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Sensitization by in vitro incubation with morphine of the myenteric plexus-longitudinal muscle preparation
Abstract:
1. Myenteric plexus-longitudinal muscle strip preparations from guinea-pig incubated in Krebs solutions at room temperature and bubbled with carbogen gas did not show any functional alteration during 24 h. 2. Moreover, preparations incubated in Krebs solutions did not show any change on the inhibition response produced by liberation of opiaceous material caused by 10 Hz tetanizing stimulation, nor in sensitivity to morphine. 3. When these preparations were incubated in 2.5 X 10(-7) M morphine solutions in Krebs in the same conditions than the preparations incubated without morphine a greater inhibitory response after the 10 Hz tetanizing shock could be seen, as well as a greater sensitivity to morphine, being both phenomena correlatable with the incubation time. Significant statistical differences could be seen for incubation times longer than one hour. From these results we conclude that prolonged in vitro exposition of the myenteric plexus-longitudinal muscle preparation to morphine produced a sensitization of the opiate receptor.
Insights
Prolonged incubation of guinea-pig myenteric plexus-longitudinal muscle strips with morphine in vitro led to increased opiate receptor sensitivity. This sensitization was observed after one hour of exposure, indicating a functional change in the myenteric plexus.
Area of Science:
- Neuroscience
- Pharmacology
- Gastroenterology
Background:
- The myenteric plexus controls gastrointestinal motility.
- Opiate receptors in the gut play a role in regulating gut function.
- Understanding how opioids affect the myenteric plexus is crucial for managing pain and gut disorders.
Purpose of the Study:
- To investigate the functional effects of prolonged morphine exposure on guinea-pig myenteric plexus-longitudinal muscle preparations.
- To determine if morphine exposure alters opiate receptor sensitivity in vitro.
- To establish the time course of any observed changes.
Main Methods:
- Myenteric plexus-longitudinal muscle strips from guinea-pigs were prepared and maintained in Krebs solution.
- Preparations were incubated with or without morphine (2.5 x 10(-7) M) at room temperature.
- Functional responses were assessed using 10 Hz tetanizing stimulation before and after incubation.
- Sensitivity to morphine was evaluated.
Main Results:
- Incubation in Krebs solution alone did not alter preparation function or response to stimulation.
- Morphine incubation led to a significantly greater inhibitory response to tetanizing stimulation.
- Increased sensitivity to morphine was observed, correlating with incubation time (significant after 1 hour).
Conclusions:
- Prolonged in vitro exposure to morphine sensitizes the opiate receptor in the myenteric plexus-longitudinal muscle preparation.
- This sensitization may contribute to altered gut motility and opioid tolerance in chronic opioid users.
- The findings highlight the dynamic nature of opioid receptor function in the enteric nervous system.