Differential interactions between ethanol and Ro 15-4513 on two anxiety tests in rats

The effects of low (2 g/kg) and high (4 g/kg) doses of ethanol and their interaction with the imidazobenzodiazepine Ro 15-4513 (a partial inverse agonist of the benzodiazepine receptor) were studied in two different models of anxiety in rats: the "elevated plus-maze" test and the early acquisition of two-way (shuttlebox) avoidance. In the elevated plus-maze, ethanol (2 g/kg) increased the percentage of entries into the open arms (%EOA) and both ethanol doses increased the percentage of time spent into the open arms (%TOA), thus indicating an anxiolytic action which was reversed by Ro 15-4513 (5 mg/kg). By contrast, Ro 15-4513 did not counteract the anxiolytic effect of the low dose of ethanol in the acquisition of shuttlebox avoidance. Thus, the treatment with 2 g/kg of ethanol (plus either vehicle or Ro 15-4513) significantly increased the total number of avoidances. Conversely, animals treated with 4 g/kg of ethanol showed impaired shuttlebox avoidance acquisition, and this effect was completely reversed by Ro 15-4513. Ro 15-4513 was without effect on its own in any of the anxiety-related parameters (i.e., %EOA, %TOA, and avoidance acquisition). The results indicate a different pattern of ethanol effects and Ethanol x Ro 15-4513 interactions depending upon the task used.