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Acetic Acid-Induced Writhing Is Temporally Dissociated from Gastrointestinal Motility in Freely Moving Rats
Honoka Kuroyanagi1, Hayato Kusakabe1, Yuji Ikegaya1,2,3
1Graduate School of Pharmaceutical Sciences, The University of Tokyo, Tokyo 113-0033, Japan.
Biological & Pharmaceutical Bulletin
|May 17, 2026
Summary
The acetic acid-induced writhing test, used for pain research, does not involve gut motor activity. This study shows writhing occurs independently of gastrointestinal contractions, indicating distinct pain signaling.
Area of Science:
- Neuroscience
- Pharmacology
- Gastroenterology
Background:
- The acetic acid-induced writhing test is a common method for evaluating visceral pain and the effectiveness of analgesics.
- It is often assumed that writhing behavior is linked to gastrointestinal motor activity, but this connection has not been directly investigated.
Purpose of the Study:
- To determine if gastrointestinal motility directly triggers writhing behavior in a visceral pain model.
- To investigate the relationship between gut motor activity and acetic acid-induced writhing in rats.
Main Methods:
- Simultaneous recording of antral and duodenal motility using strain gauge transducers in freely moving rats.
- Analysis of motility data during acetic acid-induced writhing events using a hidden Markov model.
- Pharmacological suppression of gastrointestinal motility using scopolamine butylbromide.
Main Results:
- No time-locked changes in antral or duodenal motility were observed in relation to writhing events.
- Writhing behavior continued even after gastrointestinal motility was pharmacologically suppressed.
- Acetic acid-induced writhing was found to be temporally dissociated from gastrointestinal contractions.
Conclusions:
- Writhing behavior in the acetic acid model is independent of gastrointestinal motor activity.
- The study provides direct evidence that writhing reflects visceral nociceptive signaling separate from gut motility.
- This finding clarifies the underlying mechanisms of visceral pain assessment in preclinical models.
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