Involvement of GABAB receptors in the antinociception induced by baclofen in the formalin test.
1. The effect of GABA receptor antagonists on baclofen-induced antinociception was examined in rats using the formalin test. Intraperitoneal (IP) administration of different doses of baclofen (2.5-10 mg kg-1) to rats induced antinociception in both phases of the test. 2. The response was dose-dependent and the maximum response was observed with 10 mg kg-1 of the drug. Intracerebroventricular (ICV) injection of baclofen (0.5-20 micrograms/rat) also induced dose-dependent antinociception in the second phase of the formalin test. 3. The GABAB antagonist, phaclofen (1 mg kg-1, IP) but not the GABAA antagonists picrotoxin (1 mg kg-1, IP) and bicuculline (1.5 mg kg-1, IP), decreased the antinociception induced by both ICV and IP administration of baclofen. 4. It is concluded that baclofen antinociception in the formalin test is mediated through GABAB receptor activation.
Shafizadeh
M
M
Department of Physiology, Tarbiat Modarres University, Tehran, Iran.
Semnanian
S
S
Zarrindast
M R
MR
Hashemi
B
B
D000818:Animals; D001418:Baclofen / Q000031:analogs & derivatives / Q000494:pharmacology*; D001640:Bicuculline / Q000494:pharmacology; D005557:Formaldehyde; D018755:GABA Agonists / Q000494:pharmacology*; D018756:GABA Antagonists / Q000494:pharmacology; D008297:Male; D017288:Pain Threshold / Q000187:drug effects* / Q000502:physiology; D010852:Picrotoxin / Q000494:pharmacology; D051381:Rats; D018080:Receptors, GABA-B / Q000187:drug effects* / Q000502:physiology
D001418:Baclofen; D001640:Bicuculline; D005557:Formaldehyde; D018755:GABA Agonists; D018756:GABA Antagonists; D010852:Picrotoxin; D018080:Receptors, GABA-B; C052329:phaclofen