Tachykinergic neurotransmission is enhanced in duodenum from dystrophic (mdx) mice

Motor dysfunction of the gut in Duchenne muscular dystrophy: A review

BACKGROUND

Duchenne's muscular dystrophy (DMD) is a severe type of hereditary, neuromuscular disorder caused by a mutation in the dystrophin gene resulting in the absence or production of truncated dystrophin protein. Conventionally, clinical descriptions of the disorder focus principally on striated muscle defects; however, DMD manifestations involving gastrointestinal (GI) smooth muscle have been reported, even if not rigorously studied.

PURPOSE

The objective of the present review is to offer a comprehensive perspective on the existing knowledge concerning GI manifestations in DMD, focusing the attention on evidence in DMD patients and mdx mice. This includes an assessment of symptomatology, etiological pathways, and potential corrective approaches. This paper could provide helpful information about DMD gastrointestinal implications that could serve as a valuable orientation for prospective research endeavors in this field. This manuscript emphasizes the effectiveness of mdx mice, a DMD animal model, in unraveling mechanistic insights and exploring the pathological alterations in the GI tract. The gastrointestinal consequences evident in patients with DMD and the mdx mice models are a significant area of focus for researchers. The exploration of this area in depth could facilitate the development of more efficient therapeutic approaches and improve the well-being of individuals impacted by the condition.

TAC3 Gene Products Regulate Brain and Digestive System Gene Expression in the Spotted Sea Bass (Lateolabrax maculatus)

Neurokinin B (NKB) is a member of the tachykinin (tac) family that plays important roles in mammalian growth by modulating prolactin (PRL) synthesis and secretion and causing contraction of the stomach and intestine. However, its potential role in regulating growth of teleosts is less clear. We aimed to explore the role that NKB plays in regulating fish growth using the spotted sea bass (Lateolabrax maculatus) as a model. In the present study, two tac3 and two tacr3 genes were identified in the spotted sea bass. Sequence analysis showed that two tac3 transcripts, tac3a and tac3b, encode four NKBs: NKBa-13, NKBa-10, NKBb-13, and NKBb-10. Expression analysis in different tissues showed that both genes are highly expressed in the brain, stomach and intestine of the spotted sea bass. In situ hybridization indicated that the tac3a and tac3b mRNAs are both localized in several brain regions, such as the telencephalon and hypothalamus, and that tacr3a and tacr3b are localized in the intestinal villus and gastric gland. To investigate the potential role of NKBs in regulating growth, in vitro experiments were performed to detect the effect of NKBs on growth-related gene expression in the brain and brain-gut peptide (BGP)-related genes in the stomach and intestine. NKBb-13 was the most critical ligand in regulating the expression of growth-related genes in the brain and brain-gut peptide (BGP)-related genes in the stomach. The expression of cholecystokinin (cck) was enhanced by NKBa-13, NKBa-10, and NKBb-10 but not NKBb-13 in the intestine. In general, our results showed that NKBs participate in regulating the growth of spotted sea bass.

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

AIM

To analyse the effects of angiotensin II (Ang II) on the contractility of human sigmoid colon, and to characterize the subtype(s) of receptor(s) involved and the related action mechanism.

METHODS

The contractility of sigmoid colon circular muscle strips was recorded isometrically. RT-PCR and immunohistochemistry were used to reveal the eventual existence of a local renin-angiotensin system (RAS) and the distribution of Ang II receptors.

RESULTS

Transcripts encoding for the Ang II type 1 (AT1 ) and the Ang II type 2 (AT2 ) receptor subtypes and for the angiotensin-converting enzyme in the whole-thickness muscular wall were observed. Ang II caused a concentration-dependent contractile response, which is antagonized by losartan, AT1 receptor antagonist, but not by PD123319, AT2 receptor antagonist. The joint application of losartan and PD123319 did not produce any additive effect. The contractile response to Ang II was partially reduced by tetrodotoxin, Na(+) voltage-gated neural channel blocker, and to some extent by SR48968, tachykinin NK2 receptor antagonist. However, hexamethonium, nicotinic receptor antagonist, atropine, cholinergic muscarinic receptor antagonist and SR140333, tachykinin NK1 receptor antagonist, were ineffective. Immunohistochemical analysis showed that AT1 receptors were expressed on the smooth muscle layers and myenteric plexus.

CONCLUSION

Ang II positively modulates the spontaneous contractile activity of human sigmoid colon via activation of post-junctional and pre-junctional AT1 receptors, the latter located on the enteric nerves that modulate the release of tachykinins. The presence of the components of RAS in the human colon suggests that Ang II can be also locally generated to control colonic motility.

In vitro characterization of the effects of rat/mouse hemokinin-1 on mouse colonic contractile activity: a comparison with substance P

Rat/mouse hemokinin-1 (r/m HK-1) has been identified as a member of the tachykinin family and its effect in colonic contractile activity remains unknown. We investigated the effects and mechanisms of actions of r/m HK-1 on the mouse colonic contractile activity in vitro by comparing it with that of substance P (SP). R/m HK-1 induced substantial contractions on the circular muscle of mouse colon. The maximal contractile responses to r/m HK-1 varied significantly among proximal-, mid- and distal-colon, suggesting that the action of r/m HK-1 was region-specific in mouse colon. The contractile response induced by r/m HK-1 is primarily via activation of tachykinin NK(1) receptors leading to activation of cholinergic excitatory pathways and with a minor contribution of NK(2) receptors, which may be on the smooth muscle itself. A direct action on colonic smooth muscles may be also involved. In contrast, SP induced biphasic colonic responses (contractile and relaxant responses) on the circular muscle, in which the contractile action of SP was equieffective with r/m HK-1. SP exerted its contractile effect predominantly through neural and muscular tachykinin NK(1) receptors, but unlike r/m HK-1 did not appear to act via NK(2) receptors. The relaxation induced by SP was largely due to release of nitric oxide (NO) produced via an action on neural NK(1) receptors. These results indicate that the receptors and the activation properties involved in r/m HK-1-induced mouse colonic contractile activity are different from those of SP.

Role for NK(1) and NK(2) receptors in the motor activity in mouse colon

The present study examined the effects induced by endogenous and exogenous activation of NK(1) and NK(2) receptors on the mechanical activity of mouse proximal colon. Experiments were performed in vitro recording the changes in intraluminal pressure from isolated colonic segments. Electrical field stimulation in the presence of atropine and guanethidine produced a small relaxation, followed by nonadrenergic noncholinergic (NANC) contraction. SR140333, NK(1) receptor antagonist, or SR48968, NK(2) receptor antagonist, significantly reduced the contraction, although SR48968 appeared more efficacious. The co-administration of SR140333 and SR48968 virtually abolished the NANC contraction. [Sar(9), Met(O(2))(11)]-substance P, selective NK(1) receptor agonist, induced a concentration-dependent biphasic effect, contraction followed by reduction of the mechanical spontaneous activity. Both effects were antagonized by SR140333, but not by SR48968. [beta-Ala(8)]-neurokinin A (4-10), selective NK(2) receptor agonist, evoked concentration-dependent contraction, which was antagonized by SR48968, but not by SR140333. The contraction induced by [Sar(9), Met(O(2))(11)]-substance P, but not by [beta-Ala(8)]-neurokinin A (4-10), was reduced by tetrodotoxin or atropine, and increased by N(omega)-nitro-L-arginine methyl ester (L-NAME), inhibitor of nitric oxide synthase. The inhibitory effects induced by [Sar(9), Met(O(2))(11)]-substance P were abolished by tetrodotoxin or L-NAME. The results of the present study suggest that in mouse colon both NK(1) and NK(2) receptors are junctionally activated by endogenous tachykinins to cause an additive response. NK(1) receptors appear to be located on cholinergic and on nitrergic neurons as well as on smooth muscle cells, whereas NK(2) receptors seem to be present exclusively on smooth muscle cells.

Plasticity of rat small intestine after removal of a chronic mechanical obstruction

Chronic intestinal obstruction is associated with morphological changes and functional disorders clinically reported and experimentally documented in laboratory animals. In contrast, little is known about the properties of the hypertrophied intestine after removal of the obstruction. In the present study, we removed the ileal obstruction previously applied to the ileum of rats and, after 1 or 2 weeks, studied in vitro the motor responses of de-obstructed segments of intestine to pharmacological or electrical field stimulation (EFS). By 2 weeks after de-obstruction, maximal contractile responses to receptor (acetylcholine) and non-receptor (K(+)) mediated stimuli were comparable in operated and control tissues; furthermore, the loss of sensitivity to nitric oxide (NO) unmasked in obstructed tissues was, after de-obstruction, replaced by supersensitivity to exogenous NO and vasoactive intestinal polypeptide, probably acting through cyclic nucleotide-independent pathways. Despite the complete recovery of smooth muscle responses, neurogenic contractions remained impaired in de-obstructed tissue; however, the equal contribution of cholinergic/peptidergic components to EFS responses could represent a sign of gradual but delayed recovery of enteric neurotransmission.

Altered tachykinergic influence on gastric mechanical activity in mdx mice

This study investigated whether alterations in gastric activity in dystrophic mdx mouse can be attributed to dysfunctions of tachykinins. Endoluminal pressure was recorded and the expression of neuronal nitric oxide synthase (nNOS), NK1 and NK2 neurokinin receptors was investigated by immunohistochemistry. SR48968, NK2 receptor antagonist, but not SR140333, NK1 receptor antagonist, decreased the tone only in mdx gastric preparations. In the presence of N(omega)-nitro-l-arginine methyl ester (l-NAME), inhibitor of NOS, SR48968 reduced the tone also in normal stomach. [Sar(9), Met(O(2))(11)]-SP, agonist of NK1 receptors, caused tetrodotoxin-sensitive relaxations, antagonized by SR140333 or l-NAME, with no difference in the potency or efficacy between normal and mdx preparations. [beta-Ala(8)]-NKA(4-10), an NK2 receptor agonist, induced SR48968-sensitive contractions in both types of preparations, although the maximal response of mdx tissues was significantly lower than normal preparations. Immunohistochemistry demonstrated a consistent reduction of nNOS and NK2 receptor expression in mdx stomach smooth muscle cells and no change in nNOS and NK1 receptor expression in neurones. In conclusion, in mdx stomach the activation of NK2 receptors plays a role in the development of the tone, associated with a reduced NO production by muscular nNOS. The hypo-responsiveness to NK2 receptors could depend on the reduced expression of these receptors.

Differential inhibitory control of circular and longitudinal smooth muscle layers of Balb/C mouse small intestine

We examined the inhibitory mediators acting on each of the longitudinal (LM) and circular muscle (CM) layers of mouse small intestine in the presence of atropine, prazosin and timolol. Nitric oxide (NO) and apamin-sensitive mediators exerted an inhibitory tone on pacing frequency in CM, observed as an increased frequency upon treatment with N-omega-nitro-l-arginine (LNNA) or apamin. This effect was not seen in LM. 1H-(1,2,4)oxadiazolo(4,3-A)quinazoline-1-one (ODQ) abolished the relaxation in response to electric field stimulation (EFS) in LM in a manner similar to LNNA indicating that the inhibitory mediator in this layer in NO acting via soluble guanylate cyclase. On the other hand, in CM neither LNNA nor apamin was capable of reducing the inhibition in response to EFS and their combination left a residual relaxation of 25%. ODQ reduced the EFS-evoked relaxation more effectively than LNNA at higher frequencies indicating that another ODQ-sensitive mediator was active in CM. ODQ also blocked the relaxation to exogenous vasoactive intestinal peptide in CM. In LM, the relaxation due to sodium nitroprusside was equally blocked by ODQ and apamin, while in CM, its effects were only reduced by ODQ and not apamin. These results indicate that there are differences in the inhibitory mediators and the mechanisms of action involved in LM and CM relaxation.

Role of NK1 and NK2 receptors in mouse gastric mechanical activity

1. The aim of the present study was to examine the role of NK1 and NK2 receptors in the control of mechanical activity of mouse stomach. In this view, the motor effects induced by NK1 and NK2 receptor agonists and antagonists were analyzed, measuring motility as intraluminal pressure changes in mouse-isolated stomach preparations. In parallel, immunohistochemical studies were performed to identify the location of NK1 and NK2 receptors on myenteric neurons and smooth muscle cells. 2. Substance P (SP) induced biphasic effects: a contraction followed by relaxation; neurokinin A (NKA) and [beta-Ala8]-NKA(4-10), selective agonist of NK2 receptors, evoked concentration-dependent contractions, whereas [Sar9, Met(O2)11]-SP, selective agonist of NK1 receptors, induced concentration-dependent relaxation. 3. SR48968, NK2 receptor antagonist, did not modify the spontaneous activity and reduced the contractile effects induced by tachykinins without affecting the relaxation. SR140333, NK1 receptor antagonist, did not modify the spontaneous activity and antagonized the relaxant response to tachykinins, failing to affect the contractile effects. 4. The relaxation to SP or to [Sar9, Met(O2)11]-SP was abolished by tetrodotoxin (TTX) and significantly reduced by N(omega)-nitro-L-arginine methyl ester (L-NAME). 5. NK2-immunoreactivity (NK2-IR) was seen at the level of the smooth muscle cells of both circular and longitudinal muscle layers. NK1-immunoreactive (NK1-IR) neurons were seen in the myenteric ganglia and NK1/nNOS double labeling revealed that some neurons were both NK1-IR and nNOS-IR. 6. These results suggest that, in mouse stomach, NK1 receptors, causing relaxant responses, are present on nitrergic inhibitory myenteric neurons, whereas NK2 receptors, mediating contractile responses, are present at muscular level.