Intrathecal pre-administration of fentanyl effectively suppresses formalin evoked c-Fos expression in spinal cord of rat.
OBJECTIVE
To investigate whether the timing of intrathecal administration of the opioid analgesic fentanyl, alters noxious stimulus-evoked neuronal activity in the rat spinal cord.


METHODS
A 5% formalin solution was used as the noxious stimulant. For the pretreatment group, a dose of 0.001 to 0.5 microg of fentanyl was injected intrathecally ten minutes prior to formalin injection. Early and late post-treatment groups received 0.01 to 0.5 microg fentanyl, five and 60 min after formalin injection respectively. The effect of fentanyl was confirmed with naloxone. The level of c-Fos expression was determined in each treatment group to indicate neuronal activity.


RESULTS
Pretreatment and early post-treatment groups showed suppression of c-Fos activity compared to the vehicle (P <0.01). The late post-treatment group showed no difference in c-Fos activity compared to the vehicle (P=NS). Pretreatment with fentanyl showed the most profound suppression of c-Fos expression (P <0.01). In addition, pretreatment injection showed a greater suppression of c-Fos activity in the deep (14.6% of control) compared to the superficial laminae (32.7% of control; P <0.01), whereas the early post-treatment group showed a universal decrease in c-Fos activity (49.2% of control in laminae I and II, 50.4% of control in laminae III and IV and 51.8% of control in laminae V and VI). Naloxone reversed the action of fentanyl on c-Fos activity.


CONCLUSIONS
Inasmuch as: 1) c-Fos expression can be equated with behavioural changes; 2) injection of formalin is an appropriate model of surgical trauma; and 3) animal data can be transports to humans, these results suggest that fentanyl would be an effective pre-emptive analgesic.
Nakamura
T
T
Department of Anesthesiology, Miyazaki Medical College, Miyazaki, Japan. zenigata@post1.miyazaki-med.ac.jp.
Takasaki
M
M
D000698:Analgesia / Q000379:methods*; D000701:Analgesics, Opioid / Q000494:pharmacology*; D000818:Animals; D005283:Fentanyl / Q000008:administration & dosage / Q000494:pharmacology*; D005557:Formaldehyde / Q000494:pharmacology*; D007150:Immunohistochemistry; D008297:Male; D011292:Premedication; D016760:Proto-Oncogene Proteins c-fos / Q000032:analysis*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013116:Spinal Cord / Q000737:chemistry / Q000187:drug effects* / Q000502:physiology
D000701:Analgesics, Opioid; D016760:Proto-Oncogene Proteins c-fos; D005557:Formaldehyde; D005283:Fentanyl