Plexus muscularis profundus and associated interstitial cells. II. Ultrastructural studies of mouse small intestine

Area of Science:

• Gastroenterology
• Neuroscience
• Cell Biology

Background:

• The enteric nervous system controls gastrointestinal function.
• The plexus muscularis profundus (PMP) is a key neural network within the intestinal wall.
• Understanding PMP's ultrastructure is crucial for elucidating gut motility and sensation.

Purpose of the Study:

• To investigate the ultrastructure of the plexus muscularis profundus (PMP) in the mouse small intestine.
• To characterize different nerve terminal types within the PMP.
• To explore the cellular interactions between nerve terminals, interstitial cells of Cajal (ICC-III), and muscle cells.

Main Methods:

• Vascular perfusion of mouse small intestine using ruthenium red-containing and routine aldehyde fixatives.
• Transmission electron microscopy to examine the ultrastructure of nerve terminals, ICC-III, and associated cells.
• Analysis of synaptic contacts, vesicle types, and intercellular junctions.

Main Results:

• Four distinct nerve terminal types (I-IV) were identified in the PMP based on vesicle content and morphology.
• Nerve terminals (Types I-III) formed synapse-like contacts primarily with interstitial cells of Cajal (ICC-III).
• ICC-III exhibited characteristics suggesting modulatory roles and formed gap junctions with muscle cells, while fibroblast-like cells were distinct and not involved in neural signaling.

Conclusions:

• Nerve terminals in the PMP likely innervate ICC-III, rather than directly innervating muscle cells.
• The ultrastructure of ICC-III supports their role in modulating intestinal function, potentially acting as both efferent and afferent pathways.
• This study provides detailed ultrastructural insights into the neural circuitry of the intestinal muscularis.