Formalin pretreatment attenuates tail-flick inhibition induced by beta-endorphin administered intracerebroventricularly or intrathecally in mice.
We examined the effect of the subcutaneous (s.c.) pretreatment of formalin into both hind paws of mice on the antinociception induced by the intracerebroventricularly (i.c.v.) or intrathecally (i.t.) administration of beta-endorphin using the tail-flick test. Pretreatment with formalin (5%) for 5 h had no affect on the i.c.v. administered beta-endorphin-induced tail-flick response. However, pretreatment with formalin for 40 h attenuated the tail-flick inhibition induced by i.c.v. administered beta-endorphin. This antinociceptive tolerance to i.c.v. beta-endorphin continued up to 1 week, but to a lesser extent. Pretreatment with formalin for 5 and 40 h significantly reduced the i.t. beta-endorphin-induced inhibition of the tail-flick response, which continued up to 1 week. The s.c. formalin treatment increased the hypothalamic pro-opiomelanocortin (POMC) mRNA level at 2 h, but this returned to the basal level after 40 h. Our results suggest that the increase in the POMC mRNA level in the hypothalamus appears to be involved in the supraspinal or spinal beta-endorphin-induced antinociceptive tolerance in formalin-induced inflammatory pain.
Han
Ki-Jung
KJ
Department of Pharmacology, College of Medicine and Institute of Natural Medicine, Gangwondo, Korea.
Choi
Seong-Soo
SS
Shim
Eon-Jeong
EJ
Seo
Young-Jun
YJ
Kwon
Min-Soo
MS
Lee
Jin-Young
JY
Lee
Han-Kyu
HK
Suh
Hong-Won
HW
D000818:Animals; D015152:Blotting, Northern; D005557:Formaldehyde; D007031:Hypothalamus / Q000187:drug effects / Q000378:metabolism; D007276:Injections, Intraventricular; D007278:Injections, Spinal; D008297:Male; D051379:Mice; D008813:Mice, Inbred ICR; D010147:Pain Measurement / Q000187:drug effects*; D010902:Pituitary Gland / Q000187:drug effects / Q000378:metabolism; D011333:Pro-Opiomelanocortin / Q000096:biosynthesis / Q000502:physiology; D012333:RNA, Messenger / Q000096:biosynthesis; D011930:Reaction Time / Q000187:drug effects*; D001615:beta-Endorphin / Q000008:administration & dosage / Q000037:antagonists & inhibitors* / Q000494:pharmacology*
D012333:RNA, Messenger; D005557:Formaldehyde; D001615:beta-Endorphin; D011333:Pro-Opiomelanocortin