DMCM, a benzodiazepine site inverse agonist, improves active avoidance and motivation in the rat

There are several modulatory sites at GABA(A) receptors, which mediate the actions of many drugs, among them benzodiazepine. Three kinds of allosteric modulators act through the benzodiazepine binding site: positive (agonist), neutral (antagonist), and negative (inverse agonist). The goal of the present study was to examine the influence of the inverse agonist methyl 6,7-dimethoxy-4-ethyl-beta-carboline-3-carboxylate (DMCM) acting on α GABA(A) receptor and compare its dose-response effects on memory and depression-like behavior. We independently studied the effects of DMCM (0.05-1.0 mg/kg) on retention versus acquisition of active avoidance and depression-like behavior in the forced swim test. Throughout the study, drugs were given intraperitoneally, 30 min before testing. ANOVA has showed that treatment with DMCM significantly affected retrieval of avoidance response (p<0.05), exerted promnesic effects in inverted U-shape manner. Dunnett's test indicated that the DMCM avoidance-facilitatory dose was 0.1mg/kg. At the dose facilitating retrieval of avoidance memory, DMCM significantly (p<0.05, comparison of regression coefficients by Student's t-test) and progressively increased acquisition rate during 5 days training, compared to the saline group. In forced swim test, ANOVA indicated statistically significant effects of DMCM (p<0.05). Dunnett's analysis showed that DMCM significantly decreased immobility time at the dose of 0.1mg/kg, exerted acute antidepressant-like effects. Our results experimentally support the findings that under certain circumstances, nonselective benzodiazepine site inverse agonists, produce memory-enhancing and antidepressant-like effects. The molecular and neuronal substrates linking the actions of specific GABA-benzodiazepine receptor complex subunits remains to be further elucidated.