Ondansetron does not block tramadol-induced analgesia in mice.

Tramadol is a weak opioid agonist and an inhibitor of the reuptake of noradrenaline and serotonin. This study was undertaken to assess a possible pharmacological interaction of ondansetron, a serotonin-3 (5-hydroxytryptamine-3, 5-HT3) antagonist, and tramadol in an animal model for acute pain. Sixty-three male albino mice were randomly given saline, tramadol (10, 20, and 40 mg kg(-1)), ondansetron (1, 2, and 4 mg kg(-1)), or ondansetron (1, 2, and 4 mg kg(-1)) and tramadol (20 mg kg(-1), given 10 min after ondansetron injection) intraperitoneally. Each mouse was assessed twice for tail-flick latency before saline or drug administration and 15, 30, 60, 90, and 120 min thereafter. Tramadol (10 mg kg(-1)) had no effect on pain threshold levels of mice, but tramadol doses of 20 or 40 mg kg(-1) increased pain threshold levels in a dose-dependent manner (p < 0.01 for 20 mg kg(-1) and p < 0.001 for 40 mg kg(-1)). Ondansetron doses of 1, 2, or 4 mg kg(-1) alone had no effect on pain threshold levels of mice. Tramadol (20 mg kg(-1)) and ondansetron (1, 2, and 4 mg kg(-1)) increased pain threshold levels at all doses (p < 0.001 for 1 and 2 mg kg(-1) ondansetron and p < 0.01 for 4 mg kg(-1) ondansetron). The pain threshold levels of mice given tramadol (20 mg kg(-1)) alone or tramadol and ondansetron (p > 0.05 for 1, 2, and 4 mg kg(-1)) were similar. Our results indicate that ondansetron-a 5-HT3 selective antagonist-does not decrease the analgesic effectiveness of tramadol in mice, which may be the result of different mechanisms involving 5-HT3 receptors.

Bilateral CT-guided percutaneous cordotomy for cancer pain relief.

AIM: CT-guided percutaneous cordotomy is a useful procedure for treating unilateral cancer pain, however, bilateral cordotomy can be required on some occasions. We evaluated the effectiveness and complications of bilateral cordotomy. MATERIALS AND METHODS: Two hundred and thirty-four patients who suffered from unilateral cancer pain underwent CT-guided percutaneous cordotomy. The procedure was repeated in 22 patients, and nine patients had bilateral cordotomy. Effectiveness and complications were recorded after each procedure. RESULTS: Of nine patents (three women and six men) having bilateral percutaneous cordotomy in our study, four patients had mirror pain after the first procedure. In the remaining five patients the contralateral pain was due to new pain sites. The pain scores before and after the first procedure were 9.3 (range 7-10) and 1.2 (range 0-3), respectively. After the first procedure complete or satisfactory pain relief was achieved in all patients. The duration between the two procedures ranged from 7-243 days (mean 59.8 days). The pain scores before and after the second procedure were 8.4 (range 5-10) and 1.6 (range 0-4), respectively. After the second procedure complete or satisfactory pain relief was reported in all patients. There were no complications in four patients. One patient developed transient motor deficit after the first procedure. Other complications (nausea/vomiting, headache, ipsilateral neck pain, postcordotomy dysesthesia) were mild and transient. CONCLUSION: CT-guided percutaneous cordotomy is a useful procedure for the treatment of severe unilateral cancer pain syndromes. The procedure can be repeated on the other side at least 1 week later. These results show that the success on the second side appears to be similar to the first side with low complication rate for both procedures.

The antinociceptive effect of moclobemide on the vocalization threshold to paw pressure in a rat model of unilateral mononeuropathy.

The aim of our study was to investigate the antinociceptive activity of moclobemide on the vocalization threshold to paw pressure in a rat model of unilateral mononeuropathy. The neuropathy was produced by ligation of the sciatic nerve and nociceptive thresholds were determined 15-21 days after surgery by a modification of the Randall-Sellito method. Group 1 (n= 10) received 0.2 ml peroral (p.o.) saline, Group 2 (n= 10) 5 mg x kg(-1), Group 3 (n= 10) 10 mg x kg(-1) and Group 4 (n= 10) 20 mg x kg(-1) p.o. moclobemide. Nociceptive pressure thresholds were then measured every 20 minutes after drug administration. Analysis of variance, Tukey's test and a paired Student's t-test were employed for statistical analysis. The perorally administered moclobemide (5, 10 and 20 mg x kg(-1)) produced an antinociceptive effect on both lesioned and non-lesioned hind paws ( P< 0.05). However, the analgesic effect on the lesioned paw was significantly more potent than the non-lesioned paw. The peak value ( p) remained constant while the maximal increment between the control threshold and the peak value ( I(max)) was significantly more pronounced for the lesioned paw ( P< 0.001). The results of this study may suggest that moclobemide can be a therapeutic alternative to treat some clinical symptoms in peripheral neuropathic conditions.

The antinociceptive effect of tramadol on a model of neuropathic pain in rats.

The antinociceptive activity of tramadol was investigated on the vocalization threshold to paw pressure in a rat model of unilateral mononeuropathy produced by loose ligatures around the common sciatic nerve. Despite the analgesic activity of tramadol was clearly established in motor and sensory responses of the nociceptive system in rats, the effect of this atypical opioid on experimental neuropathic pain models is not investigated. The intraperitoneally injected tramadol (2.5, 5 and 10 mg/kg) produced a potent and dose-dependent antinociceptive effect on both lesioned and non-lesioned hind paws. However, the analgesic effect on the lesioned paw was significantly more potent than the non-lesioned paw. This effect was partially antagonized by intraperitoneally administered naloxone (0.1 mg/kg) suggesting an additional non-opioid mechanism. Our results suggest that tramadol may be useful for the alleviation of some symptoms in peripheral neuropathic conditions

Electrophysiological monitoring during CT-guided percutaneous cordotomy.

During percutaneous cordotomy, impedance monitoring and electric stimulation have been widely used to enable a precise localization of the lesion electrode. The purpose of this study was to examine the possibility that the usage of additional electrophysiological techniques could help in improving the precision of the placement of the lesion electrode. Fourteen patients were monitored with 4 different techniques during CT-guided percutaneous cordotomy: 1) Median nerve somatosensory evoked potentials (mSEP): median nerve stimulation with recording from the scalp. 2) Spinal cord evoked potentials (SCEP): median nerve stimulation with recording via the cordotomy electrode. 3) Spinothalamic evoked potentials (SthEP): stimulation via the cordotomy electrode and recording from the scalp. Ipsilateral and contralateral mSEPs and SCEPs did not change after the lesion. SthEPs showed a significant decrease in 10 of 12 patients provided the stimulus intensity was kept below that producing a motor response (approx 0.5-1 mA). There was no obvious relationship between changes of the evoked potentials and the clinical outcome of the cordotomy. Our results suggest that there may be a relationship between the extent of the lesion and the decrease of the spinothalamic evoked potentials.