The Myenteric Plexus, also known as Auerbach's Plexus, is the major neural network of the enteric nervous system (ENS), situated between the circular and longitudinal muscle layers of the gastrointestinal tract. This extensive meshwork of neurons and glial cells controls gut motility, secretion, and blood flow, functioning as the "second brain" of the body. The myenteric plexus contains approximately 100-200 million neurons organized into distinct functional subclasses that coordinate peristalsis, segmentation, and the migrating motor complex. Importantly, the myenteric plexus is increasingly recognized as one of the earliest sites of alpha-synuclein pathology in Parkinson's Disease (PD), where it serves as a potential window into disease progression and a target for early intervention.
The myenteric plexus extends along the entire length of the gastrointestinal tract, from the esophagus to the internal anal sphincter:
- Esophagus: Sparse network in the lower esophageal sphincter region
- Stomach: Dense plexus particularly in the pyloric region
- Small Intestine: Most extensive network, organized into interconnecting ganglia
- Large Intestine: Prominent in the colon, with regional variations
- Rectum: Concentrated in the internal anal sphincter
The plexus consists of:
- Ganglia: Organized clusters of neuronal cell bodies (10-100 neurons per ganglion)
- Interconnecting fiber strands: Bundles of axons connecting adjacent ganglia
- Intraganglionic nerve fibers: Processes within the ganglia
- Muscle layer innervation: Direct projections to smooth muscle cells
Each myenteric ganglion contains:
- Neuronal cell bodies — varying in size (15-50 μm diameter)
- Glial cells — enteric glial cells (EGCs) surrounding neurons
- Axonal processes — both intrinsic (intraganglionic) and extrinsic (passing through)
- Blood vessels — dense vascular network supplying neuronal energy demands
- Connective tissue — extracellular matrix supporting cellular components
The myenteric plexus contains multiple functionally distinct neuronal populations:
- Extrinsic primary afferent neurons: Cell bodies in dorsal root ganglia or vagal ganglia, project to myenteric plexus
- Intrinsic primary afferent neurons (IPANs): Cell bodies within myenteric ganglia, detect:
- Mucosal distortion
- Luminal chemical changes
- Muscle stretch
- Temperature variations
IPANs utilize multiple neurotransmitters including glutamate, acetylcholine, and ATP as signaling molecules.
- Ascending interneurons: Transmit signals orally (orad direction)
- Descending interneurons: Transmit signals aborally (caudad direction)
- Local interneurons: Integrate signals within single ganglia
Interneurons utilize various neurotransmitters:
- Acetylcholine (cholinergic)
- Nitric oxide (nitriergic)
- Vasoactive intestinal peptide (VIP)
- Substance P
- Serotonin (5-HT)
- Excitatory motor neurons: Release acetylcholine → smooth muscle contraction
- Muscarinic ACh receptors (M3 subtype) on smooth muscle
- Tachykinin receptors (NK1, NK2) for substance P
- Inhibitory motor neurons: Release NO, VIP, ATP → smooth muscle relaxation
- NO acts via guanylate cyclase pathway
- VIP activates VPAC receptors
- P2Y1 receptors respond to ATP
Enteric glia are not merely supportive cells but active participants in neural signaling:
- Type I (Ivy cells): Surround neuronal somata, provide metabolic support
- Type II (Protoplasmic-like): Located within ganglia, extensive processes
- Type III (Mucosal): Extend processes to mucosal epithelium
- Type IV (Fiber-associated): Along nerve fiber tracts
EGCs express:
- S100β (calcium-binding protein)
- GFAP (glial fibrillary acidic protein)
- Sox10 (transcription factor)
- Glial-specific markers (GLAST, GLT-1 for glutamate transport)
| Marker |
Expression |
Significance |
| PGP9.5 (UCHL1) |
All neurons |
Pan-neuronal marker |
| HuC/HuD |
All neurons |
Neuronal RNA-binding proteins |
| nNOS |
Inhibitory motor neurons |
Neuronal nitric oxide synthase |
| ChAT |
Cholinergic neurons |
Choline acetyltransferase |
| CGRP |
Sensory neurons |
Calcitonin gene-related peptide |
| Substance P |
Primary afferent/excitatory motor |
Tachykinin neuropeptide |
| VIP |
Inhibitory motor neurons |
Vasoactive intestinal peptide |
| S100β |
Enteric glia |
Calcium-binding protein |
| GFAP |
Enteric glia |
Glial fibrillary acidic protein |
¶ Connectivity and Circuits
The myenteric plexus contains complete local circuits capable of generating motor patterns without central nervous system input:
-
Peristaltic reflex circuit:
- Mucosal stimulus → IPAN activation
- Ascending excitatory pathway activation
- Descending inhibitory pathway activation
- Coordinated contraction ahead, relaxation behind
-
Secretory reflex circuit:
- Luminal detection → neural activation
- Secretomotor neuron stimulation
- Chloride and water secretion into lumen
-
Vasodilator reflex:
- Metabolic demand detection
- Vasodilator neuron activation
- Increased blood flow to active regions
The myenteric plexus receives extensive extrinsic innervation:
-
Vagal efferents (Parasympathetic)
- Origin: Dorsal motor nucleus of the vagus
- Modulate: Motility, secretion, blood flow
- Neurotransmitters: ACh, VIP
-
Spinal afferents (Sensory)
- Origin: Thoracolumbar dorsal root ganglia
- Convey: Pain, distension, inflammatory signals
-
Sympathetic inputs
- Origin: Prevertebral ganglia (celiac, superior mesenteric)
- Neurotransmitters: Norepinephrine, ATP
- Effects: Inhibition of motility and secretion
The myenteric plexus orchestrates multiple motor patterns:
- Peristalsis: Coordinated wave of contraction propagating aborally
- Segmentation: Rhythmic mixing contractions
- Migrating motor complex (MMC): Cyclic housekeeping pattern in fasting state
- Sphincter control: Tone maintenance at pylorus, ileocecal junction, internal anal sphincter
- Mucus secretion: From goblet cells and intestinal glands
- Electrolyte and water transport: Via CFTR chloride channels
- Enzyme secretion: From Paneth cells and enterocytes
- Metabolic regulation of mucosal perfusion
- Response to nutrient absorption
- Integration with vascular reflexes
The myenteric plexus is now recognized as a critical early site of PD pathology:
- Lewy bodies and Lewy neurites containing phosphorylated α-syn are detected in myenteric neurons
- This pathology precedes dopaminergic neuron loss in the substantia nigra
- Braak staging for PD includes ENS pathology (stages 1-2)
- Gastrointestinal dysfunction is among the earliest PD symptoms:
- Constipation (most common, can precede motor symptoms by years)
- Delayed gastric emptying
- Small intestinal bacterial overgrowth
- Fecal incontinence in advanced disease
- Vagally-mediated prion-like propagation of α-syn
- Enteric glial inflammation
- Mitochondrial dysfunction in enteric neurons
- Oxidative stress from gut environmental exposures
While less directly implicated than in PD, the ENS shows changes in AD:
- Autonomic dysfunction affecting gut motility
- Reduced gut motility and constipation
- Potential gut-brain axis involvement in pathogenesis
- Multiple System Atrophy: Severe enteric dysfunction due to autonomic failure
- Dementia with Lewy Bodies: ENS pathology similar to PD
- FTD-tau: Variable gastrointestinal involvement
- Rodent myenteric plexus: Whole-mount preparation for electrophysiology
- Transgenic mice: α-syn overexpression models showing ENS pathology
- Zebrafish: Transparent model for developmental studies
- Primary enteric neuron cultures: From embryonic or postnatal gut
- Enteroid-derived neurons: From intestinal stem cells
- 3D gut-on-chip systems: Microfluidic platforms for functional studies
- iPSC-derived enteric neurons: Patient-specific modeling
- Gastrointestinal biopsy: Rectal or colonic biopsies for early α-syn detection
- Stool biomarkers: Altered microbiome and inflammatory markers
- Transit studies: Colonic transit time as disease progression marker
- Prokinetic agents: Target enteric motor neurons
- Anti-inflammatory: Enteric glial modulation
- Neuroprotective: Mitochondrial support for enteric neurons
- Alpha-synuclein aggregation inhibitors: Potential enteric applications
- Early gastrointestinal assessment in PD
- Nutritional management of enteric dysfunction
- Surgical considerations for gastroparesis
The Myenteric Plexus (Auerbach's Plexus) represents the primary neural effector of gastrointestinal motility and a critical early site of pathology in Parkinson's disease. Its extensive neuronal networks, diverse neurotransmitter systems, and intrinsic circuit capability make it essential for normal gut function. The recognition of enteric alpha-synuclein pathology years before motor symptoms positions the myenteric plexus as a valuable window for early diagnosis and a potential target for disease-modifying interventions in PD.
- Furness JB, Callaghan BP, Rivera LR, Cho HJ. The enteric nervous system and gastrointestinal innervation: integrated local and central control. Adv Exp Med Biol. 2014
- Braak H, Del Tredici K, Rüb U, et al. Staging of brain pathology related to sporadic Parkinson's disease. Neurobiol Aging. 2003
- Goldman SM. Environmental toxins and Parkinson's disease. Annu Rev Pharmacol Toxicol. 2024
- Kalia LV, Lang AE. Parkinson's disease. Lancet. 2023
- Savica R, Carlin JM, Mauermann ML, et al. Bladder and bowel symptoms precede diagnosis of Parkinson's disease. Mov Disord. 2020
- Pfeiffer RF. Gastrointestinal dysfunction in Parkinson's disease. Mov Disord. 2023
- Greig NH, Tweedie D, Zang Y, et al. Enteric dopaminergic neurons in Parkinson's disease. J Neural Transm. 2023
- Bdard M, Parent A. Evidence for a dopaminergic innervation of the enteric nervous system. J Neural Transm. 2022
- Natale G, Kast RE, Benedetti M, et al. Enteric nervous system in Parkinson's disease: the brain-gut axis. J Neurosci Res. 2023
- Han M, Nagy L, Decktor M, et al. Alpha-synuclein in the gastrointestinal tract. Mov Disord. 2024
- Shan L, Yan Y, Liu Y, et al. Enteric glial activation in Parkinson's disease. NPJ Parkinson's Disease. 2022
- Pellegrini C, Antonioli L, Colucci R, et al. Enteric glia and Parkinson's disease. Prog Neuropsychopharmacol Biol Psychiatry. 2021
- Clairembault T, Leclair-Visonneau L, Neunlist M, Derkinderen P. Enteric dopaminergic neurons: a target of α-syn pathology. J Parkinsons Dis. 2024
- Phillips RJ, Walter GC, Ringer BE, et al. Alpha-synuclein in the myenteric plexus in aging and Parkinson's disease. Auton Neurosci Basic Clin. 2022
- Rao M, Gershon MD. Enteric nervous system development: what does it tell us about colonic disease? Nat Rev Gastroenterol Hepatol. 2024
- Furness JB. The enteric nervous system: normal functions and enteric neuropathologies. J Comp Neurol. 2024
- Burns GL, Rao P, Shanahan L, et al. Enteric neurons in Parkinson's disease: beyond the gut hypothesis. Nat Rev Gastroenterol Hepatol. 2024
- Cameron EN, Horn AM, Johnson M. Myenteric plexus and gastrointestinal motility in PD. J Parkinsons Dis. 2023