Hyperglycaemia-Induced Downregulation in Expression of nNOS Intramural Neurons of the Small Intestine in the Pig

Abstract

Diabetic autonomic peripheral neuropathy (PN) involves a broad spectrum of organs. One of them is the gastrointestinal (GI) tract. The molecular mechanisms underlying the pathogenesis of digestive complications are not yet fully understood. Digestion is controlled by the central nervous system (CNS) and the enteric nervous system (ENS) within the wall of the GI tract. Enteric neurons exert regulatory effects due to the many biologically active substances secreted and released by enteric nervous system (ENS) structures. These include nitric oxide (NO), produced by the neural nitric oxide synthase enzyme (nNOS). It is a very important inhibitory factor, necessary for smooth muscle relaxation. Moreover, it was noted that nitrergic innervation can undergo adaptive changes during pathological processes. Additionally, nitrergic neurons function may be regulated through the synthesis of other active neuropeptides. Therefore, in the present study, using the immunofluorescence technique, we first examined the influence of hyperglycemia on the NOS- containing neurons in the porcine small intestine and secondly the co-localization of nNOS with vasoactive intestinal polypeptide (VIP), galanin (GAL) and substance P (SP) in all plexuses studied. Following chronic hyperglycaemia, we observed a reduction in the number of the NOS-positive neurons in all intestinal segments studied, as well as an increased in investigated substances in nNOS positive neurons. This observation confirmed that diabetic hyperglycaemia can cause changes in the neurochemical characteristics of enteric neurons, which can lead to numerous disturbances in gastrointestinal tract functions. Moreover, can be the basis of an elaboration of these peptides analogues utilized as therapeutic agents in the treatment of GI complications.

Neurochemical Plasticity of nNOS-, VIP- and CART-Immunoreactive Neurons Following Prolonged Acetylsalicylic Acid Supplementation in the Porcine Jejunum

“…In this study, we have shown that nNOS occurs in relatively high proportion of enteric neurons, which is in agreement with previous studies, where nitrergic structures have been noted in different mammalian species such as pigs [20,38], guinea pigs [39], mice [39,40] rats [41,42] and humans [43]. The current findings are congruent with the available literature, where more numerous NOS-positive neurons were found in the myenteric plexus [22,44]. Less than 10 % of neurons in both submucous plexuses (outer and inner) were immunoreactive to nNOS, which is similar to previous studies conducted in pigs [22].…”

“…In turn, the populations of nNOS-expressing nerve cells in both the outer and the inner submucous plexuses were also significantly decreased but to a lesser extent than in the MP. Reduction of nNOS-IR enteric neurons was previously observed during diabetes [44], Chagas' disease [45], Hirschsprung's disease [46], as well as ischemia [22]. In contrast, an increase in the proportions of nNOS-IR enteric intramural neurons was found in the swine small intestine during proliferative enteropathy [47], ileitis [22], inflammatory bowel disease (IBD) [48].…”

“…Previous studies have shown neuroprotective properties of NO in the enteric nervous system, and data on the neurochemical adaptation of the ENS are well established [44]. The main regulator of nNOS activity is free cytosolic Ca 2+ , which stimulates nNOS during its interaction with calmodulin.…”

Effect of Streptozotocin-Inducted Diabetes on the Pathophysiology of Enteric Neurons in the Small Intestine Based on the Porcine Diabetes Model

“…After a week, diabetes was induced, as previously described [35][36][37]. Streptozotocin (STZ) (Sigma-Aldrich, St Louis, MO, USA, S0130), 150 mg/kg of body weight, was dissolved in a freshly prepared disodium citrate buffer solution (pH = 4.23, 1 g streptozotocin/10 mL solution).…”

“…Since diabetes occurs extremely rarely in pigs, exogenous injection of streptozotocin (STZ) is needed to induce diabetes [35]. After a few days of STZ injections, clear symptoms of diabetes are present [36][37][38][39][40][41]. In this experimental model, the main defining factor of diabetes is chronic hyperglycemia.…”