engleski

Pain Sensitivity in Wistar and Wistar-Zagreb 5HT Rats : the Effect of Single Dose of Fluoxetine

The forebrain and spinal 5-HT (serotonin) pathways are known to be involved in pain perception. Increasing the availability of 5-HT at the synapse by blocking 5-HT reuptake with selective serotonine reuptake inhibitors (SSRI) is reported to have no effect, enhance or reduce pain sensitivity in rats, depending on the mode of pain. Therefore, we studied the effect of fluoxetine (SSRI) on the mechanical pain thresholds in Wistar rats. To gain further insight into the role played by 5-HT in control of mechanical pain sensitivity, we examined also the effect of fluoxetine on the mechanical pain thresholds in genetically selected Wistar rats with extreme values of platelet 5-HT concentration and Vmax of platelet 5-HT uptake, named « ; high 5-HT» ; and « ; low 5-HT» ; . 8 male Wistar rats (Ruđer Bošković Institute, Zagreb, Croatia), 8 male « ; high 5-HT» ; and 8 male « ; low 5-HT» ; rats (Wistar-Zagreb 5-HT rats, Ruđer Bošković Institute, Zagreb, Croatia), approximately of the same age and weight (391  62 g ) were used. A week before the start of the experiment, animals were transferred to experimental room with lights switch on constantly to prevent oscillations of pain thresholds due to daily oscillations in opioid release. 4 rats per cage were housed and provided with commercial food and top water during study. Rats were habituated to restrain and analgesymeter for two days, twice a day. The pain threshold for each rat was determinate twice, before the i.p. (intraperitoneal) injection of 10 mg/kg fluoxetine (basal pain thresholds) and 30 minute after the i.p. injection of 10 mg/kg fluoxetine (fluoxetine pain thresholds). Fluoxetine – HCl (Sigma, St. Louis MO, USA) was dissolved in saline and injected intraperitoneally in a volume of 1ml/100g body weight. The pain thresholds were measured by applying increasing force on the rat-tail with Ugo Basile analgesymeter, until the tail was withdrawn as the result of pain. The maximal force was limited to 750 g. Each single pain threshold value was the mean of triplicate measurements. Data were analyzed using Analysis of variance (ANOVA) followed by Newman-Kuels post hoc test or Student’ s t-test (paired data). The pain thresholds were expressed in grams (g), as the mean  standard deviation of the mean. The results revealed the basal pain thresholds for Wistar rats, “ high – 5-HT” and “ low 5-HT” rats were 520  119 g, 414  147 g and 313  117 g, respectively. 30 minutes after the i.p. injection of 10 mg/kg fluoxetine the pain thresholds for Wistar rats, “ high – 5-HT” and “ low 5-HT” rats were 461  76 g, 315  111 g and 385  132 g, respectively. There was no statistically significant difference between pain threshold values measured before injection of fluoxetine and 30 minutes after the injection of fluoxetine in Wistar rats, « ; high 5-HT» ; and « ; low 5-HT» ; rats The results indicate that single intraperitoneal injection of 10 mg/kg fluoxetine was unable to modulate the pain sensitivity to tail pressure in Wistar rats and Wistar derived Zagreb-5-HT rats.

pain sensitivity; Wistar-Zagreb 5HT rats; fluoxetine

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