Mesenteric afferent sensitivity to cholecystokinin and 5-hydroxytryptamine

Area of Science:

• Gastroenterology
• Neuroscience
• Physiology

Background:

• Enteroendocrine cells release hormones like CCK and 5-HT that modulate gut function.
• Gastrointestinal afferent fibers transmit sensory information from the gut to the central nervous system.
• Understanding the role of these signaling molecules in afferent nerve activity is crucial for gut physiology.

Purpose of the Study:

• To investigate the electrophysiological effects of CCK and 5-HT on gastrointestinal afferent fiber discharge.
• To identify the specific receptors involved in mediating the responses to CCK and 5-HT.
• To determine if CCK and 5-HT are essential for afferent signal transduction from the gut mucosa.

Main Methods:

• Electrophysiological recordings of mesenteric afferent fiber activity in response to CCK and 5-HT.
• Pharmacological characterization using selective agonists (2-methyl-5-HT) and antagonists (granisetron for 5-HT3, devazepide for CCKA).
• Assessment of afferent fiber responses to mechanical and chemical mucosal stimulation after receptor blockade.

Main Results:

• 5-Hydroxytryptamine (5-HT) caused a rapid, transient stimulation of mesenteric afferents, mediated by 5-HT3 receptors.
• Cholecystokinin (CCK) induced a long-lasting increase in afferent fiber excitability, mediated by CCKA receptors.
• Afferent fibers remained responsive to mechanical and chemical stimuli even after blocking 5-HT and CCK receptors.

Conclusions:

• CCK and 5-HT significantly influence mucosal afferent nerve sensitivity through specific receptor pathways.
• These gut hormones play a substantial role in modulating afferent signaling but are not obligatory for basic signal transduction.
• The findings highlight the complex interplay between gut hormones and sensory nerve activity in the gastrointestinal tract.