Enteric Neurons in Multiple System Atrophy

Enteric Neurons in Multiple System Atrophy

Introduction

<table class="infobox infobox-cell">
<tr>
<th class="infobox-header" colspan="2">Enteric Neurons in Multiple System Atrophy</th>
</tr>
<tr>
<td class="label">Taxonomy</td>
<td>ID</td>
</tr>
<tr>
<td class="label">Cell Ontology (CL)</td>
<td>[CL:0007011](https://www.ebi.ac.uk/ols4/ontologies/cl/classes/http%253A%252F%252Fpurl.obolibrary.org%252Fobo%252FCL_0007011)</td>
</tr>
<tr>
<td class="label">Database</td>
<td>ID</td>
</tr>
<tr>
<td class="label">Cell Ontology</td>
<td>[CL:0007011](https://www.ebi.ac.uk/ols4/ontologies/cl/classes/http%253A%252F%252Fpurl.obolibrary.org%252Fobo%252FCL_0007011)</td>
</tr>
<tr>
<td class="label">Cell Ontology</td>
<td>[CL:4042028](https://www.ebi.ac.uk/ols4/ontologies/cl/classes/http%253A%252F%252Fpurl.obolibrary.org%252Fobo%252FCL_4042028)</td>
</tr>
<tr>
<td class="label">Feature</td>
<td>MSA</td>
</tr>
<tr>
<td class="label">GI onset</td>
<td>Often precedes motor</td>
</tr>
<tr>
<td class="label">Constipation severity</td>
<td>Severe</td>
</tr>
<tr>
<td class="label">Alpha-syn spread</td>
<td>Oligodendrocyte-first</td>
</tr>
</table>

Enteric Neurons in Multiple System Atrophy

Introduction

<table class="infobox infobox-cell">
<tr>
<th class="infobox-header" colspan="2">Enteric Neurons in Multiple System Atrophy</th>
</tr>
<tr>
<td class="label">Taxonomy</td>
<td>ID</td>
</tr>
<tr>
<td class="label">Cell Ontology (CL)</td>
<td>[CL:0007011](https://www.ebi.ac.uk/ols4/ontologies/cl/classes/http%253A%252F%252Fpurl.obolibrary.org%252Fobo%252FCL_0007011)</td>
</tr>
<tr>
<td class="label">Database</td>
<td>ID</td>
</tr>
<tr>
<td class="label">Cell Ontology</td>
<td>[CL:0007011](https://www.ebi.ac.uk/ols4/ontologies/cl/classes/http%253A%252F%252Fpurl.obolibrary.org%252Fobo%252FCL_0007011)</td>
</tr>
<tr>
<td class="label">Cell Ontology</td>
<td>[CL:4042028](https://www.ebi.ac.uk/ols4/ontologies/cl/classes/http%253A%252F%252Fpurl.obolibrary.org%252Fobo%252FCL_4042028)</td>
</tr>
<tr>
<td class="label">Feature</td>
<td>MSA</td>
</tr>
<tr>
<td class="label">GI onset</td>
<td>Often precedes motor</td>
</tr>
<tr>
<td class="label">Constipation severity</td>
<td>Severe</td>
</tr>
<tr>
<td class="label">Alpha-syn spread</td>
<td>Oligodendrocyte-first</td>
</tr>
</table>

The enteric nervous system (ENS), often called the "second brain," is a complex network of neurons embedded in the lining of the gastrointestinal tract. Multiple system atrophy (MSA) is a fatal neurodegenerative disease characterized by autonomic failure, parkinsonism, and cerebellar ataxia. The ENS is prominently affected in MSA, with alpha-synuclein pathology occurring in enteric neurons years before central nervous system symptoms manifest. This page covers the role of enteric neurons in MSA pathogenesis, clinical implications, and diagnostic significance. [@wenning2022]

<!-- taxonomy-enrichment --> [@kalia2015]

<!-- multi-taxonomy-enrichment -->

Multi-Taxonomy Classification

Taxonomy Database Cross-References

Morphology & Electrophysiology

• Morphology: enteric neuron (source: Cell Ontology)
• Morphology can be inferred from Cell Ontology classification

PanglaoDB Marker Cross-References

• Unknown (PanglaoDB):

External Database Links

• [Cell Ontology (CL:0007011)](https://www.ebi.ac.uk/ols4/ontologies/cl/classes/http%253A%252F%252Fpurl.obolibrary.org%252Fobo%252FCL_0007011)
• [OBO Foundry (CL:0007011)](http://purl.obolibrary.org/obo/CL_0007011)
• [Allen Brain Cell Atlas](https://portal.brain-map.org/atlases-and-data/bkp/abc-atlas)
• [CellxGene Census](https://cellxgene.cziscience.com/)
• [Human Cell Atlas](https://www.humancellatlas.org/)
• [PanglaoDB](https://panglaodb.se/)

Taxonomy & Classification

PanglaoDB Marker Cross-References

• Unknown (PanglaoDB):

External Database Links

• [Cell Ontology (CL:0007011)](https://www.ebi.ac.uk/ols4/ontologies/cl/classes/http%253A%252F%252Fpurl.obolibrary.org%252Fobo%252FCL_0007011)
• [OBO Foundry (CL:0007011)](http://purl.obolibrary.org/obo/CL_0007011)
• [Allen Brain Cell Atlas](https://portal.brain-map.org/atlases-and-data/bkp/abc-atlas)
• [CellxGene Census](https://cellxgene.cziscience.com/)
• [PanglaoDB](https://panglaodb.se/)

Anatomy of the Enteric Nervous System

Structure and Organization

The ENS is the largest component of the peripheral nervous system, containing approximately 200-600 million neurons organized into two major ganglionated plexuses: [@kamelgarn2018]

• Myenteric plexus (Auerbach's plexus): Located between the longitudinal and circular muscle layers
• Primary role: Control of gut motility
• Coordinates peristalsis and segmentation
• Contains sensory neurons, interneurons, and motor neurons
• Submucosal plexus (Meissner's plexus): Located in the submucosa
• Primary role: Regulation of secretion and blood flow
• Controls intestinal permeability
• Monitors luminal content

Enteric Neuron Types

The ENS contains multiple distinct neuronal populations: [@hillburns2021]

Sensory Neurons

• Intrinsic primary afferent neurons (IPANs): Detect stretch, chemical stimuli, and luminal content
• Vagal afferents: Transduce information to the central nervous system

Motor Neurons

• Excitatory motor neurons: Release acetylcholine, promote contraction
• Inhibitory motor neurons: Release nitric oxide (NO) and vasoactive intestinal peptide (VIP)

Interneurons

• Ascending interneurons: Propagate signals orally
• Descending interneurons: Propagate signals anally

Neurochemical Phenotype

Enteric neurons express various neurotransmitters: [@jost2019]

• Acetylcholine (ACh): Primary excitatory neurotransmitter
• Nitric oxide (NO): Primary inhibitory neurotransmitter
• Vasoactive intestinal peptide (VIP): Inhibitory, promotes relaxation
• Substance P: Excitatory, involved in pain transmission
• Calcitonin gene-related peptide (CGRP): Sensory signaling
• Serotonin (5-HT): Motility regulation

Alpha-Synuclein Pathology in the ENS

Pathological Features

In MSA, enteric neurons accumulate abnormal alpha-synuclein aggregates: [@gilman2008]

Propagation Hypothesis

The "body-first" propagation model suggests:

This model is supported by:

• Detection of phosphorylated alpha-synuclein in enteric neurons of pre-motor MSA patients
• Experimental models showing vagal nerve-mediated spread
• Braak staging in synucleinopathies

Vulnerability Factors

Enteric neurons in MSA show selective vulnerability:

• Oxidative stress: High metabolic activity, mitochondrial dysfunction
• Neuroinflammation: Local immune activation
• Environmental exposures: Gut microbiome alterations
• Genetic susceptibility: GBA mutations, SNCA polymorphisms

Clinical Manifestations

Gastrointestinal Dysautonomia

Constipation

• Prevalence: Up to 90% of MSA patients
• Onset: Often precedes motor symptoms by years
• Mechanism: Loss of inhibitory enteric neurons, impaired peristalsis
• Severity: Progressive, often refractory to laxatives

Gastroparesis

• Delayed gastric emptying: Nausea, early satiety
• Small intestinal bacterial overgrowth (SIBO): Bloating, malabsorption
• Dysphagia: Oropharyngeal phase involvement

Urinary Dysfunction

Early Features

• Nocturia: Frequent nighttime urination
• Urgency: Sudden urge to urinate
• Frequency: Increased daytime urination

Later Features

• Urinary retention: Incomplete bladder emptying
• Overflow incontinence: Dribbling urination
• Neurogenic bladder: Detrusor overactivity or underactivity

Cardiovascular Dysautonomia

Orthostatic Hypotension

• Definition: ≥20 mm Hg systolic or ≥10 mm Hg diastolic drop within 3 minutes of standing
• Mechanism: Sympathetic neurocirculatory failure
• Symptoms: Lightheadedness, dizziness, syncope

Supine Hypertension

• Prevalence: Common in MSA with orthostatic hypotension
• Complication: Complicates treatment of orthostatic hypotension

Other Autonomic Features

• Erectile dysfunction: Often an early symptom in males
• Abnormal sweating: Anhidrosis or hyperhidrosis
• Temperature dysregulation: Intolerance to heat or cold

Diagnostic Significance

Biomarker Potential

The ENS offers accessible tissue for diagnosis:

Biopsy Studies

• Rectal biopsy: Detection of phosphorylated alpha-synuclein
• Colon biopsy: Higher sensitivity in early disease
• Submandibular gland biopsy: Higher yield than gastrointestinal sites

Sensitivity and Specificity

• Sensitivity: 50-80% in MSA
• Specificity: Challenging due to overlap with Parkinson's disease

Differential Diagnosis

Enteric involvement in MSA vs. other synucleinopathies:

Therapeutic Implications

Symptomatic Treatments

Gastrointestinal

• Prokinetic agents: Metoclopramide, domperidone
• Laxatives: Osmotic (polyethylene glycol), stimulant
• Botulinum toxin: For spasticity, achalasia
• Dietary modification: Fiber, hydration

Autonomic

• Orthostatic hypotension: Fludrocortisone, midodrine, droxidopa
• Urinary dysfunction: Anticholinergics, alpha-blockers, intermittent catheterization
• Erectile dysfunction: PDE5 inhibitors

Disease-Modifying Approaches

Neuroprotective Strategies

• Antioxidants: Targeting oxidative stress
• Anti-inflammatory agents: Modulating neuroinflammation
• Alpha-synuclein targeting: Immunotherapies, aggregation inhibitors

Emerging Therapies

• Gene therapy: Viral vector delivery of neurotrophic factors
• Cell replacement: Stem cell-derived neurons
• Microbiome modulation: Probiotics, fecal microbiota transplantation

Gut-Brain Axis in MSA

Bidirectional Communication

The gut-brain axis involves multiple pathways:

Microbiome Alterations

MSA patients show altered gut microbiota:

• Reduced diversity: Fewer bacterial species
• Proinflammatory shift: Increased Firmicutes/Bacteroidetes ratio
• SCFA producers: Decreased butyrate-producing bacteria
• Functional implications: May influence alpha-synuclein pathology

Therapeutic Targeting

Modulating the gut-brain axis:

• Probiotics: Restore microbial balance
• Prebiotics: Promote beneficial bacteria
• Fecal microbiota transplantation (FMT): Experimental approach
• Dietary intervention: Mediterranean diet, fiber supplementation

Research Directions

Current research areas include:

• Early detection: Biomarkers in enteric neurons before CNS symptoms
• Propagation mechanisms: Understanding alpha-synuclein spread
• Microbiome studies: Correlation with disease progression
• Neuroprotective strategies: Targeting enteric neurons
• Personalized medicine: Genetic subtypes and enteric involvement

Summary

Enteric nervous system involvement is a hallmark of Multiple System Atrophy, with alpha-synuclein pathology detectable in enteric neurons often years before central nervous system manifestations. Gastrointestinal dysautonomia, particularly constipation, is among the earliest and most prevalent symptoms. The ENS provides accessible tissue for diagnostic biopsy and offers potential therapeutic targets. Understanding the role of enteric neurons in MSA pathogenesis may lead to earlier diagnosis and disease-modifying interventions.

See Also

• [MSA](/diseases/multiple-system-atrophy)
• [Alpha-Synuclein Pathway](/mechanisms/alpha-synuclein-pathology)
• [Parkinson's Disease](/diseases/parkinsons-disease)
• [Gut-Brain Axis](/mechanisms/gut-brain-axis-neurodegeneration)
• [Autonomic Biomarkers](/biomarkers/autonomic-function-biomarkers)

External Links

• [Cell Type Database](https://portal.brain-map.org/)
• [PubMed: Cell Type Markers](https://pubmed.ncbi.nlm.nih.gov/)