title: Depressive-like states heighten the aversion to painful stimuli in a rat model of comorbid chronic pain and depression.
abstract: BACKGROUND
  Chronic pain and depression are two complex states with sensory/somatic and emotional components, and they may mutually exacerbate one another in conditions of comorbidity, leading to a poorer prognosis.
  
  
  METHODS
  The authors have evaluated the sensory and emotional components in a rat model combining chronic constriction injury (CCI, a model of chronic neuropathic pain) with unpredictable chronic mild stress (CMS, an experimental model of depression). In addition, the phosphorylation/activation of the extracellular signal-regulated kinases 1 and 2 and neuronal density was also evaluated in the anterior cingulate cortex. Four groups were tested: sham-control, sham-CMS, CCI-control, and CCI-CMS.
  
  
  RESULTS
  CMS selectively heightens aversion to painful experiences in animals subjected to CCI, as measured in the place escape/avoidance test at 20, 25, and 30 min (CCI-CMS (mean±SEM): 75.68±3.32, 66.75±4.70, 77.54±3.60 vs. CCI-control: 44.66±6.07, 43.17±6.92, 52.83±5.92, respectively), in conjunction with an increase in the accumulation of phosphorylation/activation of the extracellular signal-regulated kinases (CCI-CMS: 4.17±0.52 vs. sham-control: 0.96±0.05) and a decrease in neuronal density in the anterior cingulate cortex. In contrast, chronic pain did not exacerbate the characteristic profile of depression (anhedonia and behavioral despair) in rats subjected to CMS. Furthermore, depression enhances the perception of some specific modalities of sensorial pain such as cold allodynia but has no influence on mechanical threshold.
  
  
  CONCLUSIONS
  These findings support the theory that depression leads to emotional dysfunction in the interpretation of pain in patients suffering chronic pain. In addition, combined animal models of pain-depression may provide a valuable tool to study the comorbidity of pain and depression.
authors: Department of Neuroscience (Pharmacology and Psychiatry), University of Cádiz, Centro de Investigación Biomédica en Red de Salud Mental (CIBERSAM), Cádiz, Spain.
authors: Lidia
authors: L
authors: Bravo
authors: Juan Antonio
authors: JA
authors: Mico
authors: Raquel
authors: R
authors: Rey-Brea
authors: Beatriz
authors: B
authors: Pérez-Nievas
authors: Juan Carlos
authors: JC
authors: Leza
authors: Esther
authors: E
authors: Berrocoso
mesh_terms: D000818:Animals; D059350:Chronic Pain / Q000097:blood / Q000503:physiopathology*; D003345:Corticosterone / Q000097:blood; D003863:Depression / Q000097:blood / Q000503:physiopathology*; D004195:Disease Models, Animal; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D006179:Gyrus Cinguli / Q000502:physiology; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D048049:Extracellular Signal-Regulated MAP Kinases; D003345:Corticosterone