ISSN:
1432-1912
Keywords:
Key words GABA receptors
;
Opoids
;
Antinoiception
Source:
Springer Online Journal Archives 1860-2000
Topics:
Medicine
Notes:
Abstract The present study was designed to investigate the modulatory effects of stimulation of GABAA and GABAB receptors at supraspinal sites on antinociception induced by supraspinally administered μ-, ɛ-, δ-, and κ-opioid receptor agonists. The effects of the GABAA and GABAB receptor agonists, muscimol and baclofen respectively, on the antinociception induced by morphine (a μ-receptor agonist), β-endorphin (an ɛ-receptor agonist), D-Pen2,5-enkephalin (DPDPE,a δ-receptor agonist) and U50,488H ({trans-3,4-dichloroN-methyl-N-[2-(1-pyrrolidinyl)cyclohexyl] benzeocetamide}; a κ-receptor agonist) injected intracerebroventricularly (i.c.v.) were studied. The antinociception was assayed using the tail-flick and hot-plate tests. Muscimol at doses of 25–200 ng, administered i.c.v. alone did not affect the latencies of tail-flick and hot-plate thresholds, but attenuated dose-dependently the inhibition of the tail-flick and hot-plate responses induced by i.c.v. administered morphine (2 μg), β-endorphin (1 μg), DPDPE (10 μg), and U50,488H (60 μg). Baclofen (1.25–10 ng) administered i.c.v. alone did not affect the latencies of the tail-flick and hot-plate responses, but attenuated dose-dependently the inhibition of the tail-flick and hot-plate responses induced by β-endorphin and U50,488H, without affecting morphine- or DPDPE-induced responses. Our results indicate that activation of GABAA receptors at the supraspinal sites by i.c.v. injection of muscimol antagonizes antinociception induced by supraspinally administered μ-, ɛ-, δ-, and κ-opioid receptor agonists. On the other hand, activation of GABAB receptors at supraspinal sites by i.c.v. baclofen antagonizes antinociception induced by i.c.v. administered ɛ- and κ-opioid agonists, but not μ- or δ-opioid agonists.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00171319
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