Regulation of Gastric Electrical and Mechanical Activity by Cholinesterases in Mice

BACKGROUND/AIMS: Gastric peristalsis begins in the orad corpus and propagates to the pylorus. Directionality of peristalsis depends upon orderly generation and propagation of electrical slow waves and a frequency gradient between proximal and distal pacemakers. We sought to understand how chronotropic agonists affect coupling between corpus and antrum. METHODS: Electrophysiological and imaging techniques were used to investigate regulation of gastric slow wave frequency by muscarinic agonists in mice. We also investigated the expression and role of cholinesterases in regulating slow wave frequency and motor patterns in the stomach. RESULTS: Both acetycholinesterase (Ache) and butyrylcholine esterase (Bche) are expressed in gastric muscles and AChE is localized to varicose processes of motor neurons. Inhibition of AChE in the absence of stimulation increased slow wave frequency in corpus and throughout muscle strips containing corpus and antrum. CCh caused depolarization and increased slow wave frequency. Stimulation of cholinergic neurons increased slow wave frequency but did not cause depolarization. Neostigmine (1 muM) increased slow wave frequency, but uncoupling between corpus and antrum was not detected. Motility mapping of contractile activity in gastric muscles showed similar effects of enteric nerve stimulation on the frequency and propagation of slow waves, but neostigmine (> 1 muM) caused aberrant contractile frequency and propagation and ectopic pacemaking. CONCLUSIONS: Our data show that slow wave uncoupling is difficult to assess with electrical recording from a single or double sites and suggest that efficient metabolism of ACh released from motor neurons is an extremely important regulator of slow wave frequency and propagation and gastric motility patterns.

The Significance of Interstitial Cells in Neurogastroenterology

Smooth muscle layers of the gastrointestinal tract consist of a heterogeneous population of cells that include enteric neurons, several classes of interstitial cells of mesenchymal origin, a variety of immune cells and smooth muscle cells (SMCs). Over the last number of years the complexity of the interactions between these cell types has begun to emerge. For example, interstitial cells, consisting of both interstitial cells of Cajal (ICC) and platelet-derived growth factor receptor alpha-positive (PDGFRalpha+) cells generate pacemaker activity throughout the gastrointestinal (GI) tract and also transduce enteric motor nerve signals and mechanosensitivity to adjacent SMCs. ICC and PDGFRalpha+ cells are electrically coupled to SMCs possibly via gap junctions forming a multicellular functional syncytium termed the SIP syncytium. Cells that make up the SIP syncytium are highly specialized containing unique receptors, ion channels and intracellular signaling pathways that regulate the excitability of GI muscles. The unique role of these cells in coordinating GI motility is evident by the altered motility patterns in animal models where interstitial cell networks are disrupted. Although considerable advances have been made in recent years on our understanding of the roles of these cells within the SIP syncytium, the full physiological functions of these cells and the consequences of their disruption in GI muscles have not been clearly defined. This review gives a synopsis of the history of interstitial cell discovery and highlights recent advances in structural, molecular expression and functional roles of these cells in the GI tract.

Bone Marrow Derived Kit-positive Cells Colonize the Gut but Fail to Restore Pacemaker Function in Intestines Lacking Interstitial Cells of Cajal

BACKGROUND/AIMS: Several motility disorders are associated with disruption of interstitial cells of Cajal (ICC), which provide important functions, such as pacemaker activity, mediation of neural inputs and responses to stretch in the gastrointestinal (GI) tract. Restoration of ICC networks may be therapeutic for GI motor disorders. Recent reports have suggested that Kit+ cells can be restored to the GI tract via bone marrow (BM) transplantation. We tested whether BM derived cells can lead to generation of functional activity in intestines naturally lacking ICC. METHODS: BM cells from Kit(+/copGFP) mice, in which ICC are labeled with a green fluorescent protein, were transplanted into W/W(V) intestines, lacking ICC. After 12 weeks the presence of ICC was analyzed by immunohistochemistry and functional analysis of electrical behavior and contractile properties. RESULTS: After 12 weeks copGFP+ BM derived cells were found within the myenteric region of intestines from W/W(V) mice, typically populated by ICC. Kit+ cells failed to develop interconnections typical of ICC in the myenteric plexus. The presence of Kit+ cells was verified with Western analysis. BM cells failed to populate the region of the deep muscular plexus where normal ICC density, associated with the deep muscular plexus, is found in W/W(V) mice. Engraftment of Kit+-BM cells resulted in the development of unitary potentials in transplanted muscles, but slow wave activity failed to develop. Motility analysis showed that intestinal movements in transplanted animals were abnormal and similar to untransplanted W/W(V) intestines. CONCLUSIONS: BM derived Kit+ cells colonized the gut after BM transplantation, however these cells failed to develop the morphology and function of mature ICC.

Responses to Enteric Motor Neurons in the Gastric Fundus of Mice With Reduced Intramuscular Interstitial Cells of Cajal

BACKGROUND/AIMS: Interstitial cells of Cajal (ICC) play important functions in motor activity of the gastrointestinal tract. The role of ICC as pacemakers is well established, however their participation in neurotransmission is controversial. Studies using mutant animals that lack ICC have yielded variable conclusions on their importance in enteric motor responses. The purpose of this study was to: (1) clarify the role of intramuscular ICC (ICC-IM) in gastric motor-neurotransmission and (2) evaluate remodeling of enteric motor responses in W/W(V) mice. METHODS: Kit immunohistochemistry and post-junctional contractile responses were performed on fundus muscles from wild-type and W/W(V) mice and quantitative polymerase chain reaction (qPCR) was used to evaluate differences in muscarinic and neurokinin receptor expression. RESULTS: Although ICC-IM were greatly reduced in comparison with wild-type mice, we found that ICC-IM persisted in the fundus of many W/W(V) animals. ICC-IM were not observed in W/W(V) group 1 (46%) but were observed in W/W(V) group 2 (40%). Evoked neural responses consisted of excitatory and inhibitory components. The inhibitory component (nitrergic) was absent in W/W(V) group 1 and reduced in W/W(V) group 2. Enhanced excitatory responses (cholinergic) were observed in both W/W(V) groups and qPCR revealed that muscarinic-M3 receptor expression was significantly augmented in the W/W(V) fundus compared to wild-type controls. CONCLUSIONS: This study demonstrates that ICC-IM mediate nitrergic inhibitory neurotransmission in the fundus and provides evidence of plasticity changes in neuronal responses that may explain discrepancies in previous functional studies which utilized mutant animals to examine the role of ICC-IM in gastric enteric motor responses.