A rat model of chronic lumbar epidural catheterisation.
OBJECTIVE
There are no rodent models of chronic epidural catheterisation which can induce clinically relevant analgesic effects of morphine (potency ratio of intrathecal:epidural = 10 to 30:1). The purpose of this study was to investigate a new rat model of chronic epidural catheterisation by comparing the analgesic effect of epidural and intrathecal morphine.


METHODS
In Sprague-Dawley rats, for epidural catheterisation, a skin incision and muscle dissection were made at T13 level in the midline. The intervertebral ligament was cut to insert an epidural catheter (polyethylene tube; outer diameter 0.14 mm) 2 cm caudally. The distal end of the catheter (0.61 mm) was passed s.c. to exit in the dorsal neck area. For intrathecal catheterisation, the atlanto-occipital membrane was incised to insert a catheter (0.61 mm) 8.5 cm caudally. The effects of morphine (1, 3, 10, 30, or 100 micrograms.10 microliters-1 intrathecally, and 30, 100, or 300 micrograms.5, 10, or 20 microliters-1 epidurally) on thermal escape latency were investigated by a hot box test. Behaviour and motor function were also tested.


RESULTS
A volume of 20 microliters induced greater analgesic effect than 5 and 10 microliters epidural administration. The ED50 of epidural morphine (94.1 micrograms) was 30 times more than that of intrathecal morphine (3.1 micrograms).


CONCLUSIONS
A new rat model of chronic epidural catheterisation is described, which provides a similar analgesic epidural: intrathecal potency ratio for morphine to that in humans when morphine is administered in a volume of 20 microliters.
Nishiyama
T
T
Department of Anesthesiology, University of Tokyo, Faculty of Medicine, Japan.
D017109:Akathisia, Drug-Induced / Q000209:etiology; D015360:Analgesia, Epidural / Q000295:instrumentation / Q000379:methods*; D000701:Analgesics, Opioid / Q000008:administration & dosage / Q000009:adverse effects / Q000627:therapeutic use*; D000818:Animals; D001269:Atlanto-Occipital Joint; D001522:Behavior, Animal / Q000187:drug effects; D002375:Catalepsy / Q000139:chemically induced; D002408:Catheters, Indwelling; D004195:Disease Models, Animal; D004305:Dose-Response Relationship, Drug; D006358:Hot Temperature / Q000009:adverse effects; D007278:Injections, Spinal; D008159:Lumbar Vertebrae; D009020:Morphine / Q000008:administration & dosage / Q000009:adverse effects / Q000627:therapeutic use*; D009048:Motor Skills / Q000187:drug effects; D009619:Nociceptors / Q000187:drug effects; D051381:Rats; D017207:Rats, Sprague-Dawley; D012018:Reflex / Q000187:drug effects; D013904:Thoracic Vertebrae
D000701:Analgesics, Opioid; D009020:Morphine