Novel evidences for a role of dopamine as modulator of intestinal motility: a study on mouse distal colon

Parkinson’s disease (PD) is the second most common neurodegenerative disease after Alzheimer’s disease. It has been classically considered that the pathological hallmarks of PD affect primarily the substantia nigra. Nevertheless, it has become increasingly evident that PD is a multicentric neurodegenerative process that affects several neuronal structures outside the substantia nigra, among which is the enteric nervous system (ENS). Pathological alterations within the ENS could be involved in the gastrointestinal (GI) dysfunction frequently encountered by PD patients. Dopamine (DA) seems to be a major candidate for the impairment of GI function in PD since its levels were found to be decrea…

D1 receptors play a major role in the dopamine modulation of mouse ileum contractility

Since the role of dopamine in the bowel motility is far from being clear, our aim was to analyse pharmacologically the effects of dopamine on mouse ileum contractility. Contractile activity of mouse ileum was examined in vitro as changes in isometric tension. Dopamine caused a concentration-dependent reduction of the spontaneous contraction amplitude of ileal muscle up to their complete disappearance. SCH-23390, D1 receptor antagonist, which per se increased basal tone and amplitude of spontaneous contractions, antagonized the responses to dopamine, whilst sulpiride or domperidone, D2 receptor antagonists, were without effects. The application of both D1 and D2 antagonists had additive effe…

Adenosine negatively regulates duodenal motility in mice: role of A1 and A2A receptors

BACKGROUND AND PURPOSE Adenosine is considered to be an important modulator of intestinal motility. This study was undertaken to investigate the role of adenosine in the modulation of contractility in the mouse duodenum and to characterize the adenosine receptor subtypes involved. EXPERIMENTAL APPROACH RT-PCR was used to investigate the expression of mRNA encoding for A1, A2A, A2B and A3 receptors. Contractile activity was examined in vitro as changes in isometric tension. KEY RESULTS In mouse duodenum, all four classes of adenosine receptors were expressed, with the A2B receptor subtype being confined to the mucosal layer. Adenosine caused relaxation of mouse longitudinal duodenal muscle; …

Arginine vasopressin, via activation of post-junctional V1 receptors, induces contractile effects in mouse distal colon

The aim of this study was to analyze whether arginine vasopressin (AVP) may be considered a modulator of intestinal motility. In this view, we evaluated, in vitro, the effects induced by exogenous administration of AVP on the contractility of mouse distal colon, the subtype(s) of receptor(s) activated and the action mechanism. Isometric recordings were performed on longitudinal and circular muscle strips of mouse distal colon. AVP (0.001 nM-100 nM) caused concentration-dependent contractile effects only on the longitudinal muscle, antagonized by the V1 receptor antagonist, V-1880. AVP-induced effect was not modified by tetrodotoxin, atropine and indomethacin. Contractile response to AVP was…

Postnatal development of the dopaminergic signaling involved in the modulation of intestinal motility in mice

Background:Since antidopaminergic drugs are pharmacological agents employed in the management of gastrointestinal motor disorders at all ages, we investigated whether the enteric dopaminergic system may undergo developmental changes after birth.Methods:Intestinal mechanical activity was examined in vitro as changes in isometric tension.Results:In 2-d-old (P2) mice, dopamine induced a contractile effect, decreasing in intensity with age, replaced, at the weaning (day 20), by a relaxant response. Both responses were tetrodotoxin (TTX)-insensitive. In P2, dopaminergic contraction was inhibited by D1-like receptor antagonist and mimicked by D1-like receptor agonist. In 90-d-old (P90) mice, the …

"In medio stat virtus": Concentration-dependent effects of GABA on colonic motor patterns in mice

BACKGROUND AND AIMS: In the enteric nervous system, GABA (gamma amino butyric acid) has been shown to modulate neuronal activity via activation of different GABAergic receptors. The consequences of this modulation remain poorly understood and depend on the region of the gastrointestinal (GI) tract or on the animal species examined. Although several studies have been addressed the role of GABA as neuromodulator in the upper part of GI tract, accumulating data suggest that it may play a key role also in GI distal tract function in health and disease. Therefore, the aim of this study was to investigate the role of GABA in both spontaneous and electrically-evoked contractions and in the perista…

INVOLVEMENT OF GUANINE-BASED PURINES IN THE MODULATION OF CHOLINERGIC TRANSMISSION IN MOUSE COLONIC PREPARATIONS

AT1 receptors mediate contractile effects of Angiotensin II on mouse colon

Angiotensin II (Ang II) is a potent smooth muscle contractile neurohumoral agonist via interaction with AT1 and AT2 receptors. Although these receptors are well expressed in the gut, very little research has been devoted to analysed the physiological role played by Ang II (and its receptors) in the regulation of gastrointestinal motility. The effects of Ang II on mouse proximal and distal colon contractility, the receptor subtypes involved were investigated in vitro, using the organ bath technique. Longitudinally-oriented segments from mouse proximal and distal colon displayed ongoing contractile activity, characterized by phasic contractions. Ang II induced a concentration-dependent muscul…

ANALISI DEI MECCANISMI DI CONTROLLO DELLA MOTILITA’ GASTROINTESTINALE DA PARTE DI ORMONI COINVOLTI NEL BILANCIO IDRICO-SALINO

Opposite role played by GABAA and GABAB receptors in the modulation of peristaltic activity in mouse distal colon.

We investigated the role of GABA on intestinal motility using as model the murine distal colon. Effects induced by GABA receptors recruitment were examined in whole colonic segments and isolated circular muscle preparations to analyze their influence on peristaltic reflex and on spontaneous and neurally-evoked contractions. Using a modified Trendelenburg set-up, rhythmic peristaltic contractions were evoked by gradual distension of the colonic segments. Spontaneous and neurally-evoked mechanical activity of circular muscle strips were recorded in vitro as changes in isometric tension. GABA, at low concentrations (10-50 µM), potentiated peristaltic activity and the neural cholinergic contrac…

Angiotensin II contractile effects in mouse colon: role for pre- and post-junctional AT1A receptors

Aim This study investigates whether a local renin–angiotensin system (RAS) exists in mouse colon and whether angiotensin II (Ang II) may play a role in the regulation of the contractile activity. Methods Isometric recordings were performed in vitro on the longitudinal muscle of mouse proximal and distal colon. Transcripts encoding for RAS components were investigated by RT-PCR. Results Ang II caused, in both preparations, a concentration-dependent contractile effect, antagonized by losartan, AT1 receptor antagonist, but not by PD123319, AT2 receptor antagonist. The combination of losartan plus PD123319 caused no change on the Ang II-induced contraction than losartan alone. Tetrodotoxin, neu…

Pharmacological characterization of uracil nucleotide-preferring P2Y receptors modulating intestinal motility: a study on mouse ileum.

We investigated the possible modulation of the intestinal contractility by uracil nucleotides (UTP and UDP), using as model the murine small intestine. Contractile activity of a mouse ileum longitudinal muscle was examined in vitro as changes in isometric tension. Transcripts encoding for uracil-sensitive receptors was investigated by RT-PCR. UDP induced muscular contractions, sensitive to PPADS, suramin, or MRS 2578, P2Y(6) receptor antagonist, and mimicked by PSB 0474, P2Y(6)-receptor agonist. UTP induced biphasic effects characterized by an early inhibition of the spontaneous contractile activity followed by muscular contraction. UTP excitatory effects were antagonized by PPADS, suramin,…

Adenosine negatively regulates duodenal motility in mice: role of A1 and A2a receptors .

DEFECTS IN DOPAMINERGIC PATHWAY AFFECT CONTRACTILITY OF COLON FROM HYPOXANTHINE-GUANINE PHOSPHORIBOSYLTRANSFERASE (HPRT) KNOCKOUT MICE.

Lesch-Nyhan disease is an X-linked neurobehavioral and metabolic disorder caused by lack of hypoxanthine phosphoribosyltransferase (HPRT), a housekeeping enzyme responsible for recycling purines. The mechanisms underlying the neuropathology are not well understood, but the main neurochemical defect, in central nervous system, is linked to a dysfunction of dopaminergic pathway. In the enteric nervous system the dopaminergic nerves are a subset neurons of regulating gut motility, thus we investigated possible changes in colonic motility of HPRT ¯mice related to the dopaminergic control. We evaluated, in vitro, the mechanical activity of circular muscle strips from wild type and HPRT – mouse c…

Activation of angiotensin II type 1 receptors and contractile activity in human sigmoid colon in vitro.

We propose and validate a non-invasive method that enables accurate detection of the discharge times of a relatively large number of motor units during excitatory and inhibitory reflex stimulations. HDsEMG and intramuscular EMG (iEMG) were recorded from the tibialis anterior muscle during ankle dorsiflexions performed at 5%, 10%, and 20% of the maximum voluntary contraction (MVC) force, in 9 healthy subjects. The tibial nerve (inhibitory reflex) and the peroneal nerve (excitatory reflex) were stimulated with constant current stimuli. In total, 416 motor units were identified from the automatic decomposition of the HDsEMG. The iEMG was decomposed using a state-of-the-art decomposition tool a…

Guanine-based purines affects the enteric cholinergic neurotransmission via a mechanism not involving membrane receptors

Increasing evidence indicate that guanine-based purines, known as modulators of intracellular processes, can exert extracellular effects, raising the possibility of the existence of specific receptors for these compounds. We investigated if guaninebased purine receptors may be present in the rodent gastrointestinal tract modulating intestinal contractility, as the well known adenine-based purine receptors. Experiments were performed in vitro recording spontaneous and neurally-evoked contractile activity, as changes in isometric tension, in mouse distal colon circular muscle. Guanosine up to 3 mM or guanine up to 1 mM, did not affect the spontaneous mechanical activity, but they significantl…

GABA & “LITTLE BRAIN”: RUOLO EMERGENTE NEL CONTROLLO DELLA MOTILITÀ INTESTINALE

L’acido gamma-ammino butirrico (GABA) è ampiamente riconosciuto come principale neurotrasmettitore inibitore nel sistema nervoso centrale dei mammiferi. Tuttavia numerose evidenze sperimentali suggeriscono una sua azione anche a livello del sistema nervoso enterico (o “little brain”), sezione del sistema nervoso periferico deputata al controllo della funzionalità del tratto gastrointestinale (GI). Dal momento che, ad oggi, gli effetti del GABA rimangono ancora non chiari e sembrerebbero dipendere dalla porzione del tratto GI considerata o dal modello animale esaminato, lo scopo di questo lavoro è stato quello di studiare l’effetto del GABA sulla contrattilità della muscolatura circolare del…

POSTNATAL MATURATION OF SEROTONIN SIGNALING SYSTEM IN MOUSE DUODENUM

BACKGROUND AND AIMS: A plethora of study in animal neurodevelopmental models demonstrate that in central nervous system (CNS) temporal differences occur in the maturation of different neurotransmitter systems (Goldman-Rakic & Brown, 1982, Ehrlich et al., 2013). Although significant advances have been made in understanding the modifications in CNS, only primarily descriptive studies about the changes taking place in enteric nervous system (ENS), main regulator of gastrointestinal (GI) functions, have been underway. As the other organ systems, digestive system is still developing and maturing after birth and thus it is possible to speculate that the changes in the chemical coding of ENS may o…

POSTNATAL DEVELOPMENT OF THE 5-HYDROXYTRYPTAMINE (5-HT) SIGNALING SYSTEM IN THE MOUSE

POSTNATAL DEVELOPMENTAL CHANGES IN ENTERIC DOPAMINERGIC SYSTEM

The postnatal period is a key period of life, characterized by the maturation of various organs and in particular of the gut. Currently, we have a poor understanding of the development of neurological and endocrine factors that control intestinal motility. Such knowledge can provide indications about the potency, efficacy, or therapeutic range of a drug in premature infants. Dopaminegic antagonists are often used as prokinetic drugs to treat impaired GI propulsion, although the role of the enteric dopaminergic system in the control of intestinal motility in neonatal vs adult has not been adequately addressed. In this view the aim of this study, was to examine, the functionality of the dopam…

Can guanine-based purines be considered modulators of intestinal motility in rodents?

Adenine-based purines play a pivotal role in the control of gastrointestinal motility in rodents. Recently, guanine-based purines have been also shown to exert extracellular effects in the central nervous system raising the possibility of the existence of distinct receptors for guanine-based purines. Thus, it seems likely to speculate that also guanine-based purines may play a role in the modulation of the intestinal contractility. Spontaneous and neurally-evoked mechanical activity was recorded in vitro as changes in isometric tension in circular muscle strips from mouse distal colon. Guanosine up to 3 mM or guanine up to 1 mM failed to affect the spontaneous mechanical activity, but reduc…

Dopaminergic signaling in mouse duodenum and postanatal developmental changes