engleski

Pain sensitivity in Wistar and Wistar-Zagreb 5HT rats : the effect of habituation to experimental conditions

Conditions commonly assumed to be controlled in animal experimentation (caging density, order of testing, season, time of day) might have significant impact on the outcome of pain research. Therefore, in an attempt to find out a suitable conditions for pain research based on mechanical mode of pain, we tested the hypothesis whether brief habituation to restrain and device (Ugo Basile analgesymeter) affect pain thresholds in Wistar rats and Wistar derived rats, sub lines 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 start (non habituated animal) and after the end of habituation period (habituated animal), always between 10 a.m. and 3 p.m. 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thresholds were measured by applying increasing force on the rat-tail with Ugo Basile analgesymeter, until the tail was withdrawn as the result of pain.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 pain thresholds for non habituated Wistar rats, "high – 5-HT" and "low 5-HT" rats were 622  83 g, 479  177 g and 466  149 g, respectively. After habituation to restrain and device, the 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. The effect of habituation on pain threshold was statistically significant for Wistar rats (p  0, 05 ; t (calc)= 2, 935 ; t (95%)= 2, 365 ; 7 d.f. Student’ s t-test, paired data). In addition, significant differences (p  0, 01 ; F (5, 42) = 4, 7 ; F (99%)= 3, 51 ; ANOVA) in pain thresholds between several groups of animal appear to exist: habituated "low 5-HT" rats versus habituated Wistar rats (p  0, 05 ; Newman-Kuels test), habituated "low 5-HT" rats versus non habituated Wistar rats (p  0, 01 ; Newman-Kuels test) and habituated "high 5-HT" rats versus non habituated Wistar rats (p  0, 05 ; Newman-Kuels test) Wistar rats. The results suggest that brief habituation to restrain and analgesymeter affect pain sensitivity to tail pressure in Wistar rats and Wistar derived Zagreb-5-HT rats. Besides, these results highlight the importance of scrupulous standardization of experimental conditions in pain research.

pain sensitivity; Wistar-Zagreb 5HT rats; habituation to experimental conditions

nije evidentirano