Pharmacology of intracisternal or intrathecal glycine, muscimol, and baclofen in strychnine-induced thermal hyperalgesia of mice.
Glycine and γ-aminobutyric acid (GABA) are localized and released by the same interneurons in the spinal cord. Although the effects of glycine and GABA on analgesia are well known, little is known about the effect of GABA in strychnine-induced hyperalgesia. To investigate the effect of GABA and the role of the glycine receptor in thermal hyperalgesia, we designed an experiment involving the injection of muscimol (a GABA(A) receptor agonist), baclofen (a GABA(B) receptor agonist) or glycine with strychnine (strychnine sensitive glycine receptor antagonist). Glycine, muscimol, or baclofen with strychnine was injected into the cisterna magna or lumbar subarachnoidal spaces of mice. The effects of treatment on strychnine-induced heat hyperalgesia were observed using the pain threshold index via the hot plate test. The dosages of experimental drugs and strychnine we chose had no effects on motor behavior in conscious mice. Intracisternal or intrathecal administration of strychnine produced thermal hyperalgesia in mice. Glycine antagonize the effects of strychnine, whereas, muscimol or baclofen does not. Our results indicate that glycine has anti-thermal hyperalgesic properties in vivo; and GABA receptor agonists may lack the binding abilities of glycine receptor antagonists with their sites in the central nervous system.
Department of Anesthesiology and Pain Medicine, College of Medicine, Korea University, Seoul, Korea. iloklee@korea.ac.kr
Il Ok
IO
Lee
Jin Kook
JK
Son
Eui-Sung
ES
Lim
Yeon-Soo
YS
Kim
D000818:Animals; D001418:Baclofen / Q000008:administration & dosage* / Q000494:pharmacology; D016503:Drug Delivery Systems; D018755:GABA Agonists / Q000008:administration & dosage / Q000494:pharmacology; D018756:GABA Antagonists / Q000008:administration & dosage / Q000494:pharmacology; D005998:Glycine / Q000008:administration & dosage* / Q000494:pharmacology; D006358:Hot Temperature; D006930:Hyperalgesia / Q000139:chemically induced / Q000188:drug therapy*; D007278:Injections, Spinal; D008297:Male; D051379:Mice; D008813:Mice, Inbred ICR; D009118:Muscimol / Q000008:administration & dosage* / Q000494:pharmacology; D017288:Pain Threshold; D011897:Random Allocation; D013331:Strychnine; D005680:gamma-Aminobutyric Acid / Q000378:metabolism
D018755:GABA Agonists; D018756:GABA Antagonists; D009118:Muscimol; D005680:gamma-Aminobutyric Acid; D001418:Baclofen; D013331:Strychnine; D005998:Glycine