title: The influence of morphine on cerebral 5-HT2A availability in dogs: a SPECT study.
abstract: 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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Medicine and Clinical Biology of Small Animals, Faculty of Veterinary Medicine, Ghent University, Merelbeke, Belgium. antita.adriaens@gmail.com
authors.forename: Antita M
authors.initials: AM
authors.lastname: Adriaens
authors.forename: Ingeborgh E
authors.initials: IE
authors.lastname: Polis
authors.forename: Simon T
authors.initials: ST
authors.lastname: Vermeire
authors.forename: Tim
authors.initials: T
authors.lastname: Waelbers
authors.forename: Luc
authors.initials: L
authors.lastname: Duchateau
authors.forename: Stanislas U
authors.initials: SU
authors.lastname: Sys
authors.forename: Sylvia
authors.initials: S
authors.lastname: Van Dorpe
authors.forename: Jos L
authors.initials: JL
authors.lastname: Eersels
authors.forename: Bart
authors.initials: B
authors.lastname: De Spiegeleer
authors.forename: Kathelijne
authors.initials: K
authors.lastname: Peremans
mesh_terms: D000818:Animals; D001921:Brain / Q000000981:diagnostic imaging* / Q000187:drug effects / Q000378:metabolism*; D004285:Dogs; D005260:Female; D009020:Morphine / Q000494:pharmacology*; D044402:Receptor, Serotonin, 5-HT2A / Q000378:metabolism*; D015899:Tomography, Emission-Computed, Single-Photon
chemical_list: D044402:Receptor, Serotonin, 5-HT2A; D009020:Morphine