Differential potentiative effects of GABA receptor agonists in the production of antinociception induced by morphine and beta-endorphin administered intrathecally in the mouse.
The effect of muscimol or baclofen injected intrathecally (i.t.) on the inhibition of the tail-flick response induced by morphine and beta-endorphin administered i.t. was studied in ICR mice. The i.t. injection of muscimol (100 ng) or baclofen (10 ng) alone did not affect the basal inhibition of the tail-flick response. Morphine (0.2 microg) and beta-endorphin (0.1 microg) caused only slight inhibition of the tail-flick response. Baclofen, but not muscimol, injected i.t. enhanced the inhibition of the tail-flick response induced by i.t. administered morphine. Both muscimol and baclofen injected i.t. significantly enhanced i.t. injected beta-endorphin-induced inhibition of the tail-flick response. Our results suggest that the GABA(B), but not GABA(A), receptors located in the spinal cord appear to be involved in enhancing the inhibition of the tail-flick response induced by morphine administered spinally. In addition, both GABA(A) and GABA(B) receptors are involved in enhancing the inhibition of the tail-flick response induced by beta-endorphin administered i.t.
Suh
H W
HW
Department of Pharmacology, Institute of Natural Medicine, College of Medicine, Hallym University, Chunchon, Kangwon-Do, South Korea. hwsuh@sun.hallym.ac.kr
Song
D K
DK
Huh
S O
SO
Lee
K C
KC
Kim
Y H
YH
D000596:Amino Acids / Q000494:pharmacology; D021542:Amino Acids, Neutral; D000700:Analgesics / Q000494:pharmacology*; D000818:Animals; D001418:Baclofen / Q000494:pharmacology; D004357:Drug Synergism; D018755:GABA Agonists / Q000494:pharmacology*; D007276:Injections, Intraventricular; D008297:Male; D051379:Mice; D008813:Mice, Inbred ICR; D009118:Muscimol / Q000494:pharmacology; D011724:Pyridazines / Q000494:pharmacology; D011963:Receptors, GABA-A / Q000502:physiology; D018080:Receptors, GABA-B / Q000502:physiology; D001615:beta-Endorphin / Q000494:pharmacology*
D000596:Amino Acids; D021542:Amino Acids, Neutral; D000700:Analgesics; D018755:GABA Agonists; D011724:Pyridazines; D011963:Receptors, GABA-A; D018080:Receptors, GABA-B; D009118:Muscimol; D001615:beta-Endorphin; C013809:5-aminovaleric acid; C049853:gabazine; D001418:Baclofen