Actions of galanin on neurotransmission in the submucous plexus of guinea pig small intestine

Mechanistic Study of Coffee Effects on Gut Microbiota and Motility in Rats

Consumption of coffee has benefits in postoperative ileus. We tested the hypothesis that the benefits may be related to the effects of coffee on gut microbiota and motility and studied the mechanisms of action in rats. The in vitro and in vivo effects of regular and decaffeinated (decaf) coffee on gut microbiota of the ileum and colon were determined by bacterial culture and quantitative RT-PCR. Ileal and colonic smooth muscle contractility was determined in a muscle bath. In the in vivo studies, coffee solution (1 g/kg) was administered by oral gavage daily for 3 days. Compared to regular LB agar, the growth of microbiota in the colon and ileal contents was significantly suppressed in LB agar containing coffee or decaf (1.5% or 3%). Treatment with coffee or decaf in vivo for 3 days suppressed gut microbiota but did not significantly affect gut motility or smooth muscle contractility. However, coffee or decaf dose-dependently caused ileal and colonic muscle contractions in vitro. A mechanistic study found that compound(s) other than caffeine contracted gut smooth muscle in a muscarinic receptor-dependent manner. In conclusion, coffee stimulates gut smooth muscle contractions via a muscarinic receptor-dependent mechanism and inhibits microbiota in a caffeine-independent manner.

Galanin suppresses visceral afferent responses to noxious mechanical and inflammatory stimuli

Galanin is a neuropeptide expressed by sensory neurones innervating the gastrointestinal (GI) tract. Galanin displays inhibitory effects on vagal afferent signaling within the upper GI tract, and the goal of this study was to determine the actions of galanin on colonic spinal afferent function. Specifically, we sought to evaluate the effect of galanin on lumbar splanchnic nerve (LSN) mechanosensitivity to noxious distending pressures and the development of hypersensitivity in the presence of inflammatory stimuli and colitis. Using ex vivo electrophysiological recordings we show that galanin produces a dose-dependent suppression of colonic LSN responses to mechanical stimuli and prevents the development of hypersensitivity to acutely administered inflammatory mediators. Using galanin receptor (GalR) agonists, we show that GalR1 activation, but not GalR2/3 activation, suppresses mechanosensitivity. The effect of galanin on colonic afferent activity was not observed in tissue from mice with dextran sodium sulfate-induced colitis. We conclude that galanin has a marked suppressive effect on colonic mechanosensitivity at noxious distending pressures and prevents the acute development of mechanical hypersensitivity to inflammatory mediators, an effect not seen in the inflamed colon. These actions highlight a potential role for galanin in the regulation of mechanical nociception in the bowel and the therapeutic potential of targeting galaninergic signaling to treat visceral hypersensitivity.

The Influence of Gastric Antral Ulcerations on the Expression of Galanin and GalR1, GalR2, GalR3 Receptors in the Pylorus with Regard to Gastric Intrinsic Innervation of the Pyloric Sphincter

Gastric antrum ulcerations are common disorders occurring in humans and animals. Such localization of ulcers disturbs the gastric emptying process, which is precisely controlled by the pylorus. Galanin (Gal) and its receptors are commonly accepted to participate in the regulation of inflammatory processes and neuronal plasticity. Their role in the regulation of gastrointestinal motility is also widely described. However, there is lack of data considering antral ulcerations in relation to changes in the expression of Gal and GalR1, GalR2, GalR3 receptors in the pyloric wall tissue and galaninergic intramural innervation of the pylorus. Two groups of pigs were used in the study: healthy gilts and gilts with experimentally induced antral ulcers. By double immunocytochemistry percentages of myenteric and submucosal neurons expressing Gal-immunoreactivity were determined in the pyloric wall tissue and in the population of gastric descending neurons supplying the pyloric sphincter (labelled by retrograde Fast Blue neuronal tracer). The percentage of Gal-immunoreactive neurons increased only in the myenteric plexus of the pyloric wall (from 16.14±2.06% in control to 25.5±2.07% in experimental animals), while no significant differences in other neuronal populations were observed between animals of both groups. Real-Time PCR revealed the increased expression of mRNA encoding Gal and GalR1 receptor in the pyloric wall tissue of the experimental animals, while the expression(s) of GalR2 and GalR3 were not significantly changed. The results obtained suggest the involvement of Gal, GalR1 and galaninergic pyloric myenteric neurons in the response of pyloric wall structures to antral ulcerations.

Synaptic transmission at functionally identified synapses in the enteric nervous system: roles for both ionotropic and metabotropic receptors

Digestion and absorption of nutrients and the secretion and reabsorption of fluid in the gastrointestinal tract are regulated by neurons of the enteric nervous system (ENS), the extensive peripheral nerve network contained within the intestinal wall. The ENS is an important physiological model for the study of neural networks since it is both complex and accessible. At least 20 different neurochemically and functionally distinct classes of enteric neurons have been identified in the guinea pig ileum. These neurons express a wide range of ionotropic and metabotropic receptors. Synaptic potentials mediated by ionotropic receptors such as the nicotinic acetylcholine receptor, P2X purinoceptors and 5-HT(3) receptors are seen in many enteric neurons. However, prominent synaptic potentials mediated by metabotropic receptors, like the P2Y(1) receptor and the NK(1) receptor, are also seen in these neurons. Studies of synaptic transmission between the different neuron classes within the enteric neural pathways have shown that both ionotropic and metabotropic synaptic potentials play major roles at distinct synapses within simple reflex pathways. However, there are still functional synapses at which no known transmitter or receptor has been identified. This review describes the identified roles for both ionotropic and metabotropic neurotransmission at functionally defined synapses within the guinea pig ileum ENS. It is concluded that metabotropic synaptic potentials act as primary transmitters at some synapses. It is suggested identification of the interactions between different synaptic potentials in the production of complex behaviours will require the use of well validated computer models of the enteric neural circuitry.

Regulation of galanin and galanin receptor 2 expression by capsaicin in primary cultured dorsal root ganglion neurons

Galanin is a 29-amino-acid neuropeptide expressed in dorsal root ganglion (DRG) neurons which is thought to play a role in modulation of nociception in neuropathic states. Activation of galanin receptor 2 (GalR2) plays a pronociceptive role and enhances capsaicin-induced nociception in the periphery. GalR2 and vanilloid receptor 1 (VR1) are co-expressed in DRG neurons. Capsaicin evokes acute pain via activation of VR1 expressed in primary sensory neurons. It is not known to what extent galanin and its receptor GalR2 expression is regulated by capsaicin in DRG neurons. Effects of acute (4 h) or chronic (4 d) treatment with capsaicin at different concentrations (0.01, 0.1, 1 micromol/L) on galanin and GalR2 expression in primary cultured DRG neurons were investigated in the present study. Our results showed that acute exposure of high concentration capsaicin (1 micromol/L) increased galanin expression, whereas chronic exposure of low concentration capsaicin (0.01, 0.1 micromol/L) promoted galanin expression. Only chronic exposure of 0.1 micromol/L concentration capsaicin could elevate GalR2 expression, whereas capsaicin did not have this effect at any other conditions in this experiment. These results indicated that certain concentrations or exposure time of capsaicin stimulation may be relevant to upregulation of galanin and its receptor GalR2 expression in DRG cultures suggesting a response to peripheral neuronal stimulation. And also, capsaicin-induced GalR2 expression may be also modulated by capsaicin-induced galanin expression. The possible significance of the neurotransmission of nociceptive information involved in galanin or GalR2 expression caused by capsaicin is still to be clarified.

Involvement of galanin receptors 1 and 2 in the modulation of mouse vagal afferent mechanosensitivity

It is established that the gut peptide galanin reduces neuronal excitability via galanin receptor subtypes GALR1 and GALR3 and increases excitability via subtype GALR2. We have previously shown that galanin potently reduces mechanosensitivity in the majority of gastro-oesophageal vagal afferents, and potentiates sensitivity in a minority. These actions may have implications for therapeutic inhibition of gut afferent signalling. Here we investigated which galanin receptors are likely to mediate these effects. We performed quantitative RT-PCR on RNA from vagal (nodose) sensory ganglia, which indicated that all three GALR subtypes were expressed at similar levels. The responses of mouse gastro-oesophageal vagal afferents to graded mechanical stimuli were investigated before and during application of galanin receptor ligands to their peripheral endings. Two types of vagal afferents were tested: tension receptors, which respond to circumferential tension, and mucosal receptors which respond only to mucosal stroking. Galanin induced potent inhibition of mechanosensitivity in both types of afferents. This effect was totally lost in mice with targeted deletion of Galr1. The GALR1/2 agonist AR-M961 caused inhibition of mechanosensitivity in Galr1+/+ mice, but this was reversed to potentiation in Galr1-/- mice, indicating a minor role for GALR2 in potentiation of vagal afferents. We observed no functional evidence of GALR3 involvement, despite its expression in nodose ganglia. The current study highlights the complex actions of galanin at different receptor subtypes exhibiting parallels with the function of galanin in other systems.

Modulation of gastro-oesophageal vagal afferents by galanin in mouse and ferret

The neuropeptide galanin is found in the central and peripheral nervous systems. It may have excitatory or inhibitory actions via three subtypes of G-protein-coupled receptor, and it modulates the mechanosensitivity of somatic sensory fibres. We aimed to determine if galanin also modulates vagal afferent mechanosensitivity, and to localize endogenous sources. The responses of ferret and mouse gastro-oesophageal vagal afferents to graded mechanical stimuli were investigated in vitro. The effects of galanin and/or the galanin receptor antagonist galantide on these responses were quantified. Immunohistochemistry for galanin was performed in ferret and mouse proximal stomach and nodose ganglion. In ferrets, retrograde labelling of gastric afferents to the nodose ganglion was combined with immunohistochemistry. When exposed to galanin (1-10 nM), 18/31 ferret and 12/15 mouse gastro-oesophageal afferents (tension, mucosal and tension/mucosal receptors) showed inhibition of mechanosensitivity. Four of 31 ferret afferents showed potentiation of mechanosensitivity, and 9/31 were unaffected (2/15 and 1/15 in mouse, respectively). Galanin effects were reversed after washout or by galantide (10-30 nM). Galantide given alone increased mechanosensitivity. Galanin immunoreactivity was found in nodose neurones, including those innervating the stomach in ferret. Enteric neurones were also galanin immunoreactive, as were endings associated with myenteric ganglia and smooth muscle. We conclude that galanin potently modulates mechanosensitivity of gastro-oesophageal vagal afferents with either facilitatory or inhibitory actions on individual afferent fibres. Both intrinsic and extrinsic (vagal) neurones contain galanin and are therefore potential sources of endogenous galanin.