Functional vagal input to gastric myenteric plexus as assessed by vagal stimulation-induced Fos expression

Endocannabinoids and the Gut-Brain Control of Food Intake and Obesity

Gut-brain signaling controls food intake and energy homeostasis, and its activity is thought to be dysregulated in obesity. We will explore new studies that suggest the endocannabinoid (eCB) system in the upper gastrointestinal tract plays an important role in controlling gut-brain neurotransmission carried by the vagus nerve and the intake of palatable food and other reinforcers. A focus will be on studies that reveal both indirect and direct interactions between eCB signaling and vagal afferent neurons. These investigations identify (i) an indirect mechanism that controls nutrient-induced release of peptides from the gut epithelium that directly interact with corresponding receptors on vagal afferent neurons, and (ii) a direct mechanism via interactions between eCBs and cannabinoid receptors expressed on vagal afferent neurons. Moreover, the impact of diet-induced obesity on these pathways will be considered.

Acetylcholine Upregulates Entamoeba histolytica Virulence Factors, Enhancing Parasite Pathogenicity in Experimental Liver Amebiasis

Entamoeba histolytica is an invasive enteric protozoan, whose infections are associated to high morbidity and mortality rates. However, only less than 10% of infected patients develop invasive amebiasis. The ability of E. histolytica to adapt to the intestinal microenvironment could be determinant in triggering pathogenic behavior. Indeed, during chronic inflammation, the vagus nerve limits the immune response through the anti-inflammatory reflex, which includes acetylcholine (ACh) as one of the predominant neurotransmitters at the infection site. Consequently, the response of E. histolytica trophozoites to ACh could be implicated in the establishment of invasive disease. The aim of this study was to evaluate the effect of ACh on E. histolytica virulence. Methods include binding detection of ACh to plasma membrane, quantification of the relative expression of virulence factors by RT-PCR and western blot, evaluation of the effect of ACh in different cellular processes related to E. histolytica pathogenesis, and assessment of the capability of E. histolytica to migrate and form hepatic abscesses in hamsters. Results demonstrated that E. histolytica trophozoites bind ACh on their membrane and show a clear increase of the expression of virulence factors, that were upregulated upon stimulation with the neurotransmitter. ACh treatment increased the expression of L220, Gal/GalNAc lectin heavy subunit (170 kDa), amebapore C, cysteine proteinase 2 (ehcp-a2), and cysteine proteinase 5 (ehcp-a5). Moreover, erythrophagocytosis, cytotoxicity, and actin cytoskeleton remodeling were augmented after ACh treatment. Likewise, by assessing the formation of amebic liver abscess, we found that stimulated trophozoites to develop greater hamster hepatic lesions with multiple granulomas. In conclusion, ACh enhanced parasite pathogenicity by upregulating diverse virulence factors, thereby contributing to disease severity, and could be linked to the establishment of invasive amebiasis.

Distributions and relationships of chemically defined enteroendocrine cells in the rat gastric mucosa

This paper provides quantitative data on the distributions of enteroendocrine cells (EEC), defined by the hormones they contain, patterns of colocalisation between hormones and EEC relations to nerve fibres in the rat gastric mucosa. The rat stomach has three mucosal types: non-glandular stratified squamous epithelium of the fundus and esophageal groove, a region of oxyntic glands in the corpus, and pyloric glands of the antrum and pylorus. Ghrelin and histamine were both contained in closed cells, not contacting the lumen, and were most numerous in the corpus. Gastrin cells were confined to the antrum, and 5-hydroxytryptamine (5-HT) and somatostatin cells were more frequent in the antrum than the corpus. Most somatostatin cells had basal processes that in the antrum commonly contacted gastrin cells. Peptide YY (PYY) cells were rare and mainly in the antrum. The only numerous colocalisations were 5-HT and histamine, PYY and gastrin and gastrin and histamine in the antrum, but each of these populations was small. Peptide-containing nerve fibres were found in the mucosa. One of the most common types was vasoactive intestinal peptide (VIP) fibres. High-resolution analysis showed that ghrelin cells were closely and selectively approached by VIP fibres. In contrast, gastrin cells were not selectively innervated by VIP or CGRP fibres. The study indicates that there are distinct populations of gastric EEC and selective innervation of ghrelin cells. It also shows that, in contrast to EEC of the small intestine, the majority of EEC within the stomach contained only a single hormone.

Fasting stimulates 2-AG biosynthesis in the small intestine: role of cholinergic pathways

The endocannabinoids are lipid-derived signaling molecules that control feeding and energy balance by activating CB1-type cannabinoid receptors in the brain and peripheral tissues. Previous studies have shown that oral exposure to dietary fat stimulates endocannabinoid signaling in the rat small intestine, which provides positive feedback that drives further food intake and preference for fat-rich foods. We now describe an unexpectedly broader role for cholinergic signaling of the vagus nerve in the production of the endocannabinoid, 2-arachidonoyl-sn-glycerol (2-AG), in the small intestine. We show that food deprivation increases levels of 2-AG and its lipid precursor, 1,2-diacylglycerol, in rat jejunum mucosa in a time-dependent manner. This response is abrogated by surgical resection of the vagus nerve or pharmacological blockade of small intestinal subtype-3 muscarinic acetylcholine (m3 mAch) receptors, but not inhibition of subtype-1 muscarinic acetylcholine (m1 mAch). We further show that blockade of peripheral CB1 receptors or intestinal m3 mAch receptors inhibits refeeding in fasted rats. The results suggest that food deprivation stimulates 2-AG-dependent CB1 receptor activation through a mechanism that requires efferent vagal activation of m3 mAch receptors in the jejunum, which, in turn, may promote feeding after a fast.

A distinct vagal anti-inflammatory pathway modulates intestinal muscularis resident macrophages independent of the spleen

The cholinergic anti-inflammatory pathway (CAIP) has been proposed as a key mechanism by which the brain, through the vagus nerve, modulates the immune system in the spleen. Vagus nerve stimulation (VNS) reduces intestinal inflammation and improves postoperative ileus. We investigated the neural pathway involved and the cells mediating the anti-inflammatory effect of VNS in the gut. The effect of VNS on intestinal inflammation and transit was investigated in wild-type, splenic denervated and Rag-1 knockout mice. To define the possible role of α7 nicotinic acetylcholine receptor (α7nAChR), we used knockout and bone marrow chimaera mice. Anterograde tracing of vagal efferents, cell sorting and Ca(2+) imaging were used to reveal the intestinal cells targeted by the vagus nerve. VNS attenuates surgery-induced intestinal inflammation and improves postoperative intestinal transit in wild-type, splenic denervated and T-cell-deficient mice. In contrast, VNS is ineffective in α7nAChR knockout mice and α7nAChR-deficient bone marrow chimaera mice. Anterograde labelling fails to detect vagal efferents contacting resident macrophages, but shows close contacts between cholinergic myenteric neurons and resident macrophages expressing α7nAChR. Finally, α7nAChR activation modulates ATP-induced Ca(2+) response in small intestine resident macrophages. We show that the anti-inflammatory effect of the VNS in the intestine is independent of the spleen and T cells. Instead, the vagus nerve interacts with cholinergic myenteric neurons in close contact with the muscularis macrophages. Our data suggest that intestinal muscularis resident macrophages expressing α7nAChR are most likely the ultimate target of the gastrointestinal CAIP.

The Gut's Little Brain in Control of Intestinal Immunity

The gut immune system shares many mediators and receptors with the autonomic nervous system. Good examples thereof are the parasympathetic (vagal) and sympathetic neurotransmitters, for which many immune cell types in a gut context express receptors or enzymes required for their synthesis. For some of these the relevance for immune regulation has been recently defined. Earlier and more recent studies in neuroscience and immunology have indicated the anatomical and cellular basis for bidirectional interactions between the nervous and immune systems. Sympathetic immune modulation is well described earlier, and in the last decade the parasympathetic vagal nerve has been put forward as an integral part of an immune regulation network via its release of Ach, a system coined "the cholinergic anti-inflammatory reflex." A prototypical example is the inflammatory reflex, comprised of an afferent arm that senses inflammation and an efferent arm: the cholinergic anti-inflammatory pathway, that inhibits innate immune responses. In this paper, the current understanding of how innate mucosal immunity can be influenced by the neuronal system is summarized, and cell types and receptors involved in this interaction will be highlighted. Focus will be given on the direct neuronal regulatory mechanisms, as well as current advances regarding the role of microbes in modulating communication in the gut-brain axis.

Nesfatin-1 inhibits gastric acid secretion via a central vagal mechanism in rats

Nesfatin-1, a novel hypothalamic peptide, inhibits nocturnal feeding behavior and gastrointestinal motility in rodents. The effects of nesfatin-1 on gastrointestinal secretory function, including gastric acid production, have not been evaluated. Nesfatin-1 was injected into the fourth intracerebral ventricle (4V) of chronically cannulated rats to identify a nesfatin dose sufficient to inhibit food intake. Nesfatin-1 (2 μg) inhibited dark-phase food intake, in a dose-dependent fashion, for >3 h. Gastric acid production was evaluated in urethane-anesthetized rats. Nesfatin-1 (2 μg) was introduced via the 4V following endocrine stimulation of gastric acid secretion by pentagastrin (2 μg·kg(-1)·h(-1) iv), vagal stimulation with 2-deoxy-D-glucose (200 mg/kg sc), or no stimulus. Gastric secretions were collected via gastric cannula and neutralized by titration to determine acid content. Nesfatin-1 did not affect basal and pentagastrin-stimulated gastric acid secretion, whereas 2-deoxy-D-glucose-stimulated gastric acid production was inhibited by nesfatin-1 in a dose-dependent manner. c-Fos immunofluorescence in brain sections was used to evaluate in vivo neuronal activation by nesfatin-1 administered via the 4V. Nesfatin-1 caused activation of efferent vagal neurons, as evidenced by a 16-fold increase in the mean number of c-Fos-positive neurons in the dorsal motor nucleus of the vagus (DMNV) in nesfatin-1-treated animals vs. controls (P < 0.01). Finally, nesfatin-induced Ca(2+) signaling was evaluated in primary cultured DMNV neurons from neonatal rats. Nesfatin-1 caused dose-dependent Ca(2+) increments in 95% of cultured DMNV neurons. These studies demonstrate that central administration of nesfatin-1, at doses sufficient to inhibit food intake, results in inhibition of vagally stimulated secretion of gastric acid. Nesfatin-1 activates DMNV efferent vagal neurons in vivo and triggers Ca(2+) signaling in cultured DMNV neurons.

Spatial organization of neurons in the dorsal motor nucleus of the vagus synapsing with intragastric cholinergic and nitric oxide/VIP neurons in the rat

The dorsal motor nucleus of the vagus (DMV) contains preganglionic neurons that control gastric motility and secretion. Stimulation of different parts of the DMV results in a decrease or an increase in gastric motor activities, suggesting a spatial organization of vagal preganglionic neurons in the DMV. Little is known about how these preganglionic neurons in the DMV synapse with different groups of intragastric motor neurons to mediate contraction or relaxation of the stomach. We used pharmacological and immunohistochemical methods to characterize intragastric neural pathways involved in mediating gastric contraction and relaxation in rats. Microinjections of L-glutamate (L-Glu) into the rostral or caudal DMV produced gastric contraction and relaxation, respectively, in a dose-related manner. Intravenous infusion of hexamethonium blocked these actions, suggesting mediation via preganglionic cholinergic pathways. Atropine inhibited gastric contraction by 85.5 +/- 4.5%. Gastric relaxation was reduced by intravenous administration of N(G)-nitro-L-arginine methyl ester (L-NAME; 52.5 +/- 11.9%) or VIP antagonist (56.3 +/- 14.9%). Combined administration of L-NAME and VIP antagonist inhibited gastric relaxation evoked by L-Glu (87.8 +/- 4.3%). Immunohistochemical studies demonstrated choline acetyltransferase immunoreactivity in response to L-Glu microinjection into the rostral DMV in 88% of c-Fos-positive intragastric myenteric neurons. Microinjection of L-Glu into the caudal DMV evoked expression of nitric oxide (NO) synthase and VIP immunoreactivity in 81 and 39%, respectively, of all c-Fos-positive intragastric myenteric neurons. These data indicate spatial organization of the DMV. Depending on the location, microinjection of L-Glu into the DMV may stimulate intragastric myenteric cholinergic neurons or NO/VIP neurons to mediate gastric contraction and relaxation.

The effect of sham feeding on neurocardiac regulation in healthy human volunteers

BACKGROUND

Distension and electrical stimuli in the esophagus alter heart rate variability (HRV) consistent with activation of vagal afferent and efferent pathways. Sham feeding stimulates gastric acid secretion by means of vagal efferent pathways. It is not known, however, whether activation of vagal efferent pathways is organ- or stimulus-specific.

OBJECTIVE

To test the hypothesis that sham feeding increases the high frequency (HF) component of HRV, indicating increased neurocardiac vagal activity in association with the known, vagally mediated, increase in gastric acid secretion.

METHODS

Continuous electrocardiography recordings were obtained in 12 healthy, semirecumbent subjects during consecutive 45 min baseline, 20 min sham feeding (standard hamburger meal) and 45 min recovery periods. The R-R intervals and beat-to-beat heart rate signal were determined from digitized electrocardiography recordings; power spectra were computed from the heart rate signal to determine sympathetic (low frequency [LF]) and vagal (HF) components of HRV.

RESULTS

Heart rate increased during sham feeding (median 70.8 beats/min, 95% CI 66.0 to 77.6; P<0.001), compared with baseline (63.6, 95% CI 60.8 to 70.0) and returned to baseline levels within 45 min. Sham feeding increased the LF to HF area ratio (median: 1.55, 95% C.I 1.28 to 1.77; P<0.021, compared with baseline (1.29, 95% CI 1.05 to 1.46); this increase in LF to HF area ratio was associated with a decrease in the HF component of HRV.

CONCLUSIONS

Sham feeding produces a reversible increase in heart rate that is attributable to a decrease in neurocardiac parasympathetic activity despite its known ability to increase vagally mediated gastric acid secretion. These findings suggest that concurrent changes in cardiac and gastric function are modulated independently by vagal efferent fibres and that vagally mediated changes in organ function are stimulus- and organ-specific.

Brainstem circuits regulating gastric function

Brainstem parasympathetic circuits that modulate digestive functions of the stomach are comprised of afferent vagal fibers, neurons of the nucleus tractus solitarius (NTS), and the efferent fibers originating in the dorsal motor nucleus of the vagus (DMV). A large body of evidence has shown that neuronal communications between the NTS and the DMV are plastic and are regulated by the presence of a variety of neurotransmitters and circulating hormones as well as the presence, or absence, of afferent input to the NTS. These data suggest that descending central nervous system inputs as well as hormonal and afferent feedback resulting from the digestive process can powerfully regulate vago-vagal reflex sensitivity. This paper first reviews the essential "static" organization and function of vago-vagal gastric control neurocircuitry. We then present data on the opioidergic modulation of NTS connections with the DMV as an example of the "gating" of these reflexes, i.e., how neurotransmitters, hormones, and vagal afferent traffic can make an otherwise static autonomic reflex highly plastic.

Role of brainstem TRH/TRH-R1 receptors in the vagal gastric cholinergic response to various stimuli including sham-feeding

Pavlov's pioneering work established that sham-feeding induced by sight or smell of food or feeding in dogs with permanent esophagostomy stimulates gastric acid secretion through vagal pathways. Brain circuitries and transmitters involved in the central vagal regulation of gastric function have recently been unraveled. Neurons in the dorsal vagal complex including the dorsal motor nucleus of the vagus (DMN) express thyrotropin-releasing hormone (TRH) receptor and are innervated by TRH fibers originating from TRH synthesizing neurons in the raphe pallidus, raphe obscurus and the parapyramidal regions. TRH injected into the DMN or cisterna magna increases the firing of DMN neurons and gastric vagal efferent discharge, activates cholinergic neurons in gastric submucosal and myenteric plexuses, and induces a vagal-dependent, atropine-sensitive stimulation of gastric secretory (acid, pepsin) and motor functions. TRH antibody or TRH-R1 receptor oligodeoxynucleotide antisense pretreatment in the cisterna magna or DMN abolished vagal-dependent gastric secretory and motor responses to sham-feeding, 2-deoxy-D-glucose, cold exposure and chemical activation of cell bodies in medullary raphe nuclei. TRH excitatory action in the DMN is potentiated by co-released prepro-TRH-(160-169) flanking peptide, Ps4 and 5-HT, and inhibited by a number of peptides involved in the stress/immune response and inhibition of food-intake. These neuroanatomical, electrophysiological and neuropharmacological data are consistent with a physiological role of brainstem TRH in the central vagal stimulation of gastric myenteric cholinergic neurons in response to several vagal dependent stimuli including sham-feeding.

Experimentally induced ulcers and gastric sensory-motor function in rats

Prior studies have demonstrated that inflammation can sensitize visceral afferent neurons, contributing to the development of hyperalgesia. We hypothesized that both afferent and efferent pathways are affected, resulting in changes in motor and sensory function. Kissing ulcers (KU) were induced in the distal stomach by injecting 60% acetic acid for 45 s into a clamped area of the stomach. In controls, saline was injected into the stomach. A balloon catheter was surgically placed into the stomach, and electromyographic responses to gastric distension were recorded from the acromiotrapezius muscle at various times after ulcer induction. The accommodation reflex was assessed by slowly infusing saline into the distally occluded stomach. Gastric pressure changes in response to vagal stimulation were measured in anesthetized rats. Contractile function of circular muscle strips was examined in vitro using force-displacement transducers. KU caused gastric hypersensitivity that persisted for at least 14 days. Fluid distension of the stomach led to a rapid pressure increase in KU but not in control animals, consistent with an impaired accommodation reflex. Gastric ulcers enhanced the contractile response to vagal stimulation, whereas the effect of cholinergic stimulation on smooth muscle in vitro was not changed. These data suggest that inflammation directly alters gastric sensory and motor function. Increased activation of afferents will trigger vagovagal reflexes, thereby further changing motility and indirectly activating sensory neurons. Thus afferent and efferent pathways both contribute to the development of dyspeptic symptoms.

Cholecystokinin activates specific enteric neurons in the rat small intestine

Cholecystokinin (CCK) is a peptide hormone released from the I-cells of the upper small intestine. CCK evokes a variety of physiological responses, such as stimulation of pancreatic secretion, reduction of food intake and inhibition of gastric emptying. Previously, we reported that CCK activates enteric neurons in the rat. However the specific subpopulations of enteric neurons activated by CCK have not been identified. In the work reported here, we utilized immunohistochemical detection of nuclear Fos, a marker for neuronal activation, and selected phenotypic markers to identify some of the neuronal subpopulations activated by CCK. The phenotypic markers that we examined were: nitric oxide synthase (NOS), neurokinin-1 receptor (NK-1R), calbindin (Cal), Calretinin (Calr), and neurofilament-M (NF-M). We found that in the myenteric plexus of the rat duodenum and jejunum, CCK activated NOS immunoreactive neurons. In the submucosal plexus of duodenum and jejunum, CCK activated Cal, Calr and NF-M immunoreactive neurons. CCK failed to activate NK-1R immunoreactive neurons in either plexus. Our results indicate that CCK activates distinct enteric neurons in the rat upper small intestine. Furthermore the fact that NOS immunoreactive neurons were activated suggests that CCK modulates the activity of inhibitory motor neurons in the myenteric plexus. Expression of Fos immunoreactivity in Calr and Cal immunoreactive neurons is consistent with a role for CCK in modulation of intrinsic sensory and/or secretomotor neuronal activity in the submucosal plexus.

Capsaicin-sensitive extrinsic afferents are involved in acid-induced activation of distinct myenteric neurons in the rat stomach

Challenge of the rat gastric mucosa with 0.5 mol L(-1) HCl activates nitrergic neurons in the myenteric plexus as visualized by c-Fos immunohistochemistry. In the present study, we characterized the activated neurons more extensively by their chemical coding and investigated whether a neural pathway that involves capsaicin-sensitive extrinsic afferents and/or cholinergic neurons transmitting via nicotinic receptors contributes to the activation of myenteric neurons. In multiple labelling experiments, c-Fos was examined for co-localization with nitric oxide synthase (NOS), vasoactive intestinal peptide (VIP), neuropeptide Y (NPY), enkephalin (ENK), gastrin-releasing peptide (GRP), substance P (SP), calbindin D-28k (CALB) and neurofilament 145 (NF 145). All c-Fos-positive neurons were immunoreactive for NOS, VIP, NPY and NF 145, but not for SP, ENK, GRP and CALB. Nerve fibres co-expressing NOS, VIP and NPY were predominantly found in the external muscle layer and in the muscularis mucosae but rarely in the mucosa. Pre-treatment with capsaicin or hexamethonium or a combination of both pre-treatments reduced HCl-induced c-Fos expression by 54, 66 and 63%, respectively. Acid challenge of the stomach, therefore, leads to activation of presumably inhibitory motor neurons responsible for muscle relaxation. Activation of these neurons is partly mediated by capsaicin-sensitive afferents and involves ganglionic transmission via nicotinic receptors.

Neuronal activation of brain vagal-regulatory pathways and upper gut enteric plexuses by insulin hypoglycemia

Neuronal activation of brain vagal-regulatory nuclei and gastric/duodenal enteric plexuses in response to insulin (2 U/kg, 2 h) hypoglycemia was studied in rats. Insulin hypoglycemia significantly induced Fos expression in the paraventricular nucleus of the hypothalamus, locus coeruleus, dorsal motor nucleus of the vagus (DMN), and nucleus tractus solitarii (NTS), as well as in the gastric/duodenal myenteric/submucosal plexuses. A substantial number of insulin hypoglycemia-activated DMN and NTS neurons were choline acetyltransferase and tyrosine hydroxylase positive, respectively, whereas the activated enteric neurons included NADPH- and vasoactive intestinal peptide neurons. The numbers of Fos-positive cells in each above-named brain nucleus or in the gastric/duodenal myenteric plexus of insulin-treated rats were negatively correlated with serum glucose levels and significantly increased when glucose levels were lower than 80 mg/dl. Acute bilateral cervical vagotomy did not influence insulin hypoglycemia-induced Fos induction in the brain vagal-regulatory nuclei but completely and partially prevented this response in the gastric and duodenal enteric plexuses, respectively. These results revealed that brain-gut neurons regulating vagal outflow to the stomach/duodenum are sensitively responsive to insulin hypoglycemia.

Mucosal acid challenge activates nitrergic neurons in myenteric plexus of rat stomach

We tested the hypothesis that intrinsic neurons of the rat gastric myenteric plexus can be activated by an acid (HCl) challenge of the mucosa. Activated neurons were visualized by immunohistochemical detection of c-Fos, a marker for neuronal excitation. The neurochemical identity of the neurons activated by the HCl challenge was determined by colocalizing c-Fos with a marker for excitatory pathways, choline acetyltransferase (ChAT), and a marker for inhibitory pathways, nitric oxide synthase (NOS). Two hours after intragastric administration of HCl or saline, stomachs were removed and immunofluorescence triple labeling of myenteric neurons was carried out on whole mount preparations. Treatment with 0.35, 0.5, and 0.7 M HCl induced c-Fos in 8%, 56%, and 64%, respectively, of NOS-positive but not ChAT-positive neurons. c-Fos was also seen in glial cells of HCl-treated rats, whereas in saline-treated animals c-Fos was absent from the myenteric plexus. HCl treatment did not change the proportion of ChAT- and NOS-immunoreactive neurons in the myenteric ganglia. It is concluded that gastric acid challenge concentration-dependently stimulates a subpopulation of nitrergic, but not cholinergic, myenteric plexus neurons, which may play a role in muscle relaxation, vasodilatation, and/or secretion.

Fos expression in rat celiac ganglion: an index of the activation of postganglionic sympathetic nerves

To develop an index of the activation of abdominal sympathetic nerves, we used Fos immunostaining of the celiac ganglion (CG) taken from rats receiving nicotine, preganglionic nerve stimulation, or glucopenic agents. Subcutaneous nicotine injection moderately increased Fos expression in the principal ganglionic cells of the CG (17 +/- 4 Fos+ per mm(2), approximately 12% of all principal CG cells), whereas subcutaneous saline had no effect (0 +/- 0 Fos+ per mm(2); n = 7; P < 0.01). Greater Fos expression was obtained by applying nicotine topically to the CG (71 +/- 8 Fos+ per mm(2); 52% of all principal CG cells, n = 5; P < 0.01 vs. topical saline, n = 4) and by preganglionic nerve stimulation (126 +/- 9 Fos+ per mm(2); 94% of all principal CG cells, n = 11; P < 0.01 vs. nerve isolation, n = 7). Moderate Fos expression was also observed in the CG after intraperitoneal 2-deoxy-D-glucose (2DG) injection (21 +/- 2 Fos+ per mm(2); 16% of all principal CG cells, n = 5; P < 0.01 vs. saline ip) or insulin injection (16 +/- 2 Fos+ per mm(2); 12% of all principal CG cells, n = 6; P < 0.01 vs. saline ip). Furthermore, Fos expression induced by 2DG was dose and time dependent. These data demonstrate significant Fos expression in the CG in response to chemical, electrical, and reflexive stimulation. Thus Fos expression in the CG may be a useful index to describe various levels of activation of its postganglionic sympathetic neurons.

Acute cold exposure induces vagally mediated Fos expression in gastric myenteric neurons in conscious rats

Acute cold exposure-induced activation of gastric myenteric neurons in conscious rats was examined on longitudinal muscle-myenteric plexus whole mount preparations. Few Fos-immunoreactive (IR) cells (<1/ganglion) were observed in 24-h fasted rats semirestrained at room temperature. Cold exposure (4 degrees C) for 1-3 h induced a time-related increase of Fos-IR cells in corpus and antral myenteric ganglia with a maximal plateau response (17 +/- 3 and 18 +/- 3 cells/ganglion, respectively) occurring at 2 h. Gastric vagotomy partly prevented, whereas bilateral cervical vagotomy completely abolished, Fos expression in the myenteric cells induced by cold exposure (2 h). Hexamethonium (20 mg/kg) also prevented 3-h cold exposure-induced myenteric Fos expression by 76-80%, whereas atropine or bretylium had no effect. Double labeling revealed that cold (3 h)-induced Fos-IR myenteric cells were mainly neurons, including a substantial number of choline acetyltransferase-containing neurons and most NADPH-diaphorase-positive neurons. These results indicate that acute cold exposure activates cholinergic as well as nitrergic neurons in the gastric myenteric ganglia through vagal nicotinic pathways in conscious rats.

Intracisternal TRH analog induces Fos expression in gastric myenteric neurons and glia in conscious rats

Activation of gastric myenteric cells by intracisternal injection of the stable thyrotropin-releasing hormone (TRH) analog RX-77368, at a dose inducing near maximal vagal cholinergic stimulation of gastric functions, was investigated in conscious rats. Fos immunoreactivity was assessed in gastric longitudinal muscle-myenteric plexus whole mount preparations 90 min after intracisternal injection. Fos-immunoreactive cells were rare in controls (~1 cell/ganglion), whereas intracisternal RX-77368 (50 ng) increased the number to 24.8 +/- 1.8 and 26.8 +/- 2.2 cells/ganglion in the corpus and antrum, respectively. Hexamethonium (20 mg/kg sc) prevented Fos expression by 90%, whereas atropine (2 mg/kg sc) had no effect. The neuronal marker protein gene product 9.5 and the glial markers S-100 and glial fibrillary acidic proteins showed that RX-77368 induced Fos in both myenteric neurons and glia. Vesicular ACh transporter and calretinin were detected around the activated myenteric neurons. These results indicated that central vagal efferent stimulation by intracisternal RX-77368 activates gastric myenteric neurons as well as glial cells mainly through nicotinic ACh receptors in conscious rats.