193 Neuroendocrinology Letters Nos.3/4, Jun-Aug, Vol.24, 2003 Copyright © 2003 Neuroendocrinology Letters ISSN 0172–780X www.nel.edu ORIGINAL ARTICLE Effects of central and peripheral administration of leptin on pain threshold in rats and mice Selim Kutlu, Sinan Canpolat, Suleyman Sandal, Mete Ozcan, Mustafa Sarsilmaz & Haluk Kelestimur Firat University, The Institute of Health Science, Department of Neuroendocrinology, Elazig, TURKEY. Correspondence to: Prof. Dr. Haluk Kelestimur Firat University Faculty of Medicine Department of Physiology 23119 Elazig, TURKEY TEL : +90 424 2370000 FAX: +90 424 2333770 EMAIL : hkelestimur@firat.edu.tr Submitted: July 27, 2002 Accepted: September 19, 2002 Key words: leptin; pain threshold Neuroendocrinol Lett 2003; 24(3/4):193–196 pii: NEL243403A07 Copyright © Neuroendocrinology Letters www.nel.edu Abstract OBJECTIVE : This study was planned to investigate the effects of exogenous leptin on the pain threshold. METHODS : Adult male Wistar rats weighing 250–300 g and mice weighing 25–30 g were used in this study. Leptin was intracerebroventricularly (i. c. v.) injected in a dose of 3.5 μg/rat. Mice were intraperitoneally (i. p.) injected with leptin in a dose of 25 μg/mouse. Control animals were injected with the respective vehi- cle. The pain threshold test was performed using hot plate analgesia meter. The experiments were performed during the day and at night. The data were statistically analysed by Mann-Whitney U test. Level of significance was set at p<0.05. RESULTS : During the day, there were no significant changes in hot plate laten- cies half an hour after i.c.v. injection of vehicle or leptin in the control and leptin- treated rats, respectively. At night, like during the day, i.c.v. injection of neither vehicle nor leptin caused any significant change in pain sensitivity. In mice, i.p. injection of leptin decreased latencies significantly (p<0.05) during the day and at night. Thus, leptin caused an increase in pain sensitivity during the day and at night. CONCLUSION : These results clearly demonstrated that leptin has a decreasing- effect on pain threshold if it is peripherally administered in mice.