Small-bowel motility

Quantitative assessment of small bowel motility by nonrigid registration of dynamic MR images

Evaluation of small bowel motility from two-dimensional dynamic MRI is of increasing interest for the assessment of segmental diseases such as Crohn's disease. We propose to use nonrigid image registration for automated motility analysis. Registration is particularly difficult when localized intensity changes occur (e.g., due to intraluminal flow or through-plane motion). Therefore, displacements were extracted using a joint registration and modeling of intensity changes. Results were analyzed in 10 patients with known or suspected Crohn's disease. Bowel wall displacements were assessed by tracking bowel cross-sectional markers over time. Automated tracking with the proposed technique was in good agreement with manual tracking (similar bias, improved standard deviations). The ability to quantify different grades of bowel motility was investigated by comparing direct motion measures (i.e., changes in bowel cross-sectional diameter or area) and various parametric maps, e.g., based on the Jacobian of the measured displacements with expert grading. Among these measures, the standard deviation over time of the Jacobian was the best at predicting grades from 1 (moving normally) to 4 (not moving at all) in 50 bowel regions with normal and pathologically reduced motility, yielding 93% correct classification with a 1-class tolerance (i.e., same score as the expert ± 1).

Assessment of small bowel motility function with cine-MRI using balanced steady-state free precession sequence

PURPOSE

To evaluate the use of cine-magnetic resonance imaging (MRI) with a steady-state free precession sequence to monitor and assess small bowel motility.

MATERIALS AND METHODS

Sequential MRI, using a balanced steady-state free precession sequence, was performed in eight healthy male volunteers at 0, 15, 30, 45, and 60 minutes after oral administration of 1500 mL of nonabsorbable fluid to monitor small bowel contractions. Using the cine-mode display, small bowel contractions were reviewed and the luminal diameter was measured on each image to obtain frequency and amplitude of bowel contractions.

RESULTS

The oral preparation was well tolerated without major complications. Cine-MRI provided high temporal, spatial, and contrast resolution for monitoring bowel contractions. Mean values with standard deviations of frequency and amplitude of bowel contractions were 6.0 ± 2.98/min and 10.4 ± 4.53 mm, respectively, and were 5.1 ± 3.38/min and 9.59 ± 5.57 mm at the jejunal loops and 6.9 ± 2.22/min and 11.2 ± 3.06 mm at the ileal loops. With the passage of luminal fluid, frequency of bowel contractions decreased and the bowels tended to pause their contractions.

CONCLUSION

Cine-MRI provides sufficient dynamic images to observe small bowel contractions. Measurement of bowel caliber permits calculation of amplitude and frequency of the contractions for characterization and quantitative assessment of small bowel motility function.

The effects of quinidine and its chiral isolates on erg-1sm potassium current and correlation with gastrointestinal augmentation

Smooth-muscle erg 1 (erg1-sm) potassium channel has been recently reported to participate in the modulation of gastrointestinal contractility. Because quinidine inhibits cardiac potassium channel and as a result augments gastrointestinal contractility, it was thought that quinidine may affect erg1-sm. Studies were undertaken to evaluate the effects of quinidine and its chiral isolates on gastrointestinal erg1-sm potassium current and correlate these effects with colon contractility. Chiral separation (high-performance liquid chromatography technique), mass spectrometry, and optical rotation determination were performed to obtain chiral isolates needed for experiments. The erg1-sm potassium channel was expressed in Xenopus oocytes, and the two-electrode patch clamp technique was employed for recording. An isolated rat colon preparation was employed to measure changes in contractility. As a result of chiral separation, two peaks were obtained with elution times of 8.31 and 8.66 minutes, both with a molecular weight of 324; the optical rotations of racemate isolates X and Y were: +258 degrees, +/-0 degrees; and +217 degrees, respectively. The percentage changes in amplitudes of colon contraction (from baseline) were determined at different concentrations of quinidine and for the two isolates in five experiments in each group. Quinidine 0.1, 1, and 10 microM increased contractility by 79 +/- 34, 125 +/- 42, and 217 +/- 51 (P < or = 0.05); for isolate X, the values were 70 +/- 20, 115 +/- 32, and 272 +/- 32 (P < or = 0.05), and for isolate Y the values were 22 +/- 12, 46 +/- 17, and 59 +/- 22. The inhibition of erg1-sm currents by quinidine was 19 +/- 4, 21 +/- 5, and 48 +/- 6 (P < or = 0.05), respectively; that by isolate X was 20 +/- 4, 23 +/- 5, and 39 +/- 7 (P < or = 0.05), and that by isolate Y was 22 +/- 4, 21 +/- 4, and 31 +/- 6. One chiral isolate and quinidine markedly augmented contractility, whereas quinidine and the two chiral isolates inhibited the erg1-sm potassium currents to a similar extent. These results suggest that erg1-sm inhibition does not explain gastrointestinal contractile augmentation caused by the quinidine racemate and its chiral isolates.

GDNF rescues hyperglycemia-induced diabetic enteric neuropathy through activation of the PI3K/Akt pathway

Diabetes can result in loss of enteric neurons and subsequent gastrointestinal complications. The mechanism of enteric neuronal loss in diabetes is not known. We examined the effects of hyperglycemia on enteric neuronal survival and the effects of glial cell line-derived neurotrophic factor (GDNF) on modulating this survival. Exposure of primary enteric neurons to 20 mM glucose (hyperglycemia) for 24 hours resulted in a significant increase in apoptosis compared with 5 mM glucose (normoglycemia). Exposure to 20 mM glucose resulted in decreased Akt phosphorylation and enhanced nuclear translocation of forkhead box O3a (FOXO3a). Treatment of enteric neurons with GDNF ameliorated these changes. In streptozotocin-induced diabetic mice, there was evidence of myenteric neuronal apoptosis and reduced Akt phosphorylation. Diabetic mice had loss of NADPH diaphorase-stained myenteric neurons, delayed gastric emptying, and increased intestinal transit time. The pathophysiological effects of hyperglycemia (apoptosis, reduced Akt phosphorylation, loss of inhibitory neurons, motility changes) were reversed in diabetic glial fibrillary acidic protein-GDNF (GFAP-GDNF) Tg mice. In conclusion, we demonstrate that hyperglycemia induces neuronal loss through a reduction in Akt-mediated survival signaling and that these effects are reversed by GDNF. GDNF may be a potential therapeutic target for the gastrointestinal motility disorders related to diabetes.

Substance P induces inward current and regulates pacemaker currents through tachykinin NK1 receptor in cultured interstitial cells of Cajal of murine small intestine

We investigated whether substance P modulates pacemaker currents generated in cultured interstitial cells of Cajal of murine small intestine using whole cell patch-clamp techniques at 30 degrees C. Interstitial cells of Cajal generated spontaneous inward currents (pacemaker currents) at a holding potential of -70 mV. Tetrodotoxin, nifedipine, tetraethylammonium, 4-aminopyridine, or glibenclamide did not change the frequency and amplitude of pacemaker currents. However, divalent cations (Ni2+, Mn2+, Cd2+, and Co2+), nonselective cationic channel blockers (gadolinium and flufenamic acid), and a reduction of external Na+ from normal to 1 mM inhibited pacemaker currents indicating that nonselective cation channels are involved in their generation. Substance P depolarized the membrane potential in current clamp mode and produced tonic inward pacemaker currents with reduced frequency and amplitude in voltage clamp mode. [D-Arg1, D-Trp7,9, Leu11] substance P, a tachykinin NK1 receptor antagonist, blocked these substance P-induced responses. Furthermore, [Sar9, Met(O2)11] substance P, a specific tachykinin NK1 receptor agonist, depolarized the membrane and tonic inward currents mimicked those of substance P. Substance P continued to produce tonic inward currents in external Ca2+-free solution or in the presence of chelerythrine, a protein kinase C inhibitor. However, substance P-induced tonic inward currents were blocked by thapsigargin, a Ca2+-ATPase inhibitor in the endoplasmic reticulum or by an external 1 mM Na+ solution. Our results demonstrate that substance P may modulate intestinal motility by acting on the interstitial cells of Cajal by activating nonselective cation channels via the release of intracellular Ca2+ induced by tachykinin NK1 receptor stimulation.

Small bowel motility assessment with magnetic resonance imaging

PURPOSE

To assess primarily the feasibility of magnetic resonance imaging (MRI) as a tool to monitor small bowel peristaltic motion and secondarily to validate this technique by demonstrating drug-induced motility changes.

MATERIALS AND METHODS

After a standardized oral preparation of Ispaghula husk (Metamucil) and meglumine gadoterate (Gd-DOTA; Dotarem), 10 volunteers underwent dynamic MRI using a two-dimensional turbofast field echo (TFE) sequence with a slice repetition time of 500 msec. Intraluminal cross-sectional caliber changes over time were assessed allowing quantification of the peristaltic frequencies and amplitudes of the small gut on various regions of interest. Pharmacologically induced alterations of the peristaltic motion after spasmolytics and gastrokinetic motion enhancers were investigated.

RESULTS

Small bowel diameter measurement resulted in a peristalsis of 10.96 (SD = +/-2.51) waves per minute, oscillating regularly with mean amplitudes of 6.65 mm (SD = +/-1.15 mm). Peristaltic frequency in normal individuals is consistent with that observed with other techniques. Intravenous administration of scopolamine butylbromide (= hyoscine butylbromide/Buscopan) resulted in small bowel paralysis within 21.3 seconds (SD = +/-2.8 seconds). Prokinetic effect of intravenous metoclopramide (Paspertin) after Buscopan paralysis was tested in one volunteer, characterized by a slow recovery of peristalsis, which propagated from the proximal to the distal segments and enhanced contraction amplitudes.

CONCLUSION

Dynamic MRI allows observing and quantifying small bowel peristalsis, characterizing motion patterns, and monitoring the effects of interfering factors such as drugs.

GDNF availability determines enteric neuron number by controlling precursor proliferation

To clarify the role of Ret signaling components in enteric nervous system (ENS) development, we evaluated ENS anatomy and intestinal contractility in mice heterozygous for Ret, GFRalpha1 and Ret ligands. These analyses demonstrate that glial cell line-derived neurotrophic factor (GDNF) and neurturin are important for different aspects of ENS development. Neurturin is essential for maintaining the size of mature enteric neurons and the extent of neuronal projections, but does not influence enteric neuron number. GDNF availability determines enteric neuron number by controlling ENS precursor proliferation. However, we were unable to find evidence of programmed cell death in the wild type ENS by immunohistochemistry for activated caspase 3. In addition, enteric neuron number is normal in Bax(-/-) and Bid(-/-) mice, suggesting that, in contrast to most of the rest of the nervous system, programmed cell death is not important for determining enteric neuron numbers. Only mild reductions in neuron size and neuronal fiber counts occur in Ret(+/-) and Gfra1(+/-) mice. All of these heterozygous mice, however, have striking problems with intestinal contractility and neurotransmitter release, demonstrating that Ret signaling is critical for both ENS structure and function.