Spatiotemporal mapping of the motility of the ex vivo rabbit caecum : a thesis presented in partial fulfilment of the requirements for the degree of Masters of Physiology in Digestive Biomechanics (Physical Process of Digestion) at Massey University, Turitea, New Zealand

This work sought to determine the contractile factors influencing the coordination of inflow and out flow from the caecum, and the mixing and mass transfer within. Specifically, the work was focussed on the ileocaecal junction in the domestic rabbit (Oryctolagus cuniculus). The salient questions to answer were; 1. What are the contractile movements in the body of the caecum and associated structures of the rabbit caecum? 2. How are contractile movements coordinated at the body of the rabbit caecum and how does this affect the pattern of motility? The following two main experimental works of this thesis were all conducted using live gut rabbit caecum preparations maintained ex vivo. Spatiotemporal mapping and electromyography was used to visualize and quantify contractile activity and coordination in the caecum. 1. High definition radial, strain rate and intensity spatiotemporal mapping was used to quantify contractile movements of the body and associated structures of the rabbit caecum. 2. Coordination between contractile events at different sites in the basal portion of the rabbit caecum and its associated structures were identified by electrophysiological recordings with simultaneous one dimensional, and a novel two dimensional, spatiotemporal mapping technique. The following are the main findings and implications of the work. 1. The body of the caecum exhibited two patterns of motility that appeared autonomous, i.e. occurred independently of any contractile activity at the inlet or outlet. Firstly, a pattern termed ladder activity consisted of orderly sequential contractions in the spiral turns in the corpus ceci. Secondly, less localised, rapidly propagating synchronous contractions that were termed mass peristalsis. 2. Movements of the ileum and sacculus rotundus occurred at the same frequency and were broadly coordinated. Further, the findings suggest that the action of the sacculus rotundus may result from its distension with chyme by ileal peristalsis and that the subsequent propagation of contraction along the basal wall of the caecum toward the colon may be augmented by this local distension. 3. The caecum and proximal colon/ampulla coli act reflexly to augment colonic outflow. When the caecum is distended and mass peristalsis is instituted, the action of the latter overrides the inherent rhythm and direction of haustral propagation in the adjacent portion of the proximal colon but not in the terminal ileum. In conclusion, coordination, mixing and mass transfer in the rabbit caecum is a very complex, dynamic and largely autonomous process. Further, spatiotemporal mapping techniques enabled the identification and visualization of previously unknown contractile movements within the rabbit caecum

Quantifying Patterns of Smooth Muscle Motility in the Gut and Other Organs With New Techniques of Video Spatiotemporal Mapping

The uses and limitations of the various techniques of video spatiotemporal mapping based on change in diameter (D-type ST maps), change in longitudinal strain rate (L-type ST maps), change in area strain rate (A-type ST maps), and change in luminous intensity of reflected light (I-maps) are described, along with their use in quantifying motility of the wall of hollow structures of smooth muscle such as the gut. Hence ST-methods for determining the size, speed of propagation and frequency of contraction in the wall of gut compartments of differing geometric configurations are discussed. We also discuss the shortcomings and problems that are inherent in the various methods and the use of techniques to avoid or minimize them. This discussion includes, the inability of D-type ST maps to indicate the site of a contraction that does not reduce the diameter of a gut segment, the manipulation of axis [the line of interest (LOI)] of L-maps to determine the true axis of propagation of a contraction, problems with anterior curvature of gut segments and the use of adjunct image analysis techniques that enhance particular features of the maps

Ex vivo motility in the base of the rabbit caecum and its associated structures: an electrophysiological and spatiotemporal analysis

We examined the coordination between contractile events at different sites in the basal portion of the rabbit caecum and its associated structures that were identified by electrophysiological recordings with simultaneous one-dimensional, and a novel two-dimensional, spatiotemporal mapping technique. The findings of this work provide evidence that the caecum and proximal colon/ampulla coli act reflexly to augment colonic outflow when the caecum is distended and mass peristalsis instituted, the action of the latter overriding the inherent rhythm and direction of haustral propagation in the adjacent portion of the proximal colon but not in the terminal ileum. Further, the findings suggest that the action of the sacculus rotundus may result from its distension with chyme by ileal peristalsis and that the subsequent propagation of contraction along the basal wall of the caecum towards the colon may be augmented by this local distension

Characterisation of mixing in the proximal duodenum of the rat during longitudinal contractions and comparison with a fluid mechanical model based on spatiotemporal motility data.

The understanding of mixing and mass transfers of nutrients and drugs in the small intestine is of prime importance in creating formulations that manipulate absorption and digestibility. We characterised mixing using a dye tracer methodology during spontaneous longitudinal contractions, i.e. pendular activity, in 10 cm segments of living proximal duodenum of the rat maintained ex-vivo. The residence time distribution (RTD) of the tracer was equivalent to that generated by a small number (8) of continuous stirred tank reactors in series. Fluid mechanical modelling, that was based on real sequences of longitudinal contractions, predicted that dispersion should occur mainly in the periphery of the lumen. Comparison with the experimental RTD showed that centriluminal dispersion was accurately simulated whilst peripheral dispersion was underestimated. The results therefore highlighted the potential importance of micro-phenomena such as microfolding of the intestinal mucosa in peripheral mixing. We conclude that macro-scale modeling of intestinal flow is useful in simulating centriluminal mixing, whereas multi-scales strategies must be developed to accurately model mixing and mass transfers at the periphery of the lumen

Spatiotemporal Mapping Techniques Show Clozapine Impairs Neurogenic and Myogenic Patterns of Activity in the Colon of the Rabbit in a Dose-Dependent Manner

Background: Clozapine, an antipsychotic used in treatment-resistant schizophrenia, has adverse gastrointestinal effects with significant associated morbidity and mortality. However, its effects on defined patterns of colonic contractile activity have not been assessed.Method: We used novel radial and longitudinal spatiotemporal mapping techniques, combined with and monitoring of ambient lumen pressure, in ex vivo preparations of triply and of singly haustrated portions of rabbit colon. We identified the contractile patterns of mass peristalses, fast phasic, and ripple contractions and directly qualified the effects of clozapine, at concentrations of 10 μmol/L, 20 μmol/L, and 30 μmol/L, and of norclozapine, the main metabolite of clozapine, on contractile patterns. The effects of carbachol, serotonin and naloxone on clozapine-exposed preparations were also determined. Tetradotoxin was used to distinguish neurogenic from myogenic contractions.Results: At 10 μmol/L, clozapine temporarily abolished the longitudinal contractile components of mass peristalsis, which on return were significantly reduced in number and amplitude, as was maximal mass peristaltic pressure. These effects were reversed by carbachol (1 μmol/L) and to some extent by serotonin (15 μmol/L). At 10 μmol/L, myogenic ripple contractions were not affected. At 20 μmol/L, clozapine had a similar but more marked effect on mass peristalses with both longitudinal and radial components and corresponding maximal pressure greatly reduced. At 30 μmol/L, clozapine suppressed the radial and longitudinal components of mass peristalses for over 30 min, as well as ripple contractions. Similar dose-related effects were observed on addition of clozapine to the mid colon. At 20 μmol/L, norclozapine had opposite effects to those of clozapine, causing an increase in the frequency of mass peristalsis with slight increases in basal tone. These slightly augmented contractions were abolished on addition of clozapine. Concentrations of norclozapine below 20 μmol/L had no discernible effects.Conclusion: Clozapine, but not norclozapine, has potent effects on the motility of the rabbit colon, inhibiting neurogenic contractions at lower concentrations and myogenic contractions at higher concentrations. This is the likely mechanism for the serious and life-threatening gastrointestinal complications seen in human clozapine-users. These effects appear to be mediated by cholinergic and serotonergic mechanisms. Spatiotemporal mapping is useful in directly assessing the effects of pharmaceuticals on particular patterns of gastrointestinal motility

Theoretical step response RTDs and determination of minimal axial dispersion in the experimental layout.

<p>Left: Theoretical step response RTD for different numbers (n) of continuous stirred tanks reactors (CSTRs) in series. Plug flow reactor (PFR) configuration (no axial but perfect radial mixing) is approached as the number of CSTRs tends to infinity. Right: Experimental step response RTD (plain circles) after passage through a length of silicone rubber tubing of similar dimensions and flow rate to those of the isolated proximal duodenum. The line of best fit was for 68 CSTRs in series (R² = 0.99, plain line).</p

Schema showing the ex vivo preparation and the system for perfusion and collection of the effluent (A) and spatiotemporal L map of non propagating longitudinal contractions, i.e. pendular activity, in the proximal duodenum of the rat (B).

<p>(A) The duodenal segment is immersed in, and superperfused with, carboxygenated Earles Hepes solution maintained at 37°. Effluent is collected every minute from the distal conical cannula tip.(B) Darker shades indicate areas of relaxation (positive longitudinal strain rate, in s⁻¹) and lighter shades areas of contraction (negative longitudinal strain rate). The L map presents four spatial domains (*) in which the longitudinal strain rate oscillates between positive and negative values.</p