithelial cells that line the bladder lumen. To determine the significance of this expression pattern, we analyzed bladder function in mice lacking TRPV1. Compared with wild-type littermates, trpv1(-/-) mice had a higher frequency of low-amplitude, non-voiding bladder contractions. This alteration was accompanied by reductions in both spinal cord signaling and reflex voiding during bladder filling (under anesthesia). In vitro, stretch-evoked ATP release and membrane capacitance changes were diminished in bladders excised from trpv1(-/-) mice, as was hypoosmolality-evoked ATP release from cultured trpv1(-/-) urothelial cells. These findings indicate that TRPV1 participates in normal bladder function and is essential for normal mechanically evoked purinergic signaling by the urothelium.