title: Reproducibility of the drug effects over time on chronic lumbar epidural catheterization in rats.
abstract: Chronically implanted epidural catheters lead to a reaction that impedes drug action. The purpose of this study in a rat model with chronically implanted epidural catheters was to investigate the change in opiate activity and histology over time with this model. A skin incision of 1-2 cm was made at the T 13 level on the back of male Sprague-Dawley rats under halothane anesthesia. Muscles were dissected bluntly from the vertebrae, and the intervertebral ligament was cut to insert an epidural catheter (polyethylene tube, outer diameter of 0.14 mm) 2-cm caudally. The longer portion of the catheter was passed through a trocar subcutaneously to exit the dorsal neck area. One, two, and six days after catheterization, the effects of morphine on thermal stimulation using the hot-box test and histology were investigated. Analgesic effects of morphine 6 days after catheterization were significantly less than those on the first and second days. Histologically, evidence of inflammation around the catheter was noted as early as 4 h after catheterization. Pericatheter fibrosis was severe after 2 days. We conclude that this model of chronic epidural catheterization in the rat evoked a histologically defined, pharmacodynamically significant, local reaction 2 to 6 days after catheter implantation.
  
  
  CONCLUSIONS
  A rat model with chronically implanted epidural catheters should be used for testing the analgesic effects of drugs within two days after catheterization.
authors.affiliation: Department of Anesthesiology, The University of California, San Diego, USA.
authors.forename: T
authors.initials: T
authors.lastname: Nishiyama
authors.forename: K
authors.initials: K
authors.lastname: Hanaoka
mesh_terms: D015360:Analgesia, Epidural / Q000009:adverse effects* / Q000379:methods; D000701:Analgesics, Opioid / Q000008:administration & dosage / Q000494:pharmacology*; D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects; D002408:Catheters, Indwelling / Q000009:adverse effects*; D004305:Dose-Response Relationship, Drug; D004824:Epidural Space; D006930:Hyperalgesia / Q000209:etiology; D008161:Lumbosacral Region; D008297:Male; D009020:Morphine / Q000008:administration & dosage / Q000494:pharmacology*; D009619:Nociceptors / Q000187:drug effects; D011595:Psychomotor Agitation / Q000209:etiology; D051381:Rats; D017207:Rats, Sprague-Dawley; D015203:Reproducibility of Results; D013997:Time Factors
chemical_list: D000701:Analgesics, Opioid; D009020:Morphine