Effects of central and peripheral administration of leptin on pain threshold in rats and mice.
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 micro g/rat. Mice were intraperitoneally (i. p.) injected with leptin in a dose of 25 micro g/mouse. Control animals were injected with the respective vehicle. 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 latencies 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.


CONCLUSIONS
These results clearly demonstrated that leptin has a decreasing-effect on pain threshold if it is peripherally administered in mice.
Kutlu
Selim
S
Firat University, The Institute of Health Science, Department of Neuroendocrinology, Elazig, Turkey.
Canpolat
Sinan
S
Sandal
Suleyman
S
Ozcan
Mete
M
Sarsilmaz
Mustafa
M
Kelestimur
Haluk
H
D000818:Animals; D006358:Hot Temperature; D007274:Injections, Intraperitoneal; D007276:Injections, Intraventricular; D020738:Leptin / Q000008:administration & dosage / Q000494:pharmacology*; D008297:Male; D051379:Mice; D010147:Pain Measurement / Q000187:drug effects; D017288:Pain Threshold / Q000187:drug effects*; D051381:Rats; D017208:Rats, Wistar; D011930:Reaction Time / Q000187:drug effects
D020738:Leptin