Costa M, Dodds KN, Wiklendt L, Spencer NJ, Brookes SJ, Dinning PG. Neurogenic and myogenic motor activity in the colon of the guinea pig, mouse, rabbit, and rat. Am J Physiol Gastrointest Liver Physiol 305: G749 -G759, 2013. First published September 19, 2013 doi:10.1152/ajpgi.00227.2013.-Gastrointestinal motility involves interactions between myogenic and neurogenic processes intrinsic to the gut wall. We have compared the presence of propagating myogenic contractions of the isolated colon in four experimental animals (guinea pig, mouse, rabbit, and rat), following blockade of enteric neural activity. Isolated colonic preparations were distended with fluid, with the anal end either closed or open. Spatiotemporal maps of changes in diameter were constructed from video recordings. Distension-induced peristaltic contractions were abolished by tetrodotoxin (TTX; 0.6 M) in all animal species. Subsequent addition of carbachol (0.1-1 M) did not evoke myogenic motor patterns in the mouse or guinea pig, although some activity was observed in rabbit and rat colon. These myogenic contractions propagated both orally and anally and differed from neurogenic propagating contractions in their frequency, extent of propagation, and polarity. Niflumic acid (300 M), used to block myogenic activity, also blocked neural peristalsis and thus cannot be used to discriminate between these mechanisms. In all species, except the mouse colon, small myogenic "ripple" contractions were revealed in TTX, but in both rat and rabbit an additional, higher-frequency ripple-type contraction was superimposed. Following blockade of enteric nerve function, a muscarinic agonist can evoke propulsive myogenic peristaltic contractions in isolated rabbit and rat colon, but not in guinea pig or mouse colon. Marked differences between species exist in the ability of myogenic mechanisms to propel luminal content, but in all species there is normally a complex interplay between neurogenic and myogenic processes. colon motility; enteric neurons; spatiotemporal maps; peristalsis COLONIC MOTILITY IS CONTROLLED by complex interactive processes in the gut, involving both nerve cells (neurogenic) and spontaneous muscle activity (myogenic). A number of studies have characterized fundamental mechanisms in the colon of the guinea pig, mouse, and rabbit and have shown that propagating contractions underlying peristalsis, or other propulsive motor patterns, require activity in the enteric nervous system (8,11,13,14,17,25).In recent papers, Huizinga et al. (20) and Chen et al. (7) produced evidence that challenges this principle. In the rat colon, in vitro, they showed that, after blocking peristalsis with antagonists of enteric neuronal activity [tetrodotoxin (TTX) or lidocaine], addition of a cholinergic agonist induced a recovery in propagating contractions. From these data they suggested that networks of interstitial cells of Cajal (ICC) work cooperatively with the enteric nervous system to create colonic motor patterns and that the main propulsive mechanism is the ...

In the central nervous system, bidirectional signaling between glial cells and neurons (‘neuroimmune communication') facilitates the development of persistent pain. Spinal glia can contribute to heightened pain states by a prolonged release of neurokine signals that sensitize adjacent centrally projecting neurons. Although many persistent pain conditions are disproportionately common in females, whether specific neuroimmune mechanisms lead to this increased susceptibility remains unclear. This review summarizes the major known contributions of glia and neuroimmune interactions in pain, which has been determined principally in male rodents and in the context of somatic pain conditions. It is then postulated that studying neuroimmune interactions involved in pain attributed to visceral diseases common to females may offer a more suitable avenue for investigating unique mechanisms involved in female pain. Further, we discuss the potential for primed spinal glia and subsequent neurogenic inflammation as a contributing factor in the development of peripheral inflammation, therefore, representing a predisposing factor for females in developing a high percentage of such persistent pain conditions.

Many rodent models of endometriosis are invasive, involving surgery to implant donor endometrial tissue into recipient animals. Moreover, few studies have compared and contrasted lesions between rodent strains and estrous stages without exogenous hormone manipulation. This is despite extensive data demonstrating that genetic and hormonal factors can influence endometriosis progression. Here, we have refined a minimally invasive model of endometriosis using naturally cycling mice (donor and recipient matched for cycle phase) to investigate lesion development in two different strains (C57BL/6 and BALB/c), induced in estrous stages of high and low estrogen (proestrus or estrus, respectively), and with varying amounts of donor endometrial tissue (7.5-40 mg), injected intraperitoneally. The overall probability of developing endometriosis-like lesions was higher in proestrus than estrus, and increased with greater masses of donor tissue. Similarly, the total number of lesions (0-3) increased from 7.5 to 40 mg, and was significantly greater in proestrus C57BL/6 mice but not BALB/cs. The dominant lesion type also differed between mouse strains; C57BL/6 mice were more likely to develop dense-type lesions, whereas BALB/c mice developed a greater proportion of cystic type. These data further support a role for estrogen in the development of endometriosis, and that genetic variance can influence the degree and characteristics of lesions. Our minimally invasive model would be beneficial for studies with outcome measurements particularly sensitive to incisional injury, such as pain, or alterations to sex hormones, including fertility.

Mechanisms involved in the generation of spontaneous uterine contractions are not fully understood. Kit-expressing interstitial cells of Cajal are pacemakers of contractile rhythm in other visceral organs, and recent studies describe a role for Ca(2+)-activated Cl(-) currents as the initiating conductance in these cells. The existence and role of similar specialized pacemaker cells in the nonpregnant uterus remains undetermined. Spontaneous contractility patterns were characterized throughout the estrous cycle in isolated, nonpregnant mouse uteri using spatiotemporal mapping and tension recordings. During proestrus, estrus, and diestrus, contraction origin predominated in the oviduct end of the uterus, suggesting the existence of a dominant pacemaker site. Propagation speed of contractions during estrus and diestrus were significantly slower than in proestrus and metestrus. Five major patterns of activity were predominantly exhibited in particular stages: quiescent (diestrus), high-frequency phasic (proestrus), low-frequency phasic (estrus), multivariant (metestrus), and complex. Kit-immunopositive cells reminiscent of pacemaking ICCs were not consistently observed within the uterus. Niflumic acid (10 μM), anthracene-9-carboxylic acid (0.1-1 mM), and 5-nitro-2-(3-phenylpropylamino)benzoic acid (10 μM) each reduced the frequency of spontaneous contractions, suggesting involvement of Cl(-) channels in generating spontaneous uterine motor activity. It is unlikely that this conductance is generated by the Ca(2+)-activated Cl(-) channels, anoctamin-1 and CLCA4, as immunohistochemical labeling did not reveal protein expression within muscle or pacemaker cell networks. In summary, these results suggest that spontaneous uterine contractions may be generated by a Kit-negative pacemaker cell type or uterine myocytes, likely involving the activity of a yet-unidentified Cl(-) channel.

Kuizenga MH, Sia TC, Dodds KN, Wiklendt L, Arkwright JW, Thomas A, Brookes SJ, Spencer NJ, Wattchow DA, Dinning PG, Costa M. Neurally mediated propagating discrete clustered contractions superimposed on myogenic ripples in ex vivo segments of human ileum. Am J Physiol Gastrointest Liver Physiol 308: G1-G11, 2015. First published November 13, 2014; doi:10.1152/ajpgi.00230.2014.-Narrow muscle strips have been extensively used to study intestinal contractility. Larger specimens from laboratory animals have provided detailed understanding of mechanisms that underlie patterned intestinal motility. Despite progress in animal tissue, investigations of motor patterns in large, intact specimens of human gut ex vivo have been sparse. In this study, we tested whether neurally dependent motor patterns could be detected in isolated specimens of intact human ileum. Specimens (n ϭ 14; 7-30 cm long) of terminal ileum were obtained with prior informed consent from patients undergoing colonic surgery for removal of carcinomas. Preparations were set up in an organ bath with an array of force transducers, a fiberoptic manometry catheter, and a video camera. Spontaneous and distension-evoked motor activity was recorded, and the effects of lidocaine, which inhibits neural activity, were studied. Myogenic contractions (ripples) occurred in all preparations (6.17 Ϯ 0.36/min). They were of low amplitude and formed complex patterns by colliding and propagating in both directions along the specimen at anterograde velocities of 4.1 Ϯ 0.3 mm/s and retrogradely at 4.9 Ϯ 0.6 mm/s. In five specimens, larger amplitude clusters of contractions were seen (discrete clustered contractions), which propagated aborally at 1.05 Ϯ 0.13 mm/s and orally at 1.07 Ϯ 0.09 mm/s. These consisted of two to eight phasic contractions that aligned with ripples. These motor patterns were abolished by addition of lidocaine (0.3 mM). The ripples continued unchanged in the presence of this neural blocking agent. These results demonstrate that both myogenic and neurogenic motor patterns can be studied in isolated specimens of human small intestine. small intestine; motor patterns; enteric nervous system; myogenic; neurogenic PROPULSION AND MIXING OF INTESTINAL CONTENTS along the digestive tract are essential for normal digestion. The motor patterns underlying these functions are due to the coordinated contractions and relaxations of the smooth muscle layers of the intestine. The internal circular smooth muscle layer and the external longitudinal smooth muscle layer are controlled by two main mechanisms. Myogenic activity is driven by the nonneural pacemaker cells, the interstitial cells of Cajal. Neurogenic control is mediated by circuits in the enteric nervous system. These two types of activity combine to generate the motor patterns that mix and propel luminal content (14,29). Most of our understanding of these mechanisms has been derived from animal studies. Although the basic functions of the gastrointestinal tract are similar between human and animals, there are si...