Submucosal plexus

The innervation of the gastrointestinal tract is complex. The myenteric and submucosal plexuses contain many interneurons. These possess a number of neurotransmitters and neuromodulators, including several peptides, such as enkephalins, substance P, and vasoactive intestinal peptide. Reflex activity within the plexuses regulates peristalsis and secretion locally. The effects of sympathetic and parasympathetic nerve stimulation are superimposed on this local neural regulation. 

The myenteric and submucosal plexuses contain ganglion cells giving rise to excitatory cholinergic fibers that directly innervate the smooth muscle and gland... 

A highly simplified diagram of the intestinal wall and some of the circuitry of the enteric nervous system (ENS). The ENS receives input from both the sympathetic and the parasympathetic systems and sends afferent impulses to sympathetic ganglia and to the central nervous system. Many transmitter or neuromodulator substances have been identified in the ENS see Table 6-1. ACh, acetylcholine AC, absorptive cell CM, circular muscle layer EC, enterochromaffin cell EN, excitatory neuron EPAN, extrinsic primary afferent neuron 5HT, serotonin IN, inhibitory neuron IPAN, intrinsic primary afferent neuron LM, longitudinal muscle layer MP, myenteric plexus NE, norepinephrine NP, neuropeptides SC, secretory cell SMP, submucosal plexus. 

The enteric nervous system (see Chapter 6 Introduction to Autonomic Pharmacology) is composed of interconnected networks of ganglion cells and nerve fibers mainly located in the submucosa (submucosal plexus) and between the circular and longitudinal muscle layers (myenteric plexus). These networks give rise to nerve fibers that connect with the mucosa and deep muscle. Although extrinsic sympathetic and parasympathetic nerves project onto the submucosal and myenteric plexuses, the enteric nervous system can independently regulate gastrointestinal motility and secretion. Afferent fibers present in the mucosa and muscularis connect to cell bodies in the plexuses that mediate local reflexes. 

This difference of action may be due to the fact that endogenous enkephalins are tonically released from the submucosal plexus neurons which contains mainly delta opioid receptors, but sparsely from the myenteric plexus neurons where mu receptors are present [64-66]. 

Subsequent to the molecular cloning and cDNA sequence analysis of the delta opioid receptor, antireceptor antibodies were raised against synthetic peptides based on the deduced amino acid sequence of this receptor. To date, there have been a limited number of studies using antibodies directed toward the amino terminus of the cloned murine receptor to assess the distribution of delta opioid receptorlike immunoreactivity in the gastrointestinal tract, and these have been confined so far to the porcine small intestine. They have shown the presence of delta opioid receptor-immuno-reactive neurons and fibers in both the myenteric and submucosal plexuses and as well as in myenteric neurons maintained in primary culture [22, 23]. Receptor-like immunoreactivity in neuronal cell bodies appears to be localized in the cytoplasm and is likely to be trafficked to nerve terminals. These neurons are coimmunoreactive for the acetylcholine-synthesizing... 

Two sets of dopamine receptor are present in the gut D] receptors are located on effector cells and D2 receptors predominate on the cell bodies in the myenteric and submucosal plexuses. The result... 

The activities of the GI tract are controlled locally through a restricted part of the peripheral nervous system called the enteric nervous system (ENS). The ENS is involved in sensorimotor control and consists of both afferent sensory neurons and a number of motor nerves and intemeurons that are organized principally into two nerve plexuses the myenteric (Auerbach s) plexus and the submucosal (Meissner s) plexus. The myenteric plexus, located between the longitudinal and circular muscle layers, plays an important role in the contraction and relaxation of GI smooth muscle. The submucosal plexus is involved with secretory and absorptive functions of the GI epithelium, local blood flow, and neuroimmune activities. The ENS consists of components of the sympathetic and parasympathetic branches of the ANS and has sensory nerve connections through the spinal and nodose ganglia ("see Chapter 37). 

The intrinsic primary afferent neurons are present in both the myenteric and submucosal plexuses. They respond to luminal chemical stimuli, to mechanical deformation of the mucosa, and to stretch. The nerve endings of the primary afferent neurons can be activated by endogenous substances (e.g., serotonin) arising from local enterochromaffin cells or possibly from serotonergic nerves. 

Presence of CB, receptor markers in the myenteric and submucosal plexuses. 

The intrinsic innervation of the GIT is considered as a separate autonomic division, called the enteric nervous system (ENS) (Schemann and Neunlist 2004). Neurons and enteric glia of the ENS are embedded within the gut wall and arranged in three plexuses (Hall 2011). The myenteric (Auerbach s) plexus is located between the inner and outer circular muscle layers and the submucosal (Meissner s) plexus between the circular muscle and muscularis mucosa. The deep muscle plexus separates inner and outer circular muscle layers in the small intestine. In the large intestine, it is located at the inner border of circular muscle and is called submucosal plexus. 

---