Mechanism-Dependent Effects of the α5 GABA_A Receptor Negative Allosteric Modulator Basmisanil on Spatial Memory

Cognitive impairment may arise through multiple pathophysiological mechanisms, including altered GABAergic neurotransmission, cholinergic dysfunction, and neuroinflammation. This study investigated whether basmisanil, a selective negative allosteric modulator of α5-containing GABA_A receptors, attenuates spatial memory impairment induced by diazepam, trihexyphenidyl (THP), or lipopolysaccharide (LPS). Adult male Wistar rats were assigned to three experimental models of memory impairment, each comprising four treatment groups (control, inducing agent, basmisanil, and inducing agent plus basmisanil; n = 7/group). Spatial memory was assessed using the two-trial Y-maze paradigm. The primary outcome (Time Index U) was analyzed using two-way factorial general linear models with sensitivity analyses. Significant interactions between the inducing agent and basmisanil were observed in the diazepam and LPS models, indicating attenuation of memory impairment following basmisanil coadministration, whereas no significant interaction was detected in the THP model. The largest estimated recovery effect was observed in the diazepam model, followed by the LPS model and the THP model, although cross-model comparisons were not statistically significant. Basmisanil alone did not enhance baseline memory performance. These findings indicate that the behavioral effects of α5-containing GABA_A receptor modulation are mechanism-dependent and support further investigation of selective α5 negative allosteric modulators for benzodiazepine-associated memory impairment.