The enteric nervous system, the "second" brain, is an independent nervous system that structurally resembles the "first" brain. Appropriate rectal distension elicits rectal (R-R) reflex contractions and simultaneous internal anal sphincter (R-IAS) reflex relaxations that together comprise the defecation reflex. The enteric nervous system, pelvic nerves and lumbar colonic nerves control both reflexes. Using the plasticity of enteric nervous pathways, a new therapy for repairing enteric neural dysfunction could be developed. In vivo experiments were performed on guinea pigs anesthetized with ethyl carbamate. We performed either a lower anterior resection as used for rectal cancer, without damaging the extrinsic nerves or a resection of a 2-cm segment of distal colon, 30 mm orally from the anal verge, with subsequent end-to-end one layer anastomosis of the exposed ends. The recovery of the defecation reflex was found to be the same in both the rectal transection and distal colonic resection procedures. Eight weeks after sectioning the intrinsic reflex nerve pathways in the rectum, the defecation reflex recovered to control levels, accompanied by a regeneration of the reflex pathways. The 5-HT4 receptor agonist, mosapride (0.5 and 1.0 mg/kg), significantly (P<0.01) enhanced the recovered defecation reflex at this stage. Two weeks after local treatment with brain-derived neurotrophic factor (BDNF: 10-6 g/ml) at the rectal anastomotic site, the R-IAS reflex relaxations recovered and some bundles of fine nerve fibers were able to be seen interconnecting the oral and anal ends of the myenteric plexus. Also surprisingly, new neurons were found to have generated from neural stem cells at the anastomotic ends. These new neurons had constructed mature enteric neural networks including ganglionic-like structures eight weeks after surgery. These results revealed the plasticity of enteric neurons, allowing the proposal of a new therapy for repairing enteric neural dysfunction at least after surgery.
Although irritable bowel syndrome (IBS) is the most common gastrointestinal disease and is found in up to 50% of patients referred to gastroenterologists, its pathogenesis remains unexplained. Lately most attention has been focused on visceral hypersensitivity related to dysfunction of the autonomic nervous system. Although there have been many reports regarding the autonomic nervous system in IBS patients, the results have not always been consistent. In many studies, increased sympathetic nervous system activity and decreased parasympathetic nervous system activity have been the most frequently noted differences when IBS patients are compared with healthy controls. There are also some differences among IBS symptom subgroups and some differences between men and women. Data from previous studies have been inconsistent, with complicating factors resulting in difficulties in classification and the possibility of multiple physiological pathways for a similar symptom picture. Further studies based on the Rome III criteria are required to evaluate whether or not autonomic functions significantly differ from each other. However, although there are many methods of measurement for evaluation of the autonomic nervous system, there are few of these methods that are not only accurate but also cost-effective, non-invasive, and easy to perform. Recently, we developed a new method with the abovementioned advantages for measuring fingertip blood flow in evaluating the autonomic nervous system by continuous-wave Doppler sonography. Using this method, we found that abnormal fingertip blood flow responses suggested the presence of excess sympathetic activity.
5-Hydroxytryptamine (5-HT) released from enterochromaffin cells regulates gastrointestinal function in either an excitatory or inhibitory manner. 5-HT3 and 5-HT4 receptors in the gut have been the focus of clinical studies on the management of gastrointestinal motility disorders. 5-HT stimulates intestinal propulsive reflexes through 5-HT4 receptors. 5-HT4 receptor agonists can stimulate upper or lower gut motility, depending on their selectivity and affinity. In the guinea pig colon, the distribution of 5-HT4 receptors in the myenteric plexus and circular muscle layer differs between the proximal and distal regions. 5-HT stimulates intestinal motility via excitatory neurons while causing relaxation of the circular muscle via 5-HT4 receptors. In the light of these findings on the distribution of 5-HT4 receptors, the effects of receptor agonist compounds could vary depending on the species of experimental animal and the anatomical region studied.
Globally, primary dysmenorrhoea is one of the most frequent gynaecological disorders in young women. It is associated with increased uterine tone, and exaggerated contractility of uterine smooth muscles. In many rural African communities, a number of medicinal plants, including Psidium guajava Linn. (family: Myrtaceae), are used traditionally for the management, control and/or treatment of primary dysmenorrhoea. The present study was, therefore, undertaken to examine the spasmolytic effect of Psidium guajava leaf aqueous extract (PGE) on isolated, spontaneously-contracting and oestrogen-dominated, quiescent uterine horns of healthy, young adult, female Wistar rats. Graded, escalated concentrations of PGE (0.5-4.0 mg/ml) produced concentration-dependent and significant inhibitions of the amplitude of spontaneous phasic contractions of the isolated rat uterine horn preparations. In a concentration-related manner, PGE also significantly inhibited or abolished contractions produced by acetylcholine (ACh, 0.5-8.0 μg/ml), oxytocin (0.5-4.0 μU), bradykinin (2.5-10 ng/ml), carbachol (CCh, 0.5-8.0 μg/ml) or potassium chloride (K+, 10-80 mM) in quiescent uterine horn preparations isolated from the oestrogen-dominated rats. The spasmolytic effect of PGE observed in the present study lends pharmacological support to the traditional use of `guava' leaves in the management, control and/or treatment of primary dysmenorrhoea in some rural African communities.
Previous studies have established the hepatoprotective, gastroprotective, hypolipidemic and hypoglycemic effects of kolaviron (KV), a biflavonoid complex from Garcinia kola seeds. In this study, we investigated the mechanisms involved in the vasorelaxant effects of KV in isolated superior mesenteric arteries from normotensive rats. KV (1, 10, 30, 100, 300, 500 and 1,000 μg/ml) concentration-dependently inhibited the contractions induced by phenylephrine (PHE) (10 μM) and KCl (80 mM) in both endothelium-intact (Emax = 58.3 ± 1.7% and 51.4 ± 1.3%, respectively) and -denuded rings (Emax = 59.3 ± 5.5% and 64.3 ± 2.4%, respectively). Furthermore, KV reduced CaCl2-induced contraction in Ca2+-free medium containing KCl 60 mM, thus acting as a Ca2+-antagonist. In addition, KV inhibited the transient contraction by PHE in Ca2+-free medium containing EGTA, suggesting a possible action on the release of intracellular Ca2+ via the inositol-1,4,5-triphosphate (IP3) pathway. KV is not a specific α-adrenoceptor blocker, since it also caused a concentration-dependent inhibition of contractile responses to KCl, suggesting that KV also blocks the L-type Ca2+-channel. As a Ca2+ antagonist, KV (100 μg/ml) potentiates the relaxant effects of nifedipine in denuded rings (Emax = 97.6 ± 1.2%; control = 75.1 ± 3.0%, P<0.05). Also, the vasorelaxation induced by KV was significantly inhibited after pre-treatment of the denuded rings with 4-aminopyridine (4-AP) 1 mM, a selective blocker of voltage-dependent K+ (Kv) channels and, tetraethylammonium (TEA) 1 mM or charybdotoxin (ChTX) 0.1 μM, non-selective blockers of large and intermediate conductance Ca2+-activated K+ (BKCa) channels. In contrast, neither glibenclamide (10 μM), BaCl2 (1 mM) nor apamin (0.1 μM), blockers of KATP, KIR and SKCa channels, respectively affected the KV-induced vasorelaxation. In conclusion, our results provide functional evidence that the vasorelaxant effects by KV involve extracellular Ca2+ influx blockade, inhibition of intracellular Ca2+ release and the opening of K+ channels sensitive to 4-AP and ChTX with a resultant membrane hyperpolarization/ repolarization.
The PKC family has been implicated in a wide range of biological response in a number of different cellular systems. Although the functions of PKC have been vigorously studied using pharmacological tools, there is little information about the expression pattern of its isoforms in human bronchial smooth muscle cells (hBSMCs). In the present study, RT-PCR and immunoblot analyses were carried out to detect all the PKC isoforms expressed in cultured normal hBSMCs. The RT-PCR analyses revealed that mRNAs of the known PKC isoforms except for PKCγ and θ were detected in the hBSMCs. Among them, protein expressions of the isoforms except for PKCη and μ were also detected by immunoblottings. Thus, the present study clearly demonstrated the expression of multiple PKC isoforms, i.e., PKCα, β, δ, ε, ζ and ι in hBSMCs.
To explore the possible role of heat shock protein 20 (HSP20) -linked regulation of actin-myosin interaction in living vascular smooth muscle contraction, we studied the effects of HSP20p and TnIp, synthetic peptides originating from an actin tropomyosin binding region of human heat shock protein 20 [residues 110-121; GFVAREFHRRYR] and that of rabbit cardiac troponin I [residues 136-147; GKFKRPTLRRVR], respectively, on the active stress and phosphorylation level of myosin regulatory light chain (MLC20) during relaxation of skinned (cell membrane permeabilized) preparations from "tonic" carotid artery and "phasic" taenia cecum from guinea pig. Active stress of the skinned preparations, resulting from actin-myosin interaction, biphasically decayed following Ca2+ removal (relaxation). Decay of MLC20 phosphorylation level by Ca2+ removal was much faster than active stress in an exponential manner. In skinned carotid artery, HSP20p did neither affect relaxation time course nor MLC20 dephosphorylation, whereas, in skinned taenia cecum, the peptide slowed relaxation time course through inhibition of MLC20 dephosphorylation and slowing "latch"-bridge dissociation. On the other hand, TnIp accelerated relaxation time course without affecting MLC20 dephosphorylation in both skinned carotid artery and skinned taenia cecum. Our present results suggest that, HSP20p slows the relaxation processes through intracellular regulatory mechanisms such as Rho A/Rho-kinase mediated pathways, which are known to be dominant in "phasic" smooth muscles but to be recessive in "tonic" smooth muscles.
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