Nitric oxide-related neural components in the rat small intestine after transplantation

Induction of neuronal nitric oxide synthase by sympathetic denervation is mediated via alpha 2-adrenoceptors in the jejunal myenteric plexus

Nitric oxide (NO) is an important nonadrenergic, non-cholinergic (NANC) inhibitory neurotransmitter in the gastrointestinal tract. In previous studies, neuronal nitric oxide synthase (nNOS) in the jejunal myenteric plexus, a key enzyme responsible for the release of NO, has been demonstrated to increase after splanchinic ganglionectomy (sympathetic nerve transection). The alpha2-adrenoceptor is known to be one of the most important receptors which controls intestinal motility. In the present study, we examined the effect of application of the alpha2-adrenoceptor agonist, clonidine hydrochloride, on nNOS expression in the rat jejunal myenteric plexus after splanchinic ganglionectomy. Clonidine (0.1-1 mg/kg, i.p.) or saline was administered for 5 days after the splanchinic ganglionectomy. The nNOS expression and nNOS mRNA were detected by immunohistochemistry and in situ hybridization for nNOS mRNA, respectively. In the rats treated with vehicle after the splanchinic ganglionectomy, nNOS expression in the myenteric plexus significantly increased compared with sham-operated rats. The increases in nNOS protein and mRNA after splanchinic ganglionectomy were significantly reversed by clonidine treatment. Clonidine-treated naive rats showed no difference in nNOS expression compared with sham-operated rats. These data suggest that nNOS expression in the jejunal myenteric plexus after splanchinic ganglionectomy is regulated by the alpha2-adrenoceptor and that the alpha2-adrenoceptor may play an important role in abnormal intestinal motility following splanchinic ganglionectomy in rat jejunum.

Plasticity in the enteric nervous system

Enteric ganglia can maintain integrated functions, such as the peristaltic reflex, in the absence of input from the central nervous system, which has a modulatory role. Several clinical and experimental observations suggest that homeostatic control of gut function in a changing environment may be achieved through adaptive changes occurring in the enteric ganglia. A distinctive feature of enteric ganglia, which may be crucial during the development of adaptive responses, is the vicinity of the final effector cells, which are an important source of mediators regulating cell growth. The aim of this review is to focus on the possible mechanisms underlying neuronal plasticity in the enteric nervous system and to consider approaches to the study of plasticity in this model. These include investigations of neuronal connectivity during development, adaptive mechanisms that maintain function after suppression of a specific neural input, and the possible occurrence of activity-dependent modifications of synaptic efficacy, which are thought to be important in storage of information in the brain. One of the applied aspects of the study of plasticity in the enteric nervous system is that knowledge of the underlying mechanisms may eventually enable us to develop strategies to correct neuronal alterations described in several diseases.

Extrinsic neural control of nitric oxide synthase expression in the myenteric plexus of rat jejunum

1. The role of extrinsic innervation in the expression of nitric oxide synthase (NOS) in the myenteric plexus remains unknown. In this study, we investigated the effect of extrinsic denervation on NOS expression in rat jejunum. 2. NG-nitro-L-arginine methyl ester (L-NAME)-sensitive non-adrenergic, non-cholinergic (NANC) relaxations induced by transmural nerve stimulation were significantly increased in muscle strips obtained from rats treated with splanchnic ganglionectomy or 6-hydroxydopamine (6-OH-dopamine). Truncal vagotomy or treatment of the coeliac ganglia with capsaicin did not significantly affect NANC relaxations. 3. The number of NOS-immunopositive cells in the myenteric plexus was significantly increased in tissues obtained from rats treated with splanchnic ganglionectomy or 6-OH-dopamine. 4. Western blot analysis and Northern blot analysis showed a significant increase in the density of the immunoreactive NOS band and the NOS mRNA band, respectively, of the tissues obtained from rats treated with splanchnic ganglionectomy or 6-OH-dopamine. 5. Truncal vagotomy or treatment of the coeliac ganglia with capsaicin did not significantly affect the density of NOS band or NOS mRNA band. 6. It is concluded that neuronal NOS expression in the myenteric plexus is independent of vagus nerve and is negatively regulated by the splanchnic nerves in the rat small intestine.