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Propulsion of luminal content along the gut requires coordinated contractions and relaxations of gastrointestinal smooth muscles controlled by the enteric nervous system (ENS). Activation of excitatory motor neurons (EMNs) causes muscle contractions while inhibitory motor neuron (IMN) activation causes muscle relaxation. EMNs release acetylcholine (ACh) which acts at muscarinic receptors on smooth muscle cells and adjacent interstitial cells of Cajal (ICC) causing excitatory junction potentials (EJPs). IMNs release ATP (or another purine) and nitric oxide (NO) to cause inhibitory junction potentials (IJPs) and muscle relaxation. We used commercially available ChAT-ChR2-YFP BAC transgenic mice which express channel rhodopsin-2 (ChR2) in cholinergic neurons to study cholinergic neuromuscular transmission in the colon. Intracellular microelectrodes were used to record IJPs and EJPs from circular muscle cells. We used blue light stimulation (BLS, 470 nm, 20 mW/mm) and electrical field stimulation (EFS) to activate myenteric neurons. EFS evoked IJPs only while BLS evoked EJPs and IJPs. Mecamylamine (10 µM, nicotinic cholinergic receptor antagonist) reduced BLS-evoked IJPs by 50% but had no effect on electrically evoked IJPs. MRS 2179 (10 µM, a P2Y1 receptor antagonist) blocked BLS-evoked IJPs. MRS 2179 and NLA (100 µM, nitric oxide synthase inhibitor) isolated the EJP which was blocked by scopolamine (1 µM, muscarinic ACh receptor antagonist). Immunohistochemistry revealed choline acetyltransferase (ChAT) expression in ~88% of eYFP expressing neurons, while 12% of eYFP neurons expressed nitric oxide synthase (NOS). These data show that cholinergic interneurons synapse with excitatory and inhibitory motorneurons to cause contraction and relaxation of colonic smooth muscle.
This article was published in the following journal.
Name: American journal of physiology. Gastrointestinal and liver physiology
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The intentional interruption of transmission at the NEUROMUSCULAR JUNCTION by external agents, usually neuromuscular blocking agents. It is distinguished from NERVE BLOCK in which nerve conduction (NEURAL CONDUCTION) is interrupted rather than neuromuscular transmission. Neuromuscular blockade is commonly used to produce MUSCLE RELAXATION as an adjunct to anesthesia during surgery and other medical procedures. It is also often used as an experimental manipulation in basic research. It is not strictly speaking anesthesia but is grouped here with anesthetic techniques. The failure of neuromuscular transmission as a result of pathological processes is not included here.
The use of peripheral nerve stimulation to assess transmission at the NEUROMUSCULAR JUNCTION, especially in the response to anesthetics, such as the intensity of NEUROMUSCULAR BLOCKADE by NEUROMUSCULAR BLOCKING AGENTS.
Drugs that interrupt transmission of nerve impulses at the skeletal neuromuscular junction. They can be of two types, competitive, stabilizing blockers (NEUROMUSCULAR NONDEPOLARIZING AGENTS) or noncompetitive, depolarizing agents (NEUROMUSCULAR DEPOLARIZING AGENTS). Both prevent acetylcholine from triggering the muscle contraction and they are used as anesthesia adjuvants, as relaxants during electroshock, in convulsive states, etc.
The segment of LARGE INTESTINE between the CECUM and the RECTUM. It includes the ASCENDING COLON; the TRANSVERSE COLON; the DESCENDING COLON; and the SIGMOID COLON.
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