Related Experiment Video
Updated: May 17, 2026

Assessment of Morphine-induced Hyperalgesia and Analgesic Tolerance in Mice Using Thermal and Mechanical Nociceptive Modalities
Published on: July 29, 2014
The influence of morphine on cerebral 5-HT2A availability in dogs: a SPECT study
Antita M Adriaens1, Ingeborgh E Polis, Simon T Vermeire
1Medicine and Clinical Biology of Small Animals, Faculty of Veterinary Medicine, Ghent University, Merelbeke, Belgium. antita.adriaens@gmail.com
Unlabelled:
The opioid and serotonergic systems are closely involved in pain processing and mood disorders. The aim of this study was to assess the influence of systemic morphine on cerebral serotonin 2A receptor (5-HT(2A)) binding in dogs using SPECT with the 5-HT(2A) radioligand (123)I-5I-R91150.
Methods:
5-HT(2A) binding was estimated with and without morphine pretreatment in 8 dogs. The 5-HT(2A) binding indices in the frontal, parietal, temporal, and occipital cortex and in the subcortical region were obtained by semiquantification.
Results:
A significantly decreased 5-HT(2A) binding index was found in the morphine group for the right (morphine, 1.41 ± 0.06; control, 1.52 ± 0.10) and left (morphine, 1.44 ± 0.08; control, 1.55 ± 0.11) frontal cortices, with P = 0.012 and P = 0.040, respectively. No significant differences were noted for the other regions.
Conclusion:
Morphine decreased the frontocortical 5-HT(2A) availability, confirming an interaction between the 5-HTergic and the opioid systems. Whether this interaction is caused by decreased receptor density due to direct internalization or is the result of indirect actions, such as increased endogenous serotonin release, remains to be elucidated.
Related Concept Videos
Opioid Analgesics: Synthetic and Semisynthetic Opioids
Analgesia and Pain Management
Opioid Receptors: Overview
Opioid Analgesics: Morphine and Other Natural Cogeners
Drug Abuse and Addiction: Pharmacological Phenomena
Drugs Affecting Neurotransmitter Release or Uptake

