Regional variations in neurokinin receptor subtype contributions to muscularis mucosae and epithelial function in rat colon

Infusion of HIV-1 Nef-expressing astrocytes into the rat hippocampus induces enteropathy and interstitial pneumonitis and increases blood-brain-barrier permeability

Even though HIV-1 replication can be suppressed by combination antiretroviral therapy (cART) inflammatory processes still occur, contributing to comorbidities. Comorbidities are attributed to variety of factors, including HIV-1 mediated inflammation. Several HIV-1 proteins mediate central nervous system (CNS) inflammation, including Nef. Nef is an early HIV-1 protein, toxic to neurons and glia and is sufficient to cause learning impairment similar to some deficits observed in HIV-1 associated neurocognitive disorders. To determine whether hippocampal Nef expression by astrocytes contributes to comorbidities, specifically peripheral inflammation, we infused Sprague Dawley rats with GFP- (control) or Nef-transfected astrocytes into the right hippocampus. Brain, lung, and ileum were collected postmortem for the measurement of inflammatory markers. Increased blood-brain-barrier permeability and serum IL-1β levels were detected in the Nef-treated rats. The lungs of Nef-treated rats demonstrated leukocyte infiltration, macrophage upregulation, and enhanced vascular permeability. Ileal tissue showed reactive follicular lymphoid hyperplasia, increased permeability and macrophage infiltration. The intracerebroventricular application of IL-1 receptor antagonist reduced infiltration of immune cells into ileum and lung, indicating the important role of IL-1β in mediating the spread of inflammation from the brain to other tissues. This suggests that localized expression of a single viral protein, HIV-1 Nef, can contribute to a broader inflammatory response by upregulation of IL-1β. Further, these results suggest that Nef contributes to the chronic inflammation seen in HIV patients, even in those whose viremia is controlled by cART.

Immunohistochemical expression of SP-NK-1R-EGFR pathway and VDR in colonic inflammation and neoplasia

AIM: To determine the expression of neurokinin-1 receptor (NK-1R), phosphorylated epidermal growth factor receptor (pEGFR), cyclooxygenase-2 (Cox-2), and vitamin D receptor (VDR) in normal, inflammatory bowel disease (IBD), and colorectal neoplasia tissues from Puerto Ricans.

METHODS: Tissues from patients with IBD, colitis-associated colorectal cancer (CAC), sporadic dysplasia, and sporadic colorectal cancer (CRC), as well as normal controls, were identified at several centers in Puerto Rico. Archival formalin-fixed, paraffin-embedded tissues were de-identified and processed by immunohistochemistry for NK-1R, pEGFR, Cox-2, and VDR. Pictures of representative areas of each tissues diagnosis were taken and scored by three observers using a 4-point scale that assessed intensity of staining. Tissues with CAC were further analyzed by photographing representative areas of IBD and the different grades of dysplasia, in addition to the areas of cancer, within each tissue. Differences in the average age between the five patient groups were assessed with one-way analysis of variance and Tukey-Kramer multiple comparisons test. The mean scores for normal tissues and tissues with IBD, dysplasia, CRC, and CAC were calculated and statistically compared using one-way analysis of variance and Dunnett’s multiple comparisons test. Correlations between protein expression patterns were analyzed with the Pearson’s product-moment correlation coefficient. Data are presented as mean ± SE.

RESULTS: On average, patients with IBD were younger (34.60 ± 5.81) than normal (63.20 ± 6.13, P < 0.01), sporadic dysplasia (68.80 ± 4.42, P < 0.01), sporadic cancer (74.80 ± 4.91, P < 0.001), and CAC (57.50 ± 5.11, P < 0.05) patients. NK-1R in cancer tissue (sporadic CRC, 1.73 ± 0.34; CAC, 1.57 ± 0.53) and sporadic dysplasia (2.00 ± 0.45) were higher than in normal tissues (0.73 ± 0.19). pEGFR was significantly increased in sporadic CRC (1.53 ± 0.43) and CAC (2.25 ± 0.47) when compared to normal tissue (0.07 ± 0.25, P < 0.05, P < 0.001, respectively). Cox-2 was significantly increased in sporadic colorectal cancer (2.20 ± 0.23 vs 0.80 ± 0.37 for normal tissues, P < 0.05). In comparison to normal (2.80 ± 0.13) and CAC (2.50 ± 0.33) tissues, VDR was significantly decreased in sporadic dysplasia (0.00 ± 0.00, P < 0.001 vs normal, P < 0.001 vs CAC) and sporadic CRC (0.47 ± 0.23, P < 0.001 vs normal, P < 0.001 vs CAC). VDR levels negatively correlated with NK-1R (r = -0.48) and pEGFR (r = -0.56) in normal, IBD, sporadic dysplasia and sporadic CRC tissue, but not in CAC.

CONCLUSION: Immunohistochemical NK-1R and pEGFR positivity with VDR negativity can be used to identify areas of sporadic colorectal neoplasia. VDR immunoreactivity can distinguish CAC from sporadic cancer.

Role of tachykinin receptors in the modulation of colonic peristaltic activity in mice

Tachykinins are important mediators of neuroneuronal and neuromuscular transmission in the gastrointestinal tract, however their contribution to colonic peristalsis in mice remains unclear. Therefore, our aim was to characterise the functional role of tachykinins in mediating peristalsis by evaluating the effect of selective tachykinin NK(1), NK(2) and NK(3) receptor agonists and antagonists on in vitro colonic peristaltic activity in mice. Using a modified Trendelenburg set-up, gradual distension of proximal and distal colonic segments evoked rhythmic, aborally migrating contractions. Peristaltic activity was assessed by quantifying the amplitude and interval of the corresponding pressure waves. Stimulation of NK(1) receptors showed regional differences as both the pressure amplitude and interval were enhanced in the distal colon without affecting peristalsis proximally. Blockade of NK(1) receptors reduced the peristaltic pressure amplitude in the proximal and distal colon while the interval was not significantly altered. NK(2) receptor stimulation resulted in a modest enhancement of the amplitude in proximal and distal segments and a slightly prolonged interval distally. Blockade of NK(2) receptors reduced the peristaltic pressure amplitude and interval in the distal colon. NK(3) receptor stimulation significantly augmented the amplitude in both segments and prolonged the interval distally. However, NK(3) receptor blockade had no effect on peristaltic activity. In conclusion, tachykinins contribute to colonic peristalsis in mice by acting mainly on NK(1) and NK(2) receptors and their effects show a proximal-to-distal gradient. NK(3) receptors might play a role in conditions of excess tachykinin release but appear not to be involved under the conditions of the present study.

Adrenergic responses of rat colonic muscularis mucosae

We have investigated adrenoceptor-mediated responses of muscularis mucosae from the proximal, mid and distal regions of the rat colon. Noradrenaline-induced relaxations of the muscularis mucosae in each region were unaffected by atenolol, butoxamine or propranolol, but they were attenuated by the selective β3-adrenoceptor antagonist cyanopindolol. The β3-adrenoceptor agonist CL216343 elicited concentration-dependent relaxation of the muscularis mucosae in all regions of the colon. Isoprenaline, a non-selective β-adrenoceptor agonist, evoked concentration-dependent relaxations of the muscularis mucosae in all regions, but only in the proximal colon were these significantly larger than the maximum noradrenaline-induced relaxation. The α1-adrenoceptor agonist methoxamine caused large contractions of the proximal colonic muscularis mucosae. When proximal tissue was pretreated with phentolamine, an α1-adrenoceptor antagonist, maximal noradrenaline- and isoprenaline-induced relaxations did not differ significantly. Although the mid colonic muscularis mucosae was also found to possess excitatory α1-adrenoceptors, these were associated with small contractions and did not modify the muscle's inhibitory responses to noradrenaline. Distal colonic muscularis mucosae lacked excitatory adrenoceptors and only responded to noradrenaline with β3-adrenoceptor-mediated relaxations. No evidence was obtained for functional α2-adrenoceptors on the muscularis mucosae in any region of the rat colon. These data demonstrated that noradrenaline-induced relaxation of the rat colonic muscularis mucosae was mediated via β3-adrenoceptors throughout, but in the proximal region this was modified by concurrent excitatory α1-adrenoceptor activation. Based upon these observations it appeared unlikely that noradrenaline-induced relaxation of rat colonic muscularis mucosae would be functionally linked to the secretory responses of the corresponding mucosa during periods of increased sympathetic activity.

Experimental endometriosis in the rat is correlated with colonic motor function alterations but not with bacterial load

Endometriosis commonly presents with symptoms that mimic chronic gastrointestinal disorders. The authors used the autotransplantion model of endometriosis in rats to investigate the possible underlying mechanisms. After the rats were killed, the presence of endometriotic vesicles, colonic inflammation, and white blood cell (WBC) numbers in the peritoneal fluid was determined. Sections of colon and of jejunum were collected for measurement of myeloperoxidase (MPO) activity and bacterial counts, and isometric recording in response to acetylcholine was measured in segments of longitudinal and circular smooth muscle. Experimental animals had significantly more colonic damage, MPO activity, and WBC numbers than controls did. There was no significant difference in the total bacterial load; however, experimental animals demonstrated an increased tension in the longitudinal muscle, which correlated with WBC numbers and colonic damage. In summary, this study presents evidence for a significant effect of peritoneal endometriosis on colonic function and integrity, which may help explain the gastrointestinal symptoms associated with this disease.

Chronic inflammation alters the contribution of neurokinin receptor subtypes to epithelial function in rat colon

We have previously shown that neurokinin-1 (NK1) receptors predominantly mediate substance P-induced secretion of the non-inflamed rat colonic mucosa in vitro with a gradient in the magnitude of these responses. The aim of this study was to examine the effects of chronic inflammation on the contributions of different neurokinin receptor subtypes to colonic mucosal secretion. Colitis was induced by the intracolonic administration of 2,4,6-trinitrobenzene sulfonic acid in rats, reactivated 6 weeks later. Segments of proximal, mid- and distal colon were stripped of muscularis propria and mounted in Ussing chambers for measurement of short-circuit current. Use of selective agonists suggests that in the chronically inflamed rat colon NK1 receptors play a greater role in neurokinin-mediated mucosal secretion than do either NK2 or NK3. Selective antagonism implies that this is region-specific, with the inflammatory process altering the relative contribution of the neurokinin receptor subtypes within each region of the rat colon.