Analgesic effcacy and spinal neurotoxicity of intrathecal different doses of dexmedetomidine in rats / 中华麻醉学杂志

ABSTRACT

Objective To investigate the analgesic efficacy and spinal neurotoxicity of intrathecal (IT) different doses of dexmedetomidine in rats. Methods Sixty male SD rats weighing 180-220 g were randomly divided into 5 groups ( n = 12 each) groupnormal control (group C); group IT normal saline (group N); different doses of dexmedetomidine groups received IT dexmedetomidine 0.75, 1.50 and 3.00 μg/kg respectively (groups D1.3). Paw withdrawal threshold to mechanical stimulation (PWMT)with yon Frey filaments and tail flick latency (TFL) to a thermal nociceptive stimulus were measured before (To, baseline) and at 30 or60 rin after IT dexmedetomidine or normal saline administration (T1, T2 ) and the percentage of the maximum possible effect ( MPE ) was calculated. Lumbar segment of the spinal cord ( L4-6 ) was removed for microscopic examination and determination of c-Fos expression (by immuno-histochemistry) at 7, 24 and 48 h after IT dexmedetomidine or normal saline administration. Results PWMT, TFL and the percentage of MPE were significantly increased after IT dexmedetomidine as compared with the baseline values at T0 in groups D1-3 ( P ＜ 0.05). PWMT was significantly higher at T1 and TFL and the percentage of MPE were higher at T2 in groups D1-3 than in groups C and N,and in group D3 than in groups D1,2 ( P ＜ 0.05). At 7,24 h after IT dexmedetomidine c-Fos protein expression was significantly higher in group D3 than in groups C and N( P ＜ 0.05). There was no significant difference in c-Fos expression at 48 h after IT dexmedetomidine between group D3 and groups C and N ( P ＞ 0.05 ). At 24 h after IT dexmedetomidine c-Fos protein expression was significantly higher in group D3 than in other 4 groups( P ＜ 0.05). Slight spinal cord injury was observed at 24 h after IT dexmedetomidine in group D3. Conclusion IT dexmedetomidine has antinociceptive effect. High dose dexmedetomidine IT can produce transient reversible toxicity to the spinal cord.