Naloxone potentiates anxiolytic-like actions of diazepam, pentobarbital and meprobamate but not those of Ro19-8022 in the rat

The elevated plus-maze test was used to determine if the opiate antagonist naloxone could potentiate the anxiolytic-like effects of the benzodiazepine diazepam, the barbiturate pentobarbital, the propanediol carbamate meproba mate and the partial benzodiazepine receptor agonist [R]-1-[( 10-chloro-4-o xo-3-phenyl-4H benzo[a]quinolizin-1-yl) carbonyl]-2-pyrrolidine-methanol (R o19-8022) in the rat. A subeffective dose of each of these compounds was co mbined with naloxone, 10 mg/kg. Naloxone had no effect by itself, but poten tiated all drugs except Ro19-8022, The proportion of entries on the open ar m increased while the total number of arms entries was not modified. These results coincide with and extend data previously obtained in the mouse. One possible explanation for naloxone's effect could be that it blocks opioid inhibition of GABAergic (gamma-aminobutyric acid) neurons thereby enhancing the effects of benzodiazepines. Another possibility is that naloxone block s opioid effects on adenosinergic systems. (C) 2000 Elsevier Science B.V. A ll rights reserved.