Previous Page  3 / 7 Next Page
Information
Show Menu
Previous Page 3 / 7 Next Page
Page Background

Volume 7, Issue 4(Suppl)

J Gastrointest Dig Syst, an open access journal

ISSN: 2161-069X

Gastro Congress 2017

September 11-12, 2017

Page 21

Notes:

conference

series

.com

September 11-12, 2017 | Paris, France

12

th

Euro-Global Gastroenterology Conference

Terence K Smith, J Gastrointest Dig Syst 2017, 7:4(Suppl)

DOI: 10.4172/2161-069X-C1-051

The importance of neuronal serotonin in colonic motor patterns

5

-hydroxytryptamine (5-HT, serotonin) has two sources in the gut, descending myenteric 5-HT interneurons (~5% of all

5-HT) and enterochromaffin (EC) cells (~95% of 5-HT). 5-HT is synthesized by the rate limiting enzyme tryptophan

hydroxylase (TPH); TPH1 in EC cells and TPH2 in EC cells. In the colon, these two pools of 5-HT appear to be connected

by intrinsic primary afferent neurons (IPANs) that have sensory endings in the mucosa and synapse with 5-HT interneurons.

The prominent inhibitory effects of 5-HT1A/2B/3/4 and 7 receptor antagonists on colonic motility suggests that many of these

receptors are on various cell types including glia that are largely activated by 5-HT interneurons. Major motility patterns in

the colon involving 5-HT include tonic inhibition of the muscle layers interrupted by rhythmic peristaltic waves called colonic

migrating motor complexes (CMMCs), and secretomotor activity and possibly blood flow. In large mammals (e.g. dog, pig and

human colon) 5-HTneurons occur in both themyenteric plexus and the extensiveHenle’s plexus, that synapsewith secretomotor

neurons in Meissner’s plexus. Henle’s plexus also provides a motor innervation to submucosal pacemaker cells that generate

slow waves. Some 5-HT neurons also project to prevertebral ganglia suggesting they are viscerofugal neurons that they can

activate postganglionic sympathetic neurons, whose terminals surround 5-HT neurons. We propose that asynchronous firing

in 5-HT neurons excite inhibitory motor neurons (IMNs) to generate tonic inhibition and suppress pacemaker activity. In

contrast, 5-HT released from EC cells activates IPANs that synchronizes 5-HT neurons. Synchronized firing of 5-HT neurons

likely activates glial cells, which release PGE2, that switch off IMNs and remove tonic inhibition. Synchronized 5-HT neurons

also likely generate a slow excitatory postsynaptic potential (sEPSP) in IPANS by activating 5-HT7 receptors that generate

CMMCs that in turn excite excitatory motor neurons and pacemaker cells.

Biography

Terence Smith is Professor in the department of Physiology and Cell Physiology at the University of Nevada-Reno, USA, where he is the Director of the Dynamic Imaging

Core. He received his PhD in Neuropharmacology/Electrophysiology from Monash University, Victoria, Australia under Professors Mollie Holman and David Hirst who

first classified enteric neurons electrically. His interests have focused on how the enteric nervous system regulates gut pacemakers, and more recently optogenetics to

study gut motility.

tksmith@med.unr.edu

Terence K Smith

University of Nevada, USA