Differential Dose–Response Behavioural Profiles of Diazepam, Zolpidem and Indiplon in a Two-Trial Y-Maze Paradigm in Rats

Background: Benzodiazepines and non-benzodiazepine hypnotics (Z-drugs) act at the benzodiazepine binding site of GABAA receptors but differ in their receptor subtype selectivity and behavioural profiles. Diazepam acts as a non-selective positive allosteric modulator of benzodiazepine-sensitive GABAA receptors, whereas zolpidem and indiplon display preferential affinity for α1-containing receptor subtypes. Although these compounds have been investigated individually in experimental models of exploratory behaviour and cognition, comparative behavioural data obtained using the same experimental protocol remain limited. Methods: This study evaluated the behavioural effects of diazepam, zolpidem and indiplon in male Wistar rats using a two-trial Y-maze paradigm with a 24 h retention interval. Animals received one of three dose levels of each compound before the acquisition trial. Recall-phase behaviour was evaluated using conventional exploration measures together with time- and entry-based preference indices for the previously inaccessible arm. Primary analyses were performed separately for each compound using one-way ANOVA with appropriate post hoc comparisons. Complementary exploratory factorial analyses were subsequently conducted to examine overall behavioural patterns across drug and nominal dose categories. Results: Diazepam produced marked dose-dependent reductions in recall-phase exploration of the previously inaccessible arm and in both exploratory preference indices. In contrast, zolpidem and indiplon reduced exploratory activity during the acquisition phase without significantly affecting recall-phase exploratory behaviour. The complementary factorial analyses identified significant Drug × Nominal Dose Categories interactions across all recall-related endpoints, indicating that behavioural responses across the nominal dose categories differed among the three compound-specific experimental series. The strongest interaction effects were observed for Time Index % (F(6,72) = 10.522, p < 0.001, ηp2 = 0.467) and Entries Index % (F(6,72) = 6.870, p < 0.001, ηp2 = 0.364). Conclusions: Diazepam produced more pronounced dose-dependent alterations in recall-phase exploratory behaviour than zolpidem or indiplon in the experimental conditions employed. The complementary factorial analyses support the interpretation that the three compounds exhibited different behavioural patterns across the nominal dose categories evaluated, while these exploratory comparisons should be interpreted within the constraints of the study design. Overall, the findings contribute to the comparative behavioural characterization of benzodiazepine-site modulators in the two-trial Y-maze paradigm.