Citalopram and paroxetine are selective serotonin reuptake inhibitors and also have antinociceptive effects. We investigated the antiallodynic and antihyperalgesic effects of intrathecally administered morphine, citalopram, paroxetine, and combinations thereof, in a rat model in which peripheral inflammation was induced by complete Freund's adjuvant (CFA). Drugs were intrathecally administered via direct lumbar puncture. Mechanical allodynia was measured using a Dynamic Plantar Aesthesiometer. Thermal hyperalgesia and cold allodynia were determined by measuring latency of paw withdrawal in response to radiant heat and cold water. Behavioral tests were run before and 15, 30, 45, and 60 min after intrathecal injection. Intraplantar injection of CFA produced mechanical allodynia, thermal hyperalgesia, and cold allodynia. Intrathecally administered morphine (0.3 or 1 microg) had antiallodynic or antihyperalgesic effects (24.0%-71.9% elevation). The effects of morphine were significantly increased when a combination of citalopram (100 microg) and paroxetine (100 microg) was added (35.2%-95.1% elevation). This rise was reversed by naloxone and methysergide. The effects of citalopram and paroxetine were also reversed by naloxone and methysergide. We suggest that the mu opioid receptor and serotonin receptors play major roles in production of the antiallodynic and antihyperalgesic effects of morphine, citalopram, paroxetine, and combinations thereof, in animals experiencing inflammatory pain.
Analgesics, Opioid/administration & dosage/*pharmacology ; Animals ; Behavior, Animal/drug effects ; Citalopram/administration & dosage/pharmacology ; Disease Models, Animal ; Hyperalgesia/etiology ; Inflammation/*chemically induced/pathology ; Injections, Spinal ; Male ; Morphine/administration & dosage/*pharmacology ; Pain/*prevention & control ; Pain Measurement ; Pain Threshold/drug effects ; Paroxetine/administration & dosage/pharmacology ; Rats ; Rats, Sprague-Dawley ; Receptors, Serotonin/*chemistry/metabolism ; Serotonin Uptake Inhibitors/administration & dosage/*pharmacology ; Temperature ; Time Factors

The present study aimed at evaluation of prophylactic efficacy and possible mechanisms of asiaticoside (AS) based standardized extract of Centella asiatica (L.) Urban leaves (INDCA) in animal models of migraine. The effects of oral and intranasal (i.n.) pretreatment of INDCA (acute and 7-days subacute) were evaluated against nitroglycerine (NTG, 10 mg·kg(-1), i.p.) and bradykinin (BK, 10 μg, intra-arterial) induced hyperalgesia in rats. Tail flick latencies (from 0 to 240 min) post-NTG treatment and the number of vocalizations post-BK treatment were recorded as a measure of hyperalgesia. Separate groups of rats for negative (Normal) and positive (sumatriptan, 42 mg·kg(-1), s.c.) controls were included. The interaction of INDCA with selective 5-HT1A, 5-HT1B, and 5-HT1D receptor antagonists (NAN-190, Isamoltane hemifumarate, and BRL-15572 respectively) against NTG-induced hyperalgesia was also evaluated. Acute and sub-acute pre-treatment of INDCA [10 and 30 mg·kg(-1) (oral) and 100 μg/rat (i.n.) showed significant anti-nociception activity, and reversal of the NTG-induced hyperalgesia and brain 5-HT concentration decline. Oral pre-treatment with INDCA (30 mg·kg(-1), 7 d) showed significant reduction in the number of vocalization. The anti-nociceptive effects of INDCA were blocked by 5-HT1A and 5-HT1B but not 5-HT1D receptor antagonists. In conclusion, INDCA demonstrated promising anti-nociceptive effects in animal models of migraine, probably through 5-HT1A/1B medicated action.
Administration, Intranasal ; Administration, Oral ; Animals ; Bradykinin ; Female ; Hyperalgesia ; chemically induced ; prevention & control ; Male ; Migraine Disorders ; chemically induced ; prevention & control ; Models, Animal ; Nitroglycerin ; Nociception ; drug effects ; Plant Leaves ; chemistry ; Pre-Exposure Prophylaxis ; Rats ; Rats, Wistar ; Reaction Time ; Receptors, Serotonin, 5-HT1 ; drug effects ; Serotonin 5-HT1 Receptor Antagonists ; metabolism ; Tail ; physiology ; Triterpenes ; administration & dosage ; pharmacology