A comparison of the antinociceptive responses to the GABA-receptor agonists THIP and baclofen.
The antinociceptive action of the gamma-aminobutyric acid (GABA) agonists THIP and baclofen was evaluated in mice using hot-plate (48 and 55 degrees C) and tail-immersion (50 degrees C) procedures. It was found that atropine reversed antinociception induced by THIP but not that induced by baclofen in the 48 degrees C test, whereas the anticholinergic drug blocked the response to both GABA agonists when the stimulus was provided by a 55 degrees C hot-plate. Atropine methylnitrate, mecamylamine, picrotoxin and bicuculline had no effect on antinociception induced by THIP or baclofen. Prior treatment with haloperidol enhanced only the response to baclofen on the 55 degrees C hot-plate. A reciprocal cross-tolerance was found between THIP and baclofen in the tail-immersion assay, although only THIP exhibited cross-tolerance to morphine. These results suggest that while the analgesic response to THIP and baclofen is partially mediated by a common system, the two agents act by independent mechanisms as well.
Vaught
J L
JL
Pelley
K
K
Costa
L G
LG
Setler
P
P
Enna
S J
SJ
D000700:Analgesics / Q000494:pharmacology*; D000818:Animals; D001418:Baclofen / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004361:Drug Tolerance; D007555:Isoxazoles / Q000494:pharmacology*; D008297:Male; D051379:Mice; D010080:Oxazoles / Q000494:pharmacology*; D004856:Postural Balance / Q000187:drug effects; D011963:Receptors, GABA-A / Q000187:drug effects*
D000700:Analgesics; D007555:Isoxazoles; D010080:Oxazoles; D011963:Receptors, GABA-A; D001418:Baclofen; C015542:gaboxadol