Guinea-pig Small Intestine (guinea-pig + small_intestine)

Distribution by Scientific Domains


Selected Abstracts


Plasticity and ambiguity of the electrophysiological phenotypes of enteric neurons

NEUROGASTROENTEROLOGY & MOTILITY, Issue 9 2009
K. Nurgali
Abstract, Advances in knowledge of enteric neurons electrophysiological characteristics have led to the realisation that the properties of the neurons are dependent on the state of the intestine, the region, the method of recording and the species. Thus, under different experimental conditions, electrophysiological studies cannot provide a reliable signature that identifies the functional type of neuron. In the normal guinea-pig small intestine, taken as a model tissue, neurons can be separated into two electrophysiological groups, S and AH neurons. Combined morphological and physiological studies place several classes of motor and interneurons in the S group, and intrinsic primary afferent neurons in the AH group. There is some evidence for subgroups of S neurons, in which electrophysiological differences are correlated with functional subtypes, but these subgroups have been incompletely investigated. Morphologically characterized Dogiel type II (DII) neurons are recognisable in many species, from mouse to human, but their electrophysiological characteristics are only partly conserved across species or cannot be satisfactorily defined due to technical difficulties. There is a strong need for a comprehensive analysis of channels and currents of S/Dogiel type I neuron subtypes, similar to the comprehensive analysis of AH/DII neurons in the guinea-pig, and similar studies need to be conducted in human and other species. The purpose of this review is to highlight that criteria used for electrophysiological definition of enteric neurons might not be sufficient to distinguish between functional classes of neurons, due to intrinsic properties of neuronal subpopulations, plasticity in pathological conditions and differences in recording techniques. [source]


Nogo A expression in the adult enteric nervous system

NEUROGASTROENTEROLOGY & MOTILITY, Issue 4 2004
S. L. Osborne
Abstract, Neuronal plasticity plays an important role in physiological and pathological processes within the gastrointestinal (GI) tract. Nogo A is a major contributor to the negative effect central nervous system (CNS) myelin has on neurite outgrowth after injury and may also play a role in maintaining synaptic connections in the healthy CNS. Nogo A is highly expressed during neuronal development but in the CNS declines postnatally concomitantly with a loss of regenerative potential while ganglia of the Peripheral Nervous System (PNS) retain Nogo A. The enteric nervous system shares a number of features in common with the CNS, thus the peripheral distribution of factors affecting plasticity is of interest. We have investigated the distribution of Nogo in the adult mammalian gastrointestinal tract. Nogo A mRNA and protein are detectable in the adult rat GI tract. Nogo A is expressed heterogeneously in enteric neurons throughout the GI tract though expression levels appear not to be correlated with neuronal sub-type. The pattern of expression is maintained in cultured myenteric plexus from the guinea-pig small intestine. As is seen in developing neurons of the CNS, enteric Nogo A is present in both neuronal cell bodies and axons. Our results point to a hitherto unsuspected role for Nogo A in enteric neuronal physiology. [source]


Evidence for functional NK1 -tachykinin receptors on motor neurones supplying the circular muscle of guinea-pig small and large intestine

NEUROGASTROENTEROLOGY & MOTILITY, Issue 4 2000
Bian
The guinea-pig intestine was investigated to determine which neurones are excited via NK1 receptors. The specific NK1 receptor agonists [Sar9, Met(O2)11]-SP and septide contracted the circular muscle of all regions via a tetrodotoxin (TTX)-insensitive mechanism. In the proximal colon, they also evoked a TTX-sensitive relaxation; in the distal colon, the contractions were larger when nerve impulses were blocked with TTX, indicating that the agonists excited inhibitory motor neurones. In the duodenum and ileum, TTX reduced agonist-evoked contractions indicating that excitatory motor neurones were activated. In the presence of indomethacin, TTX enhanced contractions of ileal circular muscle evoked by these agonists suggesting that NK1 receptors were on inhibitory motor neurones. Blockade of nitric oxide synthase (NOS) enhanced NK1 receptor agonist evoked contractions of duodenal circular muscle, indicating that the agonists excite inhibitory motor neurones in duodenum. Neurones immunoreactive for NK1 receptors were studied in the duodenum and distal colon. As reported previously for the ileum,1 some neurones were immunoreactive for NOS and had Dogiel type I morphology; features characteristic of inhibitory motor neurones. In conclusion, there are functional NK1 receptors on excitatory and inhibitory motor neurones in the guinea-pig small intestine and on inhibitory motor neurones in the colon. [source]


Differences in circular muscle contraction and peristaltic motor inhibition caused by tachykinin NK1 receptor agonists in the guinea-pig small intestine

NEUROGASTROENTEROLOGY & MOTILITY, Issue 2 2000
Shahbazian
The tachykinin NK1 receptor agonist substance P methyl ester (SPOME) impedes intestinal peristalsis by releasing nitric oxide (NO) from inhibitory motor neurones. Since NK1 receptor agonists differ in their receptor interaction, we set out to compare a range of NK1 receptor agonists including SPOME, septide and GR-73 632 in their effects on propulsive peristalsis and circular muscle activity in the guinea-pig isolated small intestine. SPOME (100,300 n M) inhibited peristalsis by a rise of the pressure threshold at which peristaltic waves were triggered, whereas septide and GR-73 632 (30,300 n M) interrupted peristalsis by causing circular muscle spasms. Separate experiments showed that all three NK1 receptor agonists caused contraction of the circular muscle, which was enhanced by the NO synthase inhibitor NG -nitro- L -arginine methyl ester (300 ,M) and the P2X purinoceptor antagonist suramin (300 ,M). In contrast, tetrodotoxin (300 n M) augmented the contractile effect of septide and GR-73 632 but not that of SPOME. It is concluded that the motor response to NK1 receptor agonists involves release of NO and adenosine triphosphate from inhibitory motor neurones. However, the NK1 receptor agonists differ in the mechanism by which they cause inhibitory transmitter release, which corresponds to differences in their antiperistaltic action. [source]


Morphologies and projections of defined classes of neurons in the submucosa of the guinea-pig small intestine

THE ANATOMICAL RECORD : ADVANCES IN INTEGRATIVE ANATOMY AND EVOLUTIONARY BIOLOGY, Issue 2 2003
John B. Furness
Abstract Four types of neurons have previously been identified by neurochemical markers in the submucosal ganglia of the guinea-pig small intestine, and functional roles have been ascribed to each type. However, morphological differences among the classes have not been determined, and there is only partial information about their projections within the submucosa. In the present work, we used intracellular microelectrodes to fill neurons of each type with biocytin, which was then converted to a permanent dye, so that the shapes of the neurons could be determined and their projections within the submucosa could be followed. Cell bodies of noncholinergic secretomotor/ vasodilator neurons had Dogiel type I morphology. These neurons, which are vasoactive intestinal peptide immunoreactive, had single axons that ran through many ganglia without providing terminals around other neurons. Cholinergic secretomotor neurons with neuropeptide Y immunoreactivity had Stach type IV morphology, and cholinergic secretomotor/vasodilator neurons had stellate cell bodies. The axons of these two types ran short distances in the plexus and did not innervate other submucosal neurons. Neurons of the fourth type, intrinsic primary afferent neurons, had cell bodies with Dogiel type II morphology and their processes supplied networks of varicose processes around other nerve cells. It is concluded that each functionally defined type of submucosal neuron has a characteristic morphology and that intrinsic primary afferent neurons synapse with secretomotor neurons to form monosynaptic secretomotor reflex circuits. Anat Rec Part A 272A:475,483, 2003. © 2003 Wiley-Liss, Inc. [source]


Segmentation induced by intraluminal fatty acid in isolated guinea-pig duodenum and jejunum

THE JOURNAL OF PHYSIOLOGY, Issue 2 2004
Rachel M. Gwynne
Small intestinal movements depend on the composition of the chyme with mixing predominating at high nutrient levels and propulsion being prevalent at low nutrient levels. The mechanisms coupling nutrients to motility are unknown. We used computer analysis of video recordings of isolated guinea-pig duodenum, jejunum and ileum to examine movements induced by a fatty acid, decanoic acid. Increasing intraluminal pressure past a threshold using control saline consistently evoked propulsive reflexes: lumen-occluding constrictions appeared at the oral end propagating at 20.4 ± 2.4 mm s,1 (mean ±s.d., jejunum) to the anal end before being repeated until the intraluminal pressure was returned to control. Subthreshold pressure increases sometimes evoked a transient series of constrictions appearing at the oral end and propagating anally at 18.4 ± 4.7 mm s,1 (jejunum). At basal pressures, decanoic acid dose-dependently induced motor activity consisting of 40,60 s episodes of constrictions separated by 40,200 s periods of quiescence and lasting up to 2 h. Five contraction patterns were identified within episodes including localized stationary constrictions; constrictions that propagated slowly (5,8 mm s,1) for short distances orally or anally; and constrictions that propagated orally or anally for the length of the preparation at 14,20 mm s,1. Decanoic acid induced motor activity was reversibly abolished by tetrodotoxin (3 ,m), hyoscine (1 ,m) and hexamethonium (100 ,m), but was insensitive to blockade of P2 purinoceptors by PPADS (60 ,m). Thus, decanoic acid induces motor activity equivalent to segmentation in guinea-pig small intestine in vitro and this depends on intrinsic neural pathways. [source]


Control of non-adrenergic non-cholinergic reflex motor responses in circular muscle of guinea-pig small intestine by Met-enkephalin

AUTONOMIC & AUTACOID PHARMACOLOGY, Issue 4 2002
Chr. Ivancheva
Summary 1 A triple organ bath method allowing the synchronous recording of the motor activity of the circular muscle layer belonging to the oral and anal segments of guinea-pig small intestine adjacent to an electrically stimulated middle segment was developed to study the ascending and descending reflex motor responses. 2 Electrical field stimulation (0.8 ms, 40 V, 5 Hz, 10 s) applied to the middle part of the segments elicited tetrodotoxin (1 ,m)-sensitive ascending and descending contractile responses of the nonstimulated parts, oral and anal, respectively. The ascending contraction was more pronounced as compared with the descending contraction. 3 In the presence of phentolamine (5 ,m), propranolol (5 ,m) and atropine (3 ,m) a significant decrease in the amplitude of the ascending contraction was seen and a descending relaxation, instead of a contraction was observed. 4 Met-enkephalin applied at a single concentration (0.1 ,m) or cumulatively (0.001,1 ,m) inhibited both non-adrenergic non-cholinergic (NANC) descending relaxation and ascending contraction with similar efficacy but different potency, IC50 being 5.9 ± 0.3 and 39.0 ± 4 nm, respectively. Naloxone (0.5 ,m) prevented the effects of Met-enkephalin. 5 L-NNA (0.5 mm), an inhibitor of nitric oxide synthesis, increased the ascending contraction and strongly reduced but not abolished the descending relaxation. l -Arginine (0.5 mm) restored the motor responses to the initial level in l -NNA-pretreated preparations, d -Arginine (0.5 nm) had no effects. 6 Met-enkephalin (0.1 ,m) depressed the l -NNA-dependent increase of the ascending contraction and failed to change the l -NNA-resistant part of the descending relaxation. 7 Met-enkephalin did not alter spontaneous NANC mechanical activity. SNP (1 or 10 ,m), an exogenous donor of nitric oxide, caused a concentration-dependent relaxation. The effects of SNP persisted in Met-enkephalin (0.1 ,m)-pretreated preparations. 8 NANC reflex ascending contraction and descending relaxation were synchronously induced by a local nerve stimulation indicating a functional coactivation of NANC orally projected excitatory and anally directed inhibitory pathways. Acting prejunctionally, Met-enkephalin provided a negative controlling mechanism inhibiting both ascending and descending, mainly nitric oxide mediated, reflex responses. A higher sensitivity of the descending relaxation to Met-enkephalin was observed suggesting an essential role of opioid(s) in reducing the efficacy of descending motor activity. [source]